Principles of Inheritance and Variation: Class 12 Biology Chapter 4 Hinglish mein

Jo farmers hybrid rice ya hybrid maize ugaate hain, woh har season naya seed khareedte hain. Agar woh apni fasal ka anaaj bachakar bo dein, to agla khet ek mixed bag ban jaata hai. Kuch plants lambe aur kuch chhote, kuch jaldi aur kuch der se, aur zyaadatar kam yield dete hain. Iske ulat, traditional variety se bachaya seed saal-dar-saal bilkul apne parents jaisa hi ugta hai. Ek khet ka seed true breed kyun karta hai jabki doosre ka bikhar jaata hai? Is chapter ke end tak tum ise samjha paoge.

Aise sawaalon ke peeche ki science genetics (आनुवंशिकी) hai. Yeh do jude hue sawaal poochti hai. Characters parents se offspring tak kaise pahunchte hain? Is aage dene ko inheritance (वंशागति) kehte hain. Aur offspring kabhi apne parents ki, ya ek doosre ki, exact copy kyun nahi hote? Yeh differences variation (विविधता) hain.

Selective breeding genetics se kahin zyaada purani hai. Traditional crop varieties, aur India ki Gir aur Tharparkar cattle ya Murrah buffaloes, hazaaron saalon mein un logon ne banayi jo chunte the ki kin plants aur animals se breed karna hai, bina yeh jaane ki yeh chunna kaam kyun karta hai. Agli generation ko predict kar sakne wale pehle rules 1860s mein ek monastery ke garden se nikle.

4.1 Mendel's Laws of Inheritance

Gregor Mendel, Brno (ab Czech Republic mein) ke ek monk, ne 1856 se 1863 tak saat saal garden pea plants ko cross karne aur unke offspring ginne mein lagaye. Teen aadatein unke kaam ko alag banati thi. Woh poore plant ki jagah ek baar mein ek clear-cut character follow karte the. Unhone hazaaron plants ugaaye aur score kiye, taaki chance ke effects barabar ho jaayein. Aur woh counts se mathematically reasoning karte the, har idea ko agli generation predict karke aur phir use ugaakar test karte the. Isse pehle biology mein kisi sawaal ko settle karne ke liye numbers aur probability ka use shaayad hi kabhi hua tha.

Pea ne khud kai tarah se unki madad ki:

• Iske flowers normally band petals ke andar khud ko pollinate karte hain, isliye alag rakhi gayi line generations tak pure rehti hai.
• Jab bhi experimenter koi khaas cross chahe, inhi flowers ko khol kar haath se pollinate kiya ja sakta hai.
• Ek generation ek hi season mein ug jaati hai, aur har plant ginne ke liye bahut saare seeds deta hai.
• Iske kai characters do bilkul alag forms mein aate hain, beech ka kuch nahi, isliye har plant ko bina behas ke score kiya ja sakta hai.

Kuch bhi cross karne se pehle Mendel ne pakka kiya ki har starting line true-breeding ho: generation-dar-generation self-pollination ke baad woh line, jis character ko woh study kar rahe the, uske liye bilkul parents jaise offspring hi deti thi. Aisi chaudah lines, saat pairs mein mila kar, unka material thi. Ek pair ke partners ek character ko chhodkar baaki sab mein ek jaise the. Saat characters the seed shape (round ya wrinkled), seed colour (yellow ya green), flower colour (violet ya white), flower position (stem ke saath-saath ya uske tip par guchchhe mein), pod shape (inflated ya constricted), pod colour (green ya yellow) aur stem length (tall ya dwarf).

Do lines ko cross karne ke liye Mendel ko chune hue seed parent ko khud ko fertilise karne se rokna tha aur phir use sirf ek doosre plant ka pollen dena tha. Fig. 4.1 yeh procedure dikhata hai. Flower bud se anthers pollen girane se pehle hi hata diye jaate hain, is step ko emasculation kehte hain, aur flower ko ek bag se dhak diya jaata hai taaki koi bhatka hua pollen us tak na pahunche. Jab stigma ready hota hai, to chune hue pollen parent ka pollen us par chhidka jaata hai, bag wapas lag jaata hai, aur jo seeds bante hain woh cross ki pehli generation hain.

4.2 Ek Gene ki Inheritance

Mendel ke character pairs mein se ek lo, pod colour. Ek true-breeding line mein green pods hain, doosri mein yellow. Inhe cross karo, aur seeds ugkar first filial generation, yaani ${\mathrm{F}}_1$ (Latin mein son ya daughter ke liye) banate hain. Har ${\mathrm{F}}_1$ plant mein green pods hote hain. Yellow halka hokar yellowish green nahi bana; woh nazar se gayab ho gaya hai.

Ab ${\mathrm{F}}_1$ plants ko khud ko pollinate karne do. Second filial generation, ${\mathrm{F}}_2$, mein yellow pods wapas aa jaate hain, bilkul utne hi yellow jitne original parent mein the. Mendel ne 428 green-pod wale aur 152 yellow-pod wale ${\mathrm{F}}_2$ plants gine, yaani har yellow ke liye lagbhag teen green. Unke baaki chhe characters ne bhi aisa hi behave kiya (Table 4.1): ${\mathrm{F}}_1$ mein sirf ek form, ${\mathrm{F}}_2$ mein dono forms lagbhag 3 : 1 ratio mein, aur kabhi koi blend nahi.

Mendel ki explanation apne time ke hisaab se kaafi bold thi. Unka kehna tha ki har plant har character ke liye do hereditary particles rakhta hai, jinhe unhone factors kaha; ek gamete inmein se sirf ek leta hai, aur yeh particles kabhi mix nahi hote, na badalte hain. Aaj hum unke factors ko genes kehte hain. Gene DNA (Chapter 5) ka ek hissa hai jismein kisi character ke peeche ke instructions hote hain, aur yeh ek se zyaada versions mein ho sakta hai. Ek gene ke versions uske alleles (युग्मविकल्पी) hain: pod colour ka ek allele green ke liye hai aur ek yellow ke liye.

Geneticists har gene ko ek letter dete hain. Capital letter us allele ke liye hai jo ${\mathrm{F}}_1$ mein dikhta hai, aur usi letter ka small form uske partner ke liye. Isliye G (green) aur g (yellow) turant ek hi gene ke alleles ke roop mein pehchaan mein aa jaate hain. Har plant mein gene ki do copies hoti hain, isliye teen combinations bante hain: GG, Gg aur gg. Do ek jaise alleles wala plant, GG ya gg, homozygous hai; do alag alleles wala plant, Gg, heterozygous hai.

Yeh letters plant ka genotype batate hain, yaani us character ke liye uska genetic make-up. Jo hum dekhte hain, green ya yellow pod, woh uska phenotype hai. GG aur Gg plants ka phenotype same hai lekin genotype alag, kyunki Gg mein G allele g ko chhupa deta hai. Isliye G dominant (प्रभावी) hai aur g recessive (अप्रभावी). ${\mathrm{F}}_1$ plants ek character ke liye heterozygous hain, isliye woh monohybrids hain, aur GG × gg ek monohybrid cross hai.

Yellow wapas kyun aata hai? Alleles ko alag-alag tokens samjho. Meiosis pair ke do alleles ko alag kar deta hai, isliye har gamete mein har gene ka bilkul ek token hota hai. Green parent sirf G de sakta tha aur yellow parent sirf g, isliye har ${\mathrm{F}}_1$ plant mein ek-ek hota hai aur woh green dikhta hai. Lekin uske andar g token sahi-salaamat hai. Jab ${\mathrm{F}}_1$ gametes banata hai, to aadhe ko G aur aadhe ko g milta hai, bilkul chance se, pollen aur eggs dono mein, aur jab g pollen grain g egg se milta hai to phir se yellow-pod wala plant ban jaata hai.

Gametes ke har possible milan ka hisaab rakhne ke liye geneticists Cambridge ke Reginald C. Punnett ka banaya ek chequerboard use karte hain, Punnett square. Egg types ko ek side neeche ki taraf likho aur pollen types ko upar across. Jahan ek row aur ek column milte hain, us box mein us khaas egg aur pollen grain ka offspring hota hai. Kyunki har milan barabar likely hai, isliye har box bhi. Fig. 4.2 cross ko parents se ${\mathrm{F}}_2$ tak follow karta hai.

Boxes gino: ek GG, do Gg aur ek gg. Isliye ${\mathrm{F}}_2$ ka genotypic ratio 1 : 2 : 1 hai. Kyunki GG aur Gg dono green pods dete hain, phenotypic ratio 3 green : 1 yellow hai. Yahi answer algebra se bhi mil sakta hai: ${\mathrm{F}}_1$ gametes mein G aur g dono ki probability 1/2 hai, aur is sum ko square karne par har zygote apni probability ke saath list ho jaata hai, bilkul binomial expansion ki tarah.

Mendel ne kuch lines ko aage ki generations tak chalaya. Yellow pods wale ${\mathrm{F}}_2$ plants ko self karne par unse kabhi yellow-pod wale offspring ke alawa kuch nahi mila, isliye woh homozygous, gg, hi hone chahiye the. Green-pod wale ${\mathrm{F}}_2$ plants kam predictable the (Example).

Green pod se pata chalta hai ki plant mein kam se kam ek G hai, lekin yeh nahi ki woh GG hai ya Gg. Trick yeh hai ki use ek homozygous recessive plant se cross karo. Aisa test cross (परीक्षार्थ संकरण) isliye kaam karta hai kyunki recessive partner sirf recessive alleles de sakta hai, jo kuch nahi chhupate: test kiya gaya plant jo bhi allele aage deta hai, wahi seedhe har offspring ka phenotype decide karta hai.

Fig. 4.4 flower position ke liye ek test cross karke dikhata hai, jahan axial flowers (A: stem ke saath-saath flowers) terminal flowers (a: tip par guchchhe mein flowers) par dominant hain.

Agar har offspring axial hai, to test kiya gaya plant lagbhag pakka AA tha; agar lagbhag aadhe terminal hain, to woh Aa tha. Is asymmetry par dhyaan do: ek bhi terminal offspring saabit kar deta hai ki parent mein a hai, lekin lagaataar axial offspring sirf AA ko zyaada se zyaada likely bana sakte hain (Example).

4.2.1 Law of Dominance

Ek character wale crosses se Mendel ne do general rules nikaale. Aaj inhe law of dominance aur law of segregation kehte hain.

Isiliye monohybrid ${\mathrm{F}}_1$ apne parents mein se sirf ek jaisa dikhta hai; segregation ke saath milkar yahi ${\mathrm{F}}_2$ ka 3 : 1 bhi banata hai.

4.2.2 Law of Segregation

Dekho ki yeh law gametes ke baare mein kya predict karta hai. GG aur gg plants ek-ek tarah ke gametes banate hain, jabki Gg plant G aur g gametes 1 : 1 ratio mein banata hai, bilkul wahi jo test cross dikhata hai. Is law ka sabse mazboot saboot yellow ${\mathrm{F}}_2$ pod hai, jo ek generation chhupe rehne ke baad bhi apne grandparent jitna hi yellow hai. Kyunki har gamete mein ek single, bina mila hua allele hota hai, is law ko law of purity of gametes bhi kehte hain.

4.2.2.1 Incomplete Dominance

Mendel ke saaton characters ne complete dominance dikhaya, lekin doosre organisms ke kai characters aisa nahi karte. Four o'clock plant, Mirabilis jalapa (kai Indian gardens mein gulbas, naam un flowers par pada jo dopahar ke baad khulte hain), mein true-breeding red-flowered line ko true-breeding white-flowered line se cross karne par ${\mathrm{F}}_1$ mein pink flowers aate hain. Hybrid apne parents ke beech mein hai. Yeh incomplete dominance (अपूर्ण प्रभाविता) hai: koi bhi allele doosre ko poori tarah nahi chhupata.

Pink ${\mathrm{F}}_1$ ko self karo to ${\mathrm{F}}_2$ mein red, pink aur white plants aate hain (Table 4.2). Ise pea cross se compare karo. Punnett square bilkul same hai, 1 RR : 2 Rr : 1 rr. Ab har genotype ka apna alag look hai, isliye phenotypes 3 : 1 ki jagah 1 : 2 : 1 aate hain. Red aur white bhi bilkul waise hi wapas aate hain jaise grandparents mein the, isliye alleles khud kabhi blend nahi hue; hybrid mein sirf unke effects milte hain.

Allele ko dominant kya banata hai?

Ek allele doosre ko kyun chhupaye? Jawaab is baat mein hai ki genes kya banate hain. Ek aise flower ko socho jiska violet pigment ek single enzyme banata hai, jo do alleles wale ek gene se code hota hai. V mein kaam karne wale instructions hain, jabki v ek kharaab copy hai jo bekaar enzyme deti hai ya bilkul nahi (Fig. 4.5). VV plant bahut saara pigment banata hai. Vv plant kam enzyme banata hai, phir bhi har petal ko poora rangne ke liye kaafi, isliye woh bilkul VV jaisa dikhta hai: V dominant hai. Sirf vv plant, jiske paas koi working copy nahi, white flowers deta hai.

Isse ek general pattern samajh aata hai: recessive alleles aksar gene ke non-working versions nikalte hain, aur usually ek working copy kaafi hoti hai. Lekin har badla hua allele toota hua nahi hota. Kuch ab bhi aisa enzyme banate hain jo normally ya lagbhag normally kaam karta hai; aisa allele original ke barabar hai aur kuch aisa nahi badalta jo hum dekh sakein, aur aise pairs common hain. Aur jab phenotype product ki amount par depend karta hai, jaise four o'clock plant mein (Section 4.2.2.1), to ek working copy sirf aadha pigment deti hai aur heterozygote beech ka hota hai.

4.2.2.2 Co-dominance

Blood transfusion se pehle hospital check karta hai ki patient chaar groups, A, B, AB ya O, mein se kis group ka hai. Groups un chhoti sugar chains mein alag hote hain jo red blood cells ki surface ko sajaati hain (Fig. 4.6). Group A cells par sugar A hoti hai, group B cells par sugar B, AB cells par dono aur O cells par koi nahi.

Ek gene, I, sugar decide karta hai. Human population mein iske teen alleles hote hain: $I^A$ sugar A banata hai, $I^B$ sugar B banata hai, aur $i$ kuch nahi banata. Pehle ek $I^A{I}^B$ insaan ko dekho. Koi allele doosre ko nahi chhupata: dono sugars aati hain, har ek poori. Yeh co-dominance (सहप्रभाविता) hai: heterozygote dono alleles ke phenotypes saath-saath dikhata hai, incomplete dominance ke beech wale hybrid ya complete dominance ke ek-tarfa hybrid se alag.

Allele $i$ alag behave karta hai. Kyunki yeh koi sugar nahi jodta, ek $I^{A}i$ insaan ko $I^A{I}^A$ insaan se alag nahi pehchaana ja sakta, isliye $I^A$ aur $I^B$ dono $i$ par dominant hain. Teen alleles chhe tarah se pair ban sakte hain, jisse chhe genotypes aur chaar blood groups bante hain (Table 4.3).

Dhyaan do ki I gene ke teen alleles hain, jabki hum mein se har ek mein sirf do hote hain. Population mein do se zyaada alleles wale gene ke baare mein kaha jaata hai ki uske multiple alleles hain; inhe sirf bahut saare individuals ka survey karke hi pata lagaya ja sakta hai, ek ko study karke kabhi nahi. Rabbits mein coat colour ek aur example hai: ek gene ke chaar alleles full-coloured, chinchilla (silvery grey), Himalayan (white, dark kaan, naak aur panjon ke saath) aur albino coats dete hain.

4.3 Do Genes ki Inheritance

Iske baad Mendel ne ek saath do characters follow kiye. Unke experiment ke hamare version mein flower position aur pod colour hain. Ek true-breeding parent mein axial flowers aur green pods hain (AAGG); doosre mein terminal flowers aur yellow pods (aagg). Har parent sirf ek tarah ka gamete banata hai, AG ya ag, isliye har ${\mathrm{F}}_1$ plant AaGg hai, axial flowers aur green pods ke saath. Ab tak kuch bhi surprising nahi: har character waise hi behave karta hai jaise akele karta. Do genes ke liye heterozygous hone se ${\mathrm{F}}_1$ ek dihybrid hai, aur yeh cross ek dihybrid cross hai.

Ab ${\mathrm{F}}_1$ ko khud ko pollinate karne do. ${\mathrm{F}}_2$ mein ek baar mein ek character dekho to kuch naya nahi dikhta. Teen-chauthai plants axial hain aur ek-chauthai terminal, aur, alag se, teen-chauthai mein green pods hain aur ek-chauthai mein yellow. Har character ab bhi 3 : 1 mein batta hai, bilkul monohybrid cross ki tarah. Naya sawaal yeh hai ki dono characters aapas mein kaise judte hain.

4.3.1 Law of Independent Assortment

${\mathrm{F}}_2$ mein chaar phenotypes hain: axial green, axial yellow, terminal green aur terminal yellow, 9 : 3 : 3 : 1 ratio mein. Inmein se do, axial yellow aur terminal green, new combinations hain jo kisi bhi original parent mein nahi the. Yeh ratio bas do 3 : 1 ratios ka guna hai, jo tab expect hota hai jab har character doosre se bina matlab rakhe inherit hota hai:

(Section 4.3.3 mein hum dekhenge ki yeh alag-alag chromosomes par wale genes ke liye sahi hai, lekin ek hi chromosome par paas-paas wale genes ke liye nahi.)

AaGg plant mein gamete formation ko do independent coin tosses ki tarah socho: ek decide karta hai A ya a, doosra G ya g. Do coins se chaar barabar likely outcomes milte hain, isliye plant AG, Ag, aG aur ag gametes banata hai, har ek ek-chauthai, eggs aur pollen dono mein. Inhe Punnett square ki dono sides par rakhne se 16 barabar likely boxes ka 4 × 4 grid banta hai (Fig. 4.7).

16 boxes mein sirf nau alag genotypes hain, jo chaar phenotypes mein aate hain. Table 4.4 check karne se pehle khud inhe sort karke dekho. Genotypic ratio 9 : 3 : 3 : 1 nahi hai. Yeh 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1 hai, jo (1 : 2 : 1) × (1 : 2 : 1) hai.

4.3.2 Chromosomal Theory of Inheritance

Mendel ne apne results 1865 mein present kiye aur woh 1866 mein print hue, phir bhi tees saal se zyaada tak shaayad hi kisi ne unpar aage kaam kiya. Historians iske kai kaaran batate hain:

• Koi physical basis nahi. Koi bhi, Mendel bhi, cell mein kisi factor ki taraf ishaara nahi kar sakta tha, na bata sakta tha ki woh kis cheez ka bana hai.
• Ajeeb method. Us zamaane ke biologists describe aur compare karte the; bahut kam log ratios aur probability se nikaale gaye conclusions maanne ko taiyaar the.
• Blending obvious lagti thi. Nature mein zyaadatar variation, height, weight ya colour mein, continuous hota hai, jo is baat ka saboot lagta tha ki parental characters mix hote hain, na ki discrete factors aage jaate hain.
• Ek anjaan journal. Unka paper ek chhoti local society ki proceedings mein chhapa aur shaayad hi kisi ne padha.

Is beech cell biologists, behtar lenses aur naye dyes ke saath, nuclei ko divide hote dekh rahe the. Unhone dhaage jaisi bodies dekhi jo stain ko bahut zyaada leti thi, isiliye naam pada chromosomes, yaani 'coloured bodies'; har ek division se pehle double hota tha, aur 1902 tak meiosis mein unke move karne ka tareeka samajh aa gaya tha. 1900 mein teen botanists ne alag-alag kaam karte hue, Hugo de Vries, Carl Correns aur Erich von Tschermak, apne crosses mein Mendel ke ratios paaye aur phir unka bhula hua paper dhoondh nikaala. Kaam ki yeh do lines milne hi waali thi.

Yeh 1902 mein mile, jab United States mein Walter Sutton aur Germany mein Theodor Boveri ne bataya ki meiosis mein chromosomes bilkul waise hi behave karte hain jaise Mendel ke factors ko karna chahiye (neeche ka comparison). Unka proposal, jise Sutton ne chromosomal theory of inheritance ke roop mein rakha, kehna simple hai: Mendel ke factors chromosomes ke hisse hain, aur segregation aur independent assortment wahi hain jo chromosomes meiosis mein karte hain. Body cells mein chromosomes homologous pairs mein hote hain, har pair ka ek member har parent se. Gene ke do alleles pair ke do members par same position par baithe hote hain, jise gene ka locus kehte hain.

Fig. 4.9 dikhata hai ki isse independent assortment kaise samajh aata hai. Maan lo gene A chromosomes ke ek pair par hai aur gene G doosre pair par. Metaphase I par har pair cell ke beech mein line up karta hai, ek homologue har pole ki taraf. Kaunsa homologue kis pole ki taraf hoga, yeh har pair ke liye alag se tay hota hai, jaise do coins independently uchhale gaye hon. Ek alignment A aur G ko ek pole par aur a aur g ko doosre par bhejta hai; doosra, utna hi likely, alignment A ko g ke saath aur a ko G ke saath bhejta hai. Bahut saare meioses mein chaaron tarah ke gametes barabar number mein bante hain.

Is theory ko New York ki Columbia University mein Thomas Hunt Morgan aur unke students ne fruit fly Drosophila melanogaster ki madad se test kiya. Kai features ne is fly ko ideal banaya:

• Lagbhag har do hafte mein nayi generation, isliye ek saal mein kai generations.
• Ek single pair se saikdon offspring, reliable ratios ke liye kaafi.
• Eye colour, body colour aur wings ke kai inherited variants, jo hand lens ya low-power microscope se dikh jaate hain.
• Rakhna sasta: flies bottles mein simple artificial food par rehti hain.
• Males aur females ko pehchaanna aasaan hai, aur cells mein sirf chaar pairs chromosomes hote hain.

Morgan ke group ne dikhaya ki ek khaas gene ek khaas chromosome par hota hai, aur unke kaam ko 1933 ka Nobel Prize in Physiology or Medicine mila. Yeh fly aaj bhi biology ke sabse useful model organisms mein se ek hai.

4.3.3 Linkage and Recombination

Independent assortment ki ek built-in limit hai. Cell mein chromosomes se kahin zyaada genes hote hain (fruit fly mein hazaaron genes hain lekin chromosomes ke sirf chaar pairs), isliye kai genes ko ek chromosome share karna padta hai, aur ek chromosome share karne wale genes ko saath-saath chalna chahiye. Morgan ke group ne bilkul yahi paaya. X chromosome par do genes wale fly crosses lo, jaise eye colour aur body colour ke liye. Characters ke grandparental combinations 9 : 3 : 3 : 1 ki ijaazat se kahin zyaada baar wapas aaye, jabki new combinations rare the.

Morgan ne ek chromosome par genes ke physical judaav ko linkage (सहलग्नता) naam diya aur alleles ke naye combinations banne ko recombination (पुनर्योजन). Linked genes bhi recombine kar sakte hain, crossing over ke through: prophase I ke dauraan homologous pair ke do non-sister chromatids milte-julte points par tootte hain aur phir judte hain, aur segments exchange karte hain.

Ek saaf example fly ke chromosome 2 par do genes ka hai: body colour (grey, $b^{+}$, black, $b$, par dominant) aur wing shape (normal, $v{g}^{+}$, vestigial, $vg$, par dominant). Ek true-breeding grey, normal-winged fly ko black, vestigial-winged fly se cross karo, to har ${\mathrm{F}}_1$ female ke ek chromosome 2 par $b^{+}$ aur $v{g}^{+}$ hote hain aur uske homologue par $b$ aur $vg$. In females ko black, vestigial males se test-cross karo. (Females isliye use hoti hain kyunki male fruit flies mein crossing over nahi hota.) Independent assortment se chaaron tarah ke offspring barabar number mein aate. Iski jagah, ek typical batch Table 4.5 jaisa dikhta hai.

Do parental classes 800 mein se 664 flies hain aur do recombinant classes 136. Recombination frequency offspring ka woh fraction hai jo recombinant hai: $136\mathrm{/}800=0.17$, yaani 17 %. Fig. 4.10 dikhata hai ki recombinants kahan se aate hain: sirf un gametes mein naya combination hota hai jinmein dono genes ke beech kahin crossover hua.

Kuch linked pairs doosron se zyaada recombine kyun karte hain? Morgan ki laboratory ke ek student, Alfred Sturtevant, ne socha ki crossovers chromosome par kam-zyaada random points par hote hain. Door-door wale do genes ke beech crossover girne ke kai mauke hote hain; do padosi genes ke beech bahut kam. Isliye paas-paas ke genes tightly linked hote hain aur kabhi-kabhi hi recombine karte hain, jabki door wale genes loosely linked hote hain aur aksar recombine karte hain. 1913 mein Sturtevant ne ise ek method bana diya: recombination frequency ko distance maankar unhone kai X-chromosome genes ko ek line par order mein rakha, yeh pehla genetic map tha. Aaj 1 % recombination ek map unit, yaani ek centimorgan (cM), define karta hai.

Frequency 50 % se upar nahi ja sakti: itne door ke genes ki crossovers lagbhag hamesha unhe alag kar dete hain, woh aise assort karte hain jaise unlinked hon. Recombination se bane maps ne baad mein poore genomes ki sequencing ko guide kiya, human genome ko bhi (Chapter 5).

4.4 Polygenic Inheritance

Apni class ko height ke hisaab se line mein khada karo, to tumhe Mendel ke tall aur dwarf peas jaise do saaf groups nahi milenge, balki ek smooth range milegi jismein zyaadatar log beech ke aas-paas honge. Aisa continuous variation tab aata hai jab kai genes, har ek ka chhota effect, ek character par kaam karte hain. Environment bhi apna asar jodta hai: achha khaana khaane wala bachcha usi bachche se lamba hota hai jo kam poshan par palta. Is tarah ke characters ko polygenic kehte hain, aur polygenic inheritance (बहुजीनी वंशागति) dikhata hai ki Mendel ke discrete factors bhi smooth variation kaise bana sakte hain, wahi observation jisne kabhi biologists ko unpar shak karwaya tha.

Sabse simple model mein har contributing allele phenotype mein ek fixed amount jodta hai: effects additive hote hain. Ek classic case wheat grains ka colour hai, jise Swedish geneticist Herman Nilsson-Ehle ne lagbhag 1909 mein study kiya. Maan lo do genes, A aur B, laali ko control karte hain, har capital allele red pigment ki ek dose jodta hai aur har small allele kuch nahi. AABB grains dark red hain, aabb grains white, aur AaBb grains, do doses ke saath, medium red. AaBb plants ko self karo to ${\mathrm{F}}_2$ capital alleles ki sankhya, 0 se 4, ke hisaab se paanch shades mein batta hai, 1 : 4 : 6 : 4 : 1 ratio mein (Fig. 4.12).

Teen aise genes ke saath saat classes hoti hain, 0 se 6 doses tak, 1 : 6 : 15 : 20 : 15 : 6 : 1 ratio mein, aur bars pehle se ek bell banane lagte hain. Human skin colour ko bhi lambe samay se isi tarah model kiya gaya hai, kai genes ke roop mein jinke 'darker' alleles jud jaate hain, aur phir sunlight result ko adjust karti hai. Kisi bhi polygenic character mein environmental effects jodo to alag-alag classes dhundhli hokar wahi smooth curve ban jaati hain jo hum asal mein dekhte hain.

4.5 Pleiotropy

Untreated phenylketonuria (PKU) wale baby mein kai problems aati hain jo aapas mein judi nahi lagti. Brain theek se develop nahi hota, urine mein ek unusual acid hota hai, aur skin aur baal aksar family ke baaki logon se zyaada halke hote hain. Yeh sab ek hi faulty gene se aate hain, enzyme phenylalanine hydroxylase ka gene, jo normally amino acid phenylalanine ko tyrosine mein badalta hai (Fig. 4.13). Jab ek gene is tarah kai alag characters par asar daalta hai, to us gene ko pleiotropic kehte hain aur is effect ko pleiotropy (बहुप्रभाविता).

Ek gene itna kuch kaise kar sakta hai? Usually uska product cell ki chemistry ke ek chauraahe par kaam karta hai. PKU mein ruke hue step ke consequences dono directions mein hote hain. Phenylalanine jama hota jaata hai aur develop hote brain ko nuksaan pahunchata hai, jisse intellectual disability hoti hai; uska by-product phenylpyruvic acid urine mein aa jaata hai; aur pigment melanin banane ke liye kam tyrosine bachta hai.

Sickle-cell allele (Section 4.8.2) bhi pleiotropic hai. Ek amino-acid change se anaemia, chhoti blood vessels ka block hona, dard ke episodes, spleen jaise organs ko nuksaan aur, carriers mein, malaria se kuch protection hota hai. Marfan syndrome mein ek connective-tissue protein ki kharaabi skeleton (lambe haath-pair aur ungliyan), aankhon ke lenses aur heart se nikalne wali main artery par asar daalti hai.

4.6 Sex Determination

Kuch offspring males aur kuch females kyun bante hain? Kahani 1891 mein Hermann Henking se shuru hoti hai, jo ek insect, firebug, mein sperm bante dekh rahe the. Ek gehra stain lene wali nuclear body ne unka dhyaan kheencha: woh sirf aadhe sperm mein pahunchti thi. Yeh na jaante hue ki woh kya hai, unhone use bas 'X body' kaha. Baad mein doosron ne dikhaya ki yeh ek chromosome hai, aur naam chal pada: X chromosome. Sex decide karne wale chromosomes sex chromosomes hain; baaki saare autosomes hain.

Grasshoppers aur cockroaches mein female ke cells mein do X chromosomes hote hain aur male mein sirf ek, bina partner ke: yeh sex determination ka XO type hai. Isliye male grasshopper mein female se ek chromosome kam hota hai, aur uske sperm do tarah ke hote hain, X ke saath aur bina X ke, jabki har egg mein ek X hota hai. Kaunsa sperm egg ko fertilise karta hai, yahi sex decide karta hai: X wala sperm XX beti deta hai, bina X wala sperm XO beta.

Humans, doosre mammals aur fruit fly XY type use karte hain. Females XX hoti hain; males mein ek X aur ek chhota partner, Y chromosome, hota hai, isliye dono sexes mein chromosomes ki sankhya same hoti hai. Kyunki do tarah ke sperm male banata hai, isliye XO aur XY dono systems ko male heterogamety kehte hain (hetero, alag; gamety, gametes).

Birds mein yeh ulta hai. Hen mein do alag sex chromosomes hote hain, jinhe X aur Y se confusion se bachne ke liye Z aur W naam diya gaya, jabki cock mein do Z chromosomes hote hain; chromosome number phir se dono sexes mein same hai. Yahan female do tarah ke egg banati hai, Z wale aur W wale, barabar number mein, aur chick ka sex is par depend karta hai ki kis tarah ka egg fertilise hua. Yeh female heterogamety hai; zyaadatar butterflies aur moths mein bhi yahi hota hai. Fig. 4.14 teeno systems ko saath-saath rakhta hai.

4.6.1 Sex Determination in Humans

Har human egg ek baat mein same hai: usmein 22 autosomes aur ek X hota hai. Sperm same nahi hote. Aadmi ke cells mein autosomes ke 22 pairs aur ek X aur ek Y hote hain, aur meiosis aadhe sperm mein X aur baaki aadhe mein Y daalta hai (Table 4.6). X wale sperm se fertilise hua egg XX zygote banta hai aur ladki ke roop mein develop hota hai. Y wale sperm se fertilise hua egg XY banta hai aur ladke ke roop mein develop hota hai, kyunki Y par ek gene, SRY, develop hote gonads ko testes banane ki taraf mod deta hai.

Isse do conclusions nikalte hain. Bachche ka sex father ka sperm tay karta hai, mother nahi. Aur kyunki dono tarah ke sperm barabar number mein bante hain aur egg tak pahunchne ke barabar chances rakhte hain, har pregnancy mein ladki hone ka 1/2 chance hota hai, pehle ke bachche chahe kisi bhi sex ke hon.

4.6.2 Sex Determination in Honey Bee

Honey-bee colony mein ek queen, das-hazaaron female workers aur, season mein, kuch sau male drones hote hain. Egg female banega ya male, yeh is par depend karta hai ki woh fertilise hua bhi ya nahi. Queen apni mating flights se sperm store karti hai aur har egg dete samay use release karti hai, ya nahi karti. Fertilised egg ko do chromosome sets (2n = 32) milte hain aur woh female banta hai: worker ya, agar larva ko poore samay royal jelly khilayi jaaye, to queen. Unfertilised egg phir bhi develop hota hai, parthenogenesis se, aur haploid drone (n = 16) banta hai (Fig. 4.15). Yahan sex chromosome sets ki sankhya se tay hota hai, isliye is system ko haplodiploid kehte hain.

Aisi species mein family trees ajeeb dikhte hain. Ek drone ki ancestry banao: uski mother hai lekin father nahi, jabki uski mother ke dono the, isliye uska grandfather zaroor hai. Woh mitosis se sperm banata hai, kyunki uske paas shuru se hi chromosomes ka sirf ek set hai. Uske sperm sirf un eggs ko fertilise kar sakte hain jo betiyaan banti hain, isliye uske kabhi bete nahi ho sakte; lekin un betiyon ke through uske pote ho sakte hain.

4.7 Mutation

Recombination maujooda alleles ko naye combinations mein phenta hai. Mutation (उत्परिवर्तन) variation ka doosra bada source hai: DNA sequence mein hi badlaav, jo genotype ko aur uske through phenotype ko badal sakta hai.

Mutations bahut bade se bahut chhote tak hote hain. Bade wale end par chromosome ke poore segments kho jaate hain (deletion) ya jud jaate hain (insertion ya duplication). Kyunki chromosome asal mein ek continuous, kaskar packed DNA molecule hai (Chapter 5), aisa badlaav segment ke har gene ko hata deta hai ya repeat kar deta hai. Yeh chromosomal aberrations kai cancer cells ki pehchaan hain; jaise chronic myeloid leukaemia mein chromosomes 9 aur 22 ke hisse aapas mein jagah badal lete hain.

Sabse chhote scale par ek single base pair badal sakta hai: yeh point mutation hai. Sabse jaana-maana example sickle-cell anaemia hai, jismein ek base substitution β-globin ka ek amino acid badal deta hai (Fig. 4.16). Gene ke andar ek base insert ya delete karna usually kahin zyaada nuksaan karta hai. Cell gene ko teen-teen bases ke lagaataar groups (codons) mein padhta hai, isliye badlaav ke baad ka har codon galat padha jaata hai, jab tak ki bilkul teen bases na jude ya na ghatein. Inhe frame-shift mutations kehte hain.

Mutations chance se hote hain, jaise DNA replicate hote samay copying errors se, aur environment ke kuch agents unki rate badha dete hain. In mutagens mein physical agents jaise UV radiation (ek kaaran ki baar-baar sunburn se skin cancer ka risk badhta hai), X-rays aur gamma rays, aur chemical agents shaamil hain, jinmein tobacco smoke ke kai substances bhi hain. Mutation ke molecular mechanisms is chapter se aage ki baat hain.

4.8 Genetic Disorders

Section 4.7 ke kai mutations jo health ke liye matter karte hain, inherited hote hain, families mein waise hi neeche jaate hain jaise Mendel ke alleles. Yeh section un disorders ko dekhta hai jo yeh paida karte hain, aur yeh bhi ki geneticists unhe kaise trace karte hain.

4.8.1 Pedigree Analysis

Peas study karne wala geneticist kisi bhi do plants ko cross karke agle season saikdon offspring gin sakta hai. Insaanon ko study karne wala geneticist dono mein se kuch nahi kar sakta: families chhoti hoti hain, generations lambi hoti hain, aur koi experiment ke liye shaadiyan arrange nahi karta. Iski jagah human genetics pehle se maujood families ke records par chalti hai. Kai generations ke chart ki tarah banaya gaya, jismein har woh insaan mark ho jo koi khaas trait dikhata hai, aisa record pedigree hai. Usse yeh nikaalna ki trait kaise inherit hota hai, pedigree analysis (वंशावली विश्लेषण) hai. Log bahut pehle se jaante the ki kuch conditions families mein chalti hain, aur systematic pedigree studies Mendel ke kaam ki rediscovery ke kuch hi baad shuru hui. Fig. 4.17 standard symbols dikhata hai.

Pedigree ko upar se padho. Har row ek generation hai, Roman numerals se numbered. Ek row mein do symbols ko jodne wali line mating hai, aur unke bachche uske neeche ek horizontal line se latakte hain, sabse bada left mein. Carriers, yaani recessive allele ki ek copy wale log jo khud affected nahi hain, pata chalne ke baad aksar dot se mark kiye jaate hain.

4.8.2 Mendelian Disorders

Inherited disorders do badi tarah ke hote hain. Mendelian disorder ek gene mein badlaav se hota hai, isliye yeh generation-dar-generation Mendel ke rules follow karta hai aur pedigrees se track kiya ja sakta hai. Examples mein thalassaemia, sickle-cell anaemia, phenylketonuria, cystic fibrosis, haemophilia aur colour blindness shaamil hain. Chromosomal disorder missing, extra ya rearranged chromosomes se hota hai (Section 4.8.3).

Do sawaal Mendelian disorder ko classify karte hain: faulty allele dominant hai ya recessive, aur woh autosome par hai ya X chromosome par? Achhi tarah bana pedigree usually dono ka jawaab de deta hai. Fig. 4.18 teen common patterns mein se har ek ke liye ek family dikhata hai, us clue ke saath jo faisla karta hai:

• Autosomal recessive: do unaffected parents ka affected bachcha ho sakta hai, kyunki dono carriers hain; betiyaan aur bete barabar affected hote hain. Examples: sickle-cell anaemia, thalassaemia, phenylketonuria, cystic fibrosis.
• Autosomal dominant: har affected insaan ka kam se kam ek parent affected hota hai, isliye trait har generation mein dikhta hai; do affected parents ka unaffected bachcha ho sakta hai; yeh father se bete tak ja sakta hai. Examples: myotonic dystrophy, Huntington disease.
• X-linked recessive: females se kahin zyaada males affected hote hain; affected beton ki mothers usually unaffected carriers hoti hain; yeh kabhi father se bete tak nahi jaata, kyunki father bete ko Y deta hai, X nahi. Examples: haemophilia, red–green colour blindness.

Colour blindness. Red–green colour blindness aadmiyon mein itni zyaada common kyun hai, kai populations mein lagbhag 8 % aadmiyon mein lekin aurton mein 1 % se bhi kaafi kam? Aankh ke cone cells ke red-sensing aur green-sensing pigments ke genes X chromosome par hote hain, aur red aur green ko pehchaanna mushkil banane wale faulty alleles recessive hain. Aadmi, jiske paas ek single X hai, tab colour blind hota hai jab us X par faulty allele ho. Aurat ko apne dono X chromosomes par faulty alleles chahiye, jo kahin kam likely hai. Ek ke saath woh unaffected carrier hai, aur uske har bete ke colour blind hone ka 1/2 chance hai (Example).

Haemophilia. Haemophilia ki sabse famous carrier Britain ki Queen Victoria thi: unka ek beta affected tha, aur unki do betiyaan carriers thi jinki apni betiyaan yeh allele Spain aur Russia ke royal families tak le gayi. Yeh disorder X-linked recessive hai. Normal clotting proteins ke ek cascade par depend karti hai, jismein har ek agle ko on karta hai. Haemophilia mein inmein se ek protein missing ya faulty hota hai, isliye chhote cut se, ya joint ke andar, bleeding rokna mushkil hota hai. Affected ladkiyan bahut rare hain, kyunki ladki ko carrier mother ke saath affected father bhi chahiye, aur modern treatment se pehle kam hi affected aadmi father banne tak jee paate the.

Sickle-cell anaemia. Microscope ke neeche is disease wale insaan ke blood mein kai red cells naram, gol discs ki jagah sakht crescents mein mude dikhte hain. Kaaran haemoglobin mein hai. Jab oxygen kam hoti hai, to us insaan ke haemoglobin molecules judkar lambi rods ban jaate hain jo cell ko kheenchkar uska shape bigaad dete hain. Sickled cells chhoti blood vessels ko jam kar dete hain, jisse dard aur organ damage hota hai, aur jaldi nasht ho jaate hain, jisse anaemia hota hai.

Faulty haemoglobin normal wale se apni β chain ke 146 amino acids mein se sirf ek mein alag hai: position 6 par glutamic acid (Glu) ki jagah valine (Val). Yeh aage ek single base se aata hai: β-globin gene ka chhatha codon DNA mein GAG ki jagah GTG padhta hai, ya mRNA mein GAG ki jagah GUG (Fig. 4.16).

Yeh disorder autosomal recessive hai, do alleles ke saath, $H{b}^A$ aur $H{b}^S$. Sirf $H{b}^{S}H{b}^S$ logon ko disease hoti hai. Carriers ($H{b}^{A}H{b}^S$) usually healthy hote hain lekin average mein apne aadhe bachchon ko $H{b}^S$ dete hain, isliye do carriers ke couple ke har bachche ke affected hone ka 1/4 chance hota hai. Yeh disease central aur western India ke kai tribal communities mein common hai, jahan 2023 mein shuru hua ek national mission iski screening karne aur 2047 tak ise public-health problem ke roop mein khatam karne ka lakshya rakhta hai.

Phenylketonuria. PKU ko hum pleiotropy ke example ke roop mein mil chuke hain (Section 4.5). Yeh ek inborn error of metabolism hai jo autosomal recessive ki tarah inherit hota hai. Sirf woh bachche affected hote hain jinmein enzyme gene ki do faulty copies hon, isliye carrier parents ke har baar affected bachche ka 1/4 chance hota hai. Kidneys phenylalanine ke by-products ko theek se reabsorb nahi karti, isiliye woh urine mein dikhte hain. Janm ke kuch hi baad blood test, aur phir phenylalanine kam wali diet, brain damage ka zyaadatar hissa rok deti hai.

Thalassaemia. Adult haemoglobin do tarah ki globin chains, α aur β, se barabar number mein banta hai. Thalassaemia mein ek mutation ya deletion ek tarah ki chain ka production dheema kar deta hai, isliye cell kaafi normal haemoglobin nahi bana paata aur insaan anaemic hota hai. Sickle-cell anaemia ki tarah yeh bhi autosomal recessive hai: affected bachche usually do healthy carriers ke ghar paida hote hain. Iske do main forms us chain ke naam par hain jiski kami hoti hai:

• α-thalassaemia: α-globin ka production gir jaata hai. Chromosome 16 par do padosi genes, HBA1 aur HBA2, dono α-globin code karte hain, aur har parent se ek chromosome 16 milne se insaan mein aise chaar genes hote hain. Chaar mein se jitne zyaada delete ya damage hon, cells utna kam α-globin bana paate hain.
• β-thalassaemia: β-globin ka production gir jaata hai. Yahan sirf ek gene shaamil hai, chromosome 11 par HBB, aur disorder insaan ki do copies mein se ek ya dono mein mutations se hota hai.

4.8.3 Chromosomal Disorders

Chromosomes ki ginti bhi galat ho sakti hai. Meiosis ke dauraan pair ke do members, ya do sister chromatids, kabhi-kabhi alag nahi ho paate, is galti ko nondisjunction kehte hain. Tab ek gamete mein us chromosome ki ek extra copy hoti hai aur uske partner gamete mein ek bhi nahi (Fig. 4.19). Normal gamete se fertilise hone par inse aise zygotes bante hain jinmein us chromosome ki teen copies (trisomy, 2n + 1) ya ek copy (monosomy, 2n − 1) hoti hai. Is tarah individual chromosomes ka judna ya khona aneuploidy (असुगुणिता) hai. Human cells mein normally 46 chromosomes hote hain, autosomes ke 22 pairs aur sex chromosomes ka ek pair; zyaadatar aneuploid embryos survive nahi karte, aur jo karte hain unhe chromosomal disorder hota hai.

Ek cell chromosomes ka poora extra set bhi paa sakta hai, jaise jab telophase ke baad cytokinesis fail ho jaaye aur double hue chromosomes ek hi cell mein saath reh jaayein. Yeh polyploidy hai. Animals mein rare aur usually lethal, lekin plants mein common: bread wheat hexaploid (chhe sets) hai aur zyaadatar khaane wale kele triploid (teen sets) hain.

Chromosomal disorders ka diagnosis karyotype se hota hai, jo cell ke chromosomes ki ek picture hai jismein woh size aur shape ke hisaab se pairs mein lagaaye hote hain. Teen common examples Table 4.8 mein compare kiye gaye hain:

Down's syndrome (trisomy 21, 47 chromosomes) teeno mein sabse zyaada jaana-maana hai, aur iska risk mother ki umar ke saath badhta hai. John Langdon Down ne ise 1866 mein describe kiya, iska kaaran pata chalne se bahut pehle. Is syndrome wale logon mein typically physical, psychomotor aur mental development der se hota hai aur kad chhota hota hai. Doosre common features hain chauda palm jis par aksar ek single crease hoti hai, chhota gol sir, furrowed tongue aur thoda khula munh, aur kaafi baar janm se maujood heart defect.

Baaki do sex chromosomes se jude hain, aur dono milkar dikhate hain ki maleness Y decide karta hai, X chromosomes ki sankhya nahi. Klinefelter's syndrome wale insaan mein do X chromosomes aur ek Y hota hai (47, XXY). Y use male banata hai, lekin extra X kuch female features la sakta hai jaise breast development (gynaecomastia), aur woh sterile hota hai. Turner's syndrome wale insaan mein ek single X hota hai aur Y nahi (45, X0). Woh female ke roop mein develop hoti hai, usually chhote kad ki, lekin uske ovaries rudimentary rehte hain, isliye woh sterile hoti hai aur baaki secondary sexual characters develop nahi hote.