CH11TheBasicPrinciplesofHereditypart-2

CH11TheBasicPrinciplesofHereditypart-2 - MENDEL'S PRINCIPLE...

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Unformatted text preview: MENDEL'S PRINCIPLE of SEGREGA'IION I Before sexual reproduction 'l'he +wo alleles carried by on individual ore sepor'o'led (lie. segrego'led) P Generation Tall plant Short plant EH3 Homologous chr'om osomes F1 Generatlon ' Genes may be “hidden” in a genero'rion bu1' They are never lost Ali tall plants He‘l'er'ozygous o1 locus m for stem lengTh (T1) Homowgous chromosOmes METAPHASE | / \ METAF'HASE || Homologous c’somes sepor-oTe Tall plant Tall El E 1/2 of game'res cor'r'y T 1/2 of game'res carry 1 Stall: 1 short Principle of segrega‘l'ion is due ’ro separation of homologous chromosomes during garne‘ie formation Black female (BB) Brown male (on) PUNNETT SQUARE . - predicTs The raTios of l genoTypes and phenoTypes _- Gametes l in The offspring of a cross Figure 11-6 p 240 FI DominantB generation masks recessive!) HeTerozygous organisms produce equal numbers of gomeTes possessing dominanT and recessive alleles 1 . E Gametes from F. male 6enoTypic roTio: BB:Bb:bb : 1:2:1 gen; Pheno‘l’ypic ra'l'io: black:brown : 3:1 if F2 generation If heterozygous Homozygous A Black-:Bb) Brown (by); - a cross beTween on individual wiTh The dominonT phenoType and The homozygous recessive phenoType Figure 11-7 p 241 DominonT phenoTypes could resulT from eiTher The homozygous dominanT or heTerozygous genoTypes if homozygous Homozygous Black (88) Brown (on) i Gameles l’ bl: Homozygous brown All Sb All offspring are biack and heterozygous (a) If a black guinea pig is mated with a brown (b) If any of the offspring is brown, the black guinea gumea pig and all the offspring are black, the black pig must be heterozygous. The expected phenotypic parent probably has a homozygous genotype ratio is 1 black to 1 brown. DIHYBRID CROSS — DIFFERENT ALLELES 0+ TWO LOCI . A dihybrid cross is a mating between individuals with different alleles at two loci - Figure 11-8 p 242 Black. short-haired Brown. long-haired 9 generation 888$ 0033 l Gamatas 1 F1 generation All 3555 predicts allele combinations in gametes produced by F1 generation : Eirst — 1/1 BS Quter — 1/1 Bs lnner — '24: b8 Last — 1/: bs 4 types of gametes formed by segregation and independent assortment of alleles Gan-notes [roan FY female i® %@ %@%® Earn ates Irom F‘ male Punnett square has 16 (42) squares for F2 J ) hl— hl— hl— Isl- In 3' 0 3. F 3 generahon Phenotypic ratio of 9:3:3:1 F, phenotypes 2 § 2 l 16 as 16 16 . . Black. Black, Brown. Blown. A dlhyblflld cross. short-haired long-haired short-haired long-haired demonstrates segregation and independent assortment MENDEL'S PRINCIPLE of INDEPENDENT ASSORTMENT : Alleles of differenT loci on nonhomologous chromosomes randomly disTribuTe inTo gameTes m ' _4_ 2 ways homologous H H c'somes can line up ,. . . .\ - .166? ' I .b a. '3 ‘ METAPHASE | -' _ Each gameTe has 1 allele for each locus - 2" differen’r combinaTions of chromosomes in gameTes (n : haploid # c'somes) 2.5? humans: 223 : ~B million possible combinations ‘/2bs RULES of PROBABILITY - ‘z’zbS ‘x’zBs ProducT rule: OuTcome of firsT Toss is independenT of The ouTcome of The second Toss so ThaT The combined probabiliTies of successive Tosses are calculaTed by mulTiplying Their independenT probabiliTies Second toss our Probability is Sum rule: because There are Two ways for offspring To inheriT The heTerozygous genoType predicT Their combined probabiliTies by summing (adding) Their individual probabiliTies (Figure 11-10 p 244) ...
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CH11TheBasicPrinciplesofHereditypart-2 - MENDEL'S PRINCIPLE...

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