Law of Independent Assortment

Transcription

1 Dihybrid Crosses

2 Dihybrid Crosses Dihybrid Cross ~ genetic cross considering 2 gene traits at the same time, each consisting of nonidentical alleles. i.e. Mendel crossed numerous traits repeatedly in dihybrid crosses and found he always obtained the same ratio 9:3:3:1 ~ and thus develops Law of Independent Assortment

3 Law of Independent Assortment During gamete formation, the two alleles for one gene segregate or assort independently of the alleles for other genes.

4 Law of Independent Assortment Diploid Gamete

5 Law of Independent Assortment Diploid Gamete

6 Law of Independent Assortment Diploid Gamete

7 Law of Independent Assortment Diploid Or... Gamete

8 Law of Independent Assortment Diploid Or... Gamete

9 Law of Independent Assortment Diploid Or... Or... Gamete

10 Law of Independent Assortment Diploid Or... Or... etc... Gamete

11 Law of Independent Assortment Diploid Dad So... Gamete

12 Law of Independent Assortment Diploid Dad Mom Gamete

13 Sample Problem #1 In humans, free earlobes are controlled by the dominant allele E and attached earlobes by the recessive allele e. The widow s peak hairline is regulated by the dominant allele H, while the straight hairline by the recessive allele h. What would be the genotype and phenotype ratio of the F1 generation if a man heterozygous for both free earlobes and widow s peak has children with a woman also heterozygous for both free earlobes and widow s peak?

14 1. Let E be dominant free earlobes let e be recessive attached earlobes let H be dominant widow s peak let h recessive straight hair line 2. Parents P1 cross: EeHh x EeHh 3. Alleles: EH, Eh, eh, eh & EH, Eh, eh, How did eh you do that?

15 Step 3: EeHh x EeHh

16 Step 3: EeHh x EeHh EH

17 Step 3: EeHh x EeHh EH Eh

18 Step 3: EeHh x EeHh EH Eh eh

19 Step 3: EeHh x EeHh EH Eh eh eh

20 Step 3: EeHh x EeHh EH Eh eh eh EH

21 Step 3: EeHh x EeHh EH Eh eh eh EH Eh

22 Step 3: EeHh x EeHh EH Eh eh eh EH Eh eh

23 Step 3: EeHh x EeHh EH Eh eh eh EH Eh eh eh

24 P1 Cross: Step 3: EeHh x EeHh This is how you do step #3! Alleles for Punnet Square: EHEheHeh x EHEheHeh

25 EH Eh eh eh EH eh Eh EEHH EEHh EeHH EeHh The Alleles of each parent is EeHH placed on EeHh the outside eehhof your eehh 4x4 punnet square EEHh EEhh EeHh Eehh eh EeHh Eehh eehh eehh

26 EEHH ~ 1 eehh ~ 2 EEHh ~ 2 EEhh ~ 1 EeHH ~ 2 Eehh ~ 2 EeHh ~ 4 eehh ~ 1 eehh ~ 1 Therefore the genotype ratio is 1:2:2:4:1:2:1:2:1 for above order

27 Free earlobes & widow s peak = = 9 Attached earlobes & widow s peak = 1+2 =3 Free earlobes and straight hairline = 1+2= 3 Attached earlobes and straight hairline = 1 thus, the ratio of phenotypes is 9:3:3:1

28 Practice Crosses 1. State The phenotypes and genotype probability for a cross between a pure plant with round yellow seed and pure plant with wrinkled green seed. Round is dominant over wrinkled and yellow is dominant over green.

29 Let R be dominant round trait let r be recessive wrinkled trait let C be dominant yellow trait let c be recessive green trait Cross P1: RRCC x rrcc Alleles: RC, RC, RC, RC x rc, rc, rc, rc

30 RC RC RC RC rc RrCc RrCc RrCc RrCc rc RrCc RrCc RrCc RrCc rc RrCc RrCc RrCc RrCc rc RrCc RrCc RrCc RrCc

31 RrCc - 16 Therefore, 100% of P1 are RrCc and will be round and yellow.

32 Pedigree Charts Pedigree Chart ~ a graphic presentation of a family tree that permits patterns of inheritance to be followed for a single gene. chart contains a number of symbols that identify gender, relationships between individuals and whether an individual expresses a trait or carries the

33 Pedigree Symbols male identical twins female fraternal twins (females) mating I II Roman numerals symbolize generations. Arabic numbers symbolize individuals within a given generation. affected individuals known heterozygotes for autosomal recessive Birth order within each group of offspring is drawn left to right, oldest to youngest.

34 Sample Pedigree I 1 2 II III 1 2 3