Patterns of Inheritance

1. Patterns of Inheritance

2. I. Simple inheritance (Mendelian inheritance) • One gene controls the trait • There are two versions (alleles) of the gene • One allele is completely dominant over the other

3. II. Multiple allele inheritance • The trait is still controlled by only one gene. • There are more than two versions (alleles) for the one gene

4. Example: Multiple allele inheritance of feather color in pigeons • BA allele produces red feathers. It is dominant to all other alleles • B allele produces blue feathers. It is dominant to b but recessive to BA. • b allele produces chocolate colored feathers. It is recessive to all other alleles.

5. Genotypes and phenotypes of pigeons

6. III. Codominance • Both alleles are equally dominant so they are both expressed

7. Example: Codominance in Roan cattle

8. A cattle that is (R1R1) is red

9. A cattle that is (R2R2) is white

10. A heterozygous cattle (R1R2) is roan (both red and white)

11. IV. Incomplete dominance • Both alleles are equally dominant so they are both expressed

12. Example: Incomplete dominance in snapdragons • Snapdragons that are RR are red. • Snapdragons that are R’R’ are white. • If a snapdragon is heterozygous for these two alleles (RR’) then it is pink.

13. A white snapdragon (R’R’)

14. A red snapdragon (RR)

15. A pink snapdraon (RR’)

16. V. Polygenic inheritance • The trait is controlled by more than one gene.

17. Example: Eye color in humans • Eye color is controlled by genes found in two different spots on chromosome number 15 and also by a gene found on chromosome number 19.

18. VI. Sex linked traits • The trait is controlled by a gene that is found on the sex chromosome (the 23rd pair in humans) • Because males only have one X and females have two X’s some unique inheritance patterns emerge.

19. Example of a sex linked trait in humans.

20. The gene that controls your blood clotting factors is found on the X chromosome.

21. There are two alleles for this gene a normal, dominant H allele that clots blood, and an abnormal, recessive h allele that doesn’t clot blood. If a person doesn’t have the normal H allele then they will have the disease hemophilia.

22. Since a man only has one X chromosome, and therefore only one gene for blood clotting, he is more likely to get hemophilia.

23. Use a punnet square to solve the following problem:

24. A man that does not have hemophilia and a woman that is heterozygous for hemophilia have a child. What is the probability that their child will have hemophilia.

25. Start by showing the sex chromosomes that mom could give X X

26. Then show the alleles that are found on mom’s sex chromosomes XH Xh

27. Then show the sex chromosomes that dad could give. X Y XH Xh

28. Then show the alleles that are found on dad’s sex chromosomes XH Y XH Xh

29. Notice that there is no allele shown on the Y chromosome because it doesn’t have the same genes as the X XH Y XH Xh

30. Finally, show the different possibilities for the offspring. XH Y XH XHXH XHY Xh XHXh XhY

31. Only one of the four children would have hemophilia. XH Y XH XHXH XHY Xh XHXh XhY