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Patterns of Inheritance

Patterns of Inheritance

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Patterns of Inheritance

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  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