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1. V ARI A TIONS ON Mendel’s Law

2. VARIATIONS OF MENDE L ’S LAW ➤ Incomplete dominance ➤ Multiple allele ➤ Codominance ➤ Pleiotropy ➤ Polygenic trait/inheritance ➤ Epistasis

3. INCOMPLETE DOMINANCE ➤ A form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele ➤ Results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles

4. INCOMPLETE DOMINANCE ➤ Example ➤ cross- pollination experiments between red and white snapdragon plants ➤ allele that produces the red color ( R ) is not completely expressed over the allele that produces the white color ( r ) ➤ genotypes : Red ( RR ) x White ( rr ) = Pink ( Rr )

5. INCOMPLETE DOMINANCE

6. INCOMPLETE DOMINANCE ➤ Example ➤ hypercholesterolemia in humans ➤ dangerous high levels of cholesterol occur in the blood and heterozygotes have intermediately high cholesterol

7. INCOMPLETE DOMINANCE

8. MU L TIPLE ALLELES ➤ Three or more alternative forms of a gene (allele) that can occupy the same locus ➤ However, only two alleles can be present in a single organism

9. MU L TIPLE ALLELES ➤ Example ➤ ABO blood groups ➤ alleles A (I A ) and B (I B ) are codominant ➤ third allele is recessive (i) ➤ genotype and phenotype ➤ ii yields type O ➤ I A I B yields type AB ➤ I A I A yields type A ➤ I B I B yields type B

10. MU L TIPLE ALLELES

11. MU L TIPLE ALLELES ➤ Example ➤ Fur colors of rabbit ➤ determined by 4 alleles ➤ C - full color; dominant to all other alleles ➤ c ch - chinchilla; partial defect in pigmentation, dominant to ch and c ➤ c h - himalayan; color in certain parts of body. dominant to c allele ➤ c - albino, no color; recessive to all other alleles

12. MU L TIPLE ALLELES

13. CODOMINANCE ➤ A form of dominance wherein the alleles of a gene pair in heterozygote are fully expressed ➤ Results in o ff spring with a phenotype that is neither dominant nor recessive

14. CODOMINANCE ➤ Example ➤ AB blood types ➤ blood type is determined by multiple alleles recognized as A, B, or O and in blood type AB, both phenotypes are fully expressed

15. CODOMINANCE

16. CODOMINANCE ➤ Example ➤ Chickens ➤ black feather (F B ) is codominant to white feather (F W ) ➤ heterozygous individual is a combination of black and white feathers that results in a checkered pattern (F B F W )

17. CODOMINANCE

18. PLEIOTROPY ➤ Occurs when one gene will code and control the phenotype or expression of several di ff erent and unrelated traits ➤ Results to many diseases

19. PLEIOTROPY ➤ Example ➤ Sickle- cell disease ➤ also known as sickle- cell anemia ➤ disorder characterized by a diverse set of symptoms

20. PLEIOTROPY

21. PO L YGENIC TRAITS/INHERITANCE ➤ Occurs when one characteristic is controlled by two or more genes ➤ Traits that display a continuous distribution (height, skin color, weight, and eye color) ➤ Individuals may express varying degrees of a dominant phenotype, recessive phenotype and intermediate phenotype

22. PO L YGENIC TRAITS/INHERITANCE

23. EPISTASIS ➤ An interaction between the products of two genes in which one of the genes modified the phenotypic expression produced by the other

24. RECESSIVE EPISTASIS ➤ Recessive alleles at one locus (aa) mask the phenotypic expression of other gene locus (BB, Bb, or bb) ➤ The alleles of B locus express themselves only when epistatic locus A has dominant allele like AA or Aa ➤ The phenotypic ratio is 9:3:4

25. RECESSIVE EPISTASIS ➤ Coat color in mice ➤ C = pigment ➤ c = no pigment ➤ B = black ➤ b = brown ➤ cc = albino

26. DOMINANT EPISTASIS ➤ When dominant allele ‘ A ’ masks the expression of ‘B’, ‘ A ’ is epistatic gene of ‘B’ ➤ ‘ A ’ can express itself only in the presence of ‘B’ or ‘b’ allele ➤ ‘B’ expresses only when ‘aa’ is present ➤ Ratio is 12:3:3

27. DOMINANT EPISTASIS

28. DOMINANT EPISTASIS Genotype Fruit color Gene action 9 A_B_ White Dominant white allele negates e ff ect of G allele 3 A_bb White Dominant white allele negates e ff ect of G allele 3 aaB_ Yellow Recessive color allele allows yellow allele expression 1 aabb Green Recessive color allele allows green allele expression

29. EXAMPLE OF INCOMPLETE DOMINANCE ➤ In some cats the gene for tail length shows incomplete dominance. Cats with long tails and cats with no tails are homozygous for their respective alleles. Cross breed cats with one long tail allele and one no tail allele have short tails. ➤ a long tail cat and a cat with no tail ➤ a long tail cat and a short tail cat ➤ a short tail cat and a cat with no tail

30. EXAMPLE OF INCOMPLETE DOMINANCE ➤ In mice, when black (BB) mice are crossed with white (bb) mice it results in gray o ff spring. Cross a gray (Bb) mouse with a white mouse. What is the probability of black o ff spring? Gray o ff spring? White o ff spring?

31. EXAMPLE OF MU L TIPLE ALLELES ➤ Suppose a newborn baby was accidentally mixed up in the hospital. In an e ff ort to determine the parents of the baby, the blood types of the baby and two sets of parents were determined. Baby 1 had type O, Mrs. Brown had type B and Mr. brown had type AB, while Mrs. Smith had type B and Mr. Smith had type B. ➤ Draw a Punnet squares for each couple ➤ To which parents does baby number 1 belong? Why?

32. EXAMPLE OF MU L TIPLE ALLELES ➤ If you were to cross a female with an AB blood type with a male with an O blood type, could you end up with a child that has an O blood type? ➤ Predict the outcome between a man with type O blood and a woman that is heterozygous for blood type A.

33. EXAMPLE OF CODOMINANCE ➤ In certain fish, blue scales (B) and red scales (R) are codominant. When fish has the genotype BR, it has a patchwork of blue and red scales. What happens if you breed this fish with a fish that only has blue scales?

34. EXAMPLE OF CODOMINANCE ➤ In some species of frogs, green (G) skin and purple (P) skin are codominant. Predict the outcome between two heterozygous frogs.

35. EXAMPLE OF PO L YGENIC INHERITANCE ➤ Predict the outcomes if AaBb is crossed with AaBb. ➤ AABB = Dark ➤ AABb = Mulatto ➤ AAbb = Brown ➤ Aabb = white ➤ aabb = albino

36. EXAMPLE OF EPISTASIS ➤ What F1 and F2 genotype and phenotype ratios are attained from the cross between AACC and aacc. ➤ C- = color ➤ cc = no color ➤ A- = agouti ➤ aa = black

37. THANK YOU!!!!