1. Eye color is determined by multiple alleles at a single gene locus. There are multiple versions (alleles) of the eye color gene - blue, green, and brown. 2. Polygenic inheritance is when multiple genes contribute to a single trait. For traits determined by polygenic inheritance, there are many possible combinations of alleles across several gene loci that result in a range of phenotypes. 3. Both multiple allele inheritance and polygenic inheritance can contribute to natural variation in human eye color. Multiple alleles at a single gene locus explain some of the variation, but many genes likely have small effects, making polygenic inheritance important as well.

1. MULTIPLE ALLELES AND POLYGENIC INHERITANCEBiology 3Kent Kawashima

4. Character:eye colorTrait: blueGenotype: AAAATATTATATATCCCCGTAGCTACGATCTATCTATCATCTATCTACTATCTATCTATCTATCTATCTACTATCTATCCGGCGTATCATCGGGGGGGGGGGTACTAGCTAGCTAGCTATCTACGTAGTCTACTGATCTAGCTAGTCATGCTGATCATCGTAGCTGAGCTACTAGTCGATCGTAGCTAGTCATCTAGCTGAGCTAGCTGATCGATCTAGCTAGCTGATCGTAGCGATCGTAGCTAGCTAGTCGATGCTAGCTGATCGTAGCATGCTAGCTGATGCATGCTAGCTAGCTAGCTGATCA…Phenotype: Megan Fox’s blue eyes

5. Human have 23 pairs of chromosomes.one set comes from the motherone set comes from the father

6. A gene occurs in pairs in diploid cells.eye color gene pairThe combination of what alleles you have in your gene pair is what is called your genotype.Homologous chromosomesAA, BB, Cc, RrQq, IAIA… These letters are just representations for your genotype. They also simply represent your alleles.

7. The eye color gene located in chromosome 19…gene for eye colorblue version, green version, brown versionbluegreenbrown…can contain any of the versions for that gene.These versions are called your alleles

8. “blue” allele“green” allele“brown” allele…AAAATATTATATATCCCCGTAGCTACGATCTATCTATCATCTATCTACTATCTATCTATCTATCTATCTACTATCTATCCGGCGTATCATCGGGGGGGGGGGTACTAGCTAGCTAGCTATCTACGTAGTCTACTGATCTAGCTAGTCATGCTGATCATCGTAGCTGAGCTACTAGTCGATCGTAGCTAGTCATCTAGCTGAGCTAGCTGATCGATCTAGCTAGCTGATCGTAGCGATCGTAGCTAGCTAGTCGATGCTAGCTGATCGTAGCATGCTAGCTGATGCATGCTAGCTAGCTAGCT……AAATTATTATATATCCCCGTAGCTACGATCTATCTATCATCTATCTACTATCTATCTATCTATCTCTCTACTATCTATCCGGCGTATCATCGGGGGGGGGGGTACTAGCTAGCTAGCTATCTACGTAGTCTACTGATCTAGCTAGTCATGCTGATCATCGTAGCTGAGCTACTAGTCGATCGTAGCTAGTCATCTAGCTGAGCTAGCAGATCGATCTAGCTAGCTGATCGTAGCGATCGTAGCTAGCTAGTTGATGCTAGCTGATCGTAGCATGCTAGCTGATGCATGCTAGCTAGCTAGCT……AAACTATTATATATCCCCGTAGCTACGATCTATCTATCATCTATCTACTATCTATCTATCTATCTGTCTACTATCTATCCGGCGTATCATCGGGGGGGGGGGTACTAGCTAGCTAGCTATCTACGTAGTCTACTGATCTAGCTAGTCATGCTGATCATCGTAGCTGAGCTACTAGTCGATCGTAGCTAGTCATCTAGCTGAGCTAGCCGATCGATCTAGCTAGCTGATCGTAGCGATCGTAGCTAGCTAGTAGATGCTAGCTGATCGTAGCATGCTAGCTGATGCATGCTAGCTAGCTAGCT…versions of a gene occur because of small changes in the DNA (in pink)

9. Since your eye color gene occurs as a pair, you may have two similar allelesgreengreenGenotype: Homozygous for the green allele

10. …or you may have two different allelesbluegreenGenotype: Heterozygous

11. …or you may have two different allelesgreenbrownGenotype: Heterozygous

12. …or you may have two different allelesbrownblueGenotype: Heterozygous

13. gene for eye colorbluegreenbrownOnly one gene controls the nature of the character…

14. More than two versions of the gene exists…This is called “Multiple Allele Inheritance”

15. gene for eye colorgene for eye colorgene for eye colorgene for eye colorWhat if many genes have an effect to one character?This is called “Polygenic Inheritance”

16. In Polygenic Inheritance…gene for eye color+add more of something!gene for eye color0no effect.gene for eye colorgene for eye coloralleles that either contribute to a trait or notmany genes

17. Example.For each + allele you have, it tells your cells to add more pigment to your iris.The 0 alleles however do not add nor subtract pigment, they do not contribute to your phenotype.gene for eye color++gene for eye color+0gene for eye color+0gene for eye color++

18. + allele is called a contributory allele+00 allele is called a non-contributory allele

19. Compare.+0+0+0+0+0+0++000+++000++0+00+0++0+00+0+6 +, 2 02 +, 6 04 +, 4 08 +8 0

20. Compare.+0+0+0+0+0+0++000+++000++0+00+0++0+00+0+graydark browngreenbluelight brown

21. Arranged from least to most melanin produced+0+0+0+0+0+0++000+++000++0+00+0++0+00+0+graydark browngreenbluelight brown

22. In polygenic inheritance…Many genes contribute to affect a singular character

23. There is no dominance, an allele either contributes to a phenotype or not

24. There is an equal effect for each contributory alleleIn polygenic inheritance…Polygenes have two types of alleles, a contributory allele that adds to the phenotype, and a non-contributory allele that has no effect on the phenotypeA(BIG LETTER) - contibutory allelea(small letter) - non-contributory allele

25. In polygenic inheritance…Phenotypes show a great number of variations

26. Polygenic inheritance is usually the mode of inheritance for traits that are continuous – weight, height and skin toneSo…Is iris color inherited through multiple alleles or polygenes?

27. Shortcuts for Polygenic Inheritance Genetics

28. If you cross…AA x aaAABB x aabbAa x AaAaBb x AaBb1 AABB4 AaBB, aABB, AABb, AAbB6 AaBb, aAbB, AabB, aABb, aaBB, AAbb4aAbb, Aabb, aabB, aaBb1 aabball possible genotypes1 AA2 Aa, aA1 AArelative phenotype portions expected

29. If you cross…AA x aaPAa x AaF1Number of gene pairs: n = 1Number of phenotypes in F2: 21 + 1 = 3Number for genotypes regardless of position in the gene pair: 31 = 3(two big A, one big A, no big A)1 AA2 Aa, aA1 aaF2

30. If you cross…AABB x aabbNumber of gene pairs: n = 2Number of phenotypes in F2: 22 + 1 = 5Number for genotypes regardless of position in the gene pair: 32 = 92 big A, 2 big B2 big A, 1 big B2 big A, 0 big B1 big A, 2 big B1 big A, 1 big B1big A, 0 big B0 big A, 2 big B0 big A, 1 big B0 big A, 0 big BPAaBb x AaBbF11 AABB4 AaBB, aABB, AABb, AAbB6 AaBb, aAbB, AabB, aABb, aaBB, AAbb4aAbb, Aabb, aabB, aaBb1 aabbregardless of position in the gene pairF2

31. Use Pascal’s Triangle to get the coeefficientsof the binomial expansion Pascal’s triangle11 11 2 11 3 3 11 4 6 4 11 5 10 10 5 11 6 15 20 15 6 11 7 21 35 35 21 7 11 8 28 56 70 56 28 8 1(A + a)2nbinomial equation

32. for 1gene pair, n=1 (A + a)2 = 1A2 + 2Aa + 1a211 11 2 11 3 3 11 4 6 4 11 5 10 10 5 11 6 15 20 15 6 11 7 21 35 35 21 7 11 8 28 56 70 56 28 8 1Use Pascal’s triangle for coefficients

33. for 2gene pairs, n=2 (A + a)4 = 1A4 + 4A3a + 6A2a2 + 4Aa3 + 1a411 11 2 11 3 3 11 4 6 4 11 5 10 10 5 11 6 15 20 15 6 11 7 21 35 35 21 7 11 8 28 56 70 56 28 8 1Use Pascal’s triangle for coefficients

34. for 3gene pair, n=3 (A + a)6 = 1A6 + 6A5a + 15A4a2 + 30A3a3 + 15A2a4 + 6Aa5 + 1a611 11 2 11 3 3 11 4 6 4 11 5 10 10 5 11 6 15 20 15 6 11 7 21 35 35 21 7 11 8 28 56 70 56 28 8 1Use Pascal’s triangle for coefficients