Lec10 Genetics Recap

MULTIPLE ALLELES AND POLYGENIC INHERITANCE Biology 3 Kent Kawashima

Character:eye color Trait: blue Genotype: AAAATATTATATATCCCCGTAGCTACGATCTATCTATCATCTATCTACTATCTATCTATCTATCTATCTACTATCTATCCGGCGTATCATCGGGGGGGGGGGTACTAGCTAGCTAGCTATCTACGTAGTCTACTGATCTAGCTAGTCATGCTGATCATCGTAGCTGAGCTACTAGTCGATCGTAGCTAGTCATCTAGCTGAGCTAGCTGATCGATCTAGCTAGCTGATCGTAGCGATCGTAGCTAGCTAGTCGATGCTAGCTGATCGTAGCATGCTAGCTGATGCATGCTAGCTAGCTAGCTGATCA… Phenotype: Megan Fox’s blue eyes

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

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

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

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

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

…or you may have two different alleles blue green Genotype: Heterozygous

…or you may have two different alleles green brown Genotype: Heterozygous

…or you may have two different alleles brown blue Genotype: Heterozygous

gene for eye color blue green brown ,[object Object]

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

gene for eye color gene for eye color gene for eye color gene for eye color What if many genes have an effect to one character? This is called “Polygenic Inheritance”

In Polygenic Inheritance… gene for eye color + add more of something! gene for eye color 0 no effect. gene for eye color gene for eye color alleles that either contribute to a trait or not many genes

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 + 0 gene for eye color + 0 gene for eye color + +

+ allele is called a contributory allele + 0 0 allele is called a non-contributory allele

Compare. + 0 + 0 + 0 + 0 + 0 + 0 + + 0 0 0 + + + 0 0 0 + + 0 + 0 0 + 0 + + 0 + 0 0 + 0 + 6 +, 2 0 2 +, 6 0 4 +, 4 0 8 + 8 0

Compare. + 0 + 0 + 0 + 0 + 0 + 0 + + 0 0 0 + + + 0 0 0 + + 0 + 0 0 + 0 + + 0 + 0 0 + 0 + gray dark brown green blue light brown

Arranged from least to most melanin produced + 0 + 0 + 0 + 0 + 0 + 0 + + 0 0 0 + + + 0 0 0 + + 0 + 0 0 + 0 + + 0 + 0 0 + 0 + gray dark brown green blue light brown

In polygenic inheritance… ,[object Object]

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

There is an equal effect for each contributory allele,[object Object]

Polygenic inheritance is usually the mode of inheritance for traits that are continuous – weight, height and skin tone,[object Object]

Shortcuts for Polygenic Inheritance Genetics

If you cross… AA x aa AABB x aabb Aa x Aa AaBb x AaBb 1 AABB 4 AaBB, aABB, AABb, AAbB 6 AaBb, aAbB, AabB, aABb, aaBB, AAbb 4aAbb, Aabb, aabB, aaBb 1 aabb all possible genotypes 1 AA 2 Aa, aA 1 AA relative phenotype portions expected

If you cross… AA x aa P Aa x Aa F1 Number of gene pairs: n = 1 Number of phenotypes in F2: 21 + 1 = 3 Number for genotypes regardless of position in the gene pair: 31 = 3 (two big A, one big A, no big A) 1 AA 2 Aa, aA 1 aa F2

If you cross… AABB x aabb Number of gene pairs: n = 2 Number of phenotypes in F2: 22 + 1 = 5 Number for genotypes regardless of position in the gene pair: 32 = 9 2 big A, 2 big B 2 big A, 1 big B 2 big A, 0 big B 1 big A, 2 big B 1 big A, 1 big B 1big A, 0 big B 0 big A, 2 big B 0 big A, 1 big B 0 big A, 0 big B P AaBb x AaBb F1 1 AABB 4 AaBB, aABB, AABb, AAbB 6 AaBb, aAbB, AabB, aABb, aaBB, AAbb 4aAbb, Aabb, aabB, aaBb 1 aabb regardless of position in the gene pair F2

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

for 1gene pair, n=1 (A + a)2 = 1A2 + 2Aa + 1a2 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 1 7 21 35 35 21 7 1 1 8 28 56 70 56 28 8 1 Use Pascal’s triangle for coefficients

for 2gene pairs, n=2 (A + a)4 = 1A4 + 4A3a + 6A2a2 + 4Aa3 + 1a4 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 1 7 21 35 35 21 7 1 1 8 28 56 70 56 28 8 1 Use Pascal’s triangle for coefficients

for 3gene pair, n=3 (A + a)6 = 1A6 + 6A5a + 15A4a2 + 30A3a3 + 15A2a4 + 6Aa5 + 1a6 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 1 7 21 35 35 21 7 1 1 8 28 56 70 56 28 8 1 Use Pascal’s triangle for coefficients

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