Mendelian Genetics

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Example: snapdragons (flower)

red (RR) x white (rr)

RR = red flower

rr = white flower

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Incomplete Dominance

r

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Incomplete Dominance

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Codominance

Two alleles are expressed (multiple alleles) in heterozygous individuals.

Example: blood type

1. type A = IAIA or IAi

2. type B = IBIB or IBi

3. type AB = IAIB

4. type O = ii

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Codominance Problem

Example: homozygous male Type B (IBIB)

x heterozygous female Type A (IAi)

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Another Codominance Problem

Example: male Type O (ii) x female type AB (IAIB)

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Codominance

Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents?

boy - type O (ii) X girl - type AB (IAIB)

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Codominance

Answer:

Parents:

genotypes = IAi and IBi

phenotypes = A and B

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Sex-linked Traits

Traits (genes) located on the sex chromosomes

Sex chromosomes are X and Y

XX genotype for females

XY genotype for males

Many sex-linked traits carried on X chromosome

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Sex-linked Traits

Sex Chromosomes

Example: Eye color in fruit flies

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Sex-linked Trait Problem

Example: Eye color in fruit flies

(red-eyed male) x (white-eyed female) XRY x XrXr

Remember: the Y chromosome in males does not carry traits.

RR = red eyed

Rr = red eyed

rr = white eyed

XY = male

XX = female

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Sex-linked Trait Solution:

50% red eyed female

50% white eyed male

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Female Carriers

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Genetic Practice Problems

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Breed the P1 generation