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Mendel’s 1 st Law - Segregation

Mendel’s 1 st Law - Segregation Each individual has two alleles (copies) of every gene. These alleles separate during sperm/egg cell formation Mendel’s 2 nd Law – Independent Assortment During gamete formation, different pairs of alleles segregate independently of each other.

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Mendel’s 1 st Law - Segregation

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  1. Mendel’s 1st Law - Segregation Each individual has two alleles (copies) of every gene. These alleles separate during sperm/egg cell formation Mendel’s 2nd Law – Independent Assortment During gamete formation, different pairs of alleles segregate independently of each other

  2. Potential gametes A B 1/4 A b 1/4 a B 1/4 a b 1/4 A a B b

  3. AB & ab Ab & aB

  4. P X aa bb AA BB X F1 Aa Bb F2 100 100 100 100 ab aB AB Ab

  5. P X BB CC bb cc X F1 Bb Cc F2 151 154 1195 1339 BC bC Bc bc

  6. Gametes All parental 50% parental 50% recombinant

  7. X F1 F2 151 154 1195 1339 BC bC bc bC 10.7 m.u. RF = 10.7 % so B C

  8. DCO lead to underestimation of genetic map distances Solution is to use three point cross

  9. A female Drosophila is heterozygous at three autosomal linked gene loci: e+ brown body e ebony body h+ hairless legs h hairy legs c+ straight wings c curvy wings In order to map these genes, this heterozygote is crossed to a homozygous male recessive fly and the following phenotypes of progeny were obtained: e h c 356 e+ h+ c+ 347 e+ h c 2 e h+ c+ 3 e h c+ 42 e h+ c 19 e+ h+ c 53 e+ h c+ 22 844 Why didn’t we do the cross the other way round i.e. with a heterozygous male? (1) Which is the middle gene? (2) Calculate the map distances between the genes. (4) Is there any evidence of interference? (2)

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