BIOA01H3 Lecture Notes - Lecture 31: Eye Color, Sex Linkage, Reciprocal Cross
13 May 2018
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Department
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BIOA01
LEC 31 Where are my Genes?
Nov 19, 2015
• in a question if they do not mention if person has a disease, then we assume
that they are normal
• convert the math part into genetics terms
→ RECALL: X-Linked recessive disorders
- you only really see it when it’s next to y chromosome
- x recessive tends to appear in men → more colorblindness, etc.
→ Eye colour Phenotypes in Drosophila
FLIES
- normal→ trf wild type eye colour
- mutant→ white eye colour caused by recessive (found no x chromosome)
o sex linkage
- genetics works the same as us
o reciprocal cross: flies
A. true-breeding red-eyed female X white-eyed male
- female flies produce only X+ haploid gametes
- male flies produce Xw and Y gametes
- all F1 have red eyes (white eye recessive) → females receive one X from each
parent =, males inherit X chromosomes from mothers
- F2 → all red eyed females, ½ red eyed and ½ white eyed males
*** phenotypic ratio → 3 red: 1 white
B. White – eyed female X red-eyed male
- female flies produce only Xw haploid gametes
- male flies produce X+ and Y haploid gametes
- F1 females have red eyes, F1 males have white eyes → receive Xw allele from
the mother
- F2→ ½ white eyed and red eyed males AND females
*** phenotypic ratio→ 1 red: 1 white
→ Autosomal genes on different chromosomes
- one on chromosome A, gene A
- one on chromosome B, gene B
find more resources at oneclass.com
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Document Summary
Nov 19, 2015 in a question if they do not mention if person has a disease, then we assume that they are normal: convert the math part into genetics terms. You only really see it when it"s next to y chromosome. X recessive tends to appear in men more colorblindness, etc. Mutant white eye colour caused by recessive (found no x chromosome: sex linkage. Genetics works the same as us: reciprocal cross: flies, true-breeding red-eyed female x white-eyed male female flies produce only x+ haploid gametes. Male flies produce xw and y gametes. All f1 have red eyes (white eye recessive) females receive one x from each parent =, males inherit x chromosomes from mothers. F2 all red eyed females, red eyed and white eyed males. *** phenotypic ratio 3 red: 1 white: white eyed female x red-eyed male female flies produce only xw haploid gametes. Male flies produce x+ and y haploid gametes.
