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191104SexLinkage

191104SexLinkage - vision locus If a male receives the X n...

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Inheritance Sex Linkage
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What is Sex Linkage? In addition to their role in determining sex, the sex chromosomes have genes for many characters. Genes located on a sex chromosome are called sex linked genes. In humans the term usually refers to X-linked characters: genes located only on X chromosomes. Fathers can pass X-linked alleles to their daughters, but not sons. Mothers can pass sex-linked alleles to both sons and daughters.
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Recessive alleles If a sex linked trait is due to a recessive allele: A female will express the phenotype only if she is homozygous recessive. If a male receives the recessive allele from his mother he will express the phenotype. Far more males have disorders that are inherited as sex linked recessives than females. Examples: Colour blindness Haemophilia
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Red-green colour blindness X chromosome has a locus for colour vision with two alleles: X N = Normal colour vision X n = Red-green colour blindness Y chromosome does not have a colour
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Unformatted text preview: vision locus. If a male receives the X n allele he will have impaired colour vision, whereas a female with X N X n will not. Red-green colour blindness Parental Phenotypes Carrier Female x Normal Male Genotypes X N X n X N Y Gametes Offspring 1 Genotypes Phenotypes Normal Female : Carrier Female : Normal Male : Colour blind Male 1 : 1 : 1 : 1 X N X n X N Y Female Gametes X N X n Male Gametes X N X N X N X N X n Y X N Y X n Y Showing genetic pedigree Unaffected female: Affected female: Unaffected male: Affected male: 1 2 1 2 3 4 5 1 2 3 4 5 I II III What now? Complete WS5: Sex-Linked Genes Complete WS6: Extension questions This powerpoint was kindly donated to www.worldofteaching.com http://www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching....
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