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Understanding Non-Mendelian Sex-Linked Traits in Genetics

Explore sex-linked, sex-limited, and sex-influenced traits; discover how gender impacts gene expression and inheritance patterns. Learn through examples like color blindness, balding, and more.

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Understanding Non-Mendelian Sex-Linked Traits in Genetics

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  1. A few more non-Mendelian situations…For some traits, sex matters

  2. Sex Linked Traits • Traits located on sex chromosomes • Usually caused by recessive genes • Appear more commonly in males (only one X) • If recessive, females must carry trait on both XXs • Females with one copy are carriers • Males receive all X-linked traits from their mothers • Ex. Color blindness & hemophilia (abnormal blood clotting)

  3. Sex-Limited Traits • Generally found on autosomes • Only expressed in phenotype of one gender • Ex. Barred coloring in chickens normally is visible only in the roosters; Milk production in humans (females only)

  4. Sex-Influenced Traits • Traits located on autosomes • Genes are expressed differently for XX vs. XY • Ex. Early balding (influenced by testosterone) • Heterozygous men (Bb) lose their hair;Bb women do not. • Homozygous men or women (bb) become bald. • The trait is dominant in men, recessive in women. • Ex. Singing voice – same allele combo produces a high soprano female and low bass male

  5. Practice Problems • Cross a carrier female (for hemophilia) with a normal male. Of all their offspring, what is the probability they will produce a hemophiliac son? (H = normal blood, h = hemophilia) XH Xh XH XHXH XHXh Y XHY XhY

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