Sex-Linked Genes

Sample Problem!

• Show, using a Punnett Square, that there is a 50% of having a boy or a girl when humans

mate (aka get it on).

Determination of Sex• Girls: XX

(homologous sex chroms)

• Boys: XY (non-homol. sex

chroms)• Only ends of Y

have regions homologous to X

X

Y

Sex Linked Genes

• Found on sex chroms, mainly X (contains more DNA).• Easy to spot b/c many males will have trait XY..if trait is

on X, no competition on Y (less DNA)

Hemophilia-A Sex Linked Gene

Colorblindness- A Sex-Linked Gene

Colorblindness- A Sex-Linked Gene

Colorblindness- A Sex-Linked Gene

Colorblindness- A Sex-Linked Gene

Fruit Fly Genetics!

• Good for genetic studies (Drosophila melanogaster:

breed at a high rate A generation can be bred every 2 weeks

Only have 4 pairs of chromosomes

• Wild type = normal phenotype• Traits alternative to wild type: mutants

Some Traits are Sex Limited and Expression Depends on Sex of Individual

Let’s do another Sample Problem!

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Sex Linked Fruit Fly Sample Probs, Video Clip, and Lab