Sex-linked traits are traits determined by genes on the X or Y chromosomes. For example, colorblindness and baldness are found on the X chromosome. In humans, traits like baldness are more commonly expressed in males because they only have one X chromosome, while females need two copies of the gene to show the trait. A Punnett square shows that there is a 50% chance a child will be male or female. If the mother carries the baldness gene, there is a 25% chance their child will be bald male and 25% chance will be a carrier female. If the father is bald, all sons will be bald but daughters will be carriers. If the mother is bald, all children will be carriers and

1. Sex-Linked Traits X chromosome Y chromosome Boy or Girl? The Y Chromosome “Decides”

3. What are Sex Linked Traits ? In 1910, Thomas Morgan discovered traits linked to sex chromosomes in fruit flies. Some genes are attached to the X and Y chromosomes EXAMPLE: In humans, colorblindness and baldness are found on the X chromosomes

4. What are Sex Linked Traits ? In Men, traits expressed anytime present In Women, must have two genes to show trait Children inherit baldness from their mothers

5. Punnett Square: What sex will the offspring be? 50% chance of a male or a female child.

6. Baldness is carried by the mother Phenotype: 25% bald males 25% bald carrier females 25% not bald males 25% non-carrier females

7. If Dad is bald, will you be bald? Phenotype: 0% bald males 100% bald carrier females

8. What if Mom is bald? Phenotype: 100% carrier females 100% bald males