Sex-linked Traits Using punnett squares

INHERITANCE OF SEX CHROMOSOMES Humans have 23 pairs of chromosomes Autosomes: 22 pairs are non-sex determining chromosomes the 23rd pair determines the sex of the offspring

female sex chromosomes - XX

male sex chromosomes - XY ( y is smaller than x and has different genes)

Who determines the child's sex? the male

SEX- LINKED TRAITS an inherited trait that has a gene on the x chromosome but no corresponding gene on the y chromosome (genes that only exist only on the sex chromosomes)

Examples of human sex-linked traits Hemophilia Red-green color blindness Muscular dystrophy Male pattern baldness

How to work sex-linked trait problems Hemophilia: is a rare, inherited bleeding disorder in which your blood doesn’t clot normally. If you have hemophilia, you may bleed for a longer time than others after an injury. You also may bleed internally, especially in your knees, ankles, and elbows. This bleeding can damage your organs or tissues and, sometimes, be fatal.

All possible genotypes & phenotypes: XHXH XHXh XhXh XHY XhY Normal female Female carrier Female hemophiliac Normal male Male hemophiliac

What is a carrier? carrier - expresses the normal characteristic but has both dominant and recessive genes (have the gene for a trait but do not express the trait themselves) XHXh for sex-linked traits, males cannot be carriers

How to work sex-linked trait problems: start with this type of punnett square X X X X Y X Y X Y

Cross a normal husband with a carrier wife How to work sex-linked trait problems: put the genes on the X chromosome H h X X H H H H h X X X X X H h Y X Y X Y Cross a normal husband with a carrier wife