Sex Linked Genes The Xs and Ys of Genetics X and Y ● Humans have ___ pairs of chromosomes. One of those pairs are called the “sex chromosomes”. ● Sex chromosomes can either be __ chromosomes or ___ chromosomes. Sex Linked Genes • The ___ and ___ sex chromosomes carry the genes that determine your gender • Men have a combination of ___ and ___ sex chromosomes. • Women have two ___ chromosomes. XY XX Before we move on, • Draw a Punnett square to show the probability of having a boy in any given pregnancy. • Remember boys are XY and girls are XX Sex Linked Genes Genes that are carried by either sex chromosome (X or Y) are said to be _______________ Males • Men normally have an X and a Y combination of sex chromosomes. • Since only men inherit the Y chromosome, they are the only ones that inherit ______ _____________ Females Females have 2 X chromosomes X Linked Traits • Men and Women can get the X-linked traits, Why? Because they both ______ X chromosomes. Sex inheritance patterns for male and female children X Chromosome Traits • Men only have one X chromosome • Therefore genes on that chromosome are expressed in the male phenotype, even if it is a ___________ gene. XAY dominant, shown XaY recessive, shown X-linked traits X X • In women, a recessive allele on the X chromosome is often masked on their phenotype. • If the woman is heterozygous for the X-linked disease she is said to be a ___________ . This means she does not have the disease, but can pass it to her children. X-linked traits • In humans, at least _____ genes are known to be X-linked. • Genes for hemophilia, red-green color blindness, congenital night blindness, and Duchene muscular dystrophy. Hemophilia • An X-linked genetically inherited recessive disease • Can not clot their blood • Severe bleeding from minor cuts • Mostly in ________ Red-Green Color Blindness • X-linked • Cannot perceive the difference between red and green • Most often afflicts males Muscular Dystrophy (MD) • Characterized by a gradual irreversible wasting away of skeletal muscle. • An X-linked trait most often passed on to sons from their mothers. • Begins to weaken the legs of boys by age 3 and gets worse every year. • No cure and the individual afflicted with the disease usually dies by age 30. https://www.youtube.com/watch?v=Fw0CBMw0ios Y-linked Traits • The Y chromosome is small and therefore does not contain many genes • Y linked diseases are very rare • Only passed from father to son. • Example: Male infertility or retinitis pigmentosa (causes progressive loss of sight.) Hypertrichosis Pinnae. • Hairy ears • Can happen later in life. • Y-linked