1. Sex Linked Genes The Xs and Ys of Genetics

2. Sex Linked Genes There are 23 pairs of chromosomes and one of those pairs are the sex chromosomes. There are either X chromosomes or Y chromosomes. All other chromosome pairs are called autosomal.

3. Sex Linked Genes The X and Y sex chromosomes carry the genes that determine your gender Men have a combination of X and Y sex chromosomes. Women have two X chromosomes. XYXY XX

4. This is what they look like

5. Before we move on, Draw a Punnett square(yes draw in notebook) to show the probability of having a boy in any given pregnancy. Remember boys are XY and girls are XX

6. Sex Linked Genes These chromosomes not only carry the genes that determine male and female traits, but also those for some other characteristics as well. Genes that are carried by either sex chromosome (X or Y) are said to be SEX LINKED

7. 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 Y-linked traits.

8. Image of a male karyotype. A karyotype is an organized profile of a person's chromosomes

9. Females Women have 2 X chromosomes

10. Image of a female karyotype.

12. X Linked Traits Men and Women can get the X- linked traits, Why? Because they both inherit X chromosomes.

13. Sex inheritance patterns for male and female children

14. 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 recessive gene. X A Y dominant, shown X a Y recessive, shown

15. X-linked traits In women, a recessive allele on one X chromosome is often masked on their phenotype. Why? Because dominant normal allele may be present on the other X chromosome. If the woman is heterozygous for the X- linked disease, she is said to be a carrier. This means she does not have the disease, but can pass it to her children.

16. X A X A dominant, shown X A X a dominant masks the recessive, shown X a X a recessive, not shown

17. X-linked traits In humans, at least 120 genes are known to be X-linked. Genes for hemophilia, red-green color blindness, congenital night blindness, and Duchene muscular dystrophy.

18. Hemophilia An X-linked genetically inherited recessive disease Can not clot their blood Severe bleeding from minor cuts Mostly in males

20. Red-Green Color Blindness X-linked Cannot perceive the difference between red and green Most often afflicts males

22. 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.

24. 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.

25. Hypertrichosis Pinnae. Hairy ears Can happen later in life. Y-linked

26. Some thinking, … ( Write answers in notebook in complete sentences) Which parent determines the sex of a baby? What will be the sex of a child produced when an egg is fertilized by a sperm that has a Y chromosome? Based on the knowledge you have acquired thus far, can the sex of a child be predicted based on the number of males or females in a family? Why?