1. Genetics: Karyotypes and Sex-linked traits March 15 -19, 2010

2. Section 12.2 Summary – pages 315 - 322 Sex determination If you are female, your 23 rd pair of chromosomes are homologous, XX. If you are male, your 23 rd pair of chromosomes XY, look different. X X Female YX Male

3. Section 12.2 Summary – pages 315 - 322 Sex determination XX Female XY Male X X XY XX Female XY Male XX Female XY Male

4. What is a karyotype? Karyotypes are a chart of chromosomes pairs in metaphase. They are arranged according to length and location of the centromere.

5. What are karyotypes used for? They are used to determine the gender of an offspring and also can be used to pinpoint unusual chromosome numbers in cells.

6. What do they look like? Normal FemaleNormal Male

7. Remember... Males have an X and Y at chromosome pair 23. Females have two X’s.

8. Abnormalities - Trisomy

9. Abnormalities: Why do they happen? Nondisjunction! Nondisjunction is when sister chromosomes fail to separate properly during meiosis; this results in too many or too few chromosomes in the egg and sperm.

10. Section 12.2 Summary – pages 315 - 322 Traits controlled by genes located on sex chromosomes are called sex-linked traits. The alleles for sex-linked traits are written as superscripts of the X or Y chromosomes. Because the X and Y chromosomes are not homologous, the Y chromosome has no corresponding allele to one on the X chromosome and no superscript is used. Sex-linked inheritance

11. Example: Male-pattern baldness

12. Genotype and Phenotype Ratios