1. Genetics Continued

2. Genetic variation The major advantage of sexual reproduction is that it creates genetic variation within a species. We have 23 pairs of chromosomes so there are a possibility of 2 23 different combinations within you.

3. Genetic variation Since sperm and egg work together to create a human, it is 2 23 X 2 23 or about 70 trillion possibilities. This results in organisms with unique phenotypes.

4. Turn and talk Why is having 70 trillion possible genotypes important?

5. Crossing over Crossing over is the exchange of chromosome segments during prophase of meiosis I. Basically it occurs when part of each chromosome breaks off and reattaches to the other chromosome. Crossing over occurs anytime a germ cell divides.

6. Recombination The term recombination refers to any mixing of parental alleles, other than crossing over.

7. Disorders caused by recessive alleles 2 copies of the allele must be present for the person to have this kind of disorder. Cystic fibrosis is an example of a disorder causes by recessive alleles.

8. Disorders caused by recessive alleles A carrier is someone who has 1 allele for the disorder and 1 normal allele. With this kind of disorder, there are 3 types of people:  Normal  Carrier  Has the disorder

9. Disorders caused by recessive alleles

10. Disorders caused by dominant alleles Only 1 copy of the allele must be present for the person to have this kind of disorder. Huntington’s disease is an example of a disorders caused by dominant alleles.

11. Disorders caused by dominant alleles

12. Why is there no such thing as a “carrier” for a disorder caused by dominant alleles?

13. Sex and autosomal chromosomes Sex chromosomes are chromosomes that determine an individuals sex. Autosomal chromosomes are the rest of the chromosomes.

14. Sex chromosomes Genes, beside sex traits, are located on the sex chromosomes. You know that:  XX is female  XY is male

15. Sex chromosomes What do you notice about the X and Y chromosomes?

16. Sex chromosomes The X chromosome is much larger than the Y, and carries many more genes. The X chromosome has more influence over phenotype than the Y.

17. Sex-linked traits

18. Hemophilia Hemophilia is a sex linked genetic disorder that prevents blood from clotting properly.

19. Hemophilia