Chapter 12 - Human Genetics

How is sex determined?

• humans have 23 pairs of chromosomes: 22 match (autosomes) and 1 pair of sex chromosomes

• male is XY and female is XX

• What are the chances of having a boy or a girl?

Some traits are correlated with sex

• studies with fruit flies showed that some traits occur more frequently in males than females

• sex-linked traits

• traits whose genes are found on a sex chromosome

• if the gene is recessive and is on the X chromosome, men are more likely to express the gene than women

How do we study genetic disorders?

• pedigree analysis

• molecular genetics

Types of genetic disorders

• caused by recessive alleles

  • majority

• caused by dominant alleles

  • few

  • e.g. Huntington's disease

• some are sex-linked (e.g. color-blindness and hemophilia)

• caused by abnormal number of chromosomes

  • due to improper separation of chromosomes during meiosis

  • may have the wrong number of autosomes (e.g. Down syndrome)

  • may have the wrong number of sex chromosomes

© Carol L. Wymer, 2004