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? [Figure 11.5]
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
pedigree analysis [Figure 11.9]
molecular genetics
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) [Figure 11.12]
caused by abnormal number of chromosomes
due to improper separation of chromosomes during meiosis [Figure 11.17]
may have the wrong number of autosomes (e.g. Down syndrome) [Figure 11.18]
may have the wrong number of sex chromosomes
© Carol L. Wymer, 2003