14-2 Human Chromosomes

1. Human Genes & Chromosomes

• Genes that are located close together on the same chromosome are linked•Those genes may be inherited together

• The total human genome (all of the different genes in humans) is …………

Discuss w/ Partner•How many genes make up the human genome?

2. Sex-Linked Genes

• Sex- Linked Genes- Any gene located on a sex chromosome•Most sex-linked genes are located on the X chromosome

• Sex-Linked genetic disorders mostly affect males•b/c they only have one X c’some•Many genes on the X c’some do not exist on the Y c’some

• Common Sex-Linked Genetic Disorders•Colorblindness; a defective gene for vision color which is located on the X c’some

•Hemophilia; two defective genes to control blood clotting located on the X c’some

3. X-Chromosome Inactivation

• A scientist May Lyon discovered that in human females one X c’some is randomly switched off. •Once the X c’some is turned off a dense area in the nucleus is formed.•This dense area is called a Bar Body

• The same process happens in other mammals

4. Chromosomal Disorders

• Nondisjunction- happens when homologous c’somes do not separate. • The result: an abnormal amount of chromosomes will be in the gametes• Down Syndrome- a disorder that results from an extra copy of chromosome 21

• Down Syndrome- a disorder that results from an extra copy of chromosome 21