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