14.2 SQ3RL Human Chromosomes
What are Human Genes and Chromosomes?
Chromosomes 21 and 22 are the smallest human autosomes which contain over 30 million genes on each
Sex-linked Genes? There is a special pattern of inheritance on the sex chromosomes. Most sex-linked genes are found on the X chromosomes. The Y chromosome only contains a few genes because it is much much smaller than the X
- Colorblindness: There are three human genes that associate with colorblindness that are on the X chromosome. The most common type is red-green colorblindness. Color blindness probability: males = 1/10; females = 1/100. The difference is that since males only have one X chromosome, all the X genes are expressed in males even if they are recessive because they cannot be masked by a different sex chromosome in that or any other cell
- Hemophilia: - a sex-linked disorder. When a protein necessary for normal blood clotting is missing if someone has it, they may bleed to death can be cured with recombinant DNA injections
- Duchenne Muscular Disorder - a sex-linked disorder. Causes progressive weakening and loss of skeletal muscle
What is X-Chromosome Inactivation?
Discovered by Mary Lyon. Since males have two X chromosomes, one of them is turned off which forms a dense region in the nucleus called the Barr body. Barr bodies are not usually found in males because the X chromosome isn’t turned off
Chromosomal Disorders
- nondisjunction is when the homologous
