| A | B |
|---|
| How many base pairs of DNA are in a human diploid cell? | Over 6 billion!!! |
| How much of the DNA in a chromosome functions as genes? | Only about 2% is transcribed into RNA. |
| Which human chromosomes are the smallest human autosome? | Chromosome 21 and 22 |
| What genetic disorders are associated with chromosome 22? | There is an allele that causes a form of leukemia and another for neurofibromatosis (tumors of the nervous system). |
| Where is the gene associated with ALS (amyotrophic lateral sclerosis), otherwise known as Lou Gehrig's disease? | It is found on chromosome 21. |
| What relationship do genes located close together on the same chromosome have? | They tend to be inherited together, as they are linked. |
| Many sex-linked genes are on the X chromosome; name some of the genetic disorders associated with the X chromosome. | Duchenne muscular dystrophy; melanoma; X-linked severe combined immunodeficiency (SCID); colorblindness; hemophilia. |
| Why are sex-linked disorders more common in males than in females? | Males have just one X chromosome, while females have 2. Thus, all X-linked alleles are expressed in males, even if they are recessive. In females, there must be 2 copies of the allele, one on each of the 2 X chromosomes. |
| What controls blood clotting? | There are 2 important genes carried on the X chromosome, and these help clotting. |
| What causes hemophilia? | There is a recessive allele in either of the 2 genes that control blood clotting will cause hemophilia. |
| How is hemophilia treated? | It is treated by injections of normal clotting proteins. |
| What happens to the body when a person has Duchenne Muscular Dystrophy? | There is progressive weakening and loss of skeletal muscle. |
| What causes Duchenne Muscular Dystrophy? | It's caused by a defective verson of the gene that codes for a muscle protein. |
| If a cat has 3 colors, what sex is it? | Female--see page 352 for a discussion of having 1 X chromosome switched off. |
| What happens in nondisjunction, and what is nondisjunction? | Nondisjunction = the failure of homologous chromosomes to separate during meiosis. If it occurs, abnormal numbers of chromosomes may find their way into gametes, and the result is a disorder of chromosome numbers. |
| What is the most common form of trisomy? | Downs Syndrome in which there are 3 copies of chromosome 21. |
| What is Turner's Syndrome? | It is a sex chromosome disorder found in females; the woman inherits only one X chromsome. Women with this disorder are sterile, as their sex organs do not develop at puberty. |
| What is Klinefelter's syndrome? | It's in males who have an extra X chromosome (XXY). |
