Question

1. complete the punnett square to show how colorblindness is inherited.

x - chromosome inactivation

1. how does the cell “adjust” to the extra x chromosome in female cells?

1. what is a barr body?

1. is the following sentence true or false? barr bodies are found only in males.

1. if you saw a white cat with orange and black spots, is it most likely a male or a female? explain.

chromosomal disorders

1. what occurs during nondisjunction?

1. is the following sentence true or false? if nondisjunction occurs, gametes may have abnormal numbers of chromosomes.

1. the condition in which an individual has three copies of a chromosome is known as ____, which means “three bodies.”

Explanation:

• Question 7: In female cells, one of the X - chromosomes is inactivated. This is a mechanism to balance the gene expression between males (who have one X - chromosome) and females (who have two X - chromosomes).
• Question 8: A Barr body is an inactivated X - chromosome. It is a condensed, heterochromatic structure that is visible in the nucleus of female cells.
• Question 9: Barr bodies are found in females. Males have only one X - chromosome, so there is no need for X - inactivation in most male cells (except in some cases of chromosomal abnormalities). So the statement "Barr bodies are found only in males" is false.
• Question 10: The gene for orange and black fur in cats is located on the X - chromosome. A cat with both orange and black spots (a calico cat) has two different X - chromosomes (one with the orange allele and one with the black allele). Since males have only one X - chromosome, they can be either orange or black (or white if the white - fur gene is expressed). Females, with two X - chromosomes, can have both alleles and thus show both orange and black spots. So a white cat with orange and black spots is most likely a female.
• Question 11: During nondisjunction, homologous chromosomes (in meiosis I) or sister chromatids (in meiosis II or mitosis) fail to separate properly. This can lead to an unequal distribution of chromosomes into daughter cells.
• Question 12: If nondisjunction occurs, gametes (in meiosis) or somatic cells (in mitosis) may receive an abnormal number of chromosomes. For example, in meiosis, a gamete may receive two copies of a chromosome instead of one (or none), which is an abnormal number. So the statement is true.
• Question 13: The condition in which an individual has three copies of a chromosome is called trisomy.

Answer:

1. One of the X - chromosomes is inactivated.
2. An inactivated X - chromosome.
3. False
4. Female. The gene for orange and black fur is on the X - chromosome. Females have two X - chromosomes and can have both alleles (for orange and black), while males have only one X - chromosome.
5. Homologous chromosomes (in meiosis I) or sister chromatids (in meiosis II or mitosis) fail to separate.
6. True
7. Trisomy