The smidget is a tiny mammal whose sex (like humans) is determined by the presence/absence of a Y chromosome and whose dosage compensation mechanism is just like humans as well. But, this mammal differs from humans in having only two of its thousands of genes on its X chromosome. One of the two genes is called alb. Individuals hemizygous or homozygous for a recessive, loss-of-function mutant allele are white furred, while alb-/alb+ heterozygotes have patches of purple fur interspersed with patches of white. The product of an autosomal gene, called doc, is required for X-chromosome inactivation. What is the phenotype of an XXY smidget that is wild-type for both of these genes? Select one sex and one color phenotype
A.Male
B.Female
C.solid white fur
D.solid purple fur
E.patches of white & purple fur
What is the phenotype of an XX individual that is alb-/alb+; doc-/ doc-? Select one sex and one color phenotype.
A. male
B. female
C. solid white fur
D. solid purple fur
E. patches of white & purple fur
Would an XXX smidget that is alb-/alb-/alb+ have more, less or the same amount of white fur as an XX smidget that is alb-/alb+?
A. More
B. less
C. same
To determine the phenotypes in each scenario, let's break down the information given and apply the rules mentioned.
First question:
The smidget's sex is determined by the presence or absence of a Y chromosome, similar to humans. The dosage compensation mechanism, which balances gene expression between males (XY) and females (XX), is also similar to humans. However, the smidget differs from humans in that it only has two of its thousands of genes on its X chromosome.
One of these X-linked genes is called "alb." If an individual is hemizygous (having only one copy) or homozygous (having two copies) for a recessive, loss-of-function alb mutant allele, they will have white fur. On the other hand, heterozygotes (alb-/alb+) will have patches of purple fur interspersed with white.
The other gene mentioned is an autosomal gene called "doc," which is required for X-chromosome inactivation. X-chromosome inactivation is the process in females that ensures one X chromosome is randomly inactivated in each cell, to achieve gene dosage balance with males who have only one X chromosome.
Now, let's answer each question step by step:
1. Phenotype of an XXY smidget that is wild-type for both genes:
Since the smidget has an XXY sex determination system, it is male. In terms of fur color, it is wild-type for both alb (not alb-/alb+), which means it does not have any patches of purple fur. Therefore, the correct answer is A. Male with solid white fur.
2. Phenotype of an XX individual that is alb-/alb+; doc-/doc-:
Since the XX individual has a typical female sex determination system, it is female. In terms of fur color, it is alb-/alb+ which means it will have patches of purple fur interspersed with white. Additionally, it is doc-/doc-, which means the X-chromosome inactivation process is disrupted, and the patches may not be balanced. Therefore, the correct answer is E. Female with patches of white and purple fur.
3. Comparison between an XXX smidget that is alb-/alb-/alb+ and an XX smidget that is alb-/alb+:
Since both smidgets have a typical female sex determination system, they are both female. In terms of fur color, both individuals have the alb- allele, which means they will have white fur. However, the XXX individual has three copies of the alb- allele (alb-/alb-/alb+), while the XX individual has only two copies (alb-/alb+). Therefore, the XXX smidget will have more white fur compared to the XX smidget. The correct answer is A. More.
These answers are derived by interpreting the information provided and applying the rules mentioned.