1. A father homozygous for a dominant autosomal trait has a child with a heteroz
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Question
1. A father homozygous for a dominant autosomal trait has a child with a heterozygous mother. What is the percent chance that the child will have a homozygous recessive phenotype?
A.
0%
B.
50%
C.
100%
2. A gene linked to color blindness is found on the human X chromosome. In a female, how many alleles of this gene are found in a differentiated eye cell?
A.
4
B.
3
C.
2
3. Maple syrup urine disease is an autosomal recessive gene. The R allele leads to a normal protein product, whereas r leads to a mutant protein. Which genotype below will display the Maple syrup urine disease phenotype?
A.
rr
B.
Rr and rr
C.
Rr
A.
0%
B.
50%
C.
100%
Explanation / Answer
1.
In humans, there is 23 pair of chromosomes of which 22 pairs is autosomes and 1 pair is called allosomes or sex chromosomes. The last pair of chromosomes is called sex chromosomes.
In the given condition, a homozygous father for an autosomal dominant trait is crossed with heterozygous mother.
The cross will be as follows:
Based on the above cross no child will have a homozygous recessive phenotype.
Hence, the correct option among the following is A.
2.
In humans, there is 23 pair of chromosomes of which 22 pairs is autosomes and 1 pair is called allosomes or sex chromosomes. The last pair of chromosomes is called sex chromosomes.
The sex chromosomes are X and Y in case of males, while females contain X and X chromosomes.
In females, the number of X-chromosomes is two in number thus, the alleles in differentiated eye cell is two in number.
Hence, the correct option among the following is C.
3.
In the given condition, the maple syrup urine disease is an autosomal recessive trait. The “R” represents dominant allele, while “r” represents recessive allele that leads to mutation.
The dominant character is expressed in both homozygous (RR) and heterozygous (Rr) condition, while recessive character is expressed only in homozygous condition (rr).
Hence, the correct option among the following is A.
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