In: Biology
QUESTION 14
In a cross between AaBb x AaBb, roughly 50% of the offspring show the recessive phenotype and 50% show the dominant phenotype. This indicates that:
crossing over has occurred |
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dominance is incomplete |
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the two genes are on the same chromosome |
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homozygous recessive is lethal |
QUESTION 15
A man with hemophilia marries a woman who is normal and not a carrier. Hemophilia is a recessive X-linked allele. Which of the following is true?
None of the children will be carriers |
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All of the boys will have the disease |
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All of the girls will have the disease |
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All of the girls will be carriers |
QUESTION 16
An organism with 72 chromosomes in the G1 phase of meiosis will have how many chromosomes per gamete?
18 |
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36 |
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9 |
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72 |
QUESTION 18
A farmer plants 1000 seeds of corn. The offspring were 544 tall with yellow seeds, 188 tall with green seeds, 183 short with yellow seeds and 64 short with green seeds. What were the genotypes of the parents?
Ttyy x TtYy |
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TTYY x ttyy |
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TtYy x TtYy |
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TtYy x ttyy |
Ans14)The two genes are on the same chromosome.
We can see that normally 16 combinations would have been possible out of which some new recombinants would also be produced but it is mentioned that 50% are recessive and 50% dominant meaning that the genes are linked and present on same chromosome.
Ans15)All the girls will be carriers
This is because one X chromosome in girl comes from mother and one from father meaning that if the father is hemophilic then he will definately have abnormal gene on X chromosome and this will be passed on the the daughter while the mother is normal
So the daughter will have an abnormal X chromosome and one normal one meaning that she will be a carrier.
But the boy child will not be affected as the mother is normal and from father only Y chromosome is taken which is also healthy and normal.
Ans16)36
The number of chromosome in gametes due to meiosis reduces to half
So if there are 72 chromosomes is G1 phase then there will be 36 chromosomes in gametes after meiosis has completed.
Ans18)TtYy × TtYy
544-tall yellow
188-tall green
183-short yellow
64-short green
So the ratio will be 9:3:3:1
This phenotypic ratio is seen with a dihybrid cross so TtYy×TtYy