Principles of Inheritance and Variation Test

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Principles of Inheritance and Variation Test - 74

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Weekly Quiz Competition

Question 1
1 / -0

In human beings sex is determined

A
At the time of fertilization of ovum

B
During 6th week of foetal life when androgens are produced

C
Before fertilization of ovum

D
During 7th and 8th weeks of foetal Life when gonads differentiate into testis and ovaries

Solution

In human beings, sex is determined At the time of fertilization of ovum because the sex will depend on whether X or Y sperm fertilizes the X ovum. So, the correct option is A. ( At the time of fertilization of ovum )
Question 2
1 / -0

Failure of cytokinesis after telophase stage of cell division results in an increase in a whole Set of chromosomes in an organism. The phenomenon is called as

A
polyploidy

B
aneuploidy

C
haploidy

D
diploidy
Solution
- Polyploidy is the phenomenon of having more than two genomes or two sets of chromosomes. It occurs in nature due to the failure of chromosomes to separate at the time of anaphase either due to non-disjunction or due to non-formation of spindle. Cytokinesis does not occur after telophase stage leading to polyploidy.
- So, the correct answer is 'polyploidy'
Question 3
1 / -0

Select the disease which is caused by recessive autosomal genes when present in homozygous condition.

A
Alkaptonuria

B
Albinism

C
Cystic fibrosis

D
All of these
Question 4
1 / -0

A pedigree is shown below for a disease that is autosomal dominant. What would be the genetic make up of the first generation?

A
AA, Aa

B
Aa, aa

C
Aa, AA

D
Aa, Aa

Solution

As the disease is autosomal dominant, hence, the male parent who is normal must have the homozygous recessive genotype i.e., aa. The affected female can have either Aa or AA genotype.
If the genotype is M, all-the progenies will surely be diseased but if the genotype is Aa, then there is a 50% chance of having normal offsprings. But unfortunately the couple has produced only affected progeny and each of them must have the genotype Aa.
So, the correct answer is 'Aa, aa'.
Question 5
1 / -0

In the $$F_2$$ generation of a Mendelian dihybrid cross the number of phenotypes and genotypes are

A
Phenotypes-4; Genotypes-16

B
Phenotypes-9; Genotypes-4

C
Phenotypes-4; Genotypes-8

D
Phenotypes-4; Genotypes-9

Solution

The dihybrid cross is a cross between two different genes means a cross between two different characters.
In F2 generation - 4 phenotypes are present (yellow round, Green round, yellow wrinkled and green wrinkled)
And 9 genotypes are present (1:2:1:2:4:2:1:2:1)
So the correct answer is "Phenotypes-4, Genotypes-9".
Question 6
1 / -0

Occasionally, a single gene may express more than one effect. The phenomenon is called

A
multiple allelism

B
mosaicism

C
pleiotropy

D
polygeny.

Solution

When there are three or more alternative forms of a gene, it is called multiple allelism. Polygeny suggests that humans evolved from several different ancestors. When a single gene has more than one effects, it is called pleiotropy.
So, option C is the correct answer.
Question 7
1 / -0

A cross between two tall plants resulted in offspring having few dwarf plants. What would be the genotypes of both the parents?

A
TT and Tt

B
Tt and Tt

C
TT and TT

D
Tt and tt

Solution

(b) Tt and Tt
Explanation: In the case of TT and Tt; all offspring would be tall (TT, Tt). In the case of option ‘c’ no gene for a dwarf is present, so all offspring will be tall. In the case of option 'd’, one of the parent plants is dwarf, so it is incorrect. In the case of option ‘b’, most of the offspring will be tall and a few will be a dwarf (TT, Tt, tt). Option ‘b’ is the correct answer.
Question 8
1 / -0

In the following pedigree charts, the mutant trait is shaded black. The gene responsible for the trait is

A
Dominant and X linked

B
Dominant and autosomal or dominant and X linked

C
Recessive and X - linked

D
Recessive and Y- Linked
Solution
X-Linked Dominant features:-
Both males and females are affected; often more
Females than males are affected
Does not skip generations.
Affected sons must have an affected mother.
Affected daughters must have either an affected mother or an affected father.
Affected fathers will pass the trait on to all their daughters.
So, the correct option is 'Dominant and X linked'.
Question 9
1 / -0

Mr. Christopher is colourblind and carrier for Phenylketonuria (PKU). What percentage of sperms possesses defective allele for both?

A
0%

B
25%

C
50%

D
100%

Solution

Colourblindness is an X linked recessive disease whereas Phenylketonuria (PKU) is an autosomal recessive trait.
Since Mr. Christopher is a carrier for PKU, this means, only one allele for PKU is present in the autosome. He is colorblind this means that he has the genotype X^cY.
The sperms produced by the man will be half carrying X chromosome and half carrying Y chromosome. This means that 50% of the sperms will be carrying the defective allele for colorblindness. Out of these 50% sperms, half of these will be having the defective allele for phenylketonuria as well i.e. 25%.
So, the correct answer is '25%'.
Question 10
1 / -0

If the husband is PTC taster and wife is PTC non-taster. Their daughters are non-tasters but their son is a taster. This is not related to a sex-linked trait. Out of four a, b, c, d which pedigree is correct?

A

B

C

D

Solution

People having the ability to taste the bitter compound phenylthiocarbamide or PTC, are PTC tasters whereas, for some people, PTC seems tasteless and such people are called PTC non-tasters. The inability to taste PTC is an autosomal recessive genetic disorder i.e. it occurs when the allele responsible for this trait is present in homozygous recessive condition on the autosomes.
Since the wife is PTC non-taster, this means she has two alleles for this trait whereas, the husband is PTC taster which means he may have one allele for this trait none at all.
But it is given in the question that their son is a taster. This means the son has inherited one autosome carrying the allele for this trait, from his mother but a normal autosome from his father.
Hence, pedigree D shows correct representation for this in which wife is affected and husband is unaffected and their son is also unaffected. The daughters may be affected because one autosome they will inherit from the mother and the other one from father which may also have the allele for PTC trait.
So, the correct answer is option D.