Principles of Inheritance & Variation Test

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Principles of Inheritance & Variation Test - 6

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Weekly Quiz Competition

Question 1
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Inheritance of which of the following traits is shown in the given cross?

A
X-linked dominant trait

B
X-linked recessive trait

C
Autosomal recessive trait

D
Autosomal dominant trait
Solution
In the given cross, passing of disease is from carrier female to male progeny (criss-cross inheritance). Any trait that shows criss-cross inheritance is located on the sex chromosome.
Presence of a single recessive gene i.e. Xc in carrier individuals (XXC) does not cause the disease, thus the trait is recessive.
Question 2
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How are Mendelian disorders transmitted to offspring?

A
Through multiple gene alterations.

B
Only through the maternal lineage.

C
By alteration or mutation in a single gene following the principles of inheritance.

D
Randomly, without any pattern of inheritance.

Solution

Mendelian disorders are mainly determined by alterations or mutations in a single gene and are transmitted to the offspring based on the principles of inheritance, which can be traced using pedigree analysis.
Question 3
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Study the given pedigree chart showing the inheritance of an X-linked trait controlled by gene 'r '
What will be the genotypes of individuals A, B, C and D respectively?

A
XX , X^r Y, X^r X, XY

B
X^r X^r , XY, XX, XY

C
X^r X, X^r Y^r , X^r X^r , X^r Y

D
XX, X^r Y^r , XX, XY

Solution

Genotypes of different individuals in the given pedigree chart can be illustrated as:
Question 4
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Select the incorrect statement regarding pedigree analysis

A
Solid symbols show unaffected individuals

B
Proband is the person from which case history starts

C
It is useful for genetic counsellors

D
It is an alalysis of traits in several generations of a family

Solution

In pedigree analysis, solid symbol shows affected individuals.
Question 5
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Assertion (A): All daughters of a man affected by hemophilia will be carriers of the disease.
Reason (R): Hemophilia is a sex-linked recessive disorder carried on the X chromosome.

A
Both A and R are true, but R is not the correct explanation of A.

B
A is true, but R is false.

C
A is false, but R is true.

D
Both A and R are true, and R is the correct explanation of A

Solution

The assertion is true because a man affected by hemophilia will pass his affected X chromosome to all of his daughters, making them carriers of the disease. The reason is also true and provides the correct explanation because hemophilia is indeed a sex-linked recessive disorder carried on the X chromosome, and males pass their single X chromosome to all their daughters.
Question 6
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Fused ear lobes appear in the progeny due to an autosomal recessive gene. Work out the genotypes of members in the given pedigree.

A
d

B
b

C
c

D
a

Solution

Given pedigree chart for fused ear lobes (autosomal recessive trait) can be explained as follows:
Question 7
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In the following pedigree chart, the mutant trait is shaded black. The gene responsible for the trait is

A
dominant and sex linked

B
dominant and autosomal

C
recessive and sex linked

D
recessive and autosomal

Solution

The given trait cannot be sex-linked as sex-linked traits follow criss-cross inheritance and in the given pedigree, no criss-cross inheritance is being followed. The trait exhibited in pedigree chart is autosomal recessive. An autosomal recessive trait appears in case of marriage between two heterozygous individuals (Aa x Aa=3Aa+1aa), a recessive individual with hybrid (Aa x aa=2Aa+2aa) and two recessives (aa x aa= all aa). It expresses its effect only in pure or homozygous state.
If the trait had been controlled by dominant gene, then one of the parent must have possessed the dominant gene and hence the disease.
Question 8
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Given pedigree chart depicts the inheritance of attached ear lobes, an autosomal recessive trait.
Which of the following conclusions drawn is correct?

A
Parents are heterozygous

B
Parents are homozygous dominant

C
Parents are homozygous recessive

D
None of these

Solution

Given pedigree can be illustrated as follows:
Question 9
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Study the pedigree chart of a family showing the inheritance of myotonic dsytrophy
The trait under study is

A
dominant X-linked

B
recessive X-linked

C
autosomal dominant

D
recessive Y-linked

Solution

Autosomal domionant trait can express its effect in homozygpous as well as heterzygous condition.
Question 10
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If A = normal allele, a = albino allele, then genotypes of father and mother respectively are?

A
Aa and Aa

B
AA and Aa

C
Aa and AA

D
Aa and aa

Solution

Albinism is hereditary lack of pigmentation in an organism. It is an autosomal recessive disorder. Albino humans lack dark pigment melanin in their skin, hair or eyes. The allele responsible is recessive to allele for normal pigmentation. Father 's and mother 's genotype should be Aa. They both are carriers of the disease.
The chances of this couple 's fifth child being an albino are 1 in 4.