Principles of Inheritance and Variation Test

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Principles of Inheritance and Variation Test - 51

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Question 1
1 / -0

A phenotypic ratio of $$3 : 1$$ takes place when

A
The alleles are incompletely dominant.

B
Only recessive traits are involved.

C
Only dominant traits are involved.

D
Alleles segregate during meiosis.

E
Crossing over has occurred in anaphase II.

Solution

A monohybrid cross is a mating between individuals who have different alleles at one genetic locus of interest. The characters being studied in a monohybrid cross are governed by two alleles for a single locus. A monohybrid cross involves one character and different traits. During the formation of gametes, it carries only one factor i.e., it proves the principle of segregation also called the law of purity of gametes which states that first law of Mendel. A gamete may carry either the dominant or the recessive factor but not both as we find in F1 individuals. The gametes which are formed are always pure for a particular character or the allele pairs separate or segregate during gamete formation. Thus, the correct answer is option D.
Question 2
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Which of the following is responsible for 21 trisomy in humans?

A
Pleiotropy

B
Polygenic inheritance

C
Epistasis

D
X- inactivation

E
Nondisjunction

Solution

The presence of full or partial extra three copies of chromosome 21 causes Down syndrome. It is called as trisomy 21 and is represented as 45 +XY or 45+XX. Non-disjunction of a bivalent during meiosis produce gametes with "n+1 and n-1". Fertilisation of n+1 gamete with a normal gamete produces 2n+1 individual. Hence, non-disjunction is the direct cause of Down syndrome. Thus, the correct answer is option E.
Question 3
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If a couple has two boys and one girl, the probability of the next girl child to be born is

A
$$\displaystyle\frac{1}{4}$$

B
$$\displaystyle\frac{1}{3}$$

C
$$\displaystyle\frac{1}{2}$$

D
$$\displaystyle\frac{2}{3}$$

E
$$\displaystyle\frac{3}{4}$$

Solution

The gametes of a female are X, X' while that of a male is X and Y.
The chances of having a girl or boy depend every time on the fusion of which two gametes from male and female.
So, the four chances are:
X (from female) X (from male) - gril (XX)
X (from female) Y from male - boy (XY)
X' (from female) X (from male) - girl (X'X)
X (from female) (Y from male) - boy (X'Y)
So, the probability of the next girl child to be born is 1/2.
Question 4
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Most of the mutations occur due to

A
Certain chemicals

B
Ionizing radiation

C
Infrared radiation

D
Ultraviolet radiation

E
Random events

Solution

Mutations are random events as they do not arise out of need for some new adaptation. Rather, the mutations that confer adaptive advantage to individuals are favroed by natural selection and those with negative or neutral effects are mostly maintained as recessive allele in the gene pool. Correct answer is E.
Question 5
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Which of the following true for an offspring formed as a result of sexual reproduction?

A
The offspring gets a full set of genes from the mother and from the father.

B
The offspring gets half the genes from the mother and half the genes from the father.

C
The offspring gets all of its genes from the father.

D
The offspring gets a random mixture of genes from the mother and father.

E
The offspring gets all of its genes from the mother.

Solution

When gametes are formed in parents; each gamete has half the genetic material of the parent. When the gametes unite, the resulting offspring will receive half the genetic material of each parent. Thus, the correct answer is option B.
Question 6
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Genetic variations leading to evolution takes place due to the mutations in

A
Skin cells

B
Body cells

C
Brain cells

D
Sex cells

E
Embryo cells

Solution

Sex cells undergo meiosis and form gametes. Cross over during prophase I of meiosis produce new genetic combinations in gametes. Random fusion of these genetically diverse gametes imparts even more genetic variation to the zygote. Since the genetic material of sex cells is passed to next generation, the mutation in these cells serves as raw material for evolution. Thus, the Correct answer is D.
Question 7
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Which of the following is not caused by a mutation in DNA?

A
Sickle cells anemia

B
Phenylketonuria

C
Cystic fibrosis

D
AIDS

E
Haemophilia

Solution

AIDS (Acquired immune deficiency syndrome or acquired immunodeficiency syndrome) is a syndrome caused by a virus called HIV (Human Immunodeficiency Virus). The illness alters the immune system, making people much more vulnerable to infections and diseases
Sickle cell disease is caused by a genetic abnormality in the gene for hemoglobin, which results in the production of sickle hemoglobin.
PKU is caused by a genetic mutation (change to the DNA) in the human phenylalanine hydroxylase (PAH) gene.
A defect in the CFTR gene causes cystic fibrosis (CF). This gene makes a protein that controls the movement of salt and water in and out of your body's cells. In people who have CF, the gene makes a protein that doesn't work well. This causes thick, sticky mucus and very salty sweat.
Haemophilia is caused by an inherited genetic mutation, which mainly affects males.
A genetic mutation is a permanent alteration in the DNA sequence that makes up a gene. This means that some of the body's processes won't work in the normal way.
Thus, the correct answer is option D.
Question 8
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How is the sex of the baby determined?

A
Sex chromosomes of mother

B
Sex chromosomes of father

C
'X' chromosome of unfertilised egg

D
All 23 pairs of chromosomes

Solution

The father is responsible for determining the sex of the child. The mother has two X chromosomes and donates one X chromosome in the gamete. The father has X and Y chromosome and so the gamete can contain X or Y. The male gamete which fuses with the egg is responsible for the sex of the baby.
Thus, the correct answer is option B.
Question 9
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In human zygote male sex is determined by

A
Strength of father

B
Nutrition of mother

C
Composition of required chromosome pair

D
None of the above

Solution

Men determine the sex of a baby depending on whether their sperm is carrying an X or Y chromosome. An X chromosome combines with the mother's X chromosome to make a baby girl (XX) and a Y chromosome will combine with the mother's to make a boy (XY).

'Strength of father' and 'Nutrition of mother' has no link in determining the gender of an offspring.

So, the correct answer is 'Composition of required chromosome pair'.
Question 10
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A pleiotropic gene is one which

A
Affects one character

B
Affects more than one character

C
Supplements the effect of another gene

D
Requires another gene for expression

Solution

The ability of a gene to produce more than one phenotype in an organism is called Pleoitrophy and the genes are called Pleiotripic genes. It is not essential that the traits are equally influenced. Sometimes, the effect of the gene is more evident in case of one trait and less evident in case of another trait.

Example,gene controlling metabolism of phenylalanine

So, the correct option is ‘Affects more than one character’.

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Principles of Inheritance and Variation Test - 51

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Principles of Inheritance and Variation Test - 51

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SHARING IS CARING

Question 1

The alleles are incompletely dominant.

Only recessive traits are involved.

Only dominant traits are involved.

Alleles segregate during meiosis.

Crossing over has occurred in anaphase II.

Solution

Question 2

Pleiotropy

Polygenic inheritance

Epistasis

X- inactivation

Nondisjunction

Solution

Question 3

$$\displaystyle\frac{1}{4}$$

$$\displaystyle\frac{1}{3}$$

$$\displaystyle\frac{1}{2}$$

$$\displaystyle\frac{2}{3}$$

$$\displaystyle\frac{3}{4}$$

Solution

Question 4

Certain chemicals

Ionizing radiation

Infrared radiation

Ultraviolet radiation

Random events

Solution

Question 5

The offspring gets a full set of genes from the mother and from the father.

The offspring gets half the genes from the mother and half the genes from the father.

The offspring gets all of its genes from the father.

The offspring gets a random mixture of genes from the mother and father.

The offspring gets all of its genes from the mother.

Solution

Question 6

Skin cells

Body cells

Brain cells

Sex cells

Embryo cells

Solution

Question 7

Sickle cells anemia

Phenylketonuria

Cystic fibrosis

AIDS

Haemophilia

Solution

Question 8

Sex chromosomes of mother

Sex chromosomes of father

'X' chromosome of unfertilised egg

All 23 pairs of chromosomes

Solution

Question 9

Strength of father

Nutrition of mother

Composition of required chromosome pair

None of the above

Solution

Question 10

Affects one character

Affects more than one character

Supplements the effect of another gene

Requires another gene for expression

Solution

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