Principles of Inheritance and Variation Test

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Principles of Inheritance and Variation Test - 88

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Question 1
1 / -0

When heterozygous red flowered plant is crossed with white flowered plant, the progeny will show ratio of

A
350 red : 350 white

B
450 red : 250 white

C
380 red : 220 white

D
None of the above

Solution

Red flower colour is dominant over white; thus genotype of heterozygous red flowered plant is "Rr" and that of white flowered plant is "rr"
Parent generation : Rr x rr
Gametes
Rr ---->
rr R r
r Rr
(red) rr
(white)
Thus, phenotypic ratio 1 red: 1 white; The ratio given in option A; "350 red: 350 white" satisfies the 1:1: ratio. Correct answer is option A.
Ratio in option B gives 1.8 red : 1 white while that in option C gives 1.7 : 1; which makes these two options wrong.
Question 2
1 / -0

Exposure of an organism to UV rays causes

A
Photodynamic action

B
Formation of thymidine

C
Splitting of H-bonds of DNA

D
Splitting of phosphodiester bonds

Solution

The UV radiations can cause mutation in the cells by altering the DNA by the formation of thymine dimers or split the hydrogen bonding. This results in distortion in the structure of DNA and the cell dies due to malfunctioning of the genetic material.
Thus, the correct answer is option C.
Question 3
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Recessive mutation are expressed normally

A
Has to express always since it is a mutation

B
In heterozygous condition

C
Neither in homozygous nor in heterozygous condition

D
In homozygous condition

Solution

In recessive mutation, both the alleles must be mutant in order for the mutant phenotype to be observed and expressed only in homozygous condition. If the mutation is expressed in heterozygous condition, it is called as a dominant mutation. In the dominant mutation, the individual carries one mutant and one normal allele. Thus, option D is correct.
Question 4
1 / -0

A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as

A
TTWW

B
TTww

C
TtWW

D
TtWw

Solution

The appearance of the recessive trait in $$F_1$$ generation (dwarfism) confirms the presence of one recessive allele in the dominant parent and makes it heterozygous for plant height (Tt). Since all $$F_1$$ generation has a violet flower, the dominant parent is homozygous for flower color. If the dominant parent was double heterozygous (TtWw), the $$F_1$$ generation would exhibit recessive traits of both plant height and flower color. But all $$F_1$$ generation exhibits violet flowers which confirm that the dominant parent is homozygous for flower color.
Thus the correct answer is option C.
Question 5
1 / -0

In rabbits, black (B) coat colour is dominant over white (b) coat colour. Which Punnett square correctly represents a cross between a rabbit heterozygous for coat colour and a white rabbit?

A

B

C

D
None of the above

Solution

According to the law of dominance, a trait is represented by two contrasting factors of a gene in a heterozygous individual while the homozygous individual carries two copies of same factors. Thus, the genotype of heterozygous rabbit will be Bb and that of homozygous recessive will be bb. Law of segregation states that the two factors for a trait, present together in a heterozygous individual (Bb), do not get mixed and are separated and delivered singly during gametogenesis. Thus, the heterozygous individual produces two types of gametes: 50% gametes with “B” and 50% with “b”. The homozygous recessive individual will make all gametes with “b” allele only. Fertilization of gamete with “b” allele from a recessive parent with that carrying “b” allele from the heterozygous parent will produce homozygous recessive progeny (bb); not “Bb”. Thus, the correct answer is option C.
Question 6
1 / -0

A student completed a genetics exercise by preparing this Punnett square. [Note: 'T' represents a dominant allele and 't' represents a recessive allele.]
What were the likely genotypes of the parents ?

A
Parent 1 was homozygous, parent 2 was heterozygous.

B
Parent 1 was heterozygous, parent 2 was homozygous.

C
Both parents were heterozygous.

D
Both parents were homozygous.

Solution

The “3 dominant: 1 recessive” phenotypic ratio or “1 homozygous dominant :2 heterozygous dominant: 1 homozygous recessive” genotypic ratio is obtained by self pollination of $$F_1$$ monohybrid. Thus, both parents are heterozygous tall (Tt). The presence of one homozygous parent would given the monohybrid test cross ratio of 1:1. Homozygous varieties produce uniform $$F_1$$ generation of dominant or recessive individuals depending upon the genotype of homozygous parent. Thus, the correct answer is option C.
Question 7
1 / -0

Mating of an organism to a double recessive in order to determine whether it is homozygous or heterozygous for a character under consideration, is called as

A
Reciprocal cross

B
Test cross

C
Dihybrid cross

D
Back cross
Solution
A. Correct option is (C)

B. Explanation for the correct option.
- Cross done between unknown progeny and homozygous recessive is called test cross.
- This cross is done so as to access whether the organism whose gene are to be found is heterozygous or homozygous dominant.
- The cross used to identify the genotype behind the phenotype that can be seen.
- In other words, F1 progeny crossed with homozygous recessive is called cross test.
Question 8
1 / -0

The reason why some mutations, which are harmful, do not get eliminated from gene pool is that

A
They are recessive and carried by heterozygous individuals.

B
They are dominant and show up more frequently.

C
Genetic drift occurs because of a small population.

D
They have future survival value.

Solution

The dominant lethal mutations are not passed to next generation owing to their lethal effect on the individual. That’s why most of the mutations are recessive. The presence of the dominant allele in a heterozygote masks the harmful effect of recessive mutation and thereby these harmful mutations are silently maintained in a gene pool. The dominant harmful mutations are eliminated from the gene pool by natural selection. Genetic drift refers to the change in the frequency of a gene in a small population; it does not maintain them but brings about changes. Any harmful mutation is not maintained at the cost of the present population just for their future beneficial effects. Thus, the correct answer is option A.
Question 9
1 / -0

Mutagenic effect of $$X$$-rays was discovered by Muller in

A
Honey bee

B
Neurospora

C
Drosophila

D
Maize

Solution

Herman Joseph Muller, an American geneticist, is best known for his work on the physiological and genetic effects of radiation (X-ray mutagenesis). He was the first person, who invented mutagenic effect of X-rays using Drosophila mutants. Thus, the correct answer is option C.
Question 10
1 / -0

Which hexaploid wheat is used to make bread?

A
Triticum turgidum

B
Triticum durum

C
Triticum monococcum

D
Triticum aestivum

Solution

A. Triticum turgidum is known as Emmer wheat and is tetraploid.
B. Triticum durum is known as Pasta wheat and is tetraploid.
C. Triticum monococcum is known as Einkorn wheat and is diploid.
D. Triticum aestivum is known the bread wheat and is hexaploidy.
Hence, the hexaploidy wheat used to make bread. So, the correct answer is 'Triticum aestivum'.