Morgan, in his dihybrid crosses with Drosophila observed deviations in the phenotypic ratio of F 2 progeny in comparison to that of Mendel. With the help of a suitable example, explain how his results deviated from that of Mendel.

Morgan carried out several dihybrid crosses in Drosophila melanogaster (fruit fly) to study genes that were sex-linked. The crosses were similar to the dihybrid crosses carried out by Mendel in peas. E.g. Morgan hybridised yellow bodied white-eyed female to brown bodied red-eyed male and intercrossed their F1 progeny. He observed that the two genes did not segregate independently of each other and F2 ratio deviated vary significantly from the 9:3:3: 1 ratio. Based on the cross Morgan stated that: (i) when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combination was much higher than the non-parental type. It is due to the linkage of two genes and the nonparental gene combination is described as recombination. (ii)when genes are grouped on the same chromosome, some genes were very tightly linked (low recombination) while others are loosely linked (high recombination). For eg. The genes white(w)and yellow(y) were tightly linked and showed 1.3% recombination while white(w) and miniature wing(m) showed 37.2% recombination.

EASY

Earn 100

What is crossing over and mechanism of crossing over?

Important Questions on Principles of Inheritance and Variation

EASY

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Give one significant difference between the following:

Linkage and crossing over

EASY

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

What map unit (Centimorgan) is adopted in the construction of genetic maps?

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

A plant heterozygous for height and flower colour

(TtRr)

are selfed and

1600

of the resulting seeds are planted. If the distance between the loci controlling height and the flower colour is

1

centiMorgan (cM), then how many offsprings are expected to be short with white flower

(ttrr)

?

EASY

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

The frequency of recombination between gene pairs on the same chromosome as a measure of the distance gene was explained by:

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

In a dihybrid cross between genes yellow, white and miniature characters, the parental

%

between yellow and white and recombination % is

92

and

8

respectively, and the cross between white and miniature characters, the recombination is

38 %

and parental is

62 %

. Identify the genetic map of these.

EASY

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

The percentage of the F₂generation offspring showing parental character for the body colour and eye colour in Morgan's experiment is:

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

How many linkage groups are present in human male?

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Drosophila has four pairs of chromosomes. How many linkage groups does it have

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Chromosome maps/ genetic maps were first prepared by

HARD

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Morgan, in his dihybrid crosses with Drosophila observed deviations in the phenotypic ratio of F₂ progeny in comparison to that of Mendel. With the help of a suitable example, explain how his results deviated from that of Mendel.

EASY

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Genetic map is one that

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Number of linkage group in Pisum sativum is

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

The number of linkage groups in a sperm and ovum of human is, respectively:

EASY

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

The distance between two genes in a chromosome is measured in cross-over units which represent

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

What will be the number of linkage groups in maize if it has 10 pairs of chromosomes?

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Briefly mention the contribution of T.H. Morgan in genetics.

HARD

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

In a dihybrid cross, when would be the proportion of parental gene combination be much higher than non-parental types, as experimentally shown by Morgan and his group.

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Linkage and crossing over of genes are alternatives of each other. Justify with the help of an example.

MEDIUM

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

In maize chromosome number is 2n = 20. The number of linkage groups in it shall be

HARD

Biology>Genetics and Evolution>Principles of Inheritance and Variation>Linkage and Crossing Over

Linkage and crossing-over of genes are alternatives of each other. Justify with the help of an example.

What is crossing over and mechanism of crossing over?

Important Questions on Principles of Inheritance and Variation

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