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


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



Linkage and crossing over of genes are alternatives of each other. Linkage is the tendency of the genes present in the same chromosome to stay together during hereditary transmission, while crossing over is the mutual exchange of segments of non-sister chromatids of homologous chromosomes during the process of meiosis. An example of linkage: A double dominant female Drosophila homozygous for red eyes and normal wings is crossed with a double recessive male Drosophila homozygous for purple eyes and vestigial wings. The F1 flies are heterozygous red-eyed and normal winged. It is then test crossed with a double recessive male having purple eyes and vestigial wings. The F2 generation comprises two types of flies—red eyed, normal winged and purple eyed, vestigial winged in the ratio of 1:1. No recombinant types are formed because linkage is complete and no crossing over occurs.

An example of crossing over: A double dominant sweet pea plant homozygous for blue flowers and long pollen grains is crossed with a double recessive plant homozygous for red flowers and round pollen grains. The F1 flies are heterozygous blue flowered and long pollen grains. It is then crossed with a double recessive plant having red flowers and round pollen grains. The F2 generation of plants has a new combination of traits— blue flowers and round pollen grains and red flowers and long pollen grains. This is due to crossing over, i.e. separation of genes for flower colour and form of pollen grains during gamete formation.

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2013-2014 (March) All India Set 1

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What is criss-cross inheritance?

Name the ‘two’ types of maps generated by H.G.P.

Define Linkage.

Define the following:

test cross.

A cross between a normal couple resulted in a son who was haemophilic and a normal daughter. In course of time, when the daughter was married to a normal man, to their surprise, the grandson was also haemophilic.
(a) Represent this cross in the form of a pedigree chart. Give the genotypes of the daughter and her husband.
(b) Write the conclusion you draw of the inheritance pattern of this disease.

Define complete linkage. Give an example of a cross, showing complete linkage.

Answer the following question.
Explain linkage and recombination as put forth by T.H. Morgan based on his observations with the Drosophila melanogaster crossing experiment.

Very Short Answer Question.

What is crossing over?

Very Short Answer Question.

Give one example of complete sex linkage?

What is a linkage? How many linkage groups do occur in human being?

Give an example of complete linkage.

How many linkage groups are present in Drosophila melanogaster?

Write a note on sex linkage.

______ results in separation of linkage groups during meiosis.

Which of the following refers to tendency of genes to inherit together?

When a white eye Drosophila male (Xr Y) is crossed to a red eye female (XR XR), in the F2 generation all the females are red eyed and 50% males are white eyed. In a criss-cross test, when males are white eyed. In a criss-cross test, when a white eyed female (Xr Xr) is crossed to a red eye male (XRY), the F1 generation offspring had white eyed males while the female offspring bad red eyes. Instead of crossing of a white eyed female (Xr Xr} to a red eyed male (XRY), white eye female (XrXr) to white eye male (XrY) is crossed, the F1 generation will have the following phenotypes and genotype.

What was Morgan's observation when he hybridized yellow bodied white eyed female Drosophila to brown bodied red eyed male Drosophila and inter-crossed their progeny?

Analyse the following statements with respect to complete sex linkage and select the correct option.

  1. It is exhibited by genes located on non-homologous regions of X and Y chromosomes
  2. Y-linked trait is hypertrichosis.
  3. X-linked traits are haemophilia, red-green colour blindness, myopia (near sightedness).

Which of the following statement/s are INCORRECT with respect to crossing over?

i. Crossing over produces recombinations of genes by interchanging and exchanging corresponding segments between nonsister chromatids of homologous chromosomes.

ii. Crossing over occurs during zygotene of prophase I of meiosis.

All the linked genes in a particular chromosome, constitute a ____________.

The number of linkage groups of a particular species corresponds to its ______ number of chromosomes.

Linkage reduces the frequency of ______.

Blue eye colour is recessive to brown eye colour. A brown-eyed man whose mother was blue-eyed marries a blue-eyed woman. The children shall be ______.

The contrasting pairs of factors in Mendelian crosses are called ______.

In a given plant, red colour (R) of fruit is dominant over white fruit (r); and tallness (T) is dominant over dwarfness (t). If a plant with genotype RRTt is crossed with a plant of genotype rrtt, what will be the percentage of tall plants with red fruits in the next generation?

A and B genes are linked. What shall be the genotype of progeny in a cross between AB/ab and ab/ab?

Mr. Kapoor has Bb autosomal gene pair and d allele sex-linked. What shall be proportion of Bd in sperms?

What will be the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus?

To determine the genotype of a tall plant of F2 generation, Mendel crossed this plant with a dwarf plant. This cross represents a ______.

What is true about the crossing over between linked genes?

When ‘Aa’ is crossed with ‘aa’, (A is dominant over a)

The percent crossing over is high when ______.

Linkage groups can be separated during ______ in meiosis.

When the parental gene combine with itself; termed as

The strength of linkage between two genes is ______.

The enzyme involved in the process of crossing over is ______.


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