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प्रश्न
Linkage and crossing-over of genes are alternatives of each other. Justify with the help of an example.
उत्तर
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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संबंधित प्रश्न
Name the ‘two’ types of maps generated by H.G.P.
Answer the following question.
British geneticist R.C. Punnett developed a graphical representation of a genetic cross called “Punnett Square”. Mention the possible result this representation predicts of the genetic cross carried.
Give detail account of sex-linked inheritance.
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.
- It is exhibited by genes located on non-homologous regions of X and Y chromosomes
- Y-linked trait is hypertrichosis.
- X-linked traits are haemophilia, red-green colour blindness, myopia (near sightedness).
The contrasting pairs of factors in Mendelian crosses are called ______.
In a cross between AABB × aabb, the ratio of F2 genotypes between AABB, AaBB, Aabb, and aabb would be ______.
After crossing two plants, the progenies are found to be male sterile. This phenomenon is found to be maternally inherited and is due to some genes which are present in ______.
What is true about the crossing over between linked genes?
