Describe linkage and recombination in detail.
Describe linkage and recombination in detail.
Morgan and his group observed in Drosophila that when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combination were much higher than the non parental type.
They attributed this due to physical association of the two genes and coined the term 'linkage' to describe this physical association of genes on a chromosome and the term recombination to describe the generation of non parental gene combinations.
Thus linkage is a phenomenon of genic inheritance in which gene of a particular chromosome show their tendency to inherit together.
Morgan and his group also found that even when gene were grouped on the same chromosome, some genes were tightly linked i.e. linkage is stronger between two genes if the frequency of recombination is low.
Whereas the frequency of recombination is higher if genes are loosely linked i.e. linkage is weak between two genes.
Recombination of linked genes is by crossing over (exchange of corresponding parts between the chromatids of homologous chromosomes).
All the genes linked together in a single chromosome constitute a linkage group.
The number of linkage group in an organism is equal to there haploid number of chromosomes.
This hypothesis was proved by $TH$ Morgan by his experiments on Drosophila.
Morgan and his group hybridised yellow bodies and white eyed females with brown bodies and red eyed males (wild type) and intercrossed their Fi-progeny (cross-$A$).
It was observed that the two genes did not segregate independently of each other and the $\mathrm{F}_{2}$ ratios deviated significantly from $9: 3: 3: 1$ ratio.
In $\mathrm{F}_{2}$ generation parental combinations were $98.7 \%$ and recombinant were $1.3 \%$.
In another cross (cross-B), between white bodies fly with miniature wing and a male fly with yellow body and normal wing, parental combinations were $62.8 \%$ and recombinants were $37.2 \%$ in $\mathrm{F}_{2}$ generation.
Thus it was proved from the crosses that the linkage between genes for yellow body and white eyes is stronger than the linkage between the white body and miniature wing.
His student Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and 'mapped' their position on the chromosome.
Similar Questions
In a test cross involving $F_1$ dihybrid flies, more parentaltype offspring were produced than the recombinanttype offspring. This indicates
In a test cross involving $F_1$ dihybrid flies, more parentaltype offspring were produced than the recombinanttype offspring. This indicates
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Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in $\mathrm{F}_{2}$ generation for a dihybrid cross?
Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in $\mathrm{F}_{2}$ generation for a dihybrid cross?
The four daughter cells derived from a single meiosis differ from each other due to
The four daughter cells derived from a single meiosis differ from each other due to
Morgan hybridised yellow-bodied, white-eyed females to brown-bodied, red-eyed males and intercrossed their $F_{1}$ progeny. He observed that
$(a)$ $F_{2}$ ratio was deviated very significantly from the $9 : 3 : 3 : 1$ ratio
$(b)$ Both genes did not segregate independently of each other
$(c)$ Recombinant types are not obtained in $F_{2}$ generation
$(d)$ Both genes segregate independently of each other
Select the correct set of statements :
Morgan hybridised yellow-bodied, white-eyed females to brown-bodied, red-eyed males and intercrossed their $F_{1}$ progeny. He observed that
$(a)$ $F_{2}$ ratio was deviated very significantly from the $9 : 3 : 3 : 1$ ratio
$(b)$ Both genes did not segregate independently of each other
$(c)$ Recombinant types are not obtained in $F_{2}$ generation
$(d)$ Both genes segregate independently of each other
Select the correct set of statements :
In Drosophila, long wing and broad abdomen characters are dominant over to characters vestigeal wing and narrow abdomen. A pure breeding Drosophila having long wings and broad abdomen is crossed with a pure breeding vestigeal-winged and narrow-abdomened Drosophila. Two of the $F_1$ individuals were crossed and the following results were produced in the $F_2$ generation Long wing, broad abdomen in $482$ Drosophila. Vestigeal wing, narrow abdomen in $154$ Drosophila. Which one of the following is illustrated by these results
In Drosophila, long wing and broad abdomen characters are dominant over to characters vestigeal wing and narrow abdomen. A pure breeding Drosophila having long wings and broad abdomen is crossed with a pure breeding vestigeal-winged and narrow-abdomened Drosophila. Two of the $F_1$ individuals were crossed and the following results were produced in the $F_2$ generation Long wing, broad abdomen in $482$ Drosophila. Vestigeal wing, narrow abdomen in $154$ Drosophila. Which one of the following is illustrated by these results