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Shivam yadav

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Linkage refers to two genes located on the same chromosome. Genes that are close together on a chromosome are tightly linked. Crossing over is the process where homologous chromosomes exchange equal segments during genetic recombination. There are two theories that describe the mechanism of crossing over - the contact-first theory proposes the chromosomes first touch and break at the contact point before recombining, while the breakage-first theory states the chromosomes first break independently before recombining their segments. A three-point test cross can identify eight phenotypic classes through their frequencies or altered gene arrangements.

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Linkage and Crossing over Presented by - shivam yadav Presented to Head of department - Shree Ashok sir Msc ag 1st sem Genetics and plant breeding
Linkage :- Linkage refers to the precense of two different gene on the same chromosome. Two gene gene that occur on the same chromosome are said to be linked, and those that occur very closed together are tightly linked. Crossing over :- process in genetic by which the two chormosome of a homologus pair exchange equal segment with each other.
Coupling :- The conditioin of having the dominant allels for both genes of the parental chromosome , with both recessive on the other parental chromosome, is called coupling. Repulsion :- The opposite condition the having one dominant and one recessive on each parental chromosome is called repulsion
Theories of crossing over :- (i)Contact fist theory : According to this theory the inner to chromatids of the homologus chromosomes under going crossing over ,first touch each other and then cross over .At the point of contact breakage occurs. The broken segments again unite to from new combination . (ii)The breakage first theory : According to this theory the chromatids under going crossing over , first of all break into two without any crossing over and after that the broken segments reunite to form the new combination
Three point test cross : In a three point test cross eight different phenotypic classes are obtaind these eight classes are indentified in two different ways, viz., 1 by phenotypic frequencies and 2. by altration of gene

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Shivam yadav

  • 1. Linkage and Crossing over Presented by - shivam yadav Presented to Head of department - Shree Ashok sir Msc ag 1st sem Genetics and plant breeding
  • 2. Linkage :- Linkage refers to the precense of two different gene on the same chromosome. Two gene gene that occur on the same chromosome are said to be linked, and those that occur very closed together are tightly linked. Crossing over :- process in genetic by which the two chormosome of a homologus pair exchange equal segment with each other.
  • 3. Coupling :- The conditioin of having the dominant allels for both genes of the parental chromosome , with both recessive on the other parental chromosome, is called coupling. Repulsion :- The opposite condition the having one dominant and one recessive on each parental chromosome is called repulsion
  • 4. Theories of crossing over :- (i)Contact fist theory : According to this theory the inner to chromatids of the homologus chromosomes under going crossing over ,first touch each other and then cross over .At the point of contact breakage occurs. The broken segments again unite to from new combination . (ii)The breakage first theory : According to this theory the chromatids under going crossing over , first of all break into two without any crossing over and after that the broken segments reunite to form the new combination
  • 5. Three point test cross : In a three point test cross eight different phenotypic classes are obtaind these eight classes are indentified in two different ways, viz., 1 by phenotypic frequencies and 2. by altration of gene