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Question 11 Mark

Define the following terms:
Linkage

Answer

Linkage : The tendency of genes to stay together in hereditary transmission is called linkage. Such groups of genes form a linkage group.

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Question 21 Mark

Define the following terms:
Down's syndrome

Answer

Down's syndrome : It is caused by the trisomy of the 21 st chromosome. The 21 st pair of chromosome does not split equally during oogenesis thus, producing gametes with either $n-1$ and $n+1$ chromosomes, not the normal ' $n$ ' number of chromosomes. These upon fertilisation by a normal spermatozoa produce a zygote with three 21st chromosomes. Zygotes with less than normal number of chromosomes ( $2 n -1$ ) fail to develop while the zygote with more than normal number $(2 n+1)$ causes severe abnormalities such as Down's syndrome, characterised by mental retardation, reduced resistance to diseases, congenital heart abnormalities.

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Question 31 Mark

Define the following terms:
Law of segregation

Answer

Law of segregation : The contrasting factors separate or segregate during gamete formation and the paired condition is restored during random fertilisation.

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Question 41 Mark

Define the following terms:
Pedigree chart

Answer

Pedigree chart - It is a family chart which shows the parents and their children along with the hereditary characters.

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Question 51 Mark

Define the following terms:
Homozygous

Answer

Heterozygous - The condition in which a pair of chromosomes carries similar alleles for a particular character.

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Question 61 Mark