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CBSE Class 12 - Biology solved questions and answers

Questions
66 Centromere is the part of chromosome where
A nucleoli are formed
B crossing over takes place
C chromatids are attached
D nicking occurs

Answer: Option [C]

Centromere is the part of chromosome where chromatids are attached. The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore and helps to keep chromosomes properly aligned when cells divide.

67 Separation will occur in two genes if they are
A dominant alleles
B recessive alleles
C present on homologous chromosomes
D present on two separate chromosomes

Answer: Option [C]

Separation will occur in two genes if they are present on homologous chromosomes. During meiosis, the pairs of homologous chromosome are divided in half to form haploid cells, and this separation, or assortment, of homologous chromosomes is random. This means that all of the maternal chromosomes will not be separated into one cell, while the all paternal chromosomes are separated into another

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68 The polygenic gene show
A different genotype
B different phenotype
C different karyotype
D none of the above

Answer: Option [B]

The polygenic gene show different phenotype. A polygenic trait is governed by more than one gene where dominant allele of each gene express only a part of trait and the full trait is expressed only in presence of dominant alleles of all multiple genes. Therefore, depending on the genotype these genes exhibit multiple phenotypes.

69 Unit of distance between genes on the chromosome is
A C.DNA
B Morgan
C Cntimorgan
D Chisquare

Answer: Option [C]

Unit of distance between genes on the chromosome is Cntimorgan. In genetics, a centimorgan (abbreviated cM) or map unit (m.u.) is a unit for measuring genetic linkage. It is defined as the distance between chromosome positions (also termed loci or markers) for which the expected average number of intervening chromosomal crossovers in a single generation is 0.01.

70 The number of autosomes in fertilized egg of human beings is
A 44
B 22
C 46
D 23

Answer: Option [A]

The number of autosomes in fertilized egg of human beings is 44. Human body contains 23 pair of chromosome, in total there are 46 chromosomes. These chromosomes are present in equal pairs and they can be defined as the thread like structure found inside the nucleus of every cell. Out of which 22 pairs are autosomes and remaining 1 pair is a sex chromosome. So there will be 44 autosomes.

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