After a mutation at a genetic locus the character of an organism changes due to the change in
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Solution
Change in genetic locus, changes the gene and in turn the amino acid it codes for. This alters the nature of protein synthesized which produces change in the organism. DNA replication is not affected neither the method of protein synthesis. Synthesis of RNA over DNA template is called transcription.
Drosophila flies with XXY genotype are females but in case of humans, such individuals are abnormal males (Klinefelter’s syndrome). This indicates that
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Solution
In human the Y chromosome bears the androgenic factor or the male determining factor. Whereas in Drosophila the ratio of sex chromosomes to autosomes is the factor determining sex of the individual.
Christmas disease is another name for
Down’s syndrome is caused by an extra copy of chromosome number 21. What percentage of offspring produced by an affected mother and a normal father would be affected by this disorder?
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Solution
50% of ova will have (n + 1) chromosome which would, on fertilisation, yield abnormal zygotes (n + 1) + (n) = 2n + 1.
The recessive genes located on X-chromosome in humans are always
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Solution
Males have only one X - chromosome. Hence any gene present on the one X - chromosome expresses itself in males. Females have two X - chromosomes. The mutant allele must be present on both the X-Chromosomes to express itself phenotypically. If only one copy of allele present, then the female only becomes a carrier showing no external manifestation of the gene. Sub lethal condition can never arise in males.
In Drosophila, the sex is determined by
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Solution
Calvin Bridges demonstrated that in Drosophila, the sex is determined by ratio of the number of X chromosomes to the sets of autosomes.
The contrasting pairs of factors in Mendelian crosses are called
If a trait passes from father to all his daughters but none of his sons, the trait is
A mutation at a single locus causes a change in many different characters. This is an example of a
Sex determination in grasshoppers, humans, and Drosophila is similar because
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Solution
In these three species, females have two X chromosomes and males have one X chromosome. The ratio of X chromosomes to autosomes is important (and different in each organism) in Drosophila and grasshoppers, but not in humans. In all three species, males have one Y chromosome, but the Y chromosome is required for male fertility, not for Drosophila to be male (in Drosophila, male flies can be XO).