A normal visioned woman, whose father is colour blind, marries a normal visioned man. What would be probability of her sons and daughters to be colour blind? Explain with the help of a pedigree chart.
The genotype of parents are
$50 \%$ daughters are normal visioned but $50 \%$ will be carries and $50 \%$ of sons are likely to be colour blind and 50\% are normal visioned.
Discuss in detail the contributions of Morgan and Sturvant in the area of genetics.
T H Morgan (1866-1945) was given the Nobel Prize in 1933.
His contributions are
(i) Morgan worked on fruit fly Drosophila melanogaster and proposed the chromosomal theory of linkage.
(ii) He stated and established that genes are located on the chromosome.
(iii) He established the principle of linkage, crossing over, sex-linked inheritance and discovered the relation between gene and chromosome.
(iv) He established the technique of chromosome mapping.
(v) He observed and worked on mutation.
Alfred Henry Sturtevant (1891-1970) student of morgan was given the National Medal of Science in 1967. His contributions are
(i) He constructed the first genetic map of a chromosome while working on the Drosophila genome.
(ii) His main contributions to science include his analysis of genetic 'linkage groups,' which became classical method of chromosome mapping that is still used today. In 1913, he determined that genes were arranged on chromosomes in a linear fashion, like beads on a necklace. He also showed that the gene for any specific trait was in a fixed location (locus).
(iii) His work on Drosophila proved that two closely related species showed newly recurring mutations that were allelic and thus probably identical. His work also helped to determine genetic role in sexual selection and development and displayed the importance of chromosomal crossing over in mutations.
(iv) One of Sturtevant's principal contributions was his introduction to the concept that the frequency of crossing over between two genes could help to determine their proximity on a linear genetic map. His experiments determined that the frequency of double crossing over can be used to deduce gene order.
Define aneuploidy. How is it different from polyploidy? Describe the individuals having following chromosomal abnormalities.
(a) Trisomy of 21st Chromosome
(b) XXY
(c) $\times 0$
Aneuploidy is a phenomenon which occurs due to non-disjunction, resulting in gain or loss of one or more chromosomes during meiosis.
Aneuploidy is different from polyploidy. Polyploidy is a phenomenon in which the organisms contain more than two monoploid value or basic sets of chromosomes. i.e., $-3 n$, 4netc. Example of such organisms are certain fish and salamanders and is commonly found in plants like grapes, banana.
Chromosomal Abnormalities
(a) Down's syndrome is an autosomal disorder that is caused by the trisomy of chromosome 21.
The individual is short statured with round head, open mouth, protruding tongue, short neck, slanting eyes, and broad short hands. The individual also shows retarded mental and physical growth,under developed gonads and genitats, etc.
(b) Klinefelter's syndrome is the chromosomal disorder that is caused by the presence of an additional copy of X-chromosome resulting in the karyotype $45+$ XXY .
In this disorder sex of the individual is masculine but possess feminine characters also. The individual shows gynaecomastia, i.e., development of breasts. The individual will be often sterile having poor beard growth and feminine pitched voice.
(c) Turner's syndrome is the chromosomal disorder that is caused by the absence of one of the X-chromosomes, resulting in the karyotype 45+XO.
In this disorder the individual (female) will be sterile with rudimentary ovaries. Other symptoms include shield-shaped thorax, webbed neck, poor development of breasts, short stature, small uterus and puffy fingers.