Question

1. How could a change in a DNA sequence cause a change in a phenotype? 2. How are sex-linked traits different from autosomal traits? 3. Can you see individual genes when you look at a karyotype?

Answer 1

1. If the change is DNA sequence occurs in the exon regions, which basically are the coding regions of the DNA, that can cause a change in phenotype. The changed DNA sequence will results in a changed RNA sequence, which will ultimately give a different protein after translation. That different protein will be the cause of change im phenotype.

2. Difference between sex-linked traits and autosomal traits :

– Traits which are controlled by the autosomes are know as autosomal traits. Whereas traits controlled by the sex linked chromosomes i.e. X or Y chromosomes are known as sex-linked traits

– Autosomal traits generally show mendalian inheritance pattern but the sex-linked traits basically show criss cross inheritance pattern

– Autosomal traits equally affect both sexes. But sex-linked traits generally affects the male individual

– Both alleles of a particular gene is involved in controlling the autosomal trait. But in case of sex-linked traits, alleles in either the X chromosome or Y chromosome are involved in the determination of X-linked or Y-linked traits respectively.

3. Individual genes cannot be seen just by looking at a karyotype. A karyotype is just a way of observing the number, shape and size of the chromosome and find out if there are any abnormalities. Chromosomes are made up of DNA . And individual genes are very tiny part of a DNA. So individual genes cannot be observed through karyotype.

4. Monosomy or trisomy are numerical abnormalities im chromosomes. In trisomy an extra number of chromosome is present. And in case of monosomy, one member of a pair of chromosome is absent. As karyotype gives a clear idea about the numbers of chromosome, so in this way just by checking the numbers of chromosomes the monosomy and trisomy can be identified.

5. When maternal age advances the risk of fetal genetic disease increases. An older pregnant woman can give birth a child with some severe genetic defects e.g. down syndrome. So to detect those genetic defects before the birth, the amniocentesis test is performed or advised by the physician.

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