question_answer

Following are the pattern of inheritance that show deviation from Mendel's law. Describe each one with the help of an example.

(i) Incomplete dominance

(ii) Pleiotropy

Or

How is Human Genome Project (HGP) advantageous for the mankind? Which objectives were associated with it?

Answer:

(i) Incomplete dominance

It is a phenomenon in which phenotype of the \[{{F}_{1}}-\]hybrid offspring does not resemble any of the parent, but is an intermediate between the expression of two alleles in their homozygous state. Here, the phenotypic ratio deviates from Mendel's monohybrid ratio but the parental characters reappear in \[{{F}_{2}}-\]generation.

For example, in snapdragon (dog flower, Antirrhinum majus) and four O'clock plant (Mirabilis jalapa) there are two types of flower colours in pure state. On crossing the pure breeding red flowered and white flowered plants, hybrids of \[{{F}_{1}}-\]generation possess pink flowers. On selfing \[{{F}_{1}}-\]plants, \[{{F}_{2}}-\]generation comes as 1 red (RR) : 2 pink (Rr) : 1 white (rr) flowered plants. Here, pink flower colour is due to incomplete dominance of red flower trait over white flower trait.

(ii) Pleiotropy It is the phenomenon in which a single gene product may produce multiple or more than one phenotypic effect.

For example,

· Phenylketonuria is a disorder caused by mutation in the gene coding for the enzyme phenylalanine hyroxylase. The affected individuals show hair and skin pigmentation and mental retardation.

· In garden pea, starch synthesis, size of starch grains and the shape of seeds is controlled by one gene.

The genotypes and phenotypes for the traits are as follows

BB - Round seeds, large starch grains.

Bb - Round seeds, intermediate size starch grains.

bb - Wrinkled seeds, small starch grains.

Or

Advantages of HGP It is a revolutionary way to diagnose, treat and to prevent thousands of disorders that affect human beings. Besides these, learning about DNA sequences can lead to an understanding of their natural capabilities that can be applied in solving challenges on healthcare, agriculture, energy production, environmental remediation, etc.

Objectives of HGP These are as follows

(i) Determine the sequence and number of all the base pairs in the human genome.

(ii) Identify all the genes present in human genome.

(lii) Determine the functions of all the genes.

(iv) Identify the various genes that cause genetic disorders.

(v) Determine genetic predisposition and immunity to various disorders,

(vi) Store the information in data bases.

(vii) Improve tools for data analysis.

(viii) Find out possibilities of transfer of technology developed during HGP to industry.