Question

Describe the effect of environment, polygenes and lethal genes on phenotype. Give examples of each.

Answer 1

Answer-

According to the given question-

phenotype is trait which we can observe and this is due to genotype which is genetic makeup of any individual and the effect of environment on the development of individual. and we also know that genotype is responsible for defining phenotype. Genotype is generally the allele pair found at a single locus.

• Environmental effects
  • phenotype of the organisms also depends upon the environment because a person may be underweight or obese due to its genetic tendency but their weight can also be controlled by proper exercise and diet . e.g. hair color is also depend upon genes but we can change it by using dye into other color. human height also based on their genetic as well as on nutrition. phenylketonuria or PKU is a genetic disorder a type of pleiotropic disorder due to defects in gene coding the enzyme responsible for converting phenylalanine amino acid to tyrosine amino acid . The baby which have disorder are given a limited diet of phenylalanine amino acid.so in this case we by using low diet concentration overcome the effect of gene expression which means that environmental factor can modify the expression of gene.

• pleiotropy- We know that generally one gene responsible for one characteristic but when a single gene affect many characteristics.

  • in human there is a syndrome called Marfan syndrome which is also a genetic disorder due to mutation in single gene d have several effects on such as development as well as growth including function of heart such as rupture of blood vessel , vision problem such as lens Dislocation and height such as very tall with thin toes and fingers, are controlled by single gene.

  • The gene generally encodes a protein which are assembles in the form of chains responsible for formation of elastic fibrils which provide flexibility as well as strength to connective tissues. so Mutations changes the functional protein production in the body and due to which there is very less fibrils in the body.

• Lethality-

  • General organism have alleles which are with homozygous dominant, heterozygous and homozygous recessive, genotypes and these genes are required for survival of organism .but when an allele responsible for making nonfunctional genes then it leads to development of an abnormal, organism and due to which a organism in homozygous condition cannot survive.

  • e.g. yellow mouse- Here an allele is lethal in yellow mouse and due to which it cannot survive.

  • When we make a cross between yellow mice and normal agouti which is a brown color mice, they there is offspring equal yellow and brown. But when we make a cross between two yellow mice then there is 2 : 1 ratio of yellow and brown offspring instead of 3 : 1.

  • here homozygous which are recessive is lethal and dominant homozygous and heterozygous,are not lethal.

  • e.g. There is a genetic disorders in human where a person with heterozygous allele have shortened limbs and stature a condition of achondroplasia but it is not lethal but when the alleles are homozygous them this leads to death in the embryonic stage of development.