Penetrance and expressivity

genetics

1. Penetrance and Expressivity

2. Presented to : sir faisal iqbal Presented by : farhana shiekh Roll no : BS-BOT-F17-R03 Subject : botany Course : genetics Class : bs -botany 6 th reg Department : biological sciences

3. contents: Penetrance. Expressivity. Role of penetrance and expressivity. Reasons of phenotypic mutations other than genotype.

4. penetrance: The percentage of individuals that show at least some degree of expression of a mutant genotype defines the penetrance of the mutation.

5. Example: For example, the phenotypic expression of many of the mutant alleles found in drosophila can overlap with wild-type expression. If 15 percent of flies with a given mutant genotype show the wild-type appearance, the mutant gene is said to have a penetrance of 85 percent.

6. Expressivity: Expressivity reflects the range of expression of the mutant genotype.

7. Example: Flies homozygous for the recessive mutant gene eyeless exhibit phenotypes that range from the presence of normal eyes to a partial reduction in size to the complete absence of one or both eyes. ). Although the average reduction of eye size is one-fourth to one-half, expressivity ranges from complete loss of both eyes to completely normal eyes. Examples such as the expression of the eyeless gene have provided the basis for experiments to determine the causes of phenotypic variation

8. Uses of penetrance and expressivity Some mutant genotypes are always expressed as a distinct phenotype, whereas others produce a proportion of individuals whose phenotypes cannot be distinguished from normal (wild type). The degree of expression of a particular trait can be studied quantitatively by determining the penetrance and expressivity of the genotype under investigation

9. Reasons of phenotypic mutations other than genotype: If the laboratory environment is held constant and extensive variation is still observed, other genes may be influencing or modifying the phenotype. On the other hand, if the genetic background is not the cause of the phenotypic variation, environmental factors such as temperature, humidity, and nutrition may be involved. In the case of the eyeless phenotype, experiments have shown that both genetic background and environmental factors influence its expression.

10. Thank you