Extension of Mendelian Principles

This presentation is about extensions of Mendelian principles. Some examples of extensions of Mendelian principles are discussed in this presentation.

1. Extensions of Mendelian
principles
Presented by:
Sanjay Kr. Vishwakarma

2. Pleiotropy
•Pleiotropy is one gene affecting several traits
•Genes make proteins and often affect the overall phenotype in subtle
ways that affect many different body systems
•The Hb
s
allele provides a classic example of Pleiotropy

4. •Hb
s
causes hemolytic anemia in homozygous state (Hb
s
/Hb
s
)

6. •Provide resistance to one type of malaria caused by the parasite
Plasmodium falciparum in heterozygous state (Hb
A
/Hb
s
)
•Selective advantage in geographic regions where this type of malaria
is prevalent

7. Penetrance and expressivity
•Expression of many genes is affected by the environment or by
"background" genetic influences
•Penetrance is the percentage of offspring with the mutant genotype that
express the mutant phenotype
•Expressivity is the degree to which the mutant phenotype is expressed

8. •Polydactyly is having extra fingers and toes
•Several forms of this condition
•For one form, polydactyly is 65% penetrant: 65% of those who
carry the dominant polydactyly allele have extra digits

10. Phenocopy
•Organism has a mutant phenotype but a normal (wild type) genotype
•Mutant appearance through an environmental cause
•Drugs that cause birth defects are a common cause
•Nothing is genetically wrong with the child, but it was exposed in
uteroto toxic chemicals

12. Thank You