expressivity definition, penetrance vs expressivity,, quantified example, qualitative expressivity, types of expressivity, waardenburg syndrome.

2. Expressivity
By
Rani Summeya Seme 33
Zahra Fayyaz 12

3. Outline
• Definition
• Penetrance vs. Expressivity
• Example
• Quantified Example
• Qualitative Example
• Types
• Uniform Expressivity
• Variable Expressivity
• Waardenburg Syndrome

4. Definition
“The degree to which trait expression differs among individuals”
OR
‘’Expressivity quantifies variation in a non-binary phenotype across
individuals carrying a particular genotype”
OR
“The relative capacity of a gene to affect the phenotype of an organism
of which it is a part”
It is equal to the proportion of individual carriers of a genotype for a
trait who show the trait to a specifiable extent.

5. Penetrance vs expressivity
Penetrance measures how often a gene generates its associated
phenotype to any extent that makes an individual carrier different from
the wild type.
Expressivity characterizes non-binary qualitatively or quantitatively the
extent of phenotypic variation within a particular genotype.
‘’With binary phenotypes expressivity and penetrance are the same.’’

8. Quantified Example
• volume of blood ejected from the pumping heart
• with each contraction
• relative to the total amount of blood contained in the heart's
chamber
• can be quantified by echocardiography
• called the ejection fraction

9. Qualitative Example
• in the hypothetical example of a "blue" gene
• the gene might have an expressivity of 25% for individuals
• that express the "blue" gene & appear light blue
• while individuals who express the "blue" gene & appear dark blue
• the expressivity might be 75%.

10. Types
• Uniform expressivity
• Variable Expressivity

11. Uniform Expressivity
“ When a phenotypic expression of a gene is identical or similar in all
the individuals which carry such genes.”
Most of the qualitative characters exhibit it.

12. Variable expressivity
“it occurs when a phenotype is expressed to a different degree among
individuals with the same genotype..”.”
Example:-
• 2 extra digits vs 3 in polydactyly
• The digit can be full size or just a stub

15. WAARDENBURG SYNDROME

18. Example
• Individuals with the same allele for a gene involved in a quantitative
trait like body height might have large variance (some are taller than
others), making prediction of the phenotype from a particular
genotype alone difficult. The expression of a phenotype may be
modified by the effects of aging, other genetic loci, or environmental
factors
• Neurofibromatosis, where patients with the same genetic mutation
show different signs and symptoms of the disease.

20. Reasons
Variable expressivity may be due to the following reasons.
• 1) Modifying effect of the genetic background or modifying genes.
• 2) The effect of various environmental factors on the gene expression.