Modifying Environmental Effects on Gene Expression Flashcards
Environmental effects may modify the Mendelian phenotypic ratios…
What are the External and Internal effects?
External- temperature, light intensity, humidity, nutrition, rainfall, maternal environment
Internal- age, sex, substrate
Where and when does Environmental influence on gene expression predominantly occur?
Transcription of genes within the cell.
(N.B. environ. influence occurs within the cell while intra/inter allelic interactions occur outside the cell via enzyme reaction)
What are Oligogenic traits?
Environmental influence is relatively small for major gene traits.
Environmental influence on major gene traits is measured by gene penetrance and gene expressivity
Measures of Environ. Influence on Oligogenic Traits
What is Gene Penetrance?
Proportion of individuals with a specific genotype that show the expected phenotype
eg. There are 100 individuals with the genotype TT, but only 87 are tall.
Gene penetrance = 87/100 = 0.87
Measures of Environ. Influence on Oligogenic Traits
What is Gene Expressivity?
Degree to which a particular genotype is expressed by individuals.
eg. In Drosophila ‘LL’ results in lobed eyes. But the lobed eye gene may only express partially so that only part of the eye is closed.
What are Polygenic traits?
Environmental influence on gene expression is relatively large for minor gene traits.
Environmental influence of minor gene traits are measured by heritability estimates.
Measures of Environ. Influence on Polygenic Traits
What is heritability estimates?
Heritability estimates how well we could predict a trait from genetics and it also tells us how well we could predict the trait in you based on that trait in your parents.
The proportion of variation in a population trait that can be attributed to inherited genetic factors. Heritability estimates range from 0 to 1 and are often expressed as a percentage. A number close to 1 may be indicative of a highly heritable trait within a population. (Max % for heritability= 50%)
What are the differences between Polygenic and Oligogenic traits?
Polygenic traits
- Trait determined by many genes
- Each gene has a small effect on phenotype
- Genetic effects are largely additive in nature
- Environmental influence is large on phenotype
- Continuous distribution, symmetric, normal
- Quantitative traits
- Inheritance studied by quantitative approaches
Oligogenic traits
- Determined by a few genes
- Each gene has a major effect on phenotype (Major gene trait)
- Non-additive effects are high (dominance & epistasis)
- Environmental influences are not large.
- Discrete distribution, often non-symmetric
- Qualitative traits
- Inheritance studied by observing segregation ratios
Environmental Influence on behavioural traits
Nature vs Nurture?
Centers on the contributions of genetics and environmental factors to human development.
Twin studies: Identical vs Fraternal twins
The environment influences how a person looks and behaves regardless of how close their gene pool is… eg. Identical twin reared apart behave differently.
Are Mendelian Genotypic or Phenotypic ratios affected by Environmental Influences?
Phenotypic Ratios
Never genotypic ratios
