2. Gene Expression
The gene expression is determined by
two features called as penetrance and
expressivity of the genes. Penetrance
is the ratio of individuals exhibiting
expected phenotype and expressivity is
the extent of gene expression in an
individual.
3. Environmental Factor
Temperature in Gene Expression
- The body of the rabbit which is generally
exposed to high temperature (>34 degrees)
expressed white color whereas the other parts like
ears, nose , tail and paws which are little exposed
to temperature expressed black color. Keeping the
rabbit under cold climate resulted in the
expression of fully black colored skin.
4. Environmental Factor
Light in Gene Expression
- Maize plant carrying the homozygous gene
for pigmentation when exposed to sun light
developed bright red color and when the light was
retarded by covering the area of the plant prone to
pigmentation, the bright red phenotype was not
observed.
5. Environmental Factor
Chemicals in gene expression
- Normally, F. heteroclitus embryos feature
two eyes; however, half of the eggs placed in the
magnesium chloride mixture gave rise to one-eyed
embryos.
6. Environmental Factor
Nutrition in Gene Expression
- The deficient nutrient supplement alters the
genetic expression. What a pregnant woman eats
determines the health of her offspring.
8. Lethal Alleles
-Genes which result in viability reduction of
individual or become a cause for death of
individuals carrying them.
Types of Lethal Allele
- Recessive - Sex-linked
- Dominant - Conditional
9. Recessive Lethal Allele
Recessive lethal genes can code for either
dominant or recessive traits, but they do not
actually cause death unless an organism carries
two copies of the lethal allele.
Examples of human diseases caused by recessive
lethal alleles include cystic fibrosis, sickle-cell
anemia, and achondroplasia
12. Dominant Lethal Alleles
Dominant lethal genes are expressed in both
homozygotes and heterozygotes
Dominant lethal genes are rarely detected due to
their rapid elimination from populations. One
example of a disease caused by a dominant lethal
allele is Huntington's disease
13. Conditional Lethal Allele
An organism lives normally under one set of
conditions, but when certain changes are
introduced in its environment, lethality results.
Favism is a sex-linked, inherited condition that
results from deficiency in an enzyme called
glucose-6-phosphate dehydrogenase.
14. The lethal gene is carried on the sex chromosome,
usually X.
Hemophilia is a hereditary disease caused by
deficiencies in clotting factors, which results in
impaired blood clotting and coagulation.
Because the allele responsible for hemophilia is
carried on the X chromosome, affected individuals are
predominantly males, and they inherit the allele from
their mothers.
Sex-Linked Lethal Allele
