Gene interaction occurs when two or more genes, located or not on the same chromosome, interact and control a trait.
Many characteristics of living things result from the interaction of several genes.
Cases of Gene Interactions
1. Epistatic gene interaction
Also called epistasis.
Occurs when a trait is conditioned by two or more genes, but one of the alleles prevents the expression of another.
In this case, we have two types of genes: o epistatic gene, which exerts the inhibitory action and the hypostatic gene, which undergoes inhibition.
Based on these two types of genes, epistasis can be:
- dominant epistasis: when the presence of a single epistatic allele is sufficient to cause inhibition.
Example: Determination of chicken coat color
| Genotypes | Phenotypes |
|---|---|
| C_ii | Colored |
| C_I; ccI_; ccii | white |
The C allele conditions colored coat. The c allele conditions the white coat.
Meanwhile, the I allele prevents pigmentation. Allele I is the epistatic gene and behaves as dominant.
Thus, to display the colored coat, chickens cannot display the I allele.
- Recessive Epistasis: when the allele that determines the epistasis acts only in a double dose.
Example: Determination of mouse coat color
| Genotypes | Phenotypes |
|---|---|
| A_P_ | Aguti |
| yyP_ | black |
| A_pp or aapp | Albino |
The P allele conditions sharp fur. The A allele allows the expression of P and p.
The a allele is epistatic and its presence in a double dose determines the absence of pigments, an albino character.
2. Non-Epistatic Gene Interaction
Occurs when two or more genes interact to express a particular trait, but no allele prevents the expression of the other.
Example: Crest determination in chickens
Combinations between the different alleles can produce four types of crest: rose, pea, walnut and simple.
| Genotypes | Phenotypes |
|---|---|
| RE_ | Nut |
| R_ee | pink |
| rrE_ | Pea |
| rree | Simple |
3. Quantitative Inheritance or Polygeny
It occurs when two or more pairs of alleles add or accumulate their effects, which allows for a series of phenotypes that are different from each other.
In general, characteristics can be influenced by environmental factors.
Examples of Quantitative Inheritance are: determining the color of the wheat seed; the color of human eyes and skin; and height and weight of the human species.
Gene Interaction and Pleiotropy
THE pleiotropy it occurs when a single gene has a simultaneous effect on several traits.
This gene is called pleiotropic.
Pleiotropy is an inverse phenomenon to gene interaction.
Exercises
(FATEC-SP) - Pairs of genes, with independent segregation, can act together to determine the same phenotypic characteristic. This phenomenon is known as:
a) gene interaction
b) epistasis
c) quantitative inheritance
d) polygeny.
e) complete dominance
a) gene interaction
(UEPG-PR) - It is an inverse phenomenon to pleiotropy:
a) gene interaction
b) epistasis
c) cryptomeria
d) polyallelia
e) multiple alleles
a) gene interaction
(UNIFOR-CE) - In pumpkin, the color of the fruits is due to the following gene combinations: B_aa = yellow
B_A_ = white
bbA_ = white
drool = green
This information allows us to conclude that the gene:
a) A is epistatic about its allele
b) B is epistemic about A and about a
c) a is hypostatic in relation to A
d) b is hypostatic in relation to B
e) A is epistemic about B and about b
e) A is epistemic about B and about b
