Lecture 10: Gene and Environment Interactions

Genes don't operate in isolation. Their influence on phenotypes depends on interactions with other genes and the environment.

Genes that regulate the expression of other genes, often by binding to DNA regions near the regulated gene.

Multi-component protein complexes that work together to perform specific tasks, like molecular machines.

The process by which a gene's DNA sequence is used to create a functional protein.

The environment can influence gene expression. External factors can trigger or modify gene activity.

A change in gene activity due to environmental factors.

A gene can be 'turned on' by environmental cues.

Modifications to proteins, such as adding phosphate groups, which can affect protein activity.

A process where environmental signals trigger a series of gene-controlled reactions, like dominoes falling.

A situation where one gene's genotype influences the expression of another gene at a different location.

A type of epistasis where the epistatic gene exerts its control in the recessive form.

The gene that masks or hides the effect of another gene in epistasis.

The gene whose effect is masked by another gene in epistasis.

A lethal allele causes a 2:1 ratio in offspring because individuals homozygous for the lethal allele don't survive.

The color of labrador retrievers is influenced by two genes, one determining the base color (black or brown) and the other determining color deposition.

The 'B' gene determines the pigment produced: black (BB or Bb) or brown (bb).

The 'E' gene determines if the pigment is deposited: deposited (EE or Ee) or not deposited (ee).

Recessive epistasis occurs in Labrador Retrievers where the 'ee' genotype masks the expression of the 'B' gene, resulting in a yellow coat.

A type of epistasis where the epistatic gene masks the expression of the hypostatic gene regardless of whether the epistatic gene is homozygous or heterozygous.

In summer squash, the fruit color is determined by two genes: one for white pigment production (W) and another for yellow pigment production (Y).

A type of gene interaction where one gene's mutation reverses the effect of another gene's mutation, leading to a wild-type or near wild-type phenotype.

The interaction of two genes in a way that affects the phenotype, resulting in a 9:7 phenotypic ratio in the F2 generation.

A mutant allele of a gene that can mask or reverse the effect of another gene's mutation.

An allele that produces a normal phenotype, in contrast to a mutant allele.

A recessive mutant allele that can suppress the effect of another recessive mutant allele.

A mutant allele that results in an abnormal phenotype, in contrast to a wild-type allele.

A dominant epistatic allele is an allele that masks the expression of other alleles, even if they are dominant. If the dominant allele is present, regardless of the other alleles, the phenotype associated with the epistatic gene will be expressed.

If an allele is epistatic to another allele, it means that the epistatic allele will determine the phenotype regardless of the other allele's genotype. This is because the epistatic allele either blocks or modifies the expression of the other allele.

In the context of genetics, a 'two-step pathway' refers to a metabolic or biological process that involves two distinct steps, each controlled by a different gene. The product of the first step acts as a substrate for the second step.

Complementation is a genetic phenomenon where two recessive mutations, each affecting a different gene, can produce a wild-type phenotype in their offspring. This indicates that the mutations affect different genes that are involved in the same pathway or process.

A complementation test is a genetic experiment designed to determine whether two mutations affecting the same phenotype are allelic (at the same locus) or non-allelic (at different loci). The test involves crossing homozygous recessive mutants and observing the phenotype of the offspring.

Allelic mutations are mutations that occur at the same gene locus. They are considered variants of the same gene and can result in different phenotypes.

Non-allelic mutations are mutations that occur at different gene loci. They affect different genes and can lead to different phenotypes. However, they may still influence the same biological pathway.

In genetics, complementation occurs when two different recessive mutations in a diploid organism are complemented by the wild-type allele of each gene in the heterozygote, restoring the wild-type phenotype.

In complementation, the crossing of two different recessive mutant strains results in offspring with a wild-type phenotype. This indicates that the mutations are in different genes, and the wild-type alleles from each parent can complement each other.

When mutations in the same gene are crossed, the F1 offspring will inherit two mutant alleles, leading to a blocked pathway and a mutant phenotype. This is because the mutations cannot complement each other.

The 9:7 ratio in the F2 generation suggests that two genes are involved in the pathway, and both need to be functional for the wild-type phenotype. The 9 represent all combinations where at least one functional allele exists for each gene, while the 7 represent combinations where at least one gene is completely mutant.

If the two mutations were in different genes, the heterozygote F1 would have a wild-type phenotype due to complementation. The F2 generation, produced from selfing the F1, would then exhibit a 9:3:3:1 ratio, indicative of two independent genes.

Complementation tests are used to determine whether two mutations affect the same gene or different genes. By crossing two mutant strains and observing the phenotype of the offspring, we can infer if the mutations complement each other or not.

The results of a complementation test can be used to map genes to their respective loci on a chromosome. Mutations that fail to complement each other are likely to be in the same gene, while those that complement are in different genes.

The study of complementation helps us understand the genetic control of biochemical pathways. It reveals the functional relationships between genes and how they cooperate to produce a specific phenotype.