Genetics: Incomplete Dominance and Overdominance

Heterozygote exhibits a phenotype intermediate between the two homozygotes.

Example of incomplete dominance where heterozygotes have pink flowers.

In the F2 generation, the phenotypic ratio is 1:2:1 (instead of 3:1 in simple dominance).

Whether a trait is dominant or incompletely dominant can depend on level of observation.

Pea shape illustrates how dominance can be observed differently at varying levels of detail (e.g., macroscopic vs. microscopic).

In humans, an intermediate trait between straight and curly hair, resulting from incomplete dominance.

In incomplete dominance, the genotypic ratio in offspring from two homozygous parents is 1:2:1

In incomplete dominance, the corresponding phenotypic ratio resulting from a cross between two homozygous genotypes is also 1:2:1, which demonstrates intermediate phenotypes

A heterozygote has greater reproductive success than either homozygote.

An autosomal recessive disorder causing abnormal hemoglobin.

Encodes normal hemoglobin.

Encodes abnormal hemoglobin.

Both alleles in a heterozygote express equally.

A genetic pattern where both traits are expressed independently in offspring.

A trait where an allele is dominant in one sex but recessive in the other.

A trait where an allele only expresses in one sex.

Traits found on chromosomes other than sex chromosomes.

A gene that masks expression if the genes for type A and type B are present.

Two parents with similar recessive phenotypes produce offspring with a wild-type phenotype. This suggests the mutations were in different genes.

An allele of one gene changes the phenotypic effect of alleles of a different gene. This is a 'modifier' gene.

Loss of one gene has no effect, but loss of two genes causes a phenotype change. One gene can fully compensate for the other.

One gene masks the phenotypic effects of another gene. It's like a dominant gene 'overrides' another.

Often occurs when two proteins interact to contribute to a function, like an enzymatic pathway. If one is missing, the pathway is disrupted.

Epistasis is a relationship between alleles of different genes, while dominance is between alleles of the same gene.

White flowers from different strains cross to produce purple offspring. Each strain provided a missing 'piece' for purple pigment production.

Two genes, C and P, are needed for purple pigment. cc or pp blocks the pathway. cc is epistatic to Pp or PP.

Sex-influenced inheritance involves traits where the expression of alleles is influenced by the sex of the individual. An allele may be dominant in one sex and recessive in the other.

An allele that can cause the death of an organism when present in a homozygous state.

Lethal alleles often arise due to a loss of function in genes essential for survival. The mutated protein might be nonfunctional, or its function may be detrimental.

Overdominance, where heterozygotes have increased fitness, can provide evolutionary advantages by conferring resistance to diseases or maintaining a broader range of protein functions.

Human blood types (ABO system) exhibit codominance. An individual with both A and B alleles will have AB blood type, expressing both antigens.

The presence of horns in cattle, determined by the ScP and ScA alleles.

A trait that is expressed in only one sex due to hormonal influences or other sex-specific factors.

Distinct differences in appearance between males and females of a species, often driven by sex-limited traits.

A gene necessary for the survival of an organism.

A gene that's not crucial for survival, but can still provide benefits to the organism.

Lethal alleles can alter the expected Mendelian ratios in offspring.

A breed with a short tail due to a dominant lethal allele.

One gene affecting multiple traits or aspects of an organism's phenotype.

Pleiotropic genes can exert their effects in various ways, like affecting different cell types or stages of development.

A genetic disorder with pleiotropic effects, caused by a faulty gene that affects chloride transport, causing multiple symptoms.

A pattern of pigmentation in animals, where specific areas lack pigmentation.

A gene involved in the development of melanocytes, the pigment cells in animals.

When two or more genes influence a single trait, creating complex phenotypes.

A type of gene interaction where one gene masks the expression of another gene.