11.3 Other Inheritance Patterns Practice Quiz

Incomplete dominance results in a blending of parental traits, so the heterozygote shows an intermediate phenotype distinct from either homozygote. This is a classic example of a non-Mendelian inheritance pattern.

In codominance, both alleles are expressed equally and appear simultaneously in the phenotype. An everyday example is the AB blood type where both A and B antigens are clearly visible.

Polygenic inheritance involves the additive effect of many genes, producing a continuous range of phenotypes as seen in traits like skin color or height. This results in a broad spectrum rather than discrete categories.

Mitochondrial inheritance occurs because mitochondria, which contain their own DNA, are passed almost exclusively from the mother via the egg cell. This maternal transmission is distinct from nuclear inheritance.

X-linked inheritance is controlled by genes on the X chromosome and typically results in differing expression between males and females. This is because males have only one X chromosome and are more likely to express X-linked recessive traits.

When two heterozygotes are crossed in incomplete dominance, the offspring show three distinct phenotypes in a 1:2:1 ratio. The intermediate phenotype appears in the heterozygotes, indicating a blend of traits.

The AB blood type is a classic representation of codominance where both A and B alleles are equally expressed. This leads to both antigens being present on the surface of red blood cells.

The normal distribution of traits in polygenic inheritance is due to the small, additive effects of multiple genes. These cumulative effects produce a bell-shaped curve in the population.

Mitochondrial DNA is inherited solely from the mother since the egg contributes the mitochondria. Therefore, traits determined by mitochondrial inheritance are transmitted only maternally.

X-linked recessive disorders usually manifest more frequently in males because they possess only one X chromosome. Females are less frequently affected as they would need two copies of the recessive allele to express the trait.

Incomplete dominance yields an intermediate phenotype as a mixture of both parental traits. In contrast, codominance results in the full expression of both alleles without any blending, making them distinctly observable.

Multifactorial inheritance involves multiple genes and environmental influences, which can alter the expected Mendelian ratios. The complexity introduced by these factors results in a more variable pattern of inheritance.

Multiple alleles refer to the occurrence of more than two allele forms for a single gene within a population. A well-known example is the human blood group system, which includes several alleles.

Sex-limited inheritance refers to traits that are present in both sexes but expressed in only one due to hormonal regulation. Milk production in females is a prime example, as it is hormonally controlled and not expressed in males.

Genomic imprinting is an epigenetic process in which gene expression is determined by the parent of origin. This means that even with the same genotype, the phenotype may vary depending on which parent contributed a particular allele.

Polygenic inheritance for quantitative traits like height typically results in a normal distribution. This bell-curve pattern emerges because many genes contribute small, additive effects to the overall phenotype.

X-linked recessive disorders are characterized by affected males across generations with no male-to-male transmission, since males inherit their X chromosome solely from their mother. This pattern is a key diagnostic feature in pedigree analysis.

Since a son inherits his single X chromosome from his mother, if she is heterozygous for an X-linked recessive trait, there is a 50% chance he will inherit the mutant allele. This straightforward probability is a central concept in X-linked inheritance.

Crossing the unknown individual with a homozygous recessive allows you to reveal the genotype based on the offspring's phenotypic ratios. If the unknown is heterozygous, you would expect a 1:1 ratio, confirming the intermediate expression due to incomplete dominance.

Genomic imprinting causes differences in gene expression depending on whether an allele is inherited from the mother or father. This epigenetic mechanism can result in varied phenotypes even when the underlying genotypes are identical.