Unit 5: Heredity - Complex Patterns of Inheritance

Incomplete Dominance

A genetic scenario where neither allele is completely dominant, resulting in a heterozygote phenotype that is a blend of the two homozygous phenotypes.

Codominance

A situation in which both alleles in a heterozygote are fully expressed, resulting in distinct patches of both phenotypes.

Multiple Alleles

A condition where a single gene has more than two possible alleles in the population.

Polygenic Inheritance

A form of inheritance in which a single phenotype is determined by the additive effects of two or more genes.

ABO Blood Groups

Blood type system determined by multiple alleles: $I^A$, $I^B$, and $i$.

Phenotypic Plasticity

The ability of an organism to change its phenotype in response to environmental influences.

Nondisjunction

An error during meiosis where homologous chromosomes or sister chromatids fail to separate properly.

Trisomy 21

A chromosomal abnormality characterized by the presence of an extra chromosome 21, commonly known as Down syndrome.

X-Linked Recessive Traits

Traits associated with genes located on the X chromosome, often more common in males due to their hemizygous condition.

Hemizygous

Having only one allele for a particular gene, as seen in males with respect to X-linked traits.

Recombination Frequency

The percentage of recombinant offspring produced in a genetic crossing, used to map gene distances on chromosomes.

Map Units

A unit measuring genetic distance; 1% recombination frequency corresponds to 1 map unit (centimorgan).

Crossing Over

The process during Prophase I of meiosis where homologous chromosomes exchange genetic material.

Environmental Influences

Factors from the environment that can impact gene expression and phenotype.

Himalayan Rabbits/Siamese Cats

Examples of animals where fur color is affected by temperature-sensitive gene expression.

Aneuploidy

A chromosomal condition involving an abnormal number of chromosomes in a zygote due to nondisjunction.

Turner Syndrome

A chromosomal disorder resulting from a female missing one X chromosome.

Sex-Linked Traits

Traits that are associated with genes located on sex chromosomes, particularly the X chromosome in humans.

Dominant Allele

An allele that can mask the presence of a recessive allele in a heterozygote.

Recessive Allele

An allele that is masked by the presence of a dominant allele in a heterozygote.

Genotype

The genetic makeup of an organism, comprising all of its alleles.

Phenotype

The observable traits or characteristics of an organism, influenced by genotype and the environment.

Examples of Plasticity

Instances where phenotype variations occur due to environmental factors, such as flower color in hydrangeas.

Linked Genes

Genes located close together on the same chromosome that tend to be inherited together.

Parental Types

Offspring with phenotypes that match either of the original P-generation parents, indicating no recombination.

Recombinant Types

Offspring with new combinations of phenotypes that differ from those of the parents due to crossing over.