bio 2

Incomplete Dominance

Neither allele is dominant, resulting in a heterozygote phenotype that is intermediate between the two homozygotes.

Example of Incomplete Dominance

Red + white = pink

Co-dominance

Phenotypes of both alleles are exhibited in the heterozygote, meaning it is not an intermediate.

Example of Co-dominance

Cow spots (roan)

Multiple alleles

More than two alleles exist for a single gene, such as human blood types A, B, AB, or O.

Homozygous

Having two identical alleles for a particular gene.

Heterozygous

Having two different alleles for a particular gene.

Human diploid cell

Cell containing 46 chromosomes organized into 23 homologous pairs.

Rhesus (Rh) factor

A red blood cell surface antigen with two alleles: Rh+ (dominant) and Rh- (recessive).

Phenotypic plasticity

Influence of the environment on gene expression, leading to various physical traits.

Polygenic trait

A trait controlled by multiple genes, such as height.

Epistasis

The expression of one gene alters the expression of a second gene; involves at least two genes.

Mitosis

Nuclear division that results in two identical daughter cells.

S phase

Phase of the cell cycle where DNA replication occurs.

Centrosome

Microtubule organizing center that helps in the assembly of the mitotic spindle.

Aneuploidy

An abnormal number of chromosomes due to nondisjunction during meiosis.

X-linked traits

Traits that are only expressed on the X chromosome; males are hemizygous for X-linked traits.

X chromosome inactivation

One of the two X chromosomes in female mammals is inactivated in each cell.

Non-kinetochore microtubules

Microtubules that extend from each pole and contact the plasma membrane.

Meiosis

A process that forms four haploid gametes and increases genetic variation.

Law of Independent Assortment

Each allele pair separates independently during gamete formation.

Aneuploidy effects

Can lead to disorders such as Down syndrome, caused by an extra chromosome.

Chronic myelogenous leukemia (CML)

A type of cancer caused by a translocation between chromosomes 9 and 22.

Cell cycle control system

A system of molecules that triggers and coordinates events in the cell cycle.

Congenital generalized Hypertrichosis

An excessive amount of hair growth caused by an X-linked dominant allele.