AP Biology Unit 5 Vocabulary

Aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number (e.g., having 45 or 47 chromosomes instead of 46).

Crossing-over

The exchange of genetic material between nonsister chromatids during prophase I of meiosis, which increases genetic variation in offspring.

Diploid (2n)

A cell containing two complete sets of chromosomes, one set inherited from each parent.

Fertilization

The process in sexual reproduction in which male and female reproductive cells (haploid gametes) join to form a new diploid cell (zygote).

Gamete

A haploid reproductive cell, such as an egg or a sperm, that unites with another of the opposite sex in sexual reproduction.

Haploid (n)

A cell containing only one set of chromosomes; in humans, these are the reproductive cells (sperm and egg).

Homologous Chromosome

A pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci.

Independent Assortment

The random distribution of the pairs of genes on different chromosomes to the gametes; the orientation of one homologous pair at the metaphase plate does not affect the orientation of another.

Karyotype

A visual display or micrograph of the complete set of chromosomes in a cell, arranged in pairs and sorted by size and shape.

Locus

The specific physical location of a gene or DNA sequence on a chromosome.

Meiosis

A two-stage process of cell division in sexually reproducing organisms that results in four genetically distinct haploid daughter cells.

Monosomy

A form of aneuploidy where a diploid cell is missing one chromosome from a homologous pair (e.g., 2n - 1).

Nondisjunction

An error in meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly.

Oogenesis

The process in the ovary that results in the production of female gametes (ova/eggs).

Polar Body

A small haploid cell produced during oogenesis that contains very little cytoplasm and generally does not have the ability to be fertilized.

Spermatogenesis

The continuous process in the seminiferous tubules of the testes that produces mature sperm cells.

Trisomy

A form of aneuploidy where a diploid cell has three copies of a particular chromosome instead of the normal two (e.g., 2n + 1).

Zygote

The diploid cell produced by the union of two haploid gametes; a fertilized egg.

Allele

Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.

Autosome

A chromosome that is not directly involved in determining the sex of an individual (in humans, pairs 1 through 22).

Carrier

An individual who is heterozygous for a recessively inherited disorder; they do not show symptoms but can pass the recessive allele to offspring.

Codominance

A situation in which the phenotypes of both alleles are fully and separately expressed in a heterozygote (e.g., AB blood type).

Dominant

An allele that is fully expressed in the phenotype of a heterozygote, masking the effect of a recessive allele.

Genotype

The genetic makeup, or set of alleles, of an organism (e.g., BB, Bb, or bb).

Heterozygous

Having two different alleles for a particular gene (e.g., Aa).

Homozygous

Having two identical alleles for a particular gene (e.g., AA or aa).

Incomplete Dominance

A situation in which the phenotype of a heterozygote is a blend or intermediate between the phenotypes of the two homozygotes (e.g., red and white flowers producing pink offspring).

Law of Independent Assortment

Mendel's second law, stating that each pair of alleles segregates independently of each other pair during gamete formation.

Law of Segregation

Mendel's first law, stating that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes.

Phenotype

The observable physical and physiological traits of an organism, which are determined by its genetic makeup.

Polygenic

An additive effect of two or more genes on a single phenotypic character (e.g., human skin color or height).

Recessive

An allele whose phenotypic effect is not observed in a heterozygote; it is only expressed when the organism is homozygous for that allele.

X-linked

A gene located on the X chromosome; such genes show distinctive patterns of inheritance because males have only one X chromosome.