CH 13 BIO ploidy, mitosis, meiosis

homolog

A homologous gene (or homolog) is a gene inherited in two species by a common ancestor. While homologous genes can be similar in sequence, similar sequences are not necessarily homologous. Orthologous are homologous genes where a gene is found in two different species, but the origin of the gene is a common ancestor.

homologous pair

Homologous chromosomes are made up of chromosome pairs of approximately the same length, centromere position, and staining pattern, for genes with the same corresponding loci. One homologous chromosome is inherited from the organism's mother; the other is inherited from the organism's father.

chromosome set

Two gametes form a diploid zygote with twice this number (2n, the zygotic or diploid number) i.e. two copies of autosomal chromosomes. For humans, a diploid species, n = 23. A typical human somatic cell contains 46 chromosomes: 2 complete haploid sets, which make up 23 homologous chromosome pairs.

haploid

a cell containing only one set of chromosomes

diploid cells

a cell containing two sets of chromosomes (2n), one set inherited from each parent

recombinant chromosomes

a chromosome created when crossing over combines the DNA from two parents into a single chromosome

sexual reproduction

a type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the parents

polyploid

cells and organisms are those containing more than two paired (homologous) sets of chromosomes. Most species whose cells have nuclei (Eukaryotes) are diploid, meaning they have two sets of chromosomes—one set inherited from each parent.

independent assortment

he principle, originated by Gregor Mendel, stating that when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together. Expand. Also called Mendel's second law, Mendel's law.

ploidy

is a measure of the number of chromosomes in a cell. Chromosomes are the threadlike structures that contain the genetic material known as DNA.

cell cycle

is a series of events that takes place in a cell as it grows and divides. A cell spends most of its time in what is called interphase, and during this time it grows, replicates its chromosomes, and prepares for cell division. The cell then leaves interphase, undergoes mitosis, and completes its division.

chiasma

the X-shaped, microscopically visible region where homologous non sister chromatids have exchanged genetic material through crossing over during meiosis, the two homologs remaining associated due to sister chromatid cohesion

zygote

the diploid product of the union of haploid gametes during fertilization; a fertilized egg

meiosis I

the first division of a two-stage process of cell division in sexually reproducing organisms that result in cells with half the number of chromosome sets as the original cell

asexual reproduction

the generation of offspring from a single parent that occurs without the fusion of gametes (by budding, division of a single cell, or division of the entire organism into two or more parts) - in most cases, the offspring are genetically identical to the parent

synapsis

the physical connection of replicated homologous chromosomes during prophase I of meiosis

crossing over

the reciprocal exchange of genetic material between non sister chromatids during prophase I of meiosis

meiosis II

the second division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosome sets as the original cell

fertilization

the union of haploid gametes to produce a diploid zygote