Cell division-meiosis

Telomere

DNA at the tips of chromosomes.

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms.

Meiosis I

The first 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.

Prophase I (Meiosis)

Homologous chromosomes pair up and form tetrads, crossing over occurs.

Metaphase I (Meiosis)

Tetrads are lined up at the equator; spindle fibres attach.

Anaphase I (Meiosis)

Homologous chromosomes separate (segregation). Reduction occurs cells go from diploid to haploid

Telophase I (Meiosis)

Cytoplasm divides, 2 daughter cells are formed.

Meiosis II

The second phase of meiosis consisting of chromatids separating, along with the two diploid cells splitting in two.

Telophase II

The spindle fibres disappear, and a nuclear membrane forms around each set of chromosomes. The end result is four haploid daughter cells, none of which identical to the parent.

Haploid

An organism or cell having only one complete set of chromosomes.

Diploid

An organism or cell having two sets of chromosomes or twice the haploid number.

Homologous chromosomes

Chromosomes that have the same sequence of genes and the same structure.

Tetrad

Structure containing 4 chromatids that form during meiosis.

Synapsis

The pairing of homologous chromosomes during meiosis.

Crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis.

Nondisjunction

Error in meiosis in which homologous chromosomes fail to separate.

polyploidy

when an organism has more than two complete sets of chromosomes. (trioloidy, tetraploidy)

Trisomy

3 copies of a chromosome instead of 2.

Monosomy

Missing a chromosome.

Karyotype chart

A diagram of the chromosomes of a cell.

Down Syndrome (Trisomy 21)

A genetic disorder caused by the presence of all or part of a third copy of the chromosome 21.

Turners syndrome

Born with a single X chromosome. Female with 45 chromosomes, do not develop sexually.

Klinefelter syndrome

A chromosomal disorder in which males have an extra X chromosome, making them XXY instead of XY. Produces female sex hormones at puberty.

amniocentesis

the sampling of amniotic fluid using a hollow needle inserted into the uterus, to screen for developmental abnormalities in a fetus.

chorionic villus sampling

sampling of placental tissues for prenatal diagnosis of potential genetic defects

chaisma

site of crossing over