Vocabulary (week 3)

Meiosis

Meiosis

A pair of cell divisions that produces gametes (or spores in plants & fungi) in sexually reproducing organisms. A diploid parent produces four haploid daughter cells which are genetically different from each other and the parent.

Meiosis I

– First division of meiosis. It begins with a diploid parent cell and produces two daughter cells that will then progress through meiosis II.

Prophase I

Chromosomal DNA condenses. Homologous chromosomes pair together. Crossing over occurs between homologous pairs

Prometaphase I

Nuclear envelope dissolves

Metaphase I

Chromosomes align at middle

Anaphase I

Homologous chromosomes disconnect. Then homologous chromosomes move to opposite sides

Telophase I

Nuclear envelopes reforms; Chromosomes decondense; Cytokinesis

Meiosis II

Second division of meiosis. The two daughter cells from meiosis I will divide again to form a total of 4 daughter cells

Prophase II

Chromosomal DNA condenses

Prometaphase II

Nuclear envelope dissolves

Metaphase II

Chromosomes align on midline

Anaphase II

Sister chromatids disconnect. Then sister chromatids move to opposite sides

Telophase II

Nuclear envelope reforms; Chromosomes decondense; cytokinesis

Cytokinesis

Separation of a cell and its contents to form to daughter cells. In animals the cell membrane pinches to separate daughter cells. In plants, a cell wall is built between daughter cells. Cytokinesis usually occurs during telophase I and II of meiosis

Sexual reproduction

when a new organism is produced from the fusion of two haploid gametes to form a diploid zygote in the process called fertilization

Gamete

cells that fuse to produce a zygote during sexual reproduction. Many organisms produce male gametes called sperm and female gametes called ova

Sperm (gamete)

male sex cell. Usually small cell optimized for swimming to the egg

Egg or Ovum (plural ova)

Female sex cells. Eggs are usually large cells providing nutrients proteins for the developing organism

Somatic cell

Cells in a body of a multicellular organism that divide through mitosis but do not undergo meosis

Chromosomes

molecules of DNA containing genetic information which are coiled around proteins called histones. In eukaryotes they are linear but in prokaryotes they are circular

Gene

A region of DNA on a chromosome that encodes for a specific protein or RNA

Allele

A specific version of a gene. Different alleles can, but do not always, result in detectable differences in the gene products

Sister chromatid

one of the two replicated DNA molecules in a condensed chromosome at the start of mitosis or meiosis. Sister chromatids are held together by cohesion

Cohesion

A protein complex that holds sister chromatids together from the time DNA replicates until chromatids separate during division

Homologous chromosome pairs

homologous chromosomes contain the same genes in the same genes at the same locations but can have different alleles. They also have the same size, shape, and centromere positions

Synaptonemal complex

A protein complex that attaches the homologous chromosomes together during prophase I of meiosis

Haploid

A cell is said to be haploid when it contains only one chromosome from each homologous pair. Haploid cells have a single allele for each gene. In sexual reproducing organisms, haploid cells are generated from diploid cells by meiosis

Diploid

A cell is said to be diploid when it contains two versions of each chromosome called a homologous pair. Diploid cells have two copies of each gene but they can have different alleles in sexually reproducing organisms, one of the chromosomes in each homologous pair is from the father, the other from the mother

Ploidy

This refers to the number of chromosomes in each homologous set, and is denoted as a multiple of the symbol, n. Haploid (1n), Diploid (2n), Triploid (3n), tetraploid (4n)

Homozygous

homologous chromosomes have the same allele for the gene

heterozygous

homologous chromosomes have different alleles for the gene

Independent assortment

The random inheritance of chromosomes during meiosis I. Each daughter cell randomly and independently receives one of the two homologous chromosomes from each pair. Along with crossing over, independent assortment helps randomize combinations of alleles inherited by gametes

Crossing over (recombination

This is the swapping of alleles between homologous chromosomes during prophase I of meiosis. DNA molecules are cut in corresponding locations of each chromosome, and pieces of it are reattached to the homologous partner. The cuts and reattachment are made at the same location on both homologues, which assures that the number of alleles per chromosome does not change

Genetic linkage

Alleles from nearby genes on the same chromosomes are said to have genetic linkage, because crossing over is less likely to occur between nearby genes than between distant genes. (genes from different chromosomes are never linked)

Trisomy

An aneuploid that occurs when a cell has three homologous copies of a chromosome. Trisomy is different from triploid cells (3n): Triploid cells have 3 of every homologous chromosome whereas trisomic cells have a single extra chromosome

Monosomy

An aneuploid that occurs when a cell has a single chromosome from a homologous pair. Monosomy is different from haploid cells (1n): Haploid cells have one chromosome from every homologous pair whereas monosomic cells are missing a single chromosome

Sex chromosome

chromosomes that are instrumental in sex determination. In humans there are two distinct sex chromosomes, X and Y, that differ in size and gene content. some species do not have sex chromosomes and their sex is not determined genetically

autosomes

chromosomes that do not determine sex

hermaphrodite

organisms in kingdom animalia that possess both male and female sex organs and produce both sperm and eggs

self-fertilization

this occurs when two gametes from the same individual fuse in fertilization

Magnification

the process of enlarging the apparent size of an object

resolution

the ability of a microscope to distinguish detail: the minimum distance at which 2 distinct points of a specimen can still be seen as separate entities

cell cycle

the repeating progression of events for dividing cells. it is comprised of two growth phases (G1 and G2), mitosis (M phase) and DNA replication (S phase)

DNA replication (S phase)

the process of copying DNA molecule within the cell. DNA replicates during S phase of the cell cycle

Interphase

The collective name for the parts of the cell cycle that are the 2 growth phases (G1 and G2) and the DNA replication (S phase). In other words, everything in the cell cycle EXCEPT mitosis (M)

Mitosis (M phase)

The phase of the cell cycle where eukaryotic cells divide into two genetically equivalent daughter cells

Prophase

first stage of mitosis, during which DNA coils to form condensed chromosomes

prometaphase

the second stage of mitosis, during which the nuclear envelope dissolves and the spindle attaches to chromosomes

metaphase

the third stage of mitosis, during which the chromosome (pulled by the spindle) aligns along the middle

anaphase

the fourth stage of mitosis, during which cohesion dissolves, sister chromatids separate, and the spindle begins to pull sister chromatids to opposite poles of the cell

telophase

the fifth and final stage of mitosis, during which the nuclear envelopes reform, chromosomes decondense, and, in most cells, cytokinesis forms the daughter cells

Cytokinesis

separation of a cell and its contents to form two daughter cells. In animals the cell membrane pinches to separate daughter cells. In plants, a cell wall is built between daughter cells. Cytokinesis usually occurs during telophase of mitosis