Meiosis Flashcards

Flashcards for review of Meiosis lecture notes.

Chromosome Structure Before Replication

Consists of one DNA molecule tightly coiled around proteins, connected by a centromere before DNA replication.

Chromosome Structure After Replication

Consists of two DNA molecules. The two halves of a replicated chromosome are called identical sister chromatids, joined by a centromere after replication.

Genes

Small portions of DNA that code for specific traits carried by chromosomes.

Somatic Cells (Body Cells)

All cells in the body except sex cells. They are diploid (2n), meaning they contain two complete sets of chromosomes (46 in humans, arranged as 23 pairs).

Sex Cells (Gametes)

Reproductive cells: sperm cells (male) and egg cells (female). They are haploid (n), meaning they contain one complete set of chromosomes (23 in humans).

Homologous Chromosomes

In diploid cells, chromosomes exist in pairs. One chromosome of each pair comes from the mother, and one from the father. These pairs have the same shape, size, and carry genes for the same characteristics at the same positions (loci).

Karyotype

The number, appearance, and arrangement of a full set of chromosomes in the nucleus of a somatic cell. Human karyotypes show 23 pairs of chromosomes.

Autosomes

There are 22 pairs of these in humans that control general body characteristics, structure, and functioning. They are numbered 1 to 22.

Gonosomes (Sex Chromosomes)

The 23rd pair of chromosomes that determines sex. Females have two X chromosomes (XX), and males have one X chromosome and one Y chromosome (XY).

Gametes

Another word for sex cells.

Somatic cells

Normal body cells.

Karyotype

The number and appearance of chromosomes in the nucleus.

Haploid

Refers to having just one set of chromosomes.

Diploid

Having a double set of chromosomes

Autosomes

All the chromosomes except the sex chromosomes.

Gonosome

These are the sex chromosomes.

Meiosis

A type of cell division where one parent cell divides to form four daughter cells that are genetically different and possess half the chromosome number of the original parent cell.

Primary Outcome of Meiosis

Meiosis results in the formation of these in animals and humans, or spores in some other organisms like plants.

Gametes Produced by Meiosis

These cells have half the number of chromosomes as the original body (somatic) cell (haploid, n).

Diploid Zygote

After fertilization, this contains the correct, full number of chromosomes (diploid, 2n) characteristic of the species and develops into a multicellular adult organism.

Interphase

The preparatory phase that occurs before Meiosis I begins, during which DNA replicates.

Meiosis I

This is known as Reductional Division primarily because the number of chromosomes (ploidy level) in the cells is reduced by half from the beginning to the end of this stage.

Chromosome Condensation

The chromatin network condenses, chromosomes become shorter and thicker, and homologous chromosomes arrange themselves in pairs, forming a bivalent.

Crossing Over

A critical event for genetic variation is the overlapping and exchange between non-sister chromatids of homologous chromosomes.

Importance of Crossing Over

This leads to a physical exchange of segments of DNA between homologous chromosomes, creating genetic variation.

Metaphase I

Spindle fibers are fully formed, and homologous chromosome pairs (bivalents) move to the equator of the cell. The random arrangement of these pairs is a key source of further genetic variation.

Anaphase I

One whole chromosome from each homologous pair is pulled to opposite poles of the cell, separating the homologous chromosomes without separating sister chromatids.

Telophase I

Replicated chromosomes arrive at each pole, a new nuclear membrane forms, and cytokinesis occurs, splitting the original cell into two daughter cells with half the number of chromosomes.

Final Outcome of Meiosis I

Each new daughter cell now has half the number of chromosomes (is haploid, n) compared to the original diploid mother cell.

Meiosis II= Equational Division

The number of chromosomes (ploidy level) in the cells remains the same (equal) from the beginning to the end of this stage.

Prophase II

Chromosomes (each still composed of two chromatids joined by a centromere) become visible, but are NOT in homologous pairs at this stage.

Metaphase II

Single chromosomes (each consisting of two chromatids) align themselves randomly along the equator of each cell in a single row.

Anaphase II

The centromeres of each chromosome split in half, and the sister chromatids are pulled apart by the contracting spindle fibers.

Telophase II

A complete set of unreplicated chromosomes is present at each pole, a new nuclear membrane forms, and cytokinesis occurs, dividing the cytoplasm of each cell.

Equational Division Outcome of Meiosis II

Since Meiosis II occurred in the TWO cells produced by Meiosis I, the final result is FOUR daughter cells where Each of these four daughter cells is haploid (n).

Cytokinesis

The physical process of cell division, dividing the cytoplasm of a parental cell into daughter cells, typically after the nucleus has divided.

Prophase

PAIR up (in Meiosis I, crossing over occurs)

Metaphase

move to the MIDDLE (equator)

Anaphase

move APART to the poles

Telophase

TERMINAL phase where daughter cells are formed

Acronym PMAT - P stands for

Chromosomes PAIR up (in Meiosis I, crossing over occurs).

Summary of Prophase I

Chromosomes condense, homologous chromosomes pair up forming bivalents, and crossing over occurs at chiasmata.

Summary of Metaphase I

Bivalents align randomly at the cell's equator, undergoing independent assortment.

Summary of Anaphase I

Homologous chromosomes separate and move to opposite poles; sister chromatids remain attached.

Telophase I & Cytokinesis

Chromosomes gather at poles, nuclear envelopes may reform, and the cytoplasm divides.

Summary of Metaphase II

Individual replicated chromosomes align randomly at the equator of each cell.

Summary Anaphase II:

Centromeres divide; sister chromatids separate and are pulled to opposite poles.

Why Meiosis is Important

Is essential for producing gametes (sex cells, e.g., sperm and egg cells).

Halving of Chromosome Number

Reduces the chromosome number by half, transforming diploid cells (2n) into haploid sex cells (n).

Crossing Over

Results in in the theexchange of segments of genetic material between non-sister chromatids of homologous chromosomes.

Random Arrangement of Chromosomes

Individual chromosomes (each made of two chromatids) also align randomly at the equator before chromatids separate

Crossing over

Process involving the exchange of genetic material between members of the homologous pair.

Homologous pair

Refers to a pair of identical chromosomes, one of paternal origin and one of maternal origin.

Variation

Refers to the variety of appearance shown by organisms of the same species.

Nondisjunction

The failure of chromosomes or chromatids to separate correctly during meiosis.

Aneuploidy

A condition where a cell has one or more extra copies of a particular chromosome, or is missing one or more copies of a particular chromosome.

Trisomic/trisomy

A condition in which an extra copy of a chromosome is present in the cell nuclei.

Monosomic

Refers to a condition in a cell where there is only one chromosome instead of the normal diploid pair of a particular chromosome.

Polyploidy

Having one or more extra sets of chromosomes.

Triploid

Refers to a cell or nucleus containing three homologous sets of chromosomes.

Tetraploid

Refers to a cell or nucleus containing four homologous sets of chromosomes