Glossary
Anaphase I
The phase of Meiosis I where homologous chromosomes separate and move to opposite poles of the cell, while sister chromatids remain attached.
Example:
In Anaphase I, the entire homologous chromosome, still composed of two sister chromatids, moves away from its partner.
Anaphase II
The phase of Meiosis II where sister chromatids separate and move to opposite poles of the cell, becoming individual chromosomes.
Example:
The pulling apart of sister chromatids in Anaphase II ensures that each resulting gamete receives a single, unduplicated chromosome.
Crossing Over
The exchange of genetic material between non-sister chromatids of homologous chromosomes during Prophase I of meiosis.
Example:
Crossing over shuffles alleles between homologous chromosomes, creating new combinations of genes on the chromatids.
DNA Replication
The process by which a DNA molecule is duplicated, producing two identical DNA molecules from one original molecule.
Example:
Before meiosis begins, DNA replication ensures that each chromosome consists of two sister chromatids.
Diploid (2n)
A cell or organism containing two complete sets of chromosomes, one inherited from each parent.
Example:
Most human body cells, like a muscle cell, are diploid and contain 46 chromosomes.
Fertilization
The fusion of male and female gametes to form a zygote, restoring the diploid chromosome number.
Example:
After a sperm cell undergoes fertilization with an egg cell, a new diploid organism begins to develop.
Gametes
Reproductive cells (sperm and egg in animals) that contain a single set of chromosomes (haploid).
Example:
During sexual reproduction, the fusion of male and female gametes forms a diploid zygote.
Genetic Diversity
The variation in the genetic makeup of individuals within a population, which is crucial for evolution and species survival.
Example:
Genetic diversity allows a species to adapt to changing environmental conditions, such as the emergence of new diseases.
Haploid (n)
A cell or organism containing a single set of unpaired chromosomes.
Example:
Human sperm and egg cells are haploid, each carrying 23 chromosomes.
Homologous Chromosomes
A pair of chromosomes (one maternal, one paternal) that are similar in size, shape, and gene sequence, and pair during meiosis.
Example:
In humans, chromosome 1 from your mother and chromosome 1 from your father are a pair of homologous chromosomes.
Meiosis
A specialized type of cell division that reduces the chromosome number by half, creating four genetically unique haploid cells.
Example:
In humans, meiosis is the process that produces sperm and egg cells, each containing 23 chromosomes.
Meiosis I
The first round of meiotic division, where homologous chromosomes separate, resulting in two haploid cells with duplicated chromosomes.
Example:
A key outcome of Meiosis I is the reduction of the chromosome number by half.
Meiosis II
The second round of meiotic division, where sister chromatids separate, resulting in four genetically unique haploid cells.
Example:
Meiosis II is similar to mitosis in that sister chromatids are separated, but it occurs in haploid cells.
Metaphase I
The phase of Meiosis I where homologous chromosome pairs align randomly along the metaphase plate at the center of the cell.
Example:
The random orientation of chromosome pairs during Metaphase I is a major source of genetic variation in offspring.
Metaphase II
The phase of Meiosis II where sister chromatids align along the metaphase plate in each of the two haploid cells.
Example:
The alignment of individual chromosomes during Metaphase II resembles that of mitosis, but with half the chromosome number.
Mitosis
A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent cell, typically for growth and repair.
Example:
When you get a cut, mitosis helps replace the damaged skin cells with identical new ones.
Prophase I
The first and longest phase of Meiosis I, characterized by chromosome condensation, nuclear envelope breakdown, and the pairing of homologous chromosomes where crossing over occurs.
Example:
During Prophase I, you can observe homologous chromosomes forming bivalents and exchanging segments of DNA.
Prophase II
The first phase of Meiosis II, where chromosomes condense again and new spindle fibers form in each of the two haploid cells.
Example:
In Prophase II, the chromosomes, each still made of two chromatids, prepare for their final separation.
Random Alignment
The independent assortment of homologous chromosome pairs at the metaphase plate during Metaphase I, leading to diverse combinations of chromosomes in gametes.
Example:
Due to random alignment, a gamete could receive a mix of maternal and paternal chromosomes, not just all from one parent.
Sister Chromatids
Two identical copies of a chromosome joined together by a centromere, formed during DNA replication.
Example:
Before cell division, each chromosome consists of two identical sister chromatids that will eventually separate.
Telophase I
The final phase of Meiosis I, where chromosomes decondense, nuclear envelopes may reform, and cytokinesis typically divides the cell into two haploid daughter cells.
Example:
After Telophase I, the cell is ready to proceed to Meiosis II, with each new cell containing a haploid set of duplicated chromosomes.
Telophase II
The final phase of Meiosis II, where chromosomes decondense, nuclear envelopes reform, and cytokinesis results in four genetically unique haploid daughter cells.
Example:
The completion of Telophase II marks the end of meiosis, yielding four distinct gametes.