Genetics and Cell Division: Key Terms and Concepts

Chromatin

Refers to the DNA and protein that make up chromosomes.

Nucleosomes

The arrangement where approximately 200 nucleotides are coiled around eight histone proteins.

Chromatid

One of the two parts of a duplicated chromosome.

Centromere

The constriction point of the chromosome, which is the location used when counting chromosomes.

Kinetochore

A protein attached to microtubules.

G1 Phase

The first primary growth phase, which is a major part of the cell's life.

S Phase

The stage where DNA Replication occurs, resulting in the production of a sister chromatid.

G2 Phase

The second growth phase where organelles like mitochondria replicate.

Prophase

Chromosomes become visible, the nucleolus disappears, and the nuclear envelope breaks down.

Metaphase

Chromosomes align in the center of the cell.

Anaphase

The shortest phase of mitosis where centromeres divide, freeing the sister chromatids.

Telophase

The spindle is disassembled, the nuclear envelope forms again, and chromosomes begin to uncoil.

Cytokinesis

The process where the cell actually divides.

Binary Fission

The cell division process observed in prokaryotes.

G1 Checkpoint

The cell decides if it should divide, based on internal and external factors.

S Checkpoint

Checks for incorrect or damaged DNA replication; if issues are found, the cycle stalls.

M Checkpoint

Ensures that all chromosomes are attached to the spindle before division occurs.

Meiosis

Also known as reduction division because the daughter cells contain half the amount of chromosomes compared to the parent cell.

Prophase I

DNA coils, and homologous chromosomes pair up in a process called synapsis.

Metaphase I

Homologous chromosomes line up in pairs at the center of the cell.

Anaphase I

One homologue goes to one pole and the other goes to the opposite pole; sister chromatids do not separate at this stage.

Telophase I

Two cells are formed, each still having chromosomes in a duplicated state.

Crossing over

The process where homologous chromosomes exchange chromosomal material.

Chiasmata

The physical site of the crossing over event; this is the exchange point between non-sister chromatids.

Mitosis

Cell division resulting in two daughter cells with the same number of chromosomes as the parent cell.

Meiosis I

First division in meiosis resulting in two daughter cells with half the number of chromosomes.

Meiosis II

Second division in meiosis resulting in four daughter cells, each with half the number of chromosomes.

Chromosome number in parent cell before division

46 for mitosis, 46 for meiosis I, N/A for meiosis II.

Crossing over at Prophase

No in mitosis, yes in meiosis I, no in meiosis II.

Chromosome line up in pairs during metaphase

46 in mitosis, 23 in meiosis I, 23 in meiosis II.

Number of chromosomes in each daughter cell

2 in mitosis, 2 in meiosis I, 4 in meiosis II.

Number of daughter cells at the end of each division

2 in mitosis, 2 in meiosis I, 4 in meiosis II.

Daughter cells - haploid or diploid

Diploid in mitosis, haploid in meiosis I, haploid in meiosis II.

Purpose of the division

Cell replacement in mitosis, sexual reproduction in meiosis.

Location of cell division

Somatic cells for mitosis, germ cells for meiosis.

P generation

The parental generation, which is purebred and self-pollinates.

F1 generation

The first filial generation from cross-pollinating two P generation plants.

F2 generation

The second filial generation from allowing the F1 generation to self-pollinate.

Law of Dominance

Offspring from homozygous opposing traits will express the dominant trait.

Law of Segregation

The two alleles for a character separate when gametes are formed.

Law of Independent Assortment

Inheritance of one characteristic does not influence another, unless genes are linked.

Monohybrid

Crossing two heterozygous individuals for a single trait.

Dihybrid

Crossing two heterozygous individuals for two different traits.

Incomplete Dominance

Neither allele is completely dominant, resulting in an intermediate phenotype.

Multiple Alleles

Two or more different forms of an allele, such as human blood type.

Pleiotropy

A single gene that exerts many effects on the organism.

Polygeny

Many genes affect one characteristic, resulting in quantitative traits.

Penetrance

The proportion of the population that exhibits a trait.

Expressivity

The degree to which the genotype is expressed.

Pedigree

A diagram illustrating the occurrence and appearance of a specific trait.

Sex-linked trait

A trait determined by a gene on the sex chromosome.

Nondisjunction

Failure of homologous chromosomes to separate correctly during meiosis.

Aneuploidy

An abnormal number of chromosomes resulting from fertilization with an abnormal gamete.

Trisomy

When chromosomes are present in triplicate.

Monosomy

When a chromosome is missing.

Polyploidy

When an organism has an extra set of chromosomes.

Deletions

A fragment of the chromosome is lost.

Inversions

A chromosome fragment breaks off and reattaches in reverse order.

Translocation

A chromosomal fragment attaches to a non-homologous chromosome.

Duplication

Chromosomal segments are repeated.