Genetics Course: Key Concepts, Cell Division, and Meiosis

Study Time Recommendation

Schedule 9 hours per week outside of lecture for preparation.

Gene

A segment of DNA on a chromosome that codes for a specific trait

Allele

Multiple forms of a gene

Genotype

An organism's genetic makeup, or allele combinations.

Phenotype

The observable characteristics of an individual.

RNA

The molecule that plays a role in protein synthesis

Carries genetic information for non-living things

Chromosome

Structures that carry genetic information.

Mutation

Changes in genetic information that can be passed from cell to cell or parent to offspring.

Evolution

Frequency of genetic change over time

Prokaryotes

Cells that do not contain a membrane-bound nucleus.

Eukaryotes

Cells that contain a membrane-bound nucleus.

Chromatin

long strands of DNA found in the eukaryotic cell nucleus; condense to form chromosomes

Active form of DNA

Histones

Proteins that package DNA into nucleosomes

Limit the access to DNA from proteins directing gene transcription

Nucleosomes

DNA double-wrapped around histone proteins.

Prokaryotic cell division

Binary fission

1 origin site of duplication

Mitosis

The process of cell division that results in two identical daughter cells.

Meiosis

The process of cell division that results in four non-identical gametes.

Gametogenesis

The process of forming gametes (egg or sperm).

Somatic cell

"Body cell"

Its genes are not passed down to future generations

Only mitosis

Sex cell or germ cell

Destined to become a gamete

Genes can be passed on to future generations

Mitosis and Meiosis

Gamete

Egg or sperm cell

Diploid (2n)

A cell or organism with 2 copies of each chromosome.

Haploid (n)

A cell or organism with 1 copy of each chromosome.

Polyploid

A cell or organism with more than 2 copies of each chromosome.

Homologous chromosomes (Homologs)

Chromosome pairs that carry the same linear sequence of genes.

May carry different alleles of the same gene

Duplicated chromosome

Consists of 2 sister chromatids.

Sister chromatids

Each contains 1 copy of DNA.

Carry identical alleles

Duplicated chromosome carries

2 identical DNA double helix molecules.

Centromere

Constricted region where kinetochore assembles.

Kinetochore

A specialized region on the centromere that links each sister chromatid to the mitotic spindle.

Telomeres

Protective ends of chromosomes.

Origins of replication

Sites where DNA synthesis begins.

Interphase

Begins with a newly divided daughter cell and includes growth and DNA synthesis stages.

G1 phase (Gap 1)

Prepare for DNA replication.

Tons of proteins and nucleotides produced

S phase

DNA synthesis/replication

Chromosomes are organized as sister chromatids

G2 phase (Gap 2)

Growth, prepare for mitosis.

Makes sure everything goes well

G0 stage

Non-dividing phase

Optional phase during which the cell exits the cycle.

May or may not re-enter

M phase

Mitosis (nuclear division) and cytokinesis (cell division).

Prophase

Chromosomes condense and become visible

Mitotic spindle forms

Centrosome

A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division.

Cohesin in mitosis

Protein that holds sister chromatids together beginning at S phase until anaphase

Separase

Breaks down cohesin during anaphase so chromatids can be spit apart

Cohesin in Meiosis

In this process it joins the homologs at chiasmata only as well as the sister chromatids

Separase in Meiosis

Degrades cohesin at chiasmata in anaphase I, allowing only homologs to separate

Shugoshin

Protects cohesion from being degraded by separase at the centromeric regions

Keeping sister chromatids together

When does shugoshin degrade?

After meiosis I; so chromatids can separate at anaphase II

Prometaphase

Disintegration of the nuclear membrane

Microtubules enter the nucleus, grow, and attach to the chromosomes

Metaphase

Chromosomes become arranged in the middle

Centrosomes pull chromosomes apart to opposite ends

Anaphase

Sister chromatids separate becoming individual chromosomes that migrate to opposite poles

Telophase

Nuclear membrane reforms, and the condensed chromosomes relax

Cytokinesis

The process that divides the cytoplasm of a parental cell into two daughter cells.

Fertilization

The fusion of haploid gametes to create diploid offspring.

Meiosis I

The reduction division phase of meiosis that produces two haploid cells.

Meiosis II

The equational division phase of meiosis that produces four haploid cells.

Zygote

The diploid cell formed by the fusion of two haploid gametes.

Prophase I (Meiosis)

Synapsis occurs along with crossing over of homologs

Tetrads

The paired chromosomes consisting of four chromatids, are present during prophase I

Synapsis

Pairing of homologous chromosomes

Crossing over

Process in which homologous chromosomes exchange genetic information

Generates genetic information

Metaphase I (Meiosis)

Tetrads are lined up at the metaphase plate; Spindle fibers attach

Anaphase I (Meiosis)

Tetrads split up and head to opposite poles; homologous chromosomes separate

Sister chromatids remain attached and travel together

Telophase I/Cytokinesis I

The cell divides into two new haploid cells with double-stranded chromosomes

Interkinesis

Short period of time between meiosis I and meiosis II where the nuclear membrane reforms and spindles break down

Prophase II

The first stage of meiosis II where the chromosomes condense again and spindles reform

Metaphase II

Individual chromosomes lune up on the metaphase plate

Anaphase II

Sister chromatids separate and move as individual chromosomes toward opposite poles

Telophase II/Cytokinesis II

Cells divides into four haploid cells

Recombination

The process during meiosis where crossing over generates new combinations of alleles.

Independent Assortment

Homologous chromosome pairs separate independently or randomly