Cell Division!

Stem Cells

A relatively unspecialized cell that can divide during a single division into one identical stem cell and one more specialized daughter cell, which can undergo further differentiation.

Asymmetrical Division

This is when one cell remains a stem cell (self-renewal) and the other becomes another type of cell with a more specialized function.

Cell Differentiation

Process that leads to cell specialization.

Why do cells divide?

For growth, repair, and renewal.

The Cell Cycle

An ordered series of events that occurs in a cell leading to its division into two cells.

Interphase

Non-dividing phase of the cell cycle where the cell is doing a series of steps to prepare for division.

G1 = 1st Gap (Growth)

Cell grows.

S = DNA Synthesis

DNA is duplicated.

G2 = 2nd Gap (Growth)

Prepares for division, cell grows (more), produces organelles.

Mitotic Phase

The phase where Cell Division occurs.

Cytokinesis

Splitting of the cytoplasm, which leads to separation of the cell into two cells.

Genome

The entire collection of an organism’s DNA.

Sex Chromosomes

Chromosomes that determine an individual’s sex; ex. X & Y.

Autosomes

Any chromosome that is not a sex chromosome; ex. chromosomes 1-22 in humans.

Chromosome

A threadlike, gene-carrying structure found in the nucleus.

Chromatin

A complex of DNA and its associated histone proteins.

Sister Chromatids

Two identical copies of DNA making up a replicated chromosome.

G0

Non dividing stage where the cell has left the cell cycle.

Centrosomes

Release microtubules to form the mitotic spindle.

Prophase

Chromatin condenses into visible chromosomes.

Metaphase

Chromosomes align along middle of cell metaphase plate.

Anaphase

Sister chromatids of the duplicated chromosome separate into 2 chromosomes, which are exact copies of each other.

Telophase

Chromosomes arrive at opposite poles.

Asexual Reproduction

Offspring that inherit all their genetic material from just one parent.

Sexual Reproduction

Offspring that differ genetically from their parents because the genetic material of both parents was combined.

Advantages of Asexual Reproduction

Beneficial in stable environments, it eliminates the energy cost of finding a mate, it is successful at low population density, it eliminates the energy cost of fertilization/pollination, and it eliminates the need for pollinators in plants.

Advantages of Sexual Reproduction

Generation of offspring arising from the fusion of two gametes, offspring receive half of their genetic material from each parent, generates genetic variation in the offspring, children are genetically different from their parents and each other, and is beneficial in changing/unstable environments.

Karyotype

A display of an individual’s chromosomes.

Homologous Chromosomes (homologs)

Paired chromosomes with the same chromosome structure.

Diploid

Two sets of chromosomes (2N).

Haploid

One set of chromosomes (N).

Somatic Cells

Body cells; diploid.

Gametes

Sex cells; haploid.

Fertilization

A sperm (N) fuses with an egg cell (N) to form a zygote.

Meiosis

Starts with a diploid cell, produces 4 non-identical haploid gametes, and consists of 2 divisions.

Division 1

Splits the homologous chromosomes, reducing the chromosome number in half.

Division 2

Splits the sister chromatids like mitosis.

Independent assortment of chromosomes

Random alignment of homologous chromosomes in Metaphase 1 of meiosis.

Crossing-over

Mixing of alleles across homologous chromosomes during prophase 1 of meiosis.

Random fertilization

Which sperm fertilizes which egg.

Non-disjunction

The failure of the chromosomes to properly segregate during meiotic or mitotic anaphase, resulting in daughter cells with abnormal numbers of chromosomes.