Double-Arm

Chromosome

made up of paired, genetically identical chromatids called

"sister chromatids"

Single-Arm

Chromosome

are composed of a

single chromatid

Centromere

location where sister chromatids

are joined

Haploid

(n)

reproductive cells that contain half the number of chromosomes

(ex. egg and sperm)

Diploid

(2n)

total number of chromosomes found in the body cells of an organism that has paired chromosomes

Somatic Cells

any cell in the body except the sex cells (egg and sperm) that contains the diploid number of chromosomes

* written as 2n *

Sex Cells

(Gametes)

a cell that has a haploid number of chromosomes and is involved in reproduction.

* written as n *

Zygote

fertilized egg cell

the cell that is the result of 2 haploid sex cells joining together to form a diploid cell

Asexual Reproduction

• requires 1 parent
• no sex cells are needed
• genetic variability is low
• best in stable (non-changing) environment

Sexual Reproduction

• requires 2 parents
• sex cells are needed
• genetic variability is high
• best in an unstable (changing) environment

Homologous

Chromosomes

chromosome pairs that have:

• same size
• same centromere position
• same banding patterns
• same genes in the same location but different nucleotide sequences

Karyotype

Micrograph of the complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size

Can be used to determine if a person has a chromosomal abnormality

Mitosis

• a step in cell division in which the nucleus divides into two, genetically identical nuclei
• occurs during asexual reproduction (somatic cells) for growth and repair of cells

Meiosis

• division of nuclear material that produces sex cells (egg and sperm) with half the number of chromosomes
• occurs during sexual reproduction

Egg

• female gamete
• contains half the number of chromosomes
• haploid (n)

Sperm

• male gamete
• contains half the number of chromosomes
• haploid (n)

Fertilization

• the combining of egg and sperm

• produces a diploid cell called a zygote

Interphase I

• similar to interphase in mitosis
• DNA replicates during S phase
• centrioles in animal cells divide

Meiosis I

diploid number of double arm chromosomes is reduced to a haploid (23) number of double arm chromosomes

Prophase I

• similar to prophase in mitosis
• Synapsis takes place
• homologous chromosomes come together to form Tetrads

Crossing Over

the arms of the homologous chromosomes exchange genetic material

(occurs during prophase I)

Metaphase I

• Tetrads line up randomly on the equator of the cell
• spindle fibers atach to tetrads at the centromeres

Rule of

Independent Assortment

• Homologous chromosomes (tetrads) move in random fashion to the equator of the cell
• The two resulting cells end up with a random assortment of the mother's and father's chromosomes

Anaphase I

• spindle fibers contract causing the homologous chromosomes in each tetrad to separate
• homologs move to opposite ends of the cell

Telophase I

• spindle fibers break down and nuclear membrane reforms
• chromosomes unravel into chromatin
• burrow in animal cell form (cell plate in plant cells) and cytoplasm begins to divide

Cytokinesis or

Interphase II

• very short phase with little activity
• cell divides
• NO DNA Replication takes place
• each cell now contains a haploid number of double arm chromosomes

Meiosis II

haploid number of double arm chromosomes divide into a haploid number of single arm chromosomes

Prophase II

• chromatin condenses to show a haploid number of double arm chromosomes
• nuclear membrane breaks down, spindle fibers form and centrioles move to poles

Metaphase II

• haploid number of double arm chromosomes line up at the equator of the cell

spindle fibers attach to the centromeres joining sister chromatids

Anaphase II

• spindle fibers contract causing centromeres to split
• chromatids separate and a haploid number of single arm chromosomes move toward opposite ends or poles of the cell

Telophase II

• spindle fibers disappear
• chromosomes unravel into chromatin
• furrow or cell plate forms
• 4 cells are forming, each with a haploid number of single arm chromosomes

Cytokinesis

• cytoplasm divides
• furrow or cell plate is completed
• four different cells have been formed each with a haploid number of chromosomes

How does genetic variation occur during meiosis?

1.  Crossing over (during Prophase I)

2.  Independent assortment

           (during Metaphase I)

3.  Combination of gametes

Reduction Division

Gametogenesis

the production of gametes by the process of meiosis

(oogenesis and spermatogenesis)

Oogenesis

The production of eggs in the ovaries of the female.

Produces one egg and 3 polar bodies for every parent cell.

Spermatogenesis

Production of sperm cells in the male testes.

Produces 4 viable (functional) sperm for every parent cell

Nondisjunction