Chapter 10“Chromosomes & Cell

Reproduction”

• Gene- DNA that is organized into units and codes for a protein. Genes play an important role in determining how a person’s body develops and functions.

• Chromosome (colored body)- coiled up structure of DNA. Before a eukaryotic cell divides, the DNA & proteins coil up into a chromosome.

• Chromatid-Two exact copies of DNA that make up each chromosome. Often called “sister chromatids”.

• Centromere- The place at which the 2 chromatids are attached and held together.

Chromosome Number

• Human Somatic (“soma” means body) Cell- 46 total chromosomes or 23 pairs. The pairs differ in shape, size and set of genes contained within the chromosomes.

• Human Gamete (sex cell)- female- egg; male- sperm. Each have only 23 chromosomes.

• Homologous chromosomes- similar in size, shape & genetic content. Each homologue within the pair comes from one of the two parents.

• Diploid- Somatic (body) cells contain 2 sets of chromosomes (one set is from mom, other set is from dad).

• Haploid- Gametes (sex cells) contain 1 set of chromosomes. The fusion of 2 haploid gametes (fertilization) forms a diploid zygote.

• Zygote- fertilized egg cell. It is the first cell of a new organism.

• The number of chromosomes in cells is the same within a species. Although most species have different numbers of chromosomes, some species by chance have the same number.

Sex Determination

• Autosomes- 22 pairs of the 23 total pairs of chromosomes in human somatic cells. They are not directly involved in determining the sex (gender).

• Sex chromosomes- only one of the 23 pairs of c’somes in humans that contain genes that determine the sex of an individual.

• XX- female

• XY- male

• Because a female can only donate an “x” to her offspring, the sex of the offspring is determined by the male.

Change in chromosome number

• Trisomy (three bodies)- humans with more than 2 copies of a chromosome. Examples include Trisomy 13 & 21. Improper development is a result.

• Karyotype- a photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size.

Change in Chromosome Structure

• Deletion- a piece of a chromosome breaks off completely. Usually proves to be fatal for the developing zygote.

• Duplication- a chromosome fragment attaches to its homologous chromosome, which will then carry 2 copies of a certain set of genes.

• Inversion- a chromosome piece reattaches to the original chromosome but backwards.

• Translocation- when a piece reattaches to a non-homologous chromosome.

Cell Cycle & Mitosis and Cytokinesis

Cell Cycle• Repeated sequence of

cellular growth and division. Composed of 5 total stages (IPMAT).

• How do cells “know” when to divide? Cells have a “red-light/green-light” mechanism that is controlled by feedback from the cell.

Interphase• Cells spend 90% of

its time in the 3 stages of Interphase.

• It’s the longest and busiest stage.

• Chromosomes are copied before the cell divides and new organelles are being made.

• Mitosis aka “Cell Repro- duction” -produces new cells that are identical to the original cell. Composed of 4 stages (PMAT).

1. Prophase- Longest stage in mitosis- chromosomes coil up and become visible, nuclear envelope dissolves and spindle forms.

2. Metaphase- Chromosomes move to the middle. Spindle fibers link the chromatids of each chromosome to opposite poles.

Anaphase- Centromeres divide and the spindle fibers pull half of the chromosome to each end.

Telophase- chromosomes uncoil, spindle dissolves and CYTOKINESIS (cell pinching) begins.

Cytokinesis