Biology 30-1 - Chapter 16

DNA

• genetic information

• Found within the nucleus of each and every cell in the body

• Tightly packed into chromosomes

Chromosomes in a Human

• 23 pairs of homologous chromosomes (46 in total)

  • 22 pairs of autosomes

  • 1 pair of sex chromosomes

What do Homologous chromosomes carry?

Different forms of the same genes (alleles)

Diploid

• Human Body Cells

• 2n = 46

Haploid

• Human Sex Cells

• N = 23

Cell Cycle

• Each cell goes through three phases before it actually divides

  1. G1 Phase (cell growth)

  2. S Phase (DNA replication)

  3. G2 Phase (preparation for division)

• Collectively, phases are referred to as interphase (90% of cell life)

Mitosis

• 2n → 2n

• Produces somatic / body cells

• Produce daughter cells that are identical to the parent cell

• Growth, maintenance, repair

Cancer

• Uncontrolled cell growth due to the under-production of chemicals that regulate growth factors or the over-production of growth factors themselves

Meiosis

• 2n → n → n

• Produces gametes / sex cells

• Produces daughter cells with fewer chromosomes than parent cells

• Produces chromosomes with different combinations of genes compared to those in parent cells

Meiosis Nondisjunction

• Major cause of chromosomal abnormalities

• Most occur in oogenesis due to maternal age

  • Meiosis I: Anaphase I

    • Homologous chromosomes (tetrad) fail to separate

    • Most chromosomal abnormalities occur here

  • Meiosis II: Anaphase II

    • Sister chromatids fail to separate

Nondisjunction results in:

• Monosomy: Missing a chromosome (2n=45)

  • If missing any full chromosome, other than X, it is lethal

  • Turner Syndrome (XO) → cannot have kids (sterile)

• Trisomy: Extra chromosome (2n = 47)

  • Down syndrome (21)

Amniocentesis

• Prenatal test (16th-20th week)

• A sample of fluid surrounding baby

Chorionic villi sampling (CVS)

• Tissue taken from chorion / placenta

• 11th - 14th week

Karyotype

• Picture of the chromosomes

• Matched up by size, banding pattern, centromere location=