Add to Table of Contents: Stages of Meiosis Activity Pg. 42 Meiosis Pg. 43

Meiosis Pg. 43 Humans have 23 pairs of chromosomes = 46 total.

Mitosis: results in 2 new cells with identical genetic material as original(46) Used for growth, repair, etc. Meiosis: results in 4 different new cells and cuts chromosome # in half (23) 2 different cells must later join to form 1 whole cell = =“sexual reproduction”

Meiosis continued…. Produces Gametes: human reproductive cells (sperm/egg) 2 stages: 1) Meiosis I 2) Meiosis II

Meiosis continued…. Organisms produced by sexual reproduction (2 parents) have 2 copies of each chromosome. Homologous Chromosomes: carry genes for same traits 1 from each parent same size & shape

Meiosis I (con’t) Sometimes when tetrads form, crossing-over can occur Crossing Over: when homologous chromosomes (tetrads) exchange portions of themselves Results in new combinations of genes, different from parents Prophase I

Assignment: 1. Use pages 266-269 to determine what happens in each phase of meiosis. 2. Cut out and paste the picture of the phases and descriptions in their correct Meiosis Stage.

http://www.cellsalive.com/meiosis.htm

Crossing Over Tetrad →

Phases of Meiosis I 1) Prophase I Same as Mitosis, except… Homologous chromosomes pair up to form a tetrad. Chromatids twist around each other & exchange info. Crossing-over: creates new mixture of genetic material. Maternal & Paternal DNA exchanged

Phases of Meiosis I 2) Metaphase I Tetrads line up randomly along center of cell.

Phases of Meiosis I 3) Anaphase I Each homologous chromosome moves to either side of cell. Independent Assortment: random separation of homologous chromosomes to opposite sides of cell. Creates genetic variation

Phases of Meiosis I 4) Telophase I & Cytokinesis I Same as Mitosis, except… New cells contain 1 chromosome from each homologous pair. Different genetic material than original

Phases of Meiosis II 1) Prophase II Chromosomes form and spindles attach.

Phases of Meiosis II 2) Metaphase II Chromosomes move to center of cell.

Phases of Meiosis II 3) Anaphase II Chromatids separate and move to either side of cell.

Phases of Meiosis II 4) Telophase II & Cytokinesis II Nuclear membrane reforms 4 new cells form (gametes)

Add to Table of Contents: Karyotype Page 54 Abnormal Meiosis Page 55

Abnormal Meiosis After meiosis has occurred, 4 new cells are created: Spermatogenesis: 4 genetically different new sperm. Oogenesis: 1 new egg and 3 polar bodies(that disintegrate)

2 Chromosome Types: Sex Chromosomes: determine sex of organism (male/female)-23rd pair Male: XY Female: XX Autosomes: all others,pairs 1-22

Different species have different #’s of chromosomes: Humans = 46, Lettuce =18, but dogs = 78!! ***more chromosomes ≠ more complex!!

May be used to identify genetic disorders Karyotype: A diagram that shows a cell’s chromosomes arranged in order from largest to smallest. May be used to identify genetic disorders Humans: 22 autosome pairs 1 sex chromosome pair Homologous Chromosomes ↓ Sex Chromosomes ↑ ↑

Nondisjunction: chromosomes don’t separate during Anaphase so 1 gamete has 22 chromosomes and the other has 24. 1. Down’s syndrome (3 21’s) 2. Turner’s syndrome (X) 3. Kleinfelter’s syndrome (XXY)

Down Syndrome – Don’t write Down syndrome (or Trisomy 21) is a chromosomal disorder caused by the presence of an extra chromosome number 21. Down syndrome is estimated at 1 per 800 to 1,000 births

Down’s syndrome

Head and facial features often associated with Down Syndrome: Flattened back of head. Attractive Almond-shaped eyes, with eye lid a little droopy. Sometimes a whitish pupil. Slightly flattened bridge across nose. Smallish ears, slightly lower on the head, with a small fold on top of ears. Slightly protruding tongue.

Down Syndrome

Risk of Down Syndrome

Turner’s Syndrome

Turner’s Syndrome X It is a chromosomal disorder affecting females in which all or part of one of the X chromosomes is absent. Occurring in 1 out of every 2500 girls There are characteristic physical abnormalities, such as short stature, broad chest, low hairline, low-set ears, and webbed neck. Concurrent health concerns are also frequently present, including congenital heart disease, often infertility

Klinefelter's syndrome

Klinefelter’s Syndrome XXY Klinefelter's syndrome, 47 or XXY or syndrome is a condition caused by a chromosome aneuploidy. Affected individuals have at least two X chromosomes and at least one Y chromosome.[1] Klinefelter's syndrome is the most common sex chromosome disorder The principal effects are development of small testicles and infertility. The condition exists in roughly 1 out of every 1000 males Because of the extra chromosome, individuals with the condition are usually referred to as "XXY Males", or "47, XXY Males".