Bellringer 11/15/12 1. What are the steps of the cell cycle ALL 6 IN ORDER ? retrieve a note sheet from the front cart. Glue it to page 47 (45-honors).

Meiosis Definition: Cell division of gametes (sex cells—eggs & sperm) Purpose: To make genetically different reproductive sex cells. Cells contain ½ the normal amount of chromosomes. (haploid) Zygote: A fertilized cell (egg + sperm together)

What is Produced by Meiosis? Four haploid cells (1n) Each cell is genetically different!

Diploid Cells Two sets of chromosomes in a cell. ½ from mom, ½ from dad. 2n All body cells are diploid Made by mitosis

Haploid Cells One set of chromosomes in a cell. 1n All sex cells are haploid Made by meiosis

What is different about meiosis? Many different variations in the gametes because of crossing over. Crossing over is when tetrads bind tightly, parts break off and are swapped between the chromatids Sex cells divides twice, but only copies DNA once. Tetrad: when 2 homologous chromosomes bind together during prophase I of meiosis.

Before Meiosis Homologous chromosomes are attached to each other Homologous chromosomes: Two of the same type of chromosome Chromosomes copy themselves so that they can be passed along to the daughter cells

Before Meiosis Tetrad: 2 homologous chromosomes attached together (= 4 sister chromatids)

Comparing Mitosis and Meiosis DNA replicates in interphase ONE division of chromosomes Separate sister chromatids TWO divisions of chromosomes Separate homologous chromosomes (meiosis I) Separate sister chromatids (meiosis II) Makes 2 identical DIPLOID cells Makes 4 HAPLOID cells Chromosome # is identical to parent cell Chromosome # is HALF of the parent cell Used for replacement, repair, & growth Used to make gametes

Mistakes in Meiosis Nondisjunction: when homologous chromosomes fail to separate from each other during meiosis (either Anaphase I or II) Result: Gamete(s) may have too many chromosomes, while other gamete(s) are missing that chromosome

Mistakes in Meiosis Organisms with extra chromosomes can survive; organisms with too few usually do not survive Polyploidy: when organisms have more than the normal number of chromosome sets Can be lethal for animals but not plants (plants just usually get bigger)..Remember, we used strawberries for DNA extraction because they’re octoploids

Nondisjunction in Sex Chromosomes Turner’s Syndrome (Female) Genotype: X can cause a variety of medical and developmental problems, including short stature, failure to begin puberty, infertility, heart defects and certain learning disabilities

Trisomy X (Females) Genotype: XXX may be taller than average, but this chromosomal change typically causes no unusual physical features. most females with triple X syndrome have normal sexual development and are able to conceive children Triple X syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills

Klinefelter’s Syndrome Males-XXY MOST COMMON male sex organs; unusually small testes, sterile breast enlargement and other feminine body characteristics normal intelligence

Jacob’s Syndrome Males-XYY hard to determine individuals are somewhat taller than average and often have below normal intelligence at one time (~1970s), it was thought that these men were likely to be criminally aggressive, but this hypothesis has been disproven over time.

Nondisjunction in Autosomes Patau’s Syndrome Trisomy 13 serious eye, brain, circulatory defects, cleft palate, polydactly 1:5000 live births Children rarely live more than a few months.

Down Syndrome Trisomy 21 characteristic facial features, short stature; heart defects susceptibility to respiratory disease, shorter lifespan prone to developing early Alzheimer's and leukemia often sexually underdeveloped and sterile, usually some degree of mental retardation.

Edward’s Syndrome Trisomy 18 About 95% die before birth Of liveborn infants, only 50% live to 2 months, and only 5–10% will survive their first year of life almost every organ system affected 1:10,000 live births

Meiosis I: Separating the Homologues Prophase I Chromosomes appear Crossing-over occurs between chromosomes (now tetrads) Nuclear membrane disappears Metaphase I Tetrads line up at the equator (middle)

Meiosis I: Separating the Homologues Anaphase I Tetrads separate and move to opposite ends of the cell Telophase I/Cytokinesis Cytoplasm divides & 2 daughter cells are formed Each cell has a homologous chromosome

Meiosis II: Separating the Sister Chromatids Prophase II Nuclear membrane disappears Metaphase II Chromosomes line up along equator (not in homologous pairs)

Meiosis II: Separating the Sister Chromatids Anaphase II Sister chromatids separate and move to opposite ends of the cell Telophase II/Cytokinesis Cytoplasm divides New membranes are formed 4 HAPLOID daughter cells formed Each contains ONE chromosome from each homologous pair

Chromosomal Structural Mutations 1. Deletion: a part of one chromosome is lost during cell division so its now missing certain genes Example-- Cri du chat (cry of the cat): a specific deletion of a small portion of chromosome 5 these children have severe mental retardation, a small head with unusual facial features, and a cry that sounds like a distressed cat

Example--Fragile X: the most common form of mental retardation 2. Duplication: a part breaks off of a chromosome and joins the other homologous chromosome, so that region is repeated Example--Fragile X: the most common form of mental retardation Fragile X have over 700 repeats due to duplications Affects 1:1500 males, 1:2500 females

3. Translocation: a fragment of a chromosome is moved from one chromosome to another Example-- Acute myelogenous leukemia (AML) is a fast-growing cancer of the blood and bone marrow white blood cells (WBC) do not develop and cannot fight infections Bone marrow may also make abnormal red blood cells and platelets

Karyotypes Karyotypes: a picture of the complete number and appearance of chromosomes in a person Autosomes: a non-sex chromosome or chromosome pairs 1-22 Sex chromosomes: chromosome pair 23 which determine the sex/gender of a person