MEIOSIS … making gametes….

Quick Review Gamete = sex cells (egg and sperm) Each has 1 set of 23 chromosomes When they come together, the resulting cell has 46 chromosomes Somatic cell = body cells (everything except egg and sperm) 23 23

Cells with 1 set of chromosomes (gametes) are said to be HAPLOID (n) Each of your body (somatic) cells has 2 sets of chromosomes – one from mom, one from dad. Any cell that has 2 complete sets of chromosomes is said to be DIPLOID (2n) Cells with 1 set of chromosomes (gametes) are said to be HAPLOID (n) When 2 cells come together in fertilization to make a zygote, each can only have 1 set of chromosomes. That way, the zygote will have 46 chromosomes. (23 + 23 = 46) (Instead of 46 +46 = 92!)

What type of cells produce egg/sperm? Ovarian and testicular cells!

Meiosis is… Making the cells that make babies! (egg and sperm) The process of nuclear division that reduces the number of chromosomes by half (reduction division) Start with somatic cell End with gamete

More practice… In streptomycin fungus n = 11. What is the diploid number for this species? If 2n = 108 for black spruce trees then what is the haploid number? 2n = 14 for this species. Fill in the chromosome numbers for each cell. A C B What is process A, B, and C?

Homologous Chromosomes (pairs) In each body (somatic) cell you have 23 homologous chromosome pairs Similarities: length, centromere location, and code for same traits (have same genes) Differences: one chromosome from mom and one from dad

Homologous Chromosomes have the same banding pattern

Diploid Testicular cell Diploid ovarian cell Diploid Testicular cell How you got here: 2n 2n egg (n) sperm (n) fertilization zygote MEIOSIS MEIOSIS MITOSIS You

Products of MITOSIS: Products of MEIOSIS: 4 unique haploid (n) cells 2 identical diploid (2n) cells Products of MEIOSIS: 4 unique haploid (n) cells   2n 2n 2n 2n n n n n

Why Meiosis is important: It creates Genetic Recombination (variety): Resulting from crossing over AND independent assortment Crossing Over: Exchange of genetic material between homologous chromosomes during prophase I of Meiosis

Crossing Over: Exchange of genetic material between homologous chromosomes

Independent Assortment: ending up with random mix of genes in each gamete

MEIOSIS I 1. Interphase I: Period of cell growth and preparation for division (G1, S, G2) PROPHASE I: Tetrads appear Crossing Over (synapsis) occurs - Before Interphase After interphase

Metaphase I: Tetrads (2 homologous chromosomes) line up on metaphase plate and lock on to spindle fibers  Anaphase I: Spindle fibers pull tetrad apart; one homologous chromosome goes to each side of the cell. Independent assortment occurs  

Telophase I: nuclear membranes form around the two new nuclei Cytokinesis I: cell splits in two. Result = 2 diploid cells.

MEIOSIS II

*Special Interphase between the two divisions: NO replication!!! - so nothing changes with the chromosomes between telophase I and prophase II

Prophase II: When chromosomes show up you will see sister chromatids. Metaphase II: Chromosome made of Sister chromatids line up on equator Anaphase II: Sister chromatids are pulled apart. Telophase II: Nuclear membranes form.

Cytokinesis: cytoplasm divides Total product is 4 haploid (n) gametes

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

Uneven cytokinesis in females: In oogenesis (female meiosis), get one big egg and 3 non-functional polar bodies (non-functional cells that die)

OOGENESIS First division: results in one big primary oocyte and a little polar body. Second division: One secondary oocyte and 3 polar bodies. (polar bodies die) 2n Oogonium (what you’re born with) At puberty, oogonia mature into primary oocytes 4n Secondary oocyte Polar Body 3 Polar Bodies ovum n n n n

Equal divisions producing four useable sperm Spermatogenesis Equal divisions producing four useable sperm

Spermatagonium  primary spermatocyte  2 secondary spermatocytes  4 spermatids Spermatids mature into spermatazoa. Once spermatazoa are released, we call them sperm

Meiosis vs. Mitosis (Make a chart) Used for Sexual Reproduction Produces Gametes (Egg & Sperm) Have 23 chromosomes 2 sets of divisions Begins with a diploid cell Homologous chromosomes pair up Result: 4 genetically different HAPLOID SEX cells Used for Growth and Asexual Reproduction Produces body cells Have 46 chromosomes Somatic cells One round of division Begins with diploid cells No crossing over Homologous chromosomes don’t pair up Results in 2 genetically identical DIPLOID SOMATIC cells

Plants…the oddballs Plants have a 2-part life cycle; each cycle uses a different body structure Diploid phase: sporophyte (makes spores) Haploid phase: gametophyte (makes gametes) *Developed to protect the embryo as it grows

Flowering Plants

Sporophyte generation begins with zygote

Karyotype = picture of all chromosomes in 1 cell Used to determine: If there is an abnormality in number or structure of the chromosomes (e.g. Down’s syndrome) 2. Gender

Karyotypes can be obtained in several ways In a developing fetus: CVS (chorionic villus sampling) and amniocentesis In children and adults: Karyotypes can be obtained from any growing cells. (Can a karyotype tell if there are any GENE mutations?)

Figure 12Ba

Figure 12Bb

Non-disjunction Non-separation of chromosomes resulting in diploid or empty gametes When it happens in Meiosis I: All 4 gametes affected When it happens in Meiosis II: ½ of gametes affected

DOWN SYNDROME (trisomy 21) Figure 12.11

Turner Syndrome (Monosomy X) Infertility Webbed neck Short stature Figure 12.12a Turner Syndrome (Monosomy X) Infertility Webbed neck Short stature May fail to start puberty

Klinefelter Syndrome (XXY): Figure 12.12b Klinefelter Syndrome (XXY): Presents as male Infertility Feminine Characteristics: Enlarged breast tissue Wide-set hips Cognitive deficits Treated with testosterone

Trisomy 18 - Edward's Syndrome Failure to grow and gain weight at the expected rate and severe feeding difficulties, diminished muscle tone and episodes in which there is temporary cessation of spontaneous breathing Developmental delays and intellectual disability A prominent back portion of the head, low-set, malformed ears, an abnormally small jaw, a small mouth an upturned nose, narrow eyelid folds, widely spaced eyes, and drooping of the upper eyelids

TRISOMY 13 (also known as Patau syndrome) - Of all babies born with the extra copy of chromosome 13 in all the cells of their body, around 50% die in the first month, and the rest within the first year Median survival age for children with Patau syndrome is 2.5 days

CHROMOSOME MUTATIONS

Figure 12.13

Figure 12.13a

DELETION MUTATION (WILLIAMS SYNDROME-chromosome 7) Characteristic face shape, cardiovascular problems, affinity for music

CRI DU CHAT Deletion of Chromosome #5 Cries are high-pitched; sound like cats Eyes have downward slant Partial webbing of digits Small Jaw

Figure 12.13b

FRAGILE X - duplication mutation

Figure 12.13c

Figure 12.13d

Greig Cephalopolysyndactyly syndrome Figure 12.16 Enlarged forhead and webbed digits Greig Cephalopolysyndactyly syndrome

Figure 12.16b