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6.1, 6.2, 6.6 Meiosis.

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Presentation on theme: "6.1, 6.2, 6.6 Meiosis."— Presentation transcript:

1 6.1, 6.2, 6.6 Meiosis

2 MEIOSIS Type of cell division that produces four cells
Each new cell has half the number of chromosomes as the parent cell Meiosis reduces chromosome number and creates genetic diversity. Meiosis makes haploid cells from diploid cells Meiosis produces gametes  sperm and egg cells In animals, meiosis occurs in the sex organs—ovaries and testes

3 MEIOSIS

4 6.1 Chromosomes and Meiosis
KEY CONCEPT: Gametes have half the number of chromosomes that body cells have.

5 each species has a characteristic number of chromosomes per cell
Common Name Diploid numbers (2n) Human 46 Donkey 42 Dog 78 Cat 38 Mouse 40 Frog 26 Fruit fly 8 Corn 20 Potato 48 Yeast 32 Mold 4 This number is given for body cells, not for gametes The number of chromosomes is not related to the complexity of an organism Your body cells each contain 46 chromosomes in 23 pairs these cells are genetically identical to one another

6 You have body cells and gametes.
The cells in your body are divided into two major groups: 1) Body cells (somatic cells): - make up most of your body tissues - DNA in body cells is not passed on to offspring 2) Sex cells called gametes (egg and sperm) - Sex cells are located in the ovaries and testes. - Gametes have DNA that can be passed to offspring. body cells sex cells (sperm) sex cells (egg)

7 autosomes and sex chromosomes
Your cells have autosomes and sex chromosomes. Your body cells have 23 pairs of homologous chromosomes. Autosomes: Chromosome pairs 1-22 not related to gender Sex chromosomes: X and Y, determine gender Females: XX Males: XY homologous chromosomes sister chromatids sister chromatids

8 HOMOLOGOUS CHROMOSOMES
Paired chromosomes: one inherited from the mother and the other from the father Not the same as sister chromatids Not identical to one another Each has same genes controlling the same trait in same order homologous chromosomes From Dad From Mom Sister Chromatids Sister Chromatids

9 HOMOLOGOUS CHROMOSOMES
SAME SIZE SAME SHAPE CARRY GENES for the SAME TRAITS BUT ____________________________! (Don’t have to have the SAME CHOICES) NOT IDENTICAL

10 Diploid and haploid cells
Diploid:(2n) contain two homologous sets of chromosomes  in humans - 46 total Body (somatic) cells are diploid. Ex: Skin, Muscle, Nerve, Blood Cells Created by mitosis Haploid: (n) have a single set of chromosomes  in humans - 23 total Gametes - sperm and egg – are haploid Created by meiosis

11 Fertilization: fusing of the nucleus of a haploid sperm with the nucleus of a haploid egg
Zygote: produced as a result of fertilization  fertilized egg is diploid

12 Chromosomes (diploid)
46 Chromosomes (diploid) 23 chromosomes 23 chromosomes 23 chromosomes

13 Zygote divides by mitosis
Typical human has about 100 trillion cells 9-10 months of cells dividing later….

14 6.2 Process of Meiosis KEY CONCEPT : During meiosis, diploid cells undergo two cell divisions that result in haploid cells.

15 Process of MEIOSIS Two distinct parts:
Meiosis I: homologous chromosomes separate from each other (sister chromatids remain together) Meiosis II: sister chromatids separate from each other

16 MITOSIS vs. MEIOSIS Key differences occur in meiosis I: Prophase I:
- tetrad formation, crossing over Metaphase I: - tetrads line up at midline Anaphase I: - homologous chromosomes separate and move to opposite poles

17 MEIOSIS I: Prophase I Has 2 steps not seen in prophase of mitosis
Mom 1 MEIOSIS I: Prophase I Dad 1 Has 2 steps not seen in prophase of mitosis 1) Tetrad Formation: Pairing of homologous chromosomes Dad’s #1 chromosome pairs with Mom’s #1, etc… The four paired chromatids equals a TETRAD 2) Crossing Over: Exchange of genes

18 Meiosis I

19 MEIOSIS I PRODUCTS Two cells
Chromosomes have crossed over – unique cells Non-identical cells Haploid cells - only one chromosome from each homologous pair Each chromosome is still doubled (consists of two sister chromatids) Another cell division is needed

20 Meiosis I

21 MEIOSIS II Events are identical to those of mitosis with one exception: Chromosomes DO NOT duplicate prior to meiosis II

22 MEIOSIS II PRODUCTS Four cells Non-identical cells Haploid cells

23 Meiosis II

24 Meiosis Review

25 http://highered. mcgraw- hill. com/olcweb/cgi/pluginpop. cgi
hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/ /120074/ bio19.swf::Stages of Meiosis

26 Meiosis: crossing over and variability

27 Meiosis: the Great Divide
WorksheetL

28 6.6 Meiosis and Genetic Variation
KEY CONCEPT: Independent assortment and crossing over during meiosis result in genetic diversity.

29 MEIOSIS & GENETIC VARIATION
Meiosis results in increased genetic variation for three reasons: Independent & random assortment of chromosomes Crossing over in Prophase I Random fertilization of gametes

30 1. Independent & random assortment of chromosomes
Chromosomes in tetrads line up and separate randomly in meiosis FYI: Allows for a large amount of variation to occur at fertilization; million variations for humans (223)

31 Random orientation of chromosomes
Orientation of Chromosomes During Meiosis

32 2. Crossing over in Prophase I
Exchange of genetic material between non-sister chromatids during prophase I Results in genetic recombination Provides a second source of genetic variation

33 3. Random fertilization of gametes
Refers to the fact that any egg can be fertilized by any sperm. FYI: This means that for a particular man and woman, the number of unique combinations of genes that could occur in their offspring is 8.4 million times 8.4 million ( 70 trillion), not counting variation caused by crossing over and mutation. FYI: STATISTICALLY, THERE HAVE NEVER BEEN 2 HUMANS CREATED THAT WERE GENETICALLY IDENTICAL!!!!

34 Genetic Variation The genetic variation that results from mutations, meiosis, and fertilization cause the phenomenon with which we are all familiar: even in very large populations, such as the human population, every individual is genetically unique.

35 EPIGENETICS

36

37 KARYOTYPES Karyotype: a display of 46 chromosomes of an individual
Human body cells  chromosomes—23 pairs of homologous chromosomes Each chromosome has a twin that resembles it in size and shape (except sex chromosomes in males)

38 HUMAN KARYOTYPES


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