Meiosis Chromosomes Xsomes chromosomes come in Chromosomes Xsomes

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Meiosis

Meiosis

Chromosomes (X’somes) • chromosomes come in ____

Chromosomes (X’somes) • chromosomes come in ____

Chromosomes (X’somes) • chromosomes come in pairs • and humans have __ pairs

Chromosomes (X’somes) • chromosomes come in pairs • and humans have __ pairs

Chromosomes (X’somes) • chromosomes come in pairs • • and humans have 23 pairs

Chromosomes (X’somes) • chromosomes come in pairs • • and humans have 23 pairs this means humans have ___ total chromosomes

Chromosomes (X’somes) • chromosomes come in pairs • • and humans have 23 pairs

Chromosomes (X’somes) • chromosomes come in pairs • • and humans have 23 pairs this means humans have 46 total chromosomes

Karyotype Ø all of an organism’s chromosomes, photographed, cut out, and arranged by homologous

Karyotype Ø all of an organism’s chromosomes, photographed, cut out, and arranged by homologous pairs

1 2 3 6 7 8 13 14 15 19 20 21 4 9

1 2 3 6 7 8 13 14 15 19 20 21 4 9 22 5 10 11 16 17 12 18 XX (or XY) Human Karyotype

Autosome Ø chromosomes that do not genetically determine gender

Autosome Ø chromosomes that do not genetically determine gender

1 2 3 6 7 8 13 14 15 19 20 21 4 9

1 2 3 6 7 8 13 14 15 19 20 21 4 9 22 5 10 11 16 17 12 18 XX (or XY) Human Karyotype

Sex Chromosome Ø chromosomes that genetically determine gender l X and Y

Sex Chromosome Ø chromosomes that genetically determine gender l X and Y

1 2 3 6 7 8 13 14 15 19 20 21 4 9

1 2 3 6 7 8 13 14 15 19 20 21 4 9 22 5 10 11 16 17 12 18 XX (or XY) Human Karyotype

Alleles Ø different versions of the same type of gene l Ex: blue eye

Alleles Ø different versions of the same type of gene l Ex: blue eye color vs. brown eye color

Homologous Chromosomes Ø pairs of chromosomes that have the same structure and pair during

Homologous Chromosomes Ø pairs of chromosomes that have the same structure and pair during meiosis

Homologous Chromosomes Ø can carry different alleles l cells have two of each chromosome

Homologous Chromosomes Ø can carry different alleles l cells have two of each chromosome • one chromosome in each pair from the mother (maternal), the other from the father (paternal) • paternal and maternal chromosomes carry different alleles

Meiosis • the process by which gametes (sex cells) are produced from a parent

Meiosis • the process by which gametes (sex cells) are produced from a parent cell

Many plants produce gametes (sex cells) also! Prentice-Hall Biology Fig. 10 -3 p. 156

Many plants produce gametes (sex cells) also! Prentice-Hall Biology Fig. 10 -3 p. 156

Meiosis & Chromosome Number • meiosis halves chromosome number

Meiosis & Chromosome Number • meiosis halves chromosome number

Meiosis & Chromosome Number Ø body (somatic) cells are diploid (2 n) have two

Meiosis & Chromosome Number Ø body (somatic) cells are diploid (2 n) have two sets of chromosomes (one maternal and one paternal) l n = number of chromosomes in one set = number of chromosomes received from each parent l • in humans, n = 23

Meiosis & Chromosome Number Ø reproductive cells (gametes) are haploid (n) have only one

Meiosis & Chromosome Number Ø reproductive cells (gametes) are haploid (n) have only one set of chromosomes (half the diploid number) l gametes = sperm & egg l

Meiosis & Chromosome Number • two consecutive nuclear divisions resulting in four haploid cells

Meiosis & Chromosome Number • two consecutive nuclear divisions resulting in four haploid cells • Meiosis I and Meiosis II

Discuss the four questions on the left side of your Cornell notes with your

Discuss the four questions on the left side of your Cornell notes with your table partner.

1. ) Compare & contrast diploid cells (2 n) vs. haploid cells (n). 2.

1. ) Compare & contrast diploid cells (2 n) vs. haploid cells (n). 2. ) How many divisions occur in meiosis? 3. ) How many cells are made? 4. ) Are the cells made in meiosis haploid or diploid?

Meiosis I Holt Biology p. 144

Meiosis I Holt Biology p. 144

Meiosis I chromosome number is halved • homologous pairs are separated • Each homologue

Meiosis I chromosome number is halved • homologous pairs are separated • Each homologue in the cell pairs with its partner, then the partners separate Prentice Hall Biology, p. 158

Meiosis I and Crossing Over Holt Biology p. 144

Meiosis I and Crossing Over Holt Biology p. 144

Crossing Over Ø each chromosome becomes attached to its homologue (partner) Ø all four

Crossing Over Ø each chromosome becomes attached to its homologue (partner) Ø all four chromatids are closely aligned Ø nonsister chromatids exchange segments

Effect of Crossing Over • after crossing over, each chromosome contains both maternal and

Effect of Crossing Over • after crossing over, each chromosome contains both maternal and paternal segments • this creates new allele combinations in offspring

Independent Assortment • random distribution of homologous chromosomes

Independent Assortment • random distribution of homologous chromosomes

Meiosis 1 and Independent Assortment

Meiosis 1 and Independent Assortment

Effect of Independent Assortment • increases the number of possible different genetic combinations in

Effect of Independent Assortment • increases the number of possible different genetic combinations in gametes

Meiosis II • the two sister chromatids of each duplicated chromosome are separated from

Meiosis II • the two sister chromatids of each duplicated chromosome are separated from each other two chromosomes (unduplicated) one chromosome (duplicated) p. 158

Meiosis II Holt Biology p. 145

Meiosis II Holt Biology p. 145

Meiosis Animation

Meiosis Animation

Mitosis Graphic Organizer 2 n

Mitosis Graphic Organizer 2 n

Mitosis Graphic Organizer 2 n 2 n 2 n

Mitosis Graphic Organizer 2 n 2 n 2 n

Meiosis Graphic Organizer 2 n

Meiosis Graphic Organizer 2 n

Meiosis Graphic Organizer 2 n n n

Meiosis Graphic Organizer 2 n n n

Meiosis Graphic Organizer 2 n n n

Meiosis Graphic Organizer 2 n n n

Meiosis Graphic Organizer 2 n n n n

Meiosis Graphic Organizer 2 n n n n

Random Fertilization • remember, meiosis produces gametes, a. k. a. sex cells • sex

Random Fertilization • remember, meiosis produces gametes, a. k. a. sex cells • sex cells combine randomly during fertilization to produce a new organism • because fertilization of an egg by a sperm is random, this also increases the number of possible genetic combinations

Evolutionary Change • crossing over, independent assortment, and random fertilization all increase the number

Evolutionary Change • crossing over, independent assortment, and random fertilization all increase the number of possible genetic variations • more genetic combinations = more possibilities for organisms to evolve

Errors in Meiosis Ø sometimes a gamete can be produced with an incorrect number

Errors in Meiosis Ø sometimes a gamete can be produced with an incorrect number of chromosomes because of non-disjunction l non-disjunction – failure of chromosomes to separate during anaphase I or II of meiosis

Meiosis and Non-disjunction Normal meiosis(A) Ø Failure of homologous chromosomes to separate in anaphase

Meiosis and Non-disjunction Normal meiosis(A) Ø Failure of homologous chromosomes to separate in anaphase I of meiosis I (B) Ø Failure of sister chromatids to separate in anaphase II of meiosis II (C) Ø A B C

Meiosis and Nondisjunction

Meiosis and Nondisjunction

Meiosis and Nondisjunction

Meiosis and Nondisjunction

Errors in Meiosis Ø sometimes a gamete can be produced with an incorrect number

Errors in Meiosis Ø sometimes a gamete can be produced with an incorrect number of chromosomes because of non-disjunction l non-disjunction – failure of chromosomes to separate during anaphase I or II of meiosis • creates gametes with an extra or missing chromosome

Other Resources • Textbook pages 144 - 149

Other Resources • Textbook pages 144 - 149