10-14

10-14 - Meiosis Chapter 10 In sexually reproducing...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Meiosis Chapter 10 In sexually reproducing organisms, the zygote (fertilized egg) is a genetic mixture of the male and female parents. No Sex vs. Sex Asexual Reproduction (Mitosis) Offspring are clones Pro: can make a lot quickly and easily Con: no variability when environment changes Sexual Reproduction (Meiosis) Each offspring is unique Pro: a lot of variability when environment changes Con: neither quick nor easy Asexual vs. Sexual Reproduction Asexual Reproduction Diploid Mitosis Diploid Offspring Offspring=clone Sexual Reproduction Meiosis Mother and Father (haploid parents) Sex Diploid Offspring Gamete Formation Gametes are sex cells (sperm, eggs) Arise from germ cells Animals/humans- Testes and Ovaries Plants- anther and ovary Figure 10.2a, Page 164 Meiosis: Two Divisions Two consecutive nuclear divisions Meiosis I
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Meiosis II DNA is not duplicated between divisions Four haploid nuclei form The purpose of meiosis is to reduce the number of chromosomes by half Meiosis I In-text figure, Page 165 Meiosis II The two sister chromatids of each duplicated chromosome are separate from each other In-text figure, page 165 Meiosis I- Stages Prophase I- Homologues pair, crossing over Metaphase I- Homologues align at equator Anaphase I- Homologous chromosomes move to opposite poles Telophase I Figure 10.4, Page 167 Meiosis II- Stages (separating sister chromatids) Prophase II Metaphase II Anaphase II Telophase II (4 haploid cells with unduplicated chromosomes) Meiosis I vs. Mitosis Meiosis I Metaphase I- paired homologues line up at middle Anaphase I- paired homologues go to opposite poles Mitosis Metaphase- homologues do not pair up at middle Anaphase- sister chromatids split and go to opposite poles Crossing Over Each chromosome becomes zippered to its homologue (Prophase 1) All four chromatids are closely aligned Homologue chromosomes exchange segments Figure 10.5, Page 168 (188?)
Background image of page 2
Effect of Crossing Over After crossing over, each chromosome contains both maternal and paternal segments Creates new allele combines in offspring Possible Chromosome Combinations Metaphase 1- chromosome from mother or father can wind up on either pole Chromosomes in a gamete are a mix of maternal and paternal Figure 10.6, Page. 169 More Chromosomes = More Possible Combinations Previous Example 6 chromosomes 3 pairs of homologous chromosomes 2 x 2 x 2=2^3=8 different alignment combinations possible at metaphase I In humans 46 chromosomes 23 pairs of homologous chromosomes 2^23=8,388,698 different alignment combinations possible at metaphase I This is just for the gametes and doesn’t include recombination If an organism has a chromosomes number of 10, how many different combinations of homologous chromosomes are possible at metaphase I?
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/25/2008 for the course V 011 taught by Professor Staff during the Spring '06 term at NYU.

Page1 / 20

10-14 - Meiosis Chapter 10 In sexually reproducing...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online