BIO 201 Lecture Notes - Lecture 30: Chromosome Segregation, Sexual Reproduction, Synapsis
6 Sep 2018
School
Department
Course
Professor
Bio 201
Lara Hutson
Lecture 30: Meiosis
Overview
- Sexual vs. asexual reproduction
- Chromosome segregation during meiosis
- Diversity through recombination
- Nondisjunction
Asexual vs. sexual reproduction
- Asexual (fission and mitosis): duplication of one genome followed by cell division or budding →
2nd generation cells are genetically identical* to parents and each other.
- Sexual: combine genetic material from two parents → next generation is genetically distinct
from parents and from each other.
- * assuming DNA replication is perfect
• Advantage of sexual reproduction = diversity
Problem: how to maintain appropriate chromosome numbers from one generation to the next
Solution: Halve genomes before combining.
Meiosis
Life cycle of a sexual-reproducing diploid
Meiosis I
1A. Metaphase I: chromosomes align on Metaphase I plate. Homologs adjacent to each other
(synapsis).
1B. Homologs exchange DNA (chiasma).
2. Anaphase I: Homologous chromosomes segregate (sister chromatids remain together!)
3. Cytokinesis I
Meiosis II
Document Summary
Asexual (fission and mitosis): duplication of one genome followed by cell division or budding . 2nd generation cells are genetically identical* to parents and each other. Sexual: combine genetic material from two parents next generation is genetically distinct from parents and from each other. * assuming dna replication is perfect: advantage of sexual reproduction = diversity. Problem: how to maintain appropriate chromosome numbers from one generation to the next. Metaphase i: chromosomes align on metaphase i plate. Homologs exchange dna (chiasma): anaphase i: homologous chromosomes segregate (sister chromatids remain together!, cytokinesis i. Meiosis ii: metaphase ii: chromosomes align on metaphase plate, anaphase ii: sister chromatids separate, cytokinesis ii. X = number of copies of each homolog. Fertilization 223 x 223+ or 70,368,744,177,644 possible genetically distinct offspring! Homologs can recombine at one or more locations: homologs must align to exchange dna. If homologs fail to recombine, meiosis is arrested.
