Meiosis Flashcards
Where do homologous chromosomes come from?
one from mother, one from father
Homologs have the same ______ but potentially different _______.
genes, alleles
Trisomy 21
aka Down Syndrome, extra chromosome 21
Mitosis vs meiosis
Mitosis: 2 diploid cells with identical chromosomes (46 each)
Meiosis: 4 haploid cells with a mix of paternal and maternal DNA (23 chromosomes each)
Cell Division Cycle (Mitosis)
Interphase and Cell Division
Interphase
G1: rapid growth and metabolic activity; centriole replication (8-10 hrs)
S: chromosome replication (DNA synthesis, 6-8 hrs)
G2: growth and final prep for cell division (4-6 hrs)
Cell Division
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
< 1 hr
Human life cycle
- Meiosis
- haploid gametes (ovum and sperm cell, 23 chromosomes each)
- Fertilization
- Diploid zygote (2n = 46)
- Mitosis and development
- Growth/adulthood
Meiosis I: Prophase I
Chromatin condenses to chromosomes, crossing-over occurs, centrosomes move, nuclear envelope dissipates
Meiosis I: Metaphase I
chromosomes line up on equatorial plate, spindle fibers attach to centromeres
Meiosis I: Anaphase I
centromeres contract and pull apart homologous chromosomes away from each other and toward opposite poles
Meiosis I: Telophase I
Homologous chromosomes decondense and nuclear envelope reappears
Cytokinesis I
Cell splits into two haploid daughter cells (1n, 23 chromosomes)
Meiosis II: Prophase II
chromosomes condense, new set of spindle fibers form
Meiosis II: Metaphase II
centromeres of paired chromatids align along equatorial plate
Meiosis II: Anaphase II
spindle fibers contract and pull apart the chromosomes at the centromeres, moving them toward opposite poles
Meiosis II: Telophase II
nuclear envelope reappears, chromosomes decondense into chromatin, cells begin to separate
Cytokinesis II
The 2 daughter cells split into 4 haploid cells (1n)
Why is Prophase I particularly important?
Crossing-over and recombination happen in this step
Cross-over
2 NON-sister chromatids of the homologous chromosomes cross over each other and share DNA, resulting in recombinant chromatids
What is a chiasma?
where the non-sister chromatids cross during cross-over/recombination
What are cohesins?
protein complexes that hold sister chromatids together
What are synaptonemal complex (SC) proteins?
proteins that hold homologous chromosomes together in Synaptonemal Complex
What is Mendel’s Law of Segregation?
separation of alleles that are reunited by fertilization
What is Mendel’s Law of Independent Assortment?
genes on non-homologous chromosomes assort independently
What are the three sources of genetic diversity?
mutation, recombination, and independent assortment
