Meiosis and Mitosis
Bio 250: Genetics
Dr. Ramos
The nucleus
(Information and administrative center of the cell)
Nucleus – houses the genetic material
• During non-divisional
phases the genetic
material is uncoiled and
dispersed in the nucleus.
• During division
chromatin condenses
into chromosomes.
Chromosomes
• Distinctive shapes and lengths.
• Constricted region called centromeres.
Karyotype
Physical appearance of different pairs of homologous chromosomes.
Mitosis
• Goal: Create two daughter cells that are
genetically identical to the parent cell.
• Which cells: somatic cells (no gametes)
Interphase
Prophase
Anaphase
Telophase
Metaphase
Cytokinesis
Sexual reproduction
• Advantageous
– Novel combination of genes in each
generation.
– Each individual in a population of sexually
reproducing organisms has a distinct genetic
composition.
Highly diverse offspring!
Meiosis
• Important during production of gametes or
spores with haploid set of chromosomes.
• Sexual reproduction – 2 haploid gametes
combine = diploid
• Consists of a reduction division and an
equational division.
Mitosis vs. Meiosis
Meiosis I
Prophase I
• Tetrad or bivalent formation (pairs
of homologous chromosomes
come together).
• Recombination can occur
between any two chromatids
within this tetrad structure.
• Chiasmata – visible structure
shows crossover. Essential for
accurate meiosis.
Meiosis I
• Metaphase I – tetrad
moves metaphase plate.
• Anaphase I – Random pull
of half of tetrad to the
poles.
• Telophase I – nuclear
membrane around dyads.
Meiosis II
• Essential to insure each gamete receives one
chromatid from the original tetrad.
Spermatogenesis and Oogenesis
• Meiotic events similar but key difference
between males and females.
• Spermatogenesis
Spermatogenesis and Oogenesis
• Oogenesis
Glossary Sheet
• Terms you should know from this lecture:
• Terms you should know for the next lecture:
Product Law
Chi-Square analysis
Sum Law