Sexual Reproduction & Mendelian Genetics. Chapter 10 Pages 270-285. First, Some Vocabulary……. somatic cells – body cells, 46 chromosomes in humans gametes – sex cells, have half the number of chromosomes as compared to somatic cells, so 23 chromosomes in human gametes
somatic cells – body cells, 46 chromosomes in humans
gametes – sex cells, have half the number of chromosomes as compared to somatic cells, so 23 chromosomes in human gametes
diploid = 2n number of chromosomes
haploid = n number of chromosomes
Fertilization – the process by which one haploid gamete combines with another haploid gamete.
oogenesis – the creation of an egg
spermatogenesis – the creation of sperm
Homologues separate and get pulled to opposite poles by spindle fibers.
DNA replicates. Chromatin condenses.
Synapsis – pairing ofhomologous chromosomes to form a tetrad (4 chromatids).
- Crossing over occurs
Homologous chromosomes line up along the equator of the cell.Meiosis I
TelophaseI (not shown) – the cell divides into two haploid cells (see pg 273 of text).
Notice the grey and white chromosomes have exchanged segments. This change occurs during synapsis and is called crossing over. Crossing over is a process during which chromosomal segments are exchanged between a pair of homologous chromosomes.
Meiosis I results in two haploid (n) daughter cells, each with half the number of chromosomes as the parent cell.
The chromosomes line up on the metaphase plate (or equatorial plate).
Sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (n) daughter cells.Meiosis II
Homologous pairs form tetrads by synapsis.
Crossing over occurs.
Nuclear envelope breaks down, spindles form.
Tetrads line up on the equator.
New nuclei form and contain the n amount of DNA.
Meiosis II is just like mitosis.
Nuclear envelope breaks down
Chromosomes line up on equator
Sister chromatids separate
New nuclei form with normal chromosomesComparing Meiosis to Mitosis
1. Why is it important for chromatin to condense?
A. Normal Meiosis
B. Failure of homologous chromosome pair to separate during Meiosis I
C. Failure of sister chromatids to separate during Meiosis II