Lesson 2 - Meiosis Flashcards
(18 cards)
What is Meiosis?
Meiosis is a process of sexual reproduction.
Involves two divisions (meiosis I and meiosis II).
In humans, it occurs only in the gonads (testes or ovaries).
Male: spermatogenesis (sperm cell production)
Female: oogenesis (egg cell production)
Products: haploid gametes (sperm or egg with half of the # of chromosomes), each with different genetic information
Diploid (2n) → haploid (n)
Meisis (In Humans) (Graph)
Spermatogenesis (Testes) Diagram
Oogenesis (Ovaries) Diagram
Order and Stages of Meiosis
Interphase 1
Step 1: G1 Phase
- Growth Stage/Preparation for Miosis
Step 2: S Phase
- Chromosome Duplication/Preparation for Miosis
-Two identical sister chromatids are attached by the centromere
Step 3: G2 Phase
-Growth Stage/Preparation for Miosis
Prophase 1
What Happens:
- Chromosomes will condense
- The nuclear membrane will dissolve
- Centrioles will separate
- Spindle fibres form
What are Homologous Chromosomes
Pairs of chromosomes that are similar in
shape and size
Genes that control the same inherited traits:
- One maternal
- One paternal
Humans have 23 pairs of homologous chromosomes, 22 autosomes 01 sex chromosome (See Diagram)
Synapsis (Prophase 1)
When homologous chromosomes come together to form a tetrad
Tetrads are two chromosomes/ four chromatids
(See Diagram)
What is Crossing Over (Prophase 1):
Segments of non-sister chromatids break and
reattach to the other chromatids
Location: Chiasmata
Creates variation
(See Diagram)
Metaphase 1
The tetrads migrate towards the centre of the cell
The tetrads will align their centromeres across the middle of the cell (Metaphase plate)
Independent Assortment (Metaphase 1)
How the orientation of the homologous pair aligns on the metaphase plate random
Creates variation!
Use equation 2” to find the number of combinations.
Anaphase 1
Homologous chromosomes move to opposite poles of the cell
Sister chromatids remain attached at their centromeres
Telophase 1
The nuclear membrane forms around the chromosomes
Cytokinesis: The cell will divide to form two cells
The daughter cells are haploid
Prophase 2
Centrioles move to opposite ends of the cell
Nuclear membrane breaks down
Spindle fibres extend from centrioles to centromeres
Metaphase 2:
Spindle fibres align the chromosomes along the middle of the cell at the metaphase plate
Anaphase 2:
Centromeres divide
Sister chromatids move to opposite poles of the cell, now becoming daughter chromosomes.
Telophase 2 and Cytokinesis
Chromatids are now at opposite poles of the cell
Nucleus membrane and nucleolus forms for each daughter cell
Chromosomes disperse and spindle fibres disappear
