Sexual Reproduction Flashcards
1
Q
Meiosis requirements
A
- Sexual reproduction requires two partners to contribute their sex cells (also known as gametes)
- Include sperm cells from males, and egg cells from females
- Once sperm cell fertilizes the egg cell, they fuse to form a new individual cell called a zygote
2
Q
Meiosis:
A
- 2-stage cell division resulting in daughter cells with half the number of chromosomes as the parent cell;
- formation of gametes
- many similarities to mitosis, but
with more detail!
3
Q
Haploid #
A
- For humans, a cell containing 46 chromosomes undergoes meiosis producing gametes that each have 23 chromosomes
- We refer to “n” as the haploid number,
(# of chromosomes in a cell) - This is only one set of chromosomes, so we call it a haploid (n)
- When a species has two sets of chromosomes, like humans, we call it a diploid (2n)
4
Q
Goal of sexual reproduction
A
- The goal for sexual reproduction is that offspring receive genetic material from both parents (each parent contributes a haploid gamete)
- Two haploid gametes from the parents join together, producing a zygote
- contains one complete set of
chromosomes (now known as
diploid)
- contains one complete set of
5
Q
Homologous Chromosomes
A
- Each haploid gamete from each parent has genetic information
- When each of the 23 genes from each parent combine, they become pairs (now you have 23 pairs)
- These are homologous chromosomes
6
Q
Fertilization
A
- Once a haploid sperm cell (n=23 c) fuses
- with a haploid egg cell (n=23 c), they
produce - a diploid zygote (2n=46 c)
7
Q
Meiosis 1 - Prophase 1
A
- Like mitosis, the DNA will replicate itself in interphase
- Chromosomes shorten and thicken
- Duplicated DNA forms new chromosomes (two sister chromatids with a centromere)
- As prophase 1 continues,
chromosomes come together in
homologous pairs, now referred
to as a tetrad - In the tetrad, each SC intertwines themselves around each other (synapsis)
- They break apart and re-attach themselves to form new combinations of genetic info know as crossing over
8
Q
Meiosis 1 - Metaphase 1
A
- The tetrads migrate toward the centre of the cell and align their centromeres across the middle of the cell
9
Q
Meiosis 1 - Anaphase 1
A
- Tetra splits, homologous chromosomes move to opposite poles of the cell
- Only one chromosome from each homologous pair will be found in each new daughter cell
- This is the “reduction” stage of meiosis
10
Q
Meiosis 1 - Telophase 1
A
- Nuclear membrane begins to form around the chromosomes at each end of the cell
- Cytokinesis now occurs
- Now the 2 haploid cells are ready to undergo meiosis 2
11
Q
Meiosis 2
A
- Occurs right after telophase 1 and cytokinesis
- Each haploid cell made in meiosis 1 has one set of chromosomes (23)
- As a result of crossing over, the sister chromatids are no longer identical
12
Q
Meiosis 2 - Prophase 2
A
- Nuclear membrane dissolves and spindle fibres begin to form
13
Q
Meiosis 2 - Metaphase 2
A
The chromosomes arrange themselves at the centre of the cell
14
Q
Meiosis 2 - Anaphase 2
A
- Sister chromatids separate and move to opposite poles of the cell
- Nuclear membrane begins to form around the chromatids, now called chromosomes
15
Q
Meiosis 2 - Telophase 2 and Cytokinesis
A
Second nuclear divisions is completed and the division into four new haploid cells is official
