Meiosis

Question 1

Meiosis

Answer 1

→ Division Process that prevents doubling of genetic material
→ Creates 4 genetically diverse cells
→ Creates sex cells (sperm and egg) with half the number of chromosomes (haploid cells)
→ Fertilization is the fusion of two sex cells (male + female) to get back to the diploid number

Question 2

Diploid

Answer 2

→ “Di” for two meaning that the cells has pairs of homologous chromosomes (Chromosomes that share the same structural features)
→ 2n is used to represent the ploidy of diploid cells
→ All somatic cells are diploid

Question 3

Haploid

Answer 3

→ Cells that only have one set of chromosomes
→ Haploids are symbolized by n
→ All gametes will be haploids and are derived from diploid cells.

Question 4

Ploidy

Answer 4

The number of sets of chromosomes in a cell.

Question 5

Interphase

Answer 5

Same as Mitosis, Grows during G1, Replicates Chromosomes during S and grows more in preparation for cell division in G2
↪ Diploid

Question 6

Prophase Ⅰ

Answer 6

Early on…
→ Chromatin starts to condense into chromatids
→ Nuclear membrane starts to dissolve/disappear by phosphorylation (Adding a phosphate group to the phospholipid which activates enzymes to break it down)

Later…
→ Sister chromatids formed in the early prophase are joined together by centromeres to create chromosomes with two chromatids.
→ Centrosomes (2 Centrioles) start to go to the poles and create spindle fibers that start to attach to the centromeres of the chromosomes.
↑→ The spindle fibers attach to the centromeres and start to guide the chromosomes to the equator of the cell (Actual movement is helped by motor proteins)

Then (Special to Meiosis)…
→ Chromosomes start to pair up with homologue partner (This means that they pair based on structure [Length, Centromere location and banding pattern when stained]) [These chromosome pairs are called tetrads]
↑→ They do this so that they can do recombination
↪ Diploid
→ Synapsis occurs (Tetrads Forming)

Question 7

Recombination (Prophase Ⅰ)

Answer 7

→ After the chromosomes are aligned, they tangle up with each other in a process called crossover. This is helped by a protein structure called the synaptonemal complex that holds the homologues together. Chromosomes are positioned on top of each other.
↑→ Sites where the genes are tangled or in crossover are called Chiasma
↑→→ Sometimes this crossing over happens when DNA is still chromatin and the sites where the sets of DNA crossover in chromatin are called chiasmata. These cross shaped structures of DNA keep the chromosomes connects after the synaptonemal complex breaks down.
↑→ Then while they are tangled up, they exchange Genes in the Process called Recombination (Now even the sister chromatids are different)
→ Your sex chromosomes do not go through crossover or recombination as they have totally different sizes (males is way smaller)

Question 8

Metaphase Ⅰ

Answer 8

→ Once the chromosomes pairs (not the single chromosome, the tetrads) are aligned at the equator plate(imaginary equator line of the cell) via the spindle fibers we enter the metaphase.
→ The orientation of these tetrads (So if I had chromosomes a and b, either b can go to the right cell or a can) are completely random and also help determine genetic diversity. This is called Independent Assortment.
↪ Diploid

Question 9

Anaphase Ⅰ

Answer 9

→ Chromosomes separate from tetrads with help of the spindle fibers which are shortening
→ Once detached, they are pulled to either end of the cell as the spindle fibers shorten.
→ Cleavage starts to occur in this phase
↪ Diploid

Question 10

Telophase Ⅰ

Answer 10

→ Begins once the separated chromosomes reach the opposite ends of the cell.
→ Different actin(contracting proteins) and myosin(contracting proteins) start to squeeze the middle of the cell producing a constriction ring (Called a cleavage furrow).
→ In some organisms the nucleus re-forms with the chromatin, nuclear membrane and nucleolus. However, in other organisms this is skipped as the cells will divide once more
→ Both sides have an equal amount of ribosomes, mitochondria and cytoplasm
→ Most cells go through cytokinesis at this phase
↪ Diploid

Question 11

Results of Meiosis Ⅰ

Answer 11

Two haploid Daughter cells with half of the chromosomes of the parent cells. Ploidy of n.

Question 12

Meiosis ⅠⅠ

Answer 12

Exactly the same as mitosis but, there is not replication of chromosomes in the interphase as the goal is to end up with 4 seperate daughter haploid cells.
CELL IS HAPLOID IN ALL STAGES

Prophase ⅠⅠ
→ Nuclear envelope begins to break and spindle fibers from around the centrosomes and attach to the chromosomes

Metaphase ⅠⅠ
→ Aligned at the center

Anaphase ⅠⅠ
→ Spindle fibers contract and pull the chromosomes apart with the help of motor proteins

Telophase ⅠⅠ
→ Nuclear envelope, nucleolus and chromatin are formed
→ Spindle fibers disappear
→ Cytokinesis divides the two cells into four

Question 13

Results of Meiosis (The whole process)

Answer 13

→ 4 Haploid gamete cells with 1 allele of each gene

Question 14

Allele

Answer 14

Alleles are just variants of a gene

Question 15

Asexual Reproduction

Answer 15

Reproduction that only requires one parents and produces genetically identical offspring (Mistosis)

Question 16

Sexual Reproduction

Answer 16

Reproduction that requires two parents and produces genetically distinct offspring

Question 17

Gamete

Answer 17

A male or female reproductive cell. This is also called a germ cell.

Question 18

Zygote

Answer 18

A cell formed by the fusion of two gametes

Question 19

Fertilization

Answer 19

In humans the joining of male and female haploid gametes

Question 20

Spermatogenesis

Answer 20

In males meiosis takes place in the testes.
→ Following meiosis two male cells have developmental stages to mature
↑→ The nucleus and certain other molecules required by the cell are organized into a head region
↑→ The midsection has a lot of mitochondria
↑→ A flagellum is developed for locomotion (Ability for organism to propel itself)

Question 21

Oogenesis

Answer 21

In females Meiosis takes place in the Ovaries

Question 22

Synapsis

Answer 22

When homologous chromosomes join together to form a tetrad.