Omics-C11

Question 1

Meiosis reduces the chromosome number by half, creating ____ (two/four) ____ (identical/non-identical) haploid cells from one diploid cell.
It consists of two rounds of division: Meiosis I (which separates ____ chromosomes) and Meiosis II (which separates ____).

Answer 1

four
non-identical
homologous
sister chromatids

Question 2

Sexual reproduction requires the union of two specialized cells, called ____, each of which contains one set of chromosomes. When they unite, they form a ____, or fertilized egg that contains two sets of chromosomes.

Answer 2

gametes
zygote

gametes: Genetically different haploid cells. (results of Meiosis cell division)

Question 3

Stages of Meiosis I:
Meiosis I is the reduction division where the chromosome number is ____(halved/quartered).

a) Prophase I:
* Chromosomes condense and become visible.
* Synapsis occurs, where homologous chromosomes pair up to form tetrads (each containing four chromatids).
* Crossing over takes place between non-sister chromatids, where homologous chromosomes exchange segments of genetic material, leading to genetic diversity.
* The nuclear envelope breaks down, and spindle fibers form.

b) Metaphase I:
* Homologous chromosomes (still in tetrads) line up along the metaphase plate (the center of the cell).
* The orientation of each pair is random, which contributes to independent assortment and further genetic variation.

c) Anaphase I:
* The spindle fibers pull the homologous chromosomes apart toward opposite poles. The sister chromatids remain attached at the centromere.
* This separates the homologous chromosomes into different daughter cells but keeps the chromatids together.

d) Telophase I and Cytokinesis:
* Chromosomes arrive at opposite poles, and the nuclear envelope may briefly reform around each set of chromosomes.
* Cytokinesis occurs, resulting in two haploid daughter cells (After Meiosis I, the daughter cells are haploid because they have only one chromosome from each homologous pair (even though the chromosomes are still in their duplicated form as chromatids)). Each cell now has half the original chromosome number, but each chromosome still consists of two sister chromatids.

Answer 3

halved

Question 4

Stages of Meiosis II:
Meiosis II is similar to mitosis, but it occurs in both haploid cells produced during Meiosis I.
a) Prophase II:
Chromosomes condense again if they had decondensed after Meiosis I.
The nuclear envelope breaks down again, and spindle fibers begin to form in each of the two haploid cells.
b) Metaphase II:
Chromosomes (each still consisting of two sister chromatids) align at the metaphase plate.
The spindle fibers from opposite poles attach to the centromeres of the sister chromatids.
c) Anaphase II:
The sister chromatids are finally separated as the centromeres split.
The chromatids, now considered individual chromosomes, are pulled toward opposite poles of the cell.
d) Telophase II and Cytokinesis:
Chromosomes arrive at the poles, and the nuclear envelope reforms around each set of chromosomes.
Cytokinesis follows, resulting in four genetically unique haploid cells, each with half the chromosome number of the original diploid cell.

Question 5

Meiosis Schema

Question 6

What are the 3 Key Mechanisms for Genetic Variation?

Answer 6

Crossing Over: The exchange of genetic material between homologous chromosomes during Prophase I creates new combinations of alleles.
Independent Assortment: During Metaphase I, homologous chromosomes are randomly oriented, resulting in different combinations of maternal and paternal chromosomes being distributed to the gametes.
Fertilization: Random fusion of haploid gametes from two parents leads to even more genetic diversity.

Question 7

Sexual reproduction is the process by which two ____ (sperm and egg) fuse to form a ____, which develops into a new organism.

Answer 7

gametes
zygote