Meiosis

meiosis

Basics
Meiosis
Meiosis is a form of cell division in which a “germ” cell (short for “germination” cell) divides and produces two “first-generation daughter” cells, which “cross over” and divide to produce four nonidentical “second-generation daughter” cells with half as many chromosomes as the original germ cell.

Purpose
The purpose of meiosis is sexual reproduction and genetic diversity through the production of gametes (sex cells).

Phases
As per the image above (from nih.gov), meiosis occurs in phases.


Phases

Interphase
All chromosomes are duplicated.

Meiosis 1
Homologous chromosomes containing similar material line up next to each other in the germ cell and cross over by exchanging some of their genes (segments of DNA that code for traits like eye color, nose size, etc.).  The germ cell then divides into two
first-generation daughter cells, which, because of the crossing over of genetic material, are not identical to the germ cell.

Meiosis 2
The two first-generation daughter cells divide into four second-generation daughter cells with half as many chromosomes as the original germ cell.  In humans, such cells have one copy of 23 chromosomes and are called haploid.  These haploid cells are also known as gametes.


Sexual Reproduction

During human sexual reproduction, a haploid gamete (sperm cell) combines with a different haploid gamete (egg cell) to form a new diploid cell with two sets of 23 chromosomes (46 chromosomes altogether).  This new diploid cell is the first cell of what eventually becomes a new human baby.


Practice – Questions

1.  Meiosis is a form of cell division in which a germ cell divides and produces two
first-generation daughter cells, which cross over and divide to produce four nonidentical:
A.  grandparent cells
B.  cousin cells
C.  auntie cells
D.  second-generation daughter cells

2.  Meiosis occurs in:
A.  eons
B.  tides
C.  phases
D.  eras

3.  Chromosomes duplicate during:
A.  Interphase
B.  Meiosis 1
C.  Meiosis 2
D.  Osmosis

4.  Homologous chromosomes line up next to each other and cross over during:
A.  Interphase
B.  Meiosis 1
C.  Meiosis 2
D.  Osmosis

5.  Haploid cells, also known as gametes, form during:
A.  Interphase
B.  Meiosis 1
C.  Meiosis 2
D.  Osmosis


Practice – Answers

1.  D.  second-generation daughter cells

2.  C.  phases

3.  A.  Interphase

4.  B.  Meiosis 1

5.  C.  Meiosis 2

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