BIOLOGY 11 - Meiosis and Chromosomal Errors

2ND SEM FINAL TERM

Meiosis

Type of cellular division that occur to produce sex cells in the reproductive organs (ovaries and testes).

Reduction division

The process where in it divides the number of chromosomes into halves in the formation of gametes

Prophase 1

- Chromosomes condense and become visible.

- Homologous chromosomes pair up (synapsis).

- Tetrads form (4 chromatids). - Crossing over happens (DNA is exchanged), site Chiasma.

- Nuclear membrane breaks down.

- Spindle fibers begin to form.

Metaphase 1

- Homologous chromosome pairs line up at the center (equator).

- Each pair is called a tetrad. - Spindle fibers attach to each chromosome.

- Orientation is random (independent assortment).

Anaphase 1

- Homologous chromosomes separate.

- Each chromosome moves to opposite poles.

- Sister chromatids stay together.

Telophase 1

- Chromosomes reach opposite poles.

- Nuclear membranes may reform.

- Cell divides (cytokinesis). - Two haploid cells are formed.

Prophase 2

- Chromosomes condense again.

- Nuclear membrane breaks down.

- Spindle fibers form.

Metaphase 2

- Chromosomes line up at the cell center.

- Spindle fibers attach to sister chromatids.

Anaphase 2

- Centromere divides and sister chromatids are pulled to the opposite poles.

- Chromatids move to opposite poles.

Telophase 2

- Chromatids reach poles.
- Nuclear membranes reform.
- Cells divide (cytokinesis).
- Four haploid cells are formed.

Gametogenesis

The process involving the production of gametes.

Spermatogenesis

the process by which sperm cells are produced.

Oogenesis

the process of gamete formation in females.

Independent Assortment

It is the random distribution of homologous chromosomes during meiosis.

Random Fertilization

is the chance fusion of any sperm with any egg during fertilization

Trisomy

a nondisjunction where the cells have 3 copies of a chromosome

Monosomy

a nondisjunction where the cells have only 1 copy of a chromosome

Nondisjunction

chromosomes don’t separate properly during meiosis as problems with the meiotic spindle causes errors in the daughter cells

1. Deletion

2. Duplication

3. Inversion

4. Translocation

4 types of breakage of chromosomes

Down syndrome

it is a syndrome caused by Trisomy 21 or also known as 3 copies of chromosome 21

Chromosome 21

it is the smallest human chromosome

Klinefelter’s syndrome

XXY where in they have male sex organs but are sterile, feminine characteristics, tall, and have normal intelligence

Trisomy X

XXX produces healthy females which makes Barr bodies

Jacob’s syndrome

XYY where there is an extra Y chromosome making them slightly taller than average, more active, normal intelligence, slight learning disabilities, delayed emotional maturity, and normal asexual development

Turner syndrome

(XO) it is monosomy X and has a varied degree of effects such as webbed neck, short stature, and sterile

Barr bodies

it is when all but one X chromosome is inactivated

Deletion

It is a change in chromosome structure where in there is the loss of a chromosomal segment

Duplication

It is a change in chromosome structure where in there is a segment being repeated

Inversion

It is a change in chromosome structure where it reverses a segment

Translocation

It is a change in chromosome structure where in a segment moves from one chromosome to another