Biology Test Review (Intro To Genetics + Mitosis & Meiosis

Why Does A Cell Have To Decide Anyway?

DNA gets overloaded, exchange of materials gets less efficient, ratio of surface area to volume decreases rapidly.

Genes are…

carried on chromosomes.

How much total chromosomes do humans have?

46 chromosomes

How many pairs of chromosomes do humans have?

23 pairs

How many pairs of autosomes does a human have?

22 pairs

How many pairs of sex chromosomes does a human have?

1 pair

True or False: Chromosomes are not visible until cell division.

True

Chromosomes -

made up of two sister chromatids that are attached by a centromere

True or False: There are lots of interphase.

True!

Prophase

Chromosomes become visible, centrioles move to opposite ends of the cell, the spindle formation organizes - will help separate chromosomes

Metaphase

Chromosomes line up along the center of the cell, the centromere of each chromosome is connected to the spindle.

Anaphase

The centromeres separate, Sister chromatids become individual chromosomes, the chromosomes end up near the poles of the cell in two groups.

Telophase

The chromosomes begin to break up back into chromatin form, the nuclear envelope reforms, and the nucleolus becomes visible again.

Cytokinesis

This is the actual division of cytoplasm to form two separate cells. In plants, a special structure called a cell plate is formed.

Regulation of the Cell Cycle

Usually, cells will continue to divide until they come into contact with other cells (contact inhibition). The timing of the cell cycle is regulated by special proteins called cyclins. Internal and External regulators are also present.

Uncontrolled Cell Growth

If cells do not respond to signals that control growth, they can begin to grow out of control. Cancer is a disease where tumors form and spread throughout the body causing much damage.

Meiosis -

This is the formation of sex cells, eggs, and sperm.

Diploid or 2N

A cell that contains both sets of homologous chromosomes

Gametes only contain a single set of chromosomes, therefore being called…

haploid or N

Humans have ___ of the haploid number of chromosomes in sex cells (gametes)

23

Phases of Meiosis

Also known as reduction division, involves two separate stages: Meiosis I and Meiosis II. 2N to N

Prophase I

DNA is replicated prior to meiosis I. In prophase I, each chromosome will pair with it's homologous chromosome to form a structure known as a tetrad.

Tetrad

the structure formed during Prophase I when two homologous chromosomes, each made of two sister chromatids, pair up, creating a group of four chromatids

Crossing Over

Portions of the chromatids can be exchanged during this process

Metaphase I

At this stage, the spindle fibers attach to the chromosomes. Chromosomes will appear to be at the center of the cell, lined up.

Anaphase I

The spindle fibers pull the chromosomes toward opposite ends of the cell.

Telophase I/Cytokinesis

The nuclear membranes reform and the cell separates into two daughter cells.

Meiosis II

The two cells formed in Meiosis I now go through another set of divisions. The DNA is not replicated again. The next set of divisions are just like those that took place during Meiosis I. There is no tetrad formation. The four cells that result are haploid (N).

Gamete Formation

In males, the gametes formed are sperm cells. 4 sperm are produced after meiosis. In females, the gametes formed are egg cells. 1 egg cell and 3 polar bodies are formed.

Comparison of Mitosis and Meiosis

Mitosis: 2 identical diploid cells produced, asexual reproduction, production of body cells, one set of divisions.

Meiosis: Four genetically different haploid cells produced, sexual reproduction, production of gametes, two sets of divisions.