Nathan Biology Meiosis

The phases of Meiosis 1 include...

1. Interphase 2. Prophase 1 3. Metaphase 1 4. Anaphase 1 5. Telophase 1 and cytokinesis

The phases of Meiosis 2 include...

1. Prophase 2 2. Metaphase 2 3. Anaphase 2 4. Telophase 2 and cytokinesis

Each parent only passes on...

1/2 of each of their chromosomes, meaning 23, one from each pair of their homologous chromosomes.

What is the end result of Meiosis 2?

4 unique haploid daughter sex cells, each containing one set of chromosomes (23n).

What is a tetrad?

A cluster of 4 chromatids.

There are 3 phases to interphase...

G1: growth phase of the cell S: DNA replication G2: cells continue to grow

Gametes are sex cells. This means that they are used in the process of reproduction. The female sex cells are the eggs and the male sex cells are the sperm.

Gamete or sex cells have 23 chromosomes, which means that they are haploid. Two haploid sex cells, one egg and one sperm, come together to make a baby, which then contains 46 chromosomes, 1/2 from the mom and 1/2 from the dad.

What happens in Anaphase 1?

Homologous chromosome pairs separate, with one pair of sister chromatids going to one end of the cell and another pair of sister chromatids going to the other end of the cell. Sister chromatids remain attached.

Organisms that reproduce sexually, such as humans, fuse the genetic information from two parents to produce an offspring that are a genetic mixture of both partners.

Look at the diagram, study it.

Meiosis involves two rounds of cell division: meiosis 1 and meiosis 2. Meiosis 1: 1. Separation of homologous chromosomes 2. Homologous chromosomes are repackaged in different cells.

Meiosis 2: 1. Separation of sister chromatids. 2. Cells from meiosis 1 divide into individual chromosomes.

What is the difference between mitosis and meiosis? Mitosis: 1. Produces 2 identical daughter cells 2. For somatic cells 3. Daughter cells have diploid number 4. Takes place throughout the organism's life.

Meiosis: 1. Produces 4 genetically different sex cells 2. For sex cells 3. Resulting cells have haploid number 4. Only takes place at certain times in an organism's life cycle.

What happens in Anaphase 2?

Sister chromatids are pulled apart, and one chromatid from each pair travels to each pole.

Somatic cells are body cells. This means that they are any cell of a living organism other than the reproductive cells.

Somatic cells have 46 chromosomes, which means that they are diploid. Diploid means that they contain 23 chromosomes from one parent and 23 chromosomes from another parent. 1/2 from the mom and 1/2 from the dad.

Let's look again at the karyotype...

The maternal and paternal chromosomes in a homologous pair have the same genes at the same loci, but possibly different alleles. For example, a gene may code for eye color, but the maternal alleles code for brown while the paternal alleles code for blue.

What happens in prophase 1?

The nuclear membrane begins to disappear. The centrioles make spindle fibers. The homologous chromosomes begin to pair up and become visible. Sometimes, DNA is swapped by crossing over between the homologous chromosomes.

What happens in Prophase 2?

The nuclear membrane breaks down, and the centrioles move to opposite sides of the cell, from which, spindle fibers form.

What happens in Telophase 2?

The nuclear membrane forms around each set of chromosomes. The spindle fibers dissolve, and the cytoplasm divides (cytokinesis).

In the end, the purpose of mitosis is...

for cell growth and repair of the somatic cells of the body. It results in 2 identical daughter cells with 46 chromosomes. It is a type of asexual reproduction.

In the end, the purpose of meiosis is...

to create gametes that are 4 unique haploid sex cells with 23 chromosomes. It is a type of sexual reproduction.

What are we left with at the end of interphase?

Duplication of the cell's genetic material. There are still only 46 chromosomes, but they now look like x's because they are now sister chromatids. This means that the genetic material of one chromatid is genetically identical to that of the other chromatid. They're like identical twins.

Fertilization is...

The actual fusion of egg and sperm.

What happens in Telophase 1?

The chromosomes gather at the poles. The nuclear membrane may form, and cytokinesis occurs. The end result: homologous chromosomes are now in two different cells.

What happens in Metaphase 1?

The homologous chromosomes are lined up in the middle of the cell in pairs or tetrads. 23 chromosomes are lined up along each side of the cell equator.

What happens in Metaphase 2?

The sister chromatids line up in the middle of the cell.

What is the purpose of meiosis?

To create gametes, also called "sex cells," that contain 1/2 the number of chromosomes (haploid).

What do we mean by "crossing over"?

When homologous chromosomes cross over, sometimes they swap segments of DNA.

This is a picture of a karyotype...a karyotype is a picture of all of the chromosomes in a person.

You can see, if you enlarge the picture, that a diploid human cell contains 22 pairs of homologous chromosomes and 2 sex chromosomes.