Meiosis (Review from Science 9)

Mitosis creates…

Somatic cells

Reproductive cells aka

gametes/ sex cells

The two types of gametes are?

Egg and sperm

Gametes are formed by…

meiosis

Haploid represents…

one of each TYPE of chromosome in an organism’s cell

What type of cell in humans is the only haploid one?

Gametes

What does “n” mean?

“n” refers to the number of different types of chromosomes from a parent

How many different types of chromosomes “n” are in human gametes?

23

What does diploid mean?

Two of each type of chromosome in an organism’s cell

How many chromosomes are in each human somatic cell?

46 chromosomes 2(23)

What are the 46 paired chromosomes which form 23 pairs called?

Homologous chromosomes

How many cell divisions are in meiosis?

2 cell divisions

Are gametes produced in meiosis genetically identical to the original diploid cell?

No

What happens in meiosis I and II?

A diploid cell splits into 2 haploid cells, which go onto split into 4 haploid cells.

When does meiosis happen in males?

It begins and occurs continuously from puberty

When does meiosis happen in females?

Meiosis starts before birth and then stops. It will resume during puberty when the menstrual cycle begins.

The 4 stages of meiosis are…

PMAT , I

What happens in prophase I?

The nuclear membrane starts to disappear, homologous chromosomes pair up and crossing over can occur. Your parents’ genetic material can be exchanged between the chromosomes from either parent to create genetic variation.

What is crossing over and when does it happen?

During prophase I, your parents’ genetic material which makes up the DNA in your haploid cells can be exchanged between the chromosomes from either parent to create genetic variation.

What happens in metaphase I?

Spindle fibres guide chromosome movement and homologous chromosomes line up along the cell’s equator.

What happens during Anaphase I?

Homologous chromosomes are separated by spindle fibres and head to the poles of each cell where independent assortment occurs.

What is independent assortment?

The creation of genetic variation during Anaphase I by virtue of the fact that homologous chromosome pairs are split up randomly causing gametes to get a unique mix of DNA. Can yield more than 8 million combinations.

What happens in Telophase I?

Nuclear membrane forming around chromosome sets as each nucleus has only 1 set of chromosomes now, cytokinesis occurs after telophase I.

What is interkinesis?

Occurring be Meiosis I and II, interkinesis is when the cell grows and make proteins but DNA DOES NOT REPLICATE.

What are the stages of Meiosis II?

PMAT, II

What happens during prophase II?

Nuclear membrane begins to disappear, sister chromatids are together but not identical due to crossing over and only 1 copy of each type of chromosome is in each cell.

What happens during Metaphase II?

Chromosomes, no longer in homologous pairs and now all lonely by themselves with only sister chromatids for company, line up at the equator.

What happens during Anaphase II?

Sister chromatids are pulled apart to opposite poles of the cell

What happens during telophase II?

Spindle fibres disappear, the nuclear membrane reappears, there are 4 nuclei and all four are haploid.

What happens in cytokinesis after Telophase II?

Each haploid cell divides into 2 creating a total of 4 haploid cells.