Meiosis

What is Meiosis?

• Meiosis is a special type of cell division used by sexually-reproducing organisms to produce the gametes, such as sperm or egg cells.

It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome (haploid).

Some Definitions• Haploid = 1 copy of each chromosome

• Diploid = 2 copies of each chromosome

• Gamete = mature haploid cell capable of fusing with another to form a diploid cell. Sperm and eggs are gametes.

• Zygote = A diploid cell formed from the fusion of two haploid gametes. Often called a fertilized ovum.

Relations to Offspring

• Half of your DNA came from your mother, and half came from your father.

• Since half of their DNA came from their parents, you are 25% related to each grandparent.

Meiosis results in 4 gametes; 2 from each of your parents

Mother’s side Father’s side

You will either pass on a chromosome from your mother or

your father to your offspring.

Impacts- Huntington’s Disease is a single gene genetic disorder located on Chromosome #4.

If your mother had it, but your father did not, you will have it, and have a 50/50

chance of passing it onto your offspring.

It is a neurological disorder that causes progressive loss of physical and mental functioning beginning in your early

30’s, with death likely within 20 years of onset.

Independent Assortment• While you will get an individual chromosome from EITHER your

mother or your father, each chromosome is sorted independently.

• This means, you will get about half of your chromosomes from each parent.

• While it is theoretically possible to pass all 23 chromosomes from your mother (or father) to your offspring, the chances of that happening are 1/223 or 1 in 8,388,608 gamete combinations.

Independent Assortment• Let’s look at a simple 2 chromosome species.

• You can see here that there are 4 possible egg combinations.

25% - Both from mother 25% - Both from father 25% - One from mother and one from father25% - Other from mother and father

Meiosis Review