Biology Concepts: Meiosis

Meiosis is the process in which sex cells divide into four daughter cells, each with a haploid chromosomes (half the normal amount).

Why is meiosis in cells necessary? What does it do?

Meiosis is important because it is the process of dividing haploid cells into gametes or sex cells that allow us to reproduce. Without meiosis, we wouldn't have the sex cells necessary to sexually reproduce. The process of meiosis also divides the chromosomes into the gametes so that only one set is present as opposed to the two sets of chromosomes that are present in all other cells of the body. This allows the created cell to obtain a full copy of chromosomes from both parents without a gene overload that would cause mutations in the cell and thus mutations in the new organisms development.

Why is it that the term reduction division is sometimes used to describe the meiosis?

The term reduction division can be used to describe meiosis because the process of meiosis is reducing the number of chromosomes in a cell to half its typical number. The number of chromosomes in a gamete cell, those produced by meiosis is 23 and is represented by "N." All other cells in the body have 46 chromosomes as are represented by "2N" meaning there are two sets of chromosomes in the cell.

Here are some chromosome counts on various animals:

Ferrets have 40 chromosomes.
Chinchillas have 64 chromosomes.
Cats have 38 chromosomes.
Dogs have 78 chromosomes.
Rabbits have 44 chromosomes.
Goldfish have 94 chromosomes.

It's also interesting to note that chimpanzees have 48 chromosomes. A close number to our (human) 46 chromosomes.

Why is cross over necessary? When does it occur in meiosis?

Crossing over occurs during prophase 1 and takes almost the entire duration of prophase 1 to complete. The function of cross over to create new combinations in genes so as not to have any identical genes enter into the new gamete cell.

How are daughter cells different from their parent cell?

The daughter cells that result from meiosis have a different genetic make-up than that of their parent cell. They have a different allele combination from their parent cell due to the crossing over, independent assortment, and segregation sections of meiosis.

There are three combinations that create genetic variation in cells undergoing meiosis. What are they?

The three mechanisms leading to gene variation are...
Crossing over: Crossing over occurs when two chromosomes exchange a portion of their DNA. These chromosomes are paired up during prophase 1 of meiosis, and the exchange occurs at the end of prophase 1 and contribute to gene variation or new combinations in genes.
Independent assortment: During independent assortment the chromosomes for the new gamete is chosen at random from both the material and paternal chromosomes. This allows for a great deal of variation in gene combinations.
Segregation: The segregation phase involves separating the homologous chromosomes (similar chromosomes) from one another. Once the homologous chromosomes are separate they are segregated into one of the two diploid cells.