Meiosis

A mature haploid germ cell that which unite to create a zygote (Ex: sperm, egg)

A diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.

Ovaries + testes, which create haploid cells

Cells containing only one set of chromosomes (n) - half the usual number of sets (2n). Chromosomes are counted by the centromeres, not X’s!

Cells containing two complete sets of chromosomes (2n), with one set inherited from each parent.

Haploid - n=23 Diploid - 2n=46

Meiosis is a type of cell division that occurs in the gonads to create 4 haploid cells from one diploid parent cell.

Homologous chromosomes are the chromosomes inherited from each parents which contain the same genes, yet different alleles.

Before DNA replication, each cell has 46 individual strands of chromosomes - with 23 homologous pairs - one version from mom, one from dad. These homologous pairs are not physically paired up. During DNA replication, each strand makes a identical copy of itself which are physically attached like an X, and are sister chromatids. Therefore, there are still 46 chromosomes, yet they are all X’s now instead of single strands.

The cell is split into two haploid daughter cells with half the number of chromosomes - yet they are still homologous pairs in X shapes.

Homologous chromosomes (sister chromatids in X shapes after DNA replication) pair up inside the cell (so 2 X’s put together). They exchange fragments, called crossing over or recombination, allowing for genetic diversity.

The homologous pairs line up in the center of the cell, and the spindle fibers begin to attach.

Homologous pairs are pulled apart by the spindle fibers. Now there is only X’s on each side.

The nuclear envelope begins to reform around each side of homologous pairs, and the cell splits into two each with only one set of chromosomes (haploid n=23 in humans).

Independent assortment is when the homologous pairs line up during metaphase 1, the mom’s gene (little x) could face to the left or right, and the dad’s gene (big x) could face to the left or right. Therefore, the resulting cells have different proportions of mom and dad’s genes, allowing for more genetic variation.

Four haploid cells that have one set of single strands of DNA (23 in humans).

The chromosomes condense and the nuclear envelope breaks down to prepare for separation. Spindle fibers begin to form.

Chromosomes (n=23 X’s in humans) line up in the middle along the metaphase plate.

Sister chromatids are pulled apart and separated by spindle fibers.

The cell divides into two, each with n (23 in humans) single strands of DNA (haploid -> one set or n). There are four cells in the end.

2 to the n power (n is the number of chromosomes for a haploid cell). In humans, it would be n to the 23, because haploid cells have 23 chromosomes.

Non-disjunction is the failure of homologous chromosomes or sister chromatids to properly separate.

Errors can lead to genetic disorders, such as conditions like Down syndrome (extra chromosome).

Come on Sammy, just do it. Love ya!