Meiosis, Spermatogenesis, and Oogenesis

What happens during prophase I?

Homologous chromosomes pair up, condense, and exchange genetic material through a process called crossing over, forming tetrads (pairs of homologous chromosomes)

What happens during metaphase I?

Homologous chromosome pairs align at the cell's equator along the metaphase plate, with spindle fibers from opposite poles attaching to each pair

What happens during anaphase I?

Homologous chromosome pairs are pulled apart by spindle fibers and move to opposite poles of the cell, while sister chromatids remain attached at their centromeres

What happens during telophase I/cytokinesis?

The spindle apparatus disassembles, nuclear membranes re-form around the separated homologous chromosomes at the opposite poles of the cell, and chromosomes begin to decondense into chromatin, and cytoplasm divides

What happens during prophase II?

The two haploid cells from meiosis I re-condense their chromosomes, and a new spindle forms around the chromosomes

What happens during metaphase II?

Chromosomes align along the metaphase plate (the equator of the cell), with microtubules from opposite poles of the spindle attaching to the kinetochores of the sister chromatids in each chromosome

What happens during anaphase II?

The sister chromatids of each chromosome separate and are pulled by spindle fibers to opposite poles of the cell, becoming individual daughter chromosomes

What happens during telophase II/cytokinesis?

Four haploid daughter cells are formed, and a nuclear envelope forms around each set of chromosomes. The cytoplasm divides

Spermatogenesis

The formation of sperm cells. Begins in a diploid stem cell called a spermatogonium.

Divides mitotically, yielding two daughter cells: one that continues to specialize into a mature sperm, and the other remains a stem cell, able to self-renew and continually produce more sperm

Oogenesis

The formation of a mature egg. Begins with a diploid cell called an oogonium.

In meiosis I, the primary oocyte divides into a polar body and a larger secondary oocyte

Segregation (separation)

The correct separation of homologous chromosomes and sister chromatids

Mis-segregation (nondisjunction)

An error where the chromosomes or chromatids fail to separate correctly, leading to an abnormal number of chromosomes in the resulting gametes (aneuploidy)

Where are germ cells located in males?

Primarily in the testes

Where are germ cells located in females?

Primarily in the ovaries

Chromosome pair

Consists of two chromosomes of the same size and shape, and carry the same genes in the same location. One chromosome comes from the mother, and the other comes from the father. The basis of the two sets in a diploid organism

Chromosome set (genome)

Refers to the number of complete collections of unique chromosomes an organism has, known as its ploidy. In humans, we have two sets of 23 chromosomes

What is crossing-over?

It is the exchange of genetic material between homologous chromosomes during meiosis, specifically during prophase I. It is a continuous process within that phase.

Chromosome

It is the entire structure of condensed DNA and proteins

Chromatid

It is one of the two identical copies of a replicated chromosome joined at the centromere

Homologs = homologous pair

Homologous chromosomes are matched pairs of chromosomes in a diploid organism, with one chromosome inherited from each parent

Tetrad

The four-chromatid structure formed when a pair of homologous chromosomes, each with two sister chromatids, come together during prophase I

Allele

One of two or more versions of DNA sequence at a given genomic location

What are centromeres?

Specialized regions on chromosomes where sister chromatids attach and spindle microtubules bind, ensuring accurate chromosome separation during cell division

What are Kinetochores?

Complex protein structures that form on the centromeres of chromosomes and serve as the critical attachment points for spindle microtubules during cell division

What are telomeres?

Repetitive DNA sequences and proteins that cap the ends of chromosomes, protecting the DNA from fraying and fusing with other chromosomes

What are spindle microtubules?

Protein fibers that form the mitotic spindle, help pull the chromosomes to opposite poles of the cell during cell division, ensuring a new daughter receives a complete and identical set of genetic material

What are centrioles?

Small, barrel-shaped organelles composed of microtubules that are found in the cytoplasm of animal cells, near the nucleus. Help form centrosomes, which organize the spindle fibers that separate chromosomes

What are the products of spermatogenesis & how many produced during meiosis?

One spermatogonium, which then undergoes meiosis to form four haploid spermatids, which then mature into four spermatozoa (mature sperm cells)