Meiosis and Sexual Reproduction

Slide 1

Meiosis and Sexual ReproductionCHAPTER 7MEIOSIS: Gametes are formed during Meiosis Gametes are haploid Meiosis is the process of nuclear division that reduces the number of chromosomes by half. In meiosis, two nuclear division take place instead of one producing 4 cells. They are referred to as, Meiosis I and Meiosis IISTEPS OF MEIOSIS IProphase I: Same as in mitosis, but chromosomes line up next to a partner during a process called SYNAPSIS. The chromosomes twist around and line up with each other to form a TETRAD.

Genetic information within segments of DNA may be exchanged:CROSSING OVER

Metaphase I:

The tetrads are moved by spindle fibers to the equator of the cell.

The homologous pairs of chromosomes remain together

Anaphase I:

The homologous pairs of chromosomes are separated.

Each chromosome is still composed of two chromatids joined by a centromereTelephase I:

The cytoplasm divides and forms two daughter cells. Each has the original # of chromosomes

STEPS OF MEIOSIS IIProphase II:

If the chromosomes uncoiled, they are reformed from the chromatin

New spindles form

Metaphase II:

The chromosomes are moved to the cell equator

Each is attached to spindle fibers, at the centromere

Anaphase II:

The centromeres joining the chromatids divide, freeing the sister chromatids from each other

They move to opposite poles within the cell.

Telophase II: Spindles dissolve and nucleus reappears

Cytokinesis occurs after Telophase II. Division of cytoplasm

MITOSIS VS. MEIOSIS Mitosis: produces two exact copies of the original cell daughter cells have same # of chromosomes as parent cell process done in body cellsMeiosis produces four cells daughter cells have half the # of original chromosomes genetic information can be exchanged - crossing over process done in sex organsMeiosis and Genetic Variation3 occurrences account for genetic variation also called variability: Independent Assortment Crossing-Over Random Fertilization Importance: Essential for Evolution INDEPENDENT ASSORTMENT:The random distribution of homologous chromosomes Each of the 23 pairs segregate independently 2^23 Or 8 million gametes with different gene combinations

Crossing-Over and Random FertilizationAdds to the different possible combinations from independent assortment Unlimited number of genetic variations are possible

Meiosis and Gamete Formation: -Develop when the individual reaches PUBERTY Making of Egg Cells (oogenesis) : Form in the female OVARY Creates two cells after first division - one VIABLE and one POLAR BODY(nonfunctioning). Second division creates a total of 3 polar bodies and one viable ovum or more commonly known as egg.

Sperm: Formed in the TESTES One cell is able to create 4 new viable (usable) cells

CHANGES IN THE RATES OF MITOSIS: -Mitosis rate can speed up or slow down -Two effects caused by a change in the rate of mitosis include. AGING and CANCER

Aging: -Process of becoming older -Slows down mitosis ( hair, nails, etc )

The union of sperm and egg is called fertilization.Producing offspring is called reproduction and can be asexual or sexual.

Plants go through the sexual life cycle described as Alternation of Generations

Liverwort has a gametophyte dominant life cycle

A spore is a 1n structure formed during the sporophyte stage of alteration of generations in plants.

Budding is a type of asexual reproduction in which a new organism grows on another one. Since the reproduction is asexual, the newly created organism is a clone and is genetically identical to the parent organism. Ex. Hydra and Corals

Cancer: Disease in which the cells of the body reproduce at an unusually high rate. Agents that cause cancer include; chemicals, radiation, and viruses. Things that cause cancer are often referred to as CARCINOGENS