AP Bio Meiosis

Compare and contrast asexual and sexual reproduction.

In asexual reproduction, a single individual is the sole parent and passes copies of all its genes to its offspring. In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents

Life Cycle

the course of developmental changes in an organism from fertilized zygote to maturity when another zygote can be produced

Karyotype

The display of chromosomes in Homologous pairs starting with the longest chromosomes moving to the shortest

Homologous Chromosome

The two chromosomes that compose a pair of the same length, centromere position, and staining pattern.

Sex Chromosome

The X and Y chromosomes; they help determine the sex of an individual.

Autosomes

All chromosomes other than the x and y chromosomes

Diploid

All cells within the body other than sex cell. These cells contain two copies of each chromosomes, one from the mother and one from the father.

Haploid

A single complete set of chromosomes. (N=23 for humans)

Fertilization

Fertilization- The union of haploid gametes to produce a diploid zygote.

Zygote

The diploid product of the union of haploid gametes in conception. Or a fertilized egg.

Meiosis

A two-stage type of cell division in sexually reproducing organisms that results in cells with half the chromosome number of the original cell.

Describe the three types of life cycles

Animals- gametes are the only haploid cells- meiosis occurs during the production of gametes- the diploid zygote divides by mitosis
Plants- The diploid stage is called the sporophyte- meiosis in the sporophyte produces haploid cells called spores- spore divides mitotically to generate a multicellular haploid stage called the gametophyte
Fungi- After gametes fuse and form a diploid zygote, meiosis occurs without a diploid offspring developing. Meiosis produces not gametes but haploid cells that then divide by mitosis and give rise to a haploid multicellular adult organism.

What are the two broad goals of meiosis

1. Produce haploid daughter cells.
2. Generate Variation

How does the chromosome number change during the process of meiosis?

The cell starts a 2n. It then duplicates its chromosomes and is 4n. The cell then divides the first time. There are then two 2n cells. These two cells divide again, creating four 1n cells.

Describe in detail the three sources of genetic variation in meiosis.

-Independently assorted chromosomes- In metaphase one, there are several ways homologous chromosome pairs are arranged. When they are lined up, there is a chance that one daughter cell will get the paternal chromosome and an equal chance that it will get the maternal one. This 50/50 split can occur with any homologous chromosome pair. The greater the number of chromosomes in a set (n), the more chances a daughter cell has to divide its paternal and maternal chromosomes equally among itself, and the more diverse the gamete population will become.
-Genetic Recombination (Crossover)- In Prophase I, a specific event occurs when the chromatids of both homologous chromosome pairs (one from each parent) bring their �arms� together and attach by a protein structure called the synaptonemal complex. The sister chromatid pairs come very close together. Now, one set of non-sister chromatid pairs (one from each original pair) is close enough to cross gene strands with its foreign neighbor. When the strands of chromosome cross, they break off and attach to their adjacent chromosomes, effectively changing the codons in that gene and those of the daughter cell that will receive that chromatid. These recombinant chromosomes are like hybrids, built up of pieces from both parents (like some sort of Frankenstein chromosome). This also increases the variety of potential gametes produced in meiosis.
-Random Fertilization- Due to all the variations between individual gametes, there are many potential combinations that can occur to form a zygote. Take the human zygote. Each sperm or egg is one or 8 million potential gametes! Now match that with the probability of one sperm out of a few million wriggling its way through to the uterus, reaching the egg intact, and penetrating it successfully! There are so many outcomes; it is no wonder such broad genetic differences occur within humans. It�s impossible not to be the product of a random pairing, at least without artificial means of fertilization. More choices=greater genetic diversity=more likely to develop different traits than siblings/other members of species=favorable traits win out=Darwinism.

Describe in detail the three sources of genetic variation in meiosis.

Crossing over during prophase I of meiosis, independent orientation of chromosomes at
metaphase I, and random fertilization of gametes during fertilization.

Compare and contrast meiosis and mietosis

Mitosis produces 2 diploid cells; occurs in somatic cells for growth, repair, replacement, and
development.
Meiosis produces 4 haploid gametes (sex cells) through 2 cell divisions. Occurs in reproductive
organs.