AP Biology: Mitosis and Meiosis

How many divisions does the process of meiosis involve?

2

What cells result from meiosis?

4 haploid daughter cells; gametes (eggs or sperm)

How is variation accomplished in meiosis?

Sexual reproduction allows for the combination of chromosomes; crossing over in prophase I

Does meiosis occur in diploid or haploid cells? Explain.

Diploid, haploid cells are what is created

Explain the difference between Meiosis I and Meiosis II.

Meiosis I:

Heterotypic/ reduction division

long and complicated

chromosomes reduce to 1/2

Meiosis II:

homotypic/ equational division

simple and short

chromosomes remain the same

Explain how the centrosomes are produced for Meiosis I

They are produced by the duplication of a single centrosome during premiotic interphase

What are the functions of centrosomes?

They form spindle fibers and separate the chromosomes; they are the microtubule organizing center

Do plant cells have centrosomes? Explain

No, they have different microtubules to serve as spindle fibers. They don't have centrioles but they have centrosomes

What happens to the duplicated chromosomes during prophase I?

They become visible and pair up to form tetrads; duplicated chromosomes pair up with homologous structures, crossing over will occur.

What is crossing over?

It is a genetic rearrangement between non-sister chromatids involving DNA exchange. While the tetrad is formed the chromosomes cross over and sections of chromatids are exchanged, it creates new combinations of alleles

What makes up a tetrad?

2 homologous chromosomes, each composed of 2 identical chromatids; the 4 chromatids of the paired homologous chromosomes

When does anaphase I begin?

When the duplicated centromeres of each pair of sister chromatids separate// when the homologous pairs of chromosomes begin to separate at opposite poles.

Do the sister chromatids remain attached during anaphase I? How is this different than in anaphase II?

Yes, in anaphase II they separate and move to opposite poles on the spindle.

What happens to the tetrads in telophase I?

They are separated into pairs and the nuclear envelope forms around them

Does repication happen again prior to prohpase II? Explain,

No, meiosis produces 4 haploid cells as opposed to 4 diploid cells. No new chromosome replication occurs before meiosis II in order to produce 4 cells with half the genetic information.

What is the result of meiosis II? How many cells and how many chromosomes in each cell?

The sister chromatids within the 2 daughter cells separate, forming 4 new haploid gametes. Each dividing cells has one set of homologous chromosomes.

Explain how there are 8 million possible chromosome pairings in a haploid nuclei

2^23 where 2 is the number of cells and 23 is the number of chromosomes in each cell

Explain how the results of crossing over can be genetic recombinants

Two chromosomes exchange segments of their genetic material, forming new allele combinations.

structure that transmits the genetic material from one generation to the next

chromosomes

body cell; excludes cells that undergo meiosis and become sperm or eggs

somatic cells

haploid sex cell; egg or sperm

gametes

network of DNa strands and associated proteins observed within a nucleus of a cell

chromatin

one of 2 genetically identical chromosomal units that are the result of DNA replication and are attached to each other at the centromere

sister chromatids

constriction where sister chromatids of a chromosome are held together

centromere

stage of cellular reproduction in which nuclear division occurs with 2 daughter cells

mitosis

division of the cytoplasm following mitosis or meiosis

cytokinesis

type of nuclear division that reduces the chromosome # from 2n to n

meiosis

complex of microtubules and associated proteins that assist in separating the chromatids during cell division

mitotic spindle

central microtubule organizing center of cells

centrosome

assembly of proteins that attaches to the centromere of a chromosome during mitosis

kinetochore

the growth stage in which the cell recovers from division and increases the number of organelles

G1 phase

The phase from DNA replication to mitosis in which the cell grows and prepares to divide

G2

Growth and DNA replication stage

S phase

What is a cyclin and what does it activate?

It is a protein that activates kinases

What is cancer?

A disease in which abnormal cells divide uncontrollably and destroy body tissue