bio problem set 8

Describe the stages of meiosis.

(meiosis I: reduction (2n->n) interphase I: DNA replicates, growth occurs. prophase I: Chromosomes form, nuclear membrane disappears metaphase I: homologous chromosomes pair up on either side of the equator anaphase I: centromeres do no divide, both sister chromatids both migrate to the same pole telophase I: cleavage furrow forms, new cells have half the genetic information as parent cell (meiosis II) prophase II: new spindle fibers form (DNA still coiled) metaphase II: duplicated chromosomes line on equator anaphase II: sister chromatids seperate telophase II: cleavage of both haploid cells (1N) results in 4 haploid cells

Explain the role of crossing over and independent assortment in ensuring genetic variation.

Crossing over is an exchange of genetic material between homologous chromosomes. Independent assortment is the random distribution of maternal and paternal homologues to the gametes.

The cell cycle has four main stages- G1, S, G2 and M. What occurs in the cell during each phase?

G1 phase which is protein synthesis and metabolic activities (most cells are arrested in this phase), S phase which is where the DNA replication takes place, and G2 phase which is the cellular growth and preparation for M phase.

What are gametes? Name the organs where gametes are produced in humans.

Gametes are produced in the testes; they are a reproductive cell having the haploid number of chromosomes, especially a mature sperm or egg capable of fusing with a gamete of the opposite sex to produce the fertilized egg.

What is the functional difference between meiosis II and mitosis?

Meiosis produces 4 cells with half the normal number of chromosomes and mitosis only produces 2 cells

Name two major differences between mitotic cell division and meiosis.

Mitosis takes place within all cells that make up the body, while meiosis takes place only within gamete cells (sex cells). Mitosis results in 2 daughter cells while Meiosis results in 4 haploid gametes.

Why do cells need to divide? Provide three reasons.

They divide in order to 1) to maintain a surface area to volume ratio, this results in enough SA for diffusion/osmosis 2) in order to reproduce and pass down DNA to offspring 3) cells die eventually and need to be replaced

What joins sister chromatids together? When are they separated in Mitosis?

centromere. in anaphase when the centrioles and spindle fibers pull them to the side of the cell.

Relate the following terms: chromatin, chromosome, chromatids (sister chromatids), centromere.

chromatin make the chromosomes. chromosomes are dividing DNAs that require the chromatid which can only be a chromatid when it has a sister chromatid that is held together by a centromere.

Differentiate between a chromosome, homologous chromosomes, and sister chromatids.

chromosome is DNA tightly coiled around histones (proteins) homologous chromosomes are two different copies of the same chromosome, and sister chromatids are two identical copies of a chromatin connected by a centromere.

How does the process of cytokinesis differ from the process of mitosis?

cytokinesis divides the cytoplasm and turns the cell into two identical sister cells and mitosis divides the nucleus.

For which cells in the human body does cell division occur? Which cell types have a greater rate of cell division? Why?

eukaryotic. cancer cells have a great rate of cell division. environmental factors such as changes in temperature and pH, and declining nutrient levels lead to declining cell division rates

For which cells in the human body does mitosis occur? For which cells does meiosis occur?

mitosis occurs in somatic cells (all body cells EXCEPT sperm and ova) meiosis occurs in gamete (sex cells: sperm/eggs)

Why is it important for the nuclear membrane to disappear during prophase?

so that the spindle fibers can get to the chromatin.

How many chromosomes do human gametes normally contain?

46

During which stage of meiosis is the diploid number of chromosomes reduced to the haploid umber of chromosomes?

Anaphase II: the sister chromatids separate.

List one similarity and one difference between binary fission and mitosis. Which types of organisms use mitosis? Binary fission?

Binary Fission happens to bacteria and prokaryotes, it occurs in non-membrane bound organelles. Mitosis occurs in eukaryotes and it is the process of multiplying (splitting into two) membrane bound organelle cells. They both divide and replicate into two halves.