REVIEW SHEET –CHROMOSOMES, KARYOTYPES, MEIOSIS & CELL CYCLE

This is not for a grade. This is a guide to help you pull out the most important information from your notes, the reading, and the work you have done in class. Remember that some of these questions may be asked in the context of your labs. This is not a guarantee of everything that is on the test. You must study!

CHROMOSOMES & KARYOTYPES

1. What is asexual reproduction? Describe binary fission and draw an example.

– reproduction resulting from mitosis (or a similar process) that involves only one parent; the offspring are genetically identical to the parent (a clone)

2. Cite 2 examples of regeneration.

Starfish and planaria (a flatworm)

3. Differentiate between somatic cells and gametes in terms of chromosome #, diploid vs. haploid, cell examples.

Somatic cells = body cells

  • 46 chromosomes
  • Diploid
  • Skin, bone, muscle cells

Gametes = sex cells

  • 23 chromosomes
  • Haploid
  • Eggs and sperm

4. Differentiate between autosomes and sex chromosomes in terms of # of each in “normal” humans, male vs. female, and function of each.

Autosomes = all chromosomes except for sex chromosomes

  • 44 (in a normal somatic cell)

Sex chromosomes = chromosomes that determine an individual’s gender

  • 2 (in a normal somatic cell)
  • XX=female
  • XY=male
  1. Define karyotype. Be prepared to look at a karyotype to determine chromosome # and sex of the organism as well as disorders apparent from the photo.

Karyotype—a photograph of an organisms chromosomes, arranged in pairs

CELL CYCLE (some from this previous unit)

  1. Why do cells divide?

Growth, repair/replacement, reproduction

  1. What are the two steps of the cell cycle?

Growth and preparation (Interphase) and Cell Division (Mitosis & Cytokinesis)

  1. List and describe the events in interphase. Draw a cell in interphase.
  1. G1—most cells are in this stage of interphase for 90% of time; cell grows,

proteins made, etc.

  1. S—DNA replication takes place
  2. G2—more growth and preparation, organelles are assembled
  1. List and describe the events in mitosis. Draw a cell in each phase.

1.PROPHASE-- chromosomes evident, nuclear membrane disappearing

(P for Phat (fat), chromosomes condense/fatten and become visible)

2.METAPHASE- sister chromatids lined up in the middle/equator

(M for middle, chromosomes lined up in the middle of cell)

3.ANAPHASE- sister chromatids pulled apart (A for Apart or Away because the chromatids pull apart and move away from center)

4.TELOPHASE- chromosomes are at ends of cell, cells prepare to separate (T for Two new nuclear envelopes are forming)

  1. What is cytokinesis? Division of the cytoplasm; cell splits into two
  1. What is a chromosome composed of?DNA and proteins
  1. What is a centromere?Point where the sister chromatids attach in a chromosome
  1. Compare and contrast plant and animal mitosis & cytokinesis.
  • Both include Prophase, Metaphase, Anaphase and Telophase; then Cytokinesis
  • Animals have centrioles that make spindle fibers; plants do not
  • Animal cytokinesis involves pinching in of cell membrane (called cleavage furrow); then pinch off into two cells; Plant cytokinesis there is no pinching in, just a formation of a new cell wall along the cell plate between the two cells

MEIOSIS AND CHROMOSOMAL DISORDERS

  1. What is meiosis? What is the result of this process?

Meiosis—process that forms gametes (eggs and sperm); result is 4 haploid cells (half the number of chromosomes of original cell)

  1. Compare and contrast meiosis and mitosis.

MitosisMeiosis

•1 division=2 cells2 divisions = 4 cells

•Daughter cells identicalDaughter cells different

•Diploid cells (2n)=46•Haploid cells (n)=23

•Body/Somatic cells•Gametes (sex cells—eggs or sperm)

  1. List and draw the steps of meiosis.
  1. A rabbit has 44 chromosomes (or 22 pair). Answer the following questions based on this information.

A. What is the diploid number of chromosomes? 44 (or 22 pair)

B. How many TOTAL chromosomes would be in a somatic cell of a rabbit? 44 (or 22 pair)

C. How many autosomes would be in a somatic cell of a rabbit? 42 (or 21 pair)

D. How many sex chromosomes would be in a somatic cell of a rabbit? 2 (or 1 pair)

E. What is the haploid number of chromosomes? 22

F. How many TOTAL chromosomes would be in a gamete (egg or sperm) of a rabbit? 22

G. How many autosomes would be in a gamete (egg or sperm) of a rabbit? 21

H. How many sex chromosomes would be in a gamete (egg or sperm) of a rabbit? 1

I. Mathematically show how the egg and sperm would form a zygote after fertilization takes place.

22 chromosomes (egg) + 22 chromosomes (sperm) = 44 chromosomes in a zygote (which will be a baby rabbit)

  1. Describe crossing over.

Crossing-over—the exchange of genes that can occur between homologous chromosomes during Prophase I

  1. What things can occur from genetic variation?

New combinations of genes. This flexibility in the gene pool of a population helps insure the survival of a species, especially if there is rapid or sudden change in the environment.

  1. Why does nondisjunction occur?

Chromosomes fail to separate properly during Anaphase I or Anaphase II of meiosis

  1. Describe the following nondisjuction disorders: Klinefelter’s Syndrome, Down’s Syndrome, Edward’s Syndrome, Turner’s Syndrome.

Klinefelter’s= XXY, trisomy + of sex chromosomes; always male

Down Syndrome= 3 # 21 chromosomes, Trisomy 21; male or female

Edward’s Syndrome= 3 #18 chromosomes, Trisomy 18; male or female

Turner’s Syndrome=XO, monosomy X; always female

Patau= 3 #13 chromosomes, Trisomy 13; male or female