Chromosome theory of inheritance

Question 1

Difference between metacentric and acrocentric chromosomes

Answer 1

Symmetric and unsymmetric placement of centromere

Question 2

n indicates nr of chromastes in gametes. How many n (Xn) is normal in diploids and what is n in homo sapiens?

Answer 2

2n. n is 23 in humans

Question 3

Define:
1. centrosomes
2. centromeres
3. chromatides
4. microtubules

Answer 3

1. the centrosome (archaically cytocentre) is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell
2. The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids
3. A chromatid is one half of a duplicated chromosome. Before replication, one chromosome is composed of one DNA molecule. In replication, the DNA molecule is copied, and the two molecules are known as chromatids. During the later stages of cell division these chromatids separate longitudinally to become individual chromosomes
4. Microtubules are polymers of tubulin that attach to the chromosomes, which have already duplicated their DNA and aligned across the center of the cell. The spindle tubules then shorten and move toward the poles of the cell. As they move, they pull the one copy of each chromosome with them to opposite poles of the cell.

Question 4

Describe the 3 steps of prophase

Answer 4

(1) Chromosomes condense and
become visible.
(2) Centrosomes move apart toward opposite
poles and generate new microtubules.
(3) Nucleoli begin to disappear.

Question 5

Describe the 3 steps of prometaphase

Answer 5

(1) Nuclear envelope breaks
down.
(2) Microtubules from the centrosomes invade
the nucleus.
(3) Sister chromatids attach to microtubules from
opposite centrosomes.

Question 6

Describe metaphase

Answer 6

Chromosomes align on the
metaphase plate with sister chromatids facing
opposite poles.

Question 7

Describe the 2 steps of anaphase

Answer 7

(1) The connection between the
centromeres of the sister chromatids is severed.
(2) The now separated sister chromatids move
to opposite poles.

Question 8

describe the 3 steps of telophase

Answer 8

(1) Nuclear membranes and
nucleoli re-form.
(2) Spindle fibers disappear.
(3) Chromosomes uncoil and become a tangle
of chromatin.

Question 9

Describe cytokinesis

Answer 9

The cytoplasm divides, splitting
the elongated parent cell into two daughter
cells with identical nuclei.