Sub lesson - Chromosomal variation

Question 1

Inversion explanation:

Answer 1

• A section of chromosome may break odd, turn through 180 degrees and then join again.

Question 2

Deletion explanation:

Answer 2

A part of a chromosome, containing genes and regulatory sequences, is lost.

Question 3

Translocation explanation:

Answer 3

A piece of one chromosome breaks off and then becomes attached to another chromosome

Question 4

Non-disjunction

Answer 4

One pair of chromosomes or chromatids fail to separate

Question 5

Phases of Mitosis:

Answer 5

Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 6

Duplication

Answer 6

A piece of a chromosome may be duplicated.

Question 7

What occurs in the interphase?

Answer 7

Chromosomes invisible and DNA replicates

Question 8

What occurs in prophase?

Answer 8

Chromosomes appear and nucleus disappears

Question 9

What occurs in metaphase?

Answer 9

Chromosomes at equator and spindle forms

Question 10

What occurs at anaphase?

Answer 10

Chromatids pulled to poles

Question 11

What occurs in telophase?

Answer 11

Chromatids at poles and nucleus reforms

Question 12

What occurs in cytokinesis?

Answer 12

Cytoplasmic division

Question 13

What is the role of meiosis for variation?

Answer 13

Produces gametes which fuse in sexual reproduction to form offspring.
Produces haploid cells.
Increases variation.

Question 14

Homologous chromosomes in diploid cells?

Answer 14

Contain paternal chromosome and maternal chromosome.
- Similar length and contain same genes at the same loci, they contain different alleles.

Question 15

Structure of homologous chromosomes when they replicate?

Answer 15

• Sister-chromatids
• Linked to homologous chromosomes by centromere.

Question 16

Independent Segregation Assortment

Answer 16

• Happens in metaphase I, when the chromosomes line up on the equator.
• In humans, this means 23 homologous pairs of chromosomes lying side by side.
• Arrange themselves randomly.
• One of each pair will pass to each daughter cell.
• Each chromatid goes in the direction of the pole they are facing (random).

Question 17

Prophase I?

Answer 17

• Chromosomes shorten and thicken (condense)
• Pairs of homologous chromosomes line up closely together.
• One centriole from each pair moves towards the opposite poles of the cell
• Nuclear membrane break down.
• Unique to meiosis I, chromosomes cross over and exchange genetic material.

Question 18

Crossing over:

Answer 18

During crossing over, a chiasma randomly forms and creates a point of contact between chromatids. This allows for the exchange of genetic material.
The chiasma forms between non-sister chromatids as there are not identical and therefore the exchange of genetic material can lead to new combinations of alleles that were not seen in the parents.

Question 19

Why is does crossing over increase variation?

Answer 19

The formation of the chiasma is completely random event and can form at any point along the length between the two non-sister chromatids.