Cell Divsion & Replication

Question 1

What are homologous chromosomes?

Answer 1

• Homologous chromosomes pairs of matching chromosomes - carry same genes.

Question 2

what are diploid cells?

Answer 2

• diploid (2n): Cells that carry homologous chromosomes (where n= number of types of chromosomes) and contain two sets of each chromosome.
  • Each diploid cell has one set of chromosomes from the father and one set from the mother.

Question 3

what are haploid cells?

Answer 3

haploid (n): contain only one type of each chromosome. example sex cells

Question 4

what is mitosis?

Answer 4

• Takes place during growth of an organism and in asexual reproduction.
• Basis of growth, repair, budding and vegetative propagation in multicellular organisms.
• Yields daughter cells that have the same number and types of chromosomes as the parent cell.

Question 5

what does crossing over mean?

Answer 5

Crossing-over occurs during Prophase I which results in a recombination of genes, increasing variation.

Question 6

what is a karyotype?

Answer 6

• A karyotype is a pictorial display of the total complement of a species’ chromosomes

Question 7

what are the 5 stages of Mitosis?

Answer 7

Prophase, Metaphase, Anaphase, Telophase, Cytokinesis

Question 8

What are the steps in prophase?

Answer 8

• DNA threads or chromatin condense to form distinct , thickened chromosomes.
• Each chromosome consists of two strands (chromatids).
• Series of protein threads create a spindle that extends the length of the cell.
• The two ends of the spindle are called poles, which the middle region is the equator.
• The nuclear membrane breaks down.

Question 9

What are the steps in metaphase?

Answer 9

• Chromosomes migrate to the centre (equator) of the cell and attach their centromere to an individual spindle fibre.

Question 10

What are the steps in anaphase?

Answer 10

• The chromatids of each chromosome separate so that they are no longer attached by their centromeres.
• Once separated, the chromatids are called sister chromosomes.
• Each of the identical sister chromosomes are pulled to the opposite poles of the cell.

Question 11

What are the steps in telophase?

Answer 11

• The chromosomes congregate tightly together at each pole.
• The spindle breaks down and a new nuclear membrane is formed.
• Chromosomes uncoil to revert to chromatin threads.

Question 12

What are the steps in Cytokinesis?

Answer 12

• During the events of telophase, division of the cytoplasm between the new groups of chromosomes commences.
• The cell membrane constricts across the equator of the cell to form two new cells.

Question 13

what are the 8 stages of Mitosis?

Answer 13

Prophase I, Metaphase I, Anaphase I, Telophase I & Cytokinesis I, Prophase II, Metaphase II, Anaphase II and Telophase II & Cytokinesis II.

Question 14

What are the steps in Prophase I ?

Answer 14

• The nucleolus disappears and the nuclear membrane breaks down.
  
  • In animal cells centrioles migrate to opposite poles and spindle fibres form.
  • The bivalent chromosomes (two chromatids joined at the centromere) become visible and align themselves in pairs as homologous chromosomes (consisting of 4 sister chromatids, called a tetrad).
  • diploid, chromatin → chromones → (synapses) ninds to homologous chromosomes (tetrad) → exchange of gene combinations (crossing over) → nuclear membrane disappear, spindle fibres.
• The chromatids may become entwined and genetic information can be exchanged, called crossing-over
• Chromosomes from the organism’s father can exchange genes with chromosomes from the organism’s mother, resulting in a recombination of genes.
• Gametes have unique combinations of genes that are different from the original parental combinations, increasing variation.

Question 15

What are the steps in Metaphase I ?

Answer 15

• homologous chromosomes arrange themselves along the equator (middle) of the cell.
  • The kinetochore proteins (linking the two chromatids together at the centromere) attach to the spindle fibres.
  • Each homologous chromosome (containing two chromatids) randomly aligns itself towards an opposite pole.

Question 16

What are the steps in Anaphase I ?

Answer 16

• Contraction of the spindle fibres separates the homologous chromosomes, pulling them towards opposite poles of the cell.
  • Each end of the cell contains one of each type of bivalent chromosome, each consisting of two chromatids.

Question 17

What are the steps in Telophase I & Cytokinesis I?

Answer 17

• The cell divides across the equator of the spindle and spindle fibres break down.
  • A nuclear membrane is formed around the chromosomes at this stage.
  • The cell divides to form two complete cells and there is a short break. Then meiosis II begins.

Question 18

What are the steps of Prophase II?

Answer 18

• A new spindle is formed perpendicular to that of the original cell.

Question 19

What are the steps of Metaphase II?

Answer 19

• Individual chromosomes (each consisting of two chromatids) migrate to the equator of the spindle and attach at the kinetochore proteins that surround the centromeres.

Question 20

What are the steps of Anaphase II?

Answer 20

• Contraction of spindle fibres separate the kinetochore proteins.
• chromatids separate at the centromere.
• Each sister chromatid is pulled to the opposite poles of the cell.

Question 21

What are the steps of Telophase II & Cytokinesis II?

Answer 21

• Spindle fibres disappear and the cell divides across the equator.
  
  • A new nuclear membrane is formed around the chromosomes.