F mitotic cell division

Question 1

what are homologous chromosomes?

Answer 1

same length, same genes at the same loci, same position of centromeres, may have different alleles

Question 2

explain crossing over

Answer 2

CO between non sister chromatids on homologous chromosomes results in chiasma formation during prophase I of meiosis -> involving the breakage of a corresponding DNA segment from each non-sister chromatid at the chiasma, followed by exchange of corresponding section of DNA between non-sister chromatids and rejoining of DNA segment to the other chromatid -> separating alleles of linked genes and creating new allelic combinations in the chromatid

Question 3

role of centrioles

Answer 3

• during cell division, a pair of centrioles replicates during interphase and each pair will migrate to opposite POLES of the cell during prophase
• they are are involved in organising the microtubules into spindle fibres which result in the alignment of chromosomes along the metaphase plate during metaphase

Question 4

anaphase

Answer 4

1. centromere of each chromosome separates and two sister chromatids separate, becoming two daughter chromosomes
2. daughter chromosomes migrate to opposite poles of the cell with centromere leading the way as kinetochore microtubules shorten
3. non-kinetochore microtubules lengthen, leading to cell elongation

Question 5

role of centromeres

Answer 5

• hold sister chromatids together
• site of attachment by spindle fibres via kinetochore proteins
• spindle fibres can attach to the centromeres via kinetochore to align centromeres of chromosomes along metaphase plate during metaphase

Question 6

why does each chromosome appear as a double structure?

Answer 6

1. each DNA molecule undergoes semi conservative replication during synthesis phase of interphase
2. thus giving rise to two DNA molecules which CONDENSE to form TWO identical sister chromatids held together at the centromere

Question 7

haploid vs diploid

Answer 7

1. haploid cells contain one set of chromosomes while diploid cells contain TWO sets of chromosomes (one from maternal + one from paternal)
2. gametes are haploid cells whereas somatic cells are diploid
3. haploid cells have half the number of chromosomes to diploid cells

Question 8

what happens to the nuclear envelope during mitosis?

Answer 8

1. During prophase, the nuclear envelope FRAGMENTS allowing microtubules from centrosomes to access and attach to kinetochore at centromere of chromosomes
2. During telophase, the nuclear envelope reforms from the fragments of the endomembrane system around the complete set of chromosomes at both poles of the cell to form two genetically identical nuclei

Question 9

meiosis 1!

Answer 9

• P1, chromatin fibre becomes tightly coiled, condensing to from chromosomes which appear as two identical sister chromatids joined at their centromeres + HC pair to form bivalents and CO between non sister chromatids of HC may occur resulting in chiasma formation
• M1, bivalents align themselves at the metaphase plate, with one chromosome in each pair facing each pole + pairs of HC are randomly orientated along the metaphase plate
• A1, HC separate and migrate to opposite POLES of the cell with the centromere leading the way
• T1, chromosomes become less condensed to from chromatin