cell division

Question 1

Describe the appearance and
behaviour of chromosomes
during mitosis

Answer 1

interphase
cell grows and dna replicates prophase
1.Chromosomes condense to become visible
2.Chromosomes appear as two identical sister chromatids joined at the centromere
metaphase
3.Chromosomes line up on the equator of the cell
4.spindle fibres attach to chromosomes at the centromere
anaphase
5.spindle fibres shorten to split the centromere and Sister chromatids are pulled to opposite poles of the cell making a V shape
telophase
6.chromosomes uncoil and become thinner

Question 2

Describe the process of independent segregation and explain how it increases genetic diversity

Answer 2

The Homologous chromosomes randomly pair up along the equator of the cell.
Independent segregation leads to maternal and paternal chromosomes being re-shuffled in any combination.

Question 3

Describe the process of crossing over and explain how it increases genetic diversity

Answer 3

The homologous chromosomes form a bivalent
Chiasmata form between non-sister chromatids of homologous chromosomes
Equal lengths of non-sister chromatids / alleles are exchanged.
Producing new combinations of alleles

Question 4

Contrast meiosis and mitosis (learn at least 3)

Answer 4

1.  One division in mitosis whereas two divisions in meiosis;
2.  (Daughter) cells genetically identical in mitosis whereas daughter cells genetically different in meiosis;
3.  Two cells produced in mitosis whereas (usually) four cells produced in meiosis;
4.  Diploid to diploid/haploid to haploid in mitosis whereas diploid to haploid in meiosis;
5.  separation of sister chromatids in mitosis, whereas Separation of homologous chromosomes only in meiosis (in first division. ;
6.  Crossing over only in meiosis whereas not in mitosis;
7.  Independent segregation only in meiosis whereas not in mitosis

Question 5

What is the importance of mitosis for organisms?

Answer 5

Mitosis:
Growth and repair of tissues
Asexual reproduction- 2n to 2n or n to n
(note: only some organisms can do this)

Question 6

What is the importance of meiosis for organisms?

Answer 6

Meiosis:
Create genetically different gametes, diploid to haploid cells, to be used in
sexual reproduction

Question 7

Describe binary fission in bacteria

Answer 7

1.Replication of circular DNA;
2.Replication of plasmids;
3.Division of cytoplasm (to produce daughter cells);

Question 8

chromosome mutations

Answer 8

mutations in the number of chromosomes car arise spontaneously by chromosome non-disjunction during meiosis

Question 9

what is non-disjunction

Answer 9

when chromosomes or chromatids do not split equally during anaphase

Question 10

stages of interphase

Answer 10

G1 - cell increases in size + new biomass made
S - DNA replicates by semi - conservative replication
G2 - cell prepares for division

Question 11

homologous chromosomes

Answer 11

have the same gene in the same loci but may have different alleles
one chromosome maternal and one paternal

Question 12

mitotic index =

Answer 12

mitotic index = number of cells in mitosis / total number of cells x 100