mitosis, meiosis cell cycle

Question 1

mitosis
what are the four stages in mitosis:

Answer 1

-prophase
-metaphsae
-anaphase
-telophase

Question 2

what is interphase and when does it occur

Answer 2

interphase is the process in which the DNA is replicated and the cell increases its number of organelles. interphase occurs inbetween cell divisions.
before replication, each chromosome exists as a single chromatid however after replication, two sister chromatids are joined together at the centromere forming a chromosome.

Question 3

definition of homologous pair of chromosomes

Answer 3

matching pair of chromosomes, one donated from each parent. there are two copies of every chromosome in every cell, one from our mother and one from our father.

Question 4

the overall process of mitosis involves the separation of chromosomes to opposite parts of the cell so that the cells can….

Answer 4

divide,
the overall process of mitosis involves the separation of chromosomes to opposite parts of the cell so that the cells can divide.

Question 5

what is the first stage of mitosis:

Answer 5

prophase

Question 6

describe the main features of prophase:

Answer 6

-supercoiling of DNA into chromosomes
-the disintegration of the nuclear envelope
-centrioles forming spindle fibres from two opposite ends of the cell.

Question 7

prophase each stage explained in detail

Answer 7

firstly in prophase, the DNA supercoils into chromosomes. before prophase the dna is long and tangled threads however during prophase, the dna supercoils into a shortened and more condensed structure.
-then, the nuclear envelope begins to break down and disintegerate allowing the genetic material of the cell to move more freely through the cell
-centrioles, cylindrical hollow protein bundles that divide moving to opposite ends of the cell from where they produce spindle fibres that run across the cell from one pole to the oppsite pole on the other end of the cell. spindle fibres form the centrioles and are long fibres of proteins.
plant cells do not have centrioles, there spindle fibres form from their cytoplasm.

Question 8

metaphase:

Answer 8

second stage of mitsosis
chromosomes line up at equator of the cell
the chromosomes become attached to the spindle fibres at their centromere. the chromosomes are then pulled along the spindle fibres to the equator of the cell.
this prepares chromatids in each chromosome ready for separation in anaphase.

Question 9

anaphase:
(centromeres split and chromatids move to separate poles of the cell)

Answer 9

the chromatids on each chromsome are separated and pulled to opposite poles of the cell. chromosomes split while still attached to the spindle fibres, they move to the poles with the help of motor proteins. the process requires ATP so mitochondria gather around the spindle fibres to provide it.

Question 10

telophase:
(nucleus starts to re appear around each set of chromosomes)

Answer 10

-nucleus starts to reappear around each set of chromosomes.
and the chromosomes become invisible under the microscope because they disperse and become less condensed.
once the separated chromatids begin to reach the poles. the spinlde fibres begin to disintegrate.
the chromosomes lengthen and uncoil so cannot be seen under the microscope.
the nuclear envelope begins to reform around the lengthening chromosomes.
at the end of telophase, the cell ends up with 2 distinct nuclei.
the cell is now ready for the cytoplasm to split in cytokinesis to make two new cells

Question 11

cytokinesis: after telophase cell is split to create two new daughter cells with identical nuclei

Answer 11

the cell is split to create two new daughter cells with identical nuclei.
in animal cells, the plasma membrane folds inwards until the two dents meet to separate the two daughter cells.
in plant cells, cellulose builds up at the equator this is called the end plate. plasma membrane forms in the middle of the end plate resulting in two fully separated plant cells.

Question 12

cytokinesis in plants

Answer 12

in plants, cellulose builds up at the equator of the cell, this is known as the end plate. plasma membrane forms in the middle of the end plate resulting in two fully separated plant cells.

Question 13

cytokinesis in animal cells

Answer 13

in animals, the plasma membrane folds inwards until the two dents meet to separate the two daughter cells.

Question 14

explain why a cell’s DNA must replicate itself before mitotic cell division.

Answer 14

the DNA must be replicated before mitosis so that each of the 2 identical daughter cells has a complete copy of the genetic material from the parent cell.

Question 15

diploid cells

Answer 15

2n
two sets of chromosomes
(both mitosis and meiosis start from a diploid cell)

Question 16

halpoid cell

Answer 16

n
contains one set of chromosomes
one set of chromosomes as in 23 chromosomes

Question 17

why do gametes need to have half of the number of chromosomes as the rest of the cells in the body

Answer 17

to maintain a constant number of of chromosomes in adults of a species
during fertilisation gametes (haploid) fuse together to form a zygote which is a diploid

Question 18

where does meosis occur

Answer 18

reproductive organs
ovaries and testes

Question 19

human cells have a diploid number of

Answer 19

46 chromosomes

Question 20

human cells have a halpoid number of

Answer 20

23 chromosomes

Question 21

in a diploid cell where does each of the two sets of chromsomes come from

Answer 21

one set of chromsomes come from the father (paternal chromsomes)
one set of chromosomes comes from the mother ( maternal chromosomes)

Question 22

homologous pair

Answer 22

a pair of chromosomes ( one maternal and one paternal) that have their genes in the same locations athough they may have different alleles for the same genes.

Question 23

meosis overview

Answer 23

meiosis is the process of creating halpoid cells ( gametes) from diploid cells through two divisions meiosis 1 and meiosis 2. however before meiosis occurs every chromosome is replicated during the s phase of interphase

Question 24

what are the four stages of meiosis 1

Answer 24

prophase 1
metaphase 1
anaphsae 1
telophase 1

Question 25

meiosis 1 overview

Answer 25

in meiosis 1, homologous pairs are separated with one chromsome from each pair going into one of the two daughter cells

Question 26

what could happen before the second meiotic division (metaphase 2) begins

Answer 26

cell may enter short interphase before starting the second meiotic division

Question 27

what happens in meiosis 2

Answer 27

the chromatids from each chromsome is separated

Question 28

how many cells produced at the end of meiosis

Answer 28

4 haploid , genetically unique cells ( gametes) will be produced

Question 29

prophase 1 of meiosis

Answer 29

first stage of meiosis
DNA supercoils, chromatin condenses into chromsomes. condensed and shortened structure
nuclear envelope disintegrates allowing genetic material to move more freely through cell
spindle fibres form from centrioles dividing into two and moving to opposite poles of the cells.
homologous pairs of chromosomes find each other and pair up forming a tetrad ( synapse)
crossing over occurs- dna is exchanged between chromatids on homologous chromosomes.
they wrap around each other causing sections of chromatids to break off and swap over the non sister chromatids. they join at chiasmata
because chromsomes are homologous the crossed over chromosomes contain the same genes as before but genetic variation is introduced by shuffling of all the alleles on different homologous chromosomes.- recombination as new allele combinations are formed

Question 30

metaphase 1 meiosis

Answer 30

chromosomes line up at equator
homologous pairs line up at equator
firstly chromosomes attach to spindle fibres at their centromeres
Each chromosome lies next to its homologous partner at the equator* Within the homologous pair, the chromosomes are randomly organised on either side of theequator— this is independent assortment* The way these pairs line up determines how they will segregate when they’re pulledapart during anaphase
one chromosome in the pair will be on each side- which on of them is random