3.24 b

3.24 b understand that division of a diploid cell by mitosis produces 2 cells which contain identical sets of chromosomes.

copying chromosomes is called DNA replication.
in this process each chromosome undergoes a copying process to form an identical copy of itself with the same genes and alleoles. these 2 copies are held together by a 'centomere'
while the chromosomes are in a copied pair held together by a centomere we refer to them as a 'pair of chromatids'
process of DNA replication takes place inside the nucleus while the nucleus is stil intact. this is the 'interphase' of the cell cycle.

3.24 a mitosis 1

3.24 a
understand that the division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes

mitosis-form of cell division which results in growth and the growth occurs by an increase in the number of cells#
begin with a cell with nucleus. no. of chromosomes in a nucleus is the diploid (2n)
for humans= 2n= 46
in mitosis the cell divides into 2 identical cells. each with a nucleus. in the nucleus cells are identical 'daughter cells'
1. same number of chromosomes
2. same set of chromosomes

3.16

objective 3.16. describe a DNA molecule as 2 strands coiled to form a double helix. the strands being linked by a series of paired bases adenine (a) with thymine (t) and cytosine (c) with guanine (g)

one chromosome is likely to contain thousands of genes
on the gene loci expand it and you will find a double helix. the helix appear to be parallel
zoom in and the 2 helix are known as the 'sugar phosphate backbone'
inbetween/centered between these you will find a group of molecules called bases
there are 4 different bases known. adenine, thymine, cytosine and guanine.
in a molecule the bases are holding together th 3 helixes. they are held together by pairing between a+t and c+g. these are known as base pairs.
they are always found in dna holding each sides together.
an example on oneside of a double helix an order could be a,c,t,g,a,a,c,c,a,g. this is 'order of the bases.
this order is called the gene. the gene is inside the nucleus.

gene- order of the bases (a,t,c,g) on one side of double helix and number of base.

this is the code for construction of protein in cytoplasm. this gives a characteristic

3.15

objective 3.15. understand that a gene is a section of a molecule of D.N.A.

*D.N.A. is in a double helix shape. a section of the molecule is called a gene

*genes have information which has a characteristic of an organism e.g. blood group or petal colour -in a flower-

genes are located in the nucleus. this information passed to cytoplasm

in cytoplasm genetic information is transformed into a protein which controls the production of the characteristic,

the information flows to the gene (in nucleus) to protein (in cytoplasm)

3.14

objective 3.14. recall that the nucleus of a cell contains chromosomes on which genes are located.

chromosomes= genetic information in a cell

typical cell has a nucleus, within the nucleus there are a number of chromosomes depending on the species.

a chromosome is composed of d.n.a.

which forms a shape known as a double helix.

sections of this molecule are called genes. one chromosome may have up to 1000 genes.

each gene carries the information for the construction of a protein. the protein gives the characteristic associated with the gene for instance blood group.

so a gene controls the production of a protien, which controls the production of the characteristic of the cell.

different organisms have different numbers of chromosomes here are some examples:

cat=38. chicken=78. chimpanzee=42. human=46. chromosomes per cell.

chromosomes operate in pairs called homologous pairs.

homologous nature based on length of chromosome

on any homologous pair they have same gene but different variation in same area. (2 versions of each gene for one characteristic) a characteristic is an 'alleles'

Objective 3.1

objective 3.1: describe the differences between sexual and asexual reproduction

sexual reproduction:

1. sexually reproducing organisms have 'sexes' and you can determine between male and female.

2. they produce celles called gametes. the male gamete is known as sperm and female gamete as the egg. in plants the male is the pollen grain and the female is the ovule.

3. meiosis produces gametes by cell division halving the chromosome in an adult cell.

4. total number of chromosomes per ordinary cell:46. per gamete (m+f) is 23.

5. . fertilisation is when the egg and sperm fuse.

6. there are broad variations in organism with sexual reprooduction.

asexual reproduction

1.no sexes exist

2. no gametes exist either

3. no miosis, just mitosis and binary fission which cause duplication in the cell not dividing chromosomes.

4. no cell fusion so no fertilisation,

5. there are small variations between organisms due to mutation, otherwise they are identical or clone.

question: why are there 46 chromosomes per ordinary cell? why not any other number?