dna def
the molecule that passes information from one generation to the next
what does dna stand for
deoxyribonucleic acid
gene def
small molecule of DNA that codes for a paticular protein
chromosome def
contains one double stranded dna molecule
genotype def
the alleles each cell has for a certain feature
phenotype def
the feature that results from the genotype
allele def
different forms of a gene
heterozygous def
genotypes with different allels of a gene
homozygous def
genotype with the same alleles of a gene
dominant def
this genotype will show its effect whether it is attached to a recessive allele or nto
recessive def
this genotype will only show its effect if there is no dominant allele present
diploid def
cells with homologous pairs of matching chromosomes
haploid def
cells with only half the normal diploid number of chromosomes
gamete def
male and female sex cells, formed by meiosis
F1 generation def
first generation of offspring
mitosis def
two cells are formed - these have the same number and type of chromosomes as the original cell.
meiosis
Four cells are formed - these only have half the number of chromosomes of the original cell. Forms gametes
mutation
Random events that occur in all organisms
homogolous pairs
Pairs of chromosomes that carry genes controlling the same features at the same positions on each chromosome. The members of each homologous pair are the same size and shape.
genome
The entire DNA of an organism
what copies the genetic code of DNA and then transfers the copy out of the nucleus to the cytoplasm
a different type of nucleic acid called ribonucleic acid, RNA
give three differences between DNA and RNA
dna contains a double helix, rna is a single strand
dna contains the sugar deoxyribose, rna contains ribose
rna contains the base Uracil instead of the base Thymine which is in dna
what does messenger RNA do
form a copy of the DNA code
what does transfer RNA do
carries amino acids to the ribosomes to make the protein
what are the two stages of protein synthesis
transcription and then translation
what is transcription
the DNA unwinds and unzips exposing the bases along the template strand. mRNA bases line up with the template strand according to the base pairing rules. the RNA nucleotides link up to form a mRNA molecule. when a section has been transcribed, the mRNA molecules leaves through pores in the nuclus and the DNA zips up again. because of the complementary base pairing the triplet code of the DNA is converted into a triplet code in the mRNA.
what is translation
the process of converting the code in the mRNA into a protein at the ribosomes. by this stage the code consists of sets of three bases in the mRNA (e.g. AUG, CCG) these triplets are codons and they code for a paticular amino acid. the mRNA molecule attaches to a ribosome, and the tRNA molecules (which have an anticodon of three base at one end complementary to a particular codon on the mRNA. at the other end is a site where a specific amino acid can attach. (one tRNA molecule for each type of amino acid). the tRNA molecule carries its amino acid to the ribosome, where its specific anticodon pairs up with the three bases of the corresponding mRNA codon. it starts at the start codon (always AUG) and stops at the stop codon.
what is dna coiled around
proteins called histones
which human cells don’t contain 46 chromosomes
red blood cells
gametes
what is a zygote
when two nuclei of gametes join to form a single diploid cell
what is the genome
the entire DNA of an organism
phases of mitosis
prophase metaphase anaphase telophase cytokenesis
1st stage of mitosis
prophase. the DNA replicates and the chromosomes form two exact copies called chromatids. they are joined at a centromere. the nuclear membrane breaks down
2nd stage of mitosis
metaphase. a structure called the spindle formed. the chromosomes line up in the middle centre of the spindle attached by their centromeres
3rd stage of mitosis
anaphase. the spindle fibres shorten and pull the chromatids to opposite ends of the cell. the chromatids separate to become the chromosomes of the two daughter cells
4th stage of mitosis
telophase. two new nuclei form at each pole of the cell. the cytoplasm starts to divide to produce two daughter cells. both daughter cells have a copy of each chromosome from the parent cell
examples of where mitosis takes place
the skin
gut lining
red blood cells in the spleen
cancer cells
types of blood
A
B
AB
O
what is distinctive about type AB
it is the universal recipient:
can recieve blood from any type but cannot donate to any type
what is distinctive about type O
universal doner.
can give blood to any type but can only receive blood from other type O’s
what happens during cytokinesis
the cell splits in two
where does mitosis occur
all over the body
where does meiosis occur
sex organs
number of divisions in mitosis
1
number of divisions in meiosis
2
what cells does mitosis create
all human cells except red blood cells and gametes
what cells does meiosis create
gametes
number of chromosomes in mitosis
46
number of chromosomes in meiosis
23
how many daughter cells does mitosis produce
2
how many daughter cells does meiosis produce
4
genetic makeup of daughter cell as compared to parent cells in mitosis
genetically identical
genetic makeup of daughter cell as comapared to parent cells in meiosis
genetic variation
genetic makeup of daughter cells as compared to other daughter cells in mitosis
genetically identical
genetic makeup of daughter cells as compared to other daughter cells in meiosis
genetic variation
function of mitosis
produce cells for growth and repair
function of meiosis
produce gametes for reproduction
where is a gene
on a chromosome
how many copies of each chromosome and each gene are ther
two
how many alleles are there of each gene
two
classify the types of gene
dominant and recessive
what is codominance
when there are genes with alleles that both contrubute to the phenotype, both alleles are expressed in the phenotype
what is our sex determined by
the presence or absence of a Y chromosome
what are the sex chromosomes
the X and Y chromosomes
what chromosomes are there in all the cells of females (apart from the 44 non-sex chromosomes)
2 X chromosomes
key principles of natural selection
there is variation within species
changinc onditions in the envrionment facours one paticular form of the species
the frequency of the favoured form increases
the frequency of the less well adapted form decreases under these conditions
