3.4 Genetic Information, Variation and Relationships between Organisms Flashcards
describe the difference between DNA in prokaryotes and eukaryotes
in Pk, it is short, circular, not wound around histones and not found in the nucleus. in Eu it is long, linear, wound around histones and in the nucleus.
define a gene
a section of DNA which codes for the amino acid sequence of a polypeptide and functional RNA
define locus
the particular points on a DNA where the genes are found
how many pairs of chromosomes are present in the human body
23 pairs, 46 individuals
describe 3 features of the genetic code
universal - the same triplets code for the same amino acids in all living organisms
degenerate - the same amino acid is coded for by more than one triplet
non-overlapping - each base is only read once in its triplet, each is only part of one triplet
define genome and proteome
the genome is the complete set of genes in a cell and the proteome is the full range of proteins that a cell can produce
define exons and introns
exons code for amino acids and introns don’t code for anything, they are remove during protein synthesis to prevent disruption to the order of amino acids
define non-coding multiple repeats
areas in the genome between genes which repeat over and over but do not code for any amino acids, used in DNA fingerprinting
where does transcription occur
in the nucleus in eukaryotes and in the cytoplasm in prokaryotes
why does prokaryotic mRNA not require splicing
it contains no introns so there is no threat to the primary structure
describe splicing
when the base sequences corresponding to the introns are removed and functional exons are joined together to make mRNA, which happens in the nucleus
describe the role of a ribosome in the production of a polypeptide
the ribosomes has two codons which allow the tRNA anticodons to bind
also catalyses the peptide bonds between amino acids
define diploid
2 of each chromosomes in pairs
where are gametes in plants and animals
in the ovule + pollen in plants
the sperm + egg in animals
where are gametes made in animals and plants
the ovary + anther in plants
the testes + ovary in animals
are gametes haploid or diploid
haploid (n), they have one copy of a homologous pair. the haploid number for humans is 23.
what are the products of meiosis
4 genetically different daughter cells which are haploid
what happens in meiosis 1 and 2
in 1, homologous chromosomes pair up and the chromatids wrap around each other (crossing over)
in 2, the chromatids move apart
describe crossing over
when homologous pairs line up next to each other and their chromatids wind around each other
define independent segregation/assortment
the daughter cells have different combinations of chromosomes because the pairs line up in a random order
define alleles
different forms of the same gene
what does an increased genetic diversity mean positively
that the organisms are more blé to adapt and cope with disease
two factors that increase genetic diversity
mutations and migration (causes a gene flow as alleles from other populations are introduced)
define a genetic bottleneck
when there is a reduction in population so the gene pool decreases which in turn decreases genetic diversity as there are less alleles
define the founder effect
when a small number of individuals start a new population and there is a small gene pool as a result due to a small number of alleles
define behavioural, anatomical and physiological adaptations
behavioural - changes in behaviour to increase chances of survival
anatomical - changes in the structure of the organism
physiological - biochemical processes inside
what is recombination
when the portions of chromatids that broke off during crossing over recombine
which type of mutation doesn’t always cause a change and which does
not all substitutions produce different amino acids because the code is degenerate
all deletions cause a change because they cause a shift in the triplets read
define mutagenic agents and their way of working
mutagenic agents increase the chance of mutations, they can act as a base or alter the bases and change the DNA structure
define chromosome non-dysjunction
when chromosomes don’t separate properly during independent assortment
define directional and stabilising selection
directional is when an individual in the population has alleles for an extreme characteristic, the selection favours those outside of the mean. in response to an environnement change.
stabilising is when alleles for characteristics are in the middle range and so are more likely to survive and reproduce, the mean is favoured and the environnement isn’t changing
define normal distribution and standard deviation
when values are spread about the mean symmetrically and how much a set of data points range around the mean
define phylogeny and taxonomy
the study of evolutionary relationships between organisms and their ancestors, and taxonomy is the putting of those organisms into groups within a hierarchy
define genetic diversity
the total number of different alleles in a population
how does courtship benefit species
means they can recognise members of their own species
can identify a mate capable of breeding/sexually mature
define artificial classification
classifying species based on the characteristics useful at the time e.g wings, not very accurate as doesn’t prove evolutionary connections
which factors affect the representation of a sample
sampling bias and chance
how can samples be made more representative
increase the sample size so chance is less likely to influence the result
analysis of data to understand how much influence chance has had
define hierarchy
smaller groups within larger groups with no overlap at each levels
how do you calculate standard deviation
calculate the mean and for each value subtract the mean and square the answer.
add all these numbers together and divide by the total number of values.
square root this number and round to 2 significant figures.
explain the steps of transcription
DNA polymerase breaks the hydrogen bonds between DNA strands causing them to separate
free complementary nucleotides pair up to the exposed nucleotide bases on the template strand via complementary base pairing rules
RNA polymerase joins the nucleotides together to form a pre-mRNA molecule
when the RNA polymerase reaches the stop codon it detaches and completes the production of pre-mRNA
explain the steps of translation
a ribosomes attaches to the start codon at the end of an mRNA molecule
the tRNA with the complementary anti codon sequence pairs with the next codon on the mRNA, this t carries a specific amino acid
a t molecule that is complementary then pairs to the next mRNA codon, carrying another amino acid
the ribosome moves along the mRNA, bringing together two t molecules
the 2 amino acids on the tRNA are joined by a peptide bond and ATP which is hydrolysed to provide the energy
the ribosome moves along to the next codon, linking the amino acids on the second and third tRNA molecules.
as this happens, the first tRNA is released from its amino acid and is free to collect another amino acid from the pool
the process continues until a polypeptide chain is built up and the ribosome reaches the stop codon where all 3 molecules involved separate.
