Genetic Information And Variation Flashcards
Chromosome structure
• Chromosomes are wrapped around histone proteins forming a
nucleosome
• Replicated chromosomes are formed of two sister chromatids
attached at the centre by a centromere
How DNA codes for proteins
• DNA has a specific sequence of bases where a triplet of three bases
codes for a specific amino acid.
• The order of the triplets codes for a specific sequence of animo acids
of a polypeptide/primary structure
Transcription
• DNA strands are separated by breaking hydrogen bonds
• Transcription is the synthesis of an mRNA copy of a gene;
• The copy is complementary to the DNA template/antisense strand;
• RNA polymerase attaches to DNA
• RNA nucleotides matched to exposed complementary bases;
• Adjacent nucleotides are joined by a phosphodiester bond together to
make a strand of mRNA;
• mRNA molecule separates from DNA
• In eukaryotes only: mRNA is spliced to remove introns
• Mature mRNA leaves the nucleus through nuclear pores
Splicing
• Eukaryotic DNA forms pre-mRNA when transcribed
• Pre-mRNA contains introns (non-coding DNA) this must be spliced out
• Pre-mRNA is spliced and introns are removed
• Mature mRNA is transcribed
Translation
• mRNA attaches to the ribosome at a start codon
• tRNA with a complementary anticodon attaches to the mRNA codon
• This tRNA is attached to a specific amino acid
• Amino Acids are joined by a peptide bond
• Using energy from ATP
• tRNA is released from the ribosome and a new on enters
• Ribosome moves along the mRNA to synthesise a complete
polypeptide
Mutations- change in DNA sequence
• Can be spontenous or induced(radiation, chemicals)
• Substitution changes a single base
• Insertion or deletion cause a frameshift
• Harmful mutations e.g change in the active site shape of enzyme
• Unharmful due to the degenerate nature of the genetic code.
Meiosis
• DNA is replicated in interphase before meiosis begins
• In the first division there is a separation of homologous
chromosomes, halving the chromosome number
• In the second division there is separation of the sister chromatids
• This produced four genetically different daughter cells
Genetic variation
of new alleles
• In the first division of meiosis there is crossing over where homologous chromosomes swap DNA producing new combinations of alleles
• In meiosis homologous chromosomes may be independently segregated, separating into different daughter cells producing new combinations of alleles
• During fertilisation there is random fusion of gametes this produces new combinations of alleles
Non disjunction
• During meiosis, homologous chromosomes fail to separate (meiosis 1)
or sister chromatids fail to separate, meiosis 2,.
• This results in gametes with too many or too few chromosomes.
• It can lead to significant implications for the offspring such as genetic
disorders.
Describe how taxonomy techniques are used to classify organisms
• Smaller groups within larger groups that are non-overlapping
• Comparisons of DNA base sequences to identify similarities and
differences
• Comparisons of mRNA base sequences to identify similarities and
differences
• Comparisons of amino acid sequences to identify similarities and
differences
• Identify points of divergence/common ancestor
• Use courtship behavior to identify species
• Define species as organisms that can breed to produce fertile offspring
Natural selection
• Mutation leads to variation in a species by developing a new allele
• The new allele provides an advantage e.g. give an example from the
question
• Organisms with the new allele can survive and reproduce
• Advantageous allele is passed on to offspring
• The advantageous allele increases in frequency in the population
Gene pool and genetic drift
• Gene Pool – all of the alleles in a certain population usually measured
as a frequency
• Genetic drift – changes in the frequency of alleles caused by random
chance
Why is genetic drift important in small populations?
• Changes in population frequency is more pronounced in small
populations because of genetic bottlenecks, founder effect, loss off
and fixation of alleles.
Directional selection
• If e.g an environment changes.
• The ‘selection pressure’ will be exerted
on a particular portion of the population
Stabilising selection
When a both ends of the
population are selected against
Disruptive selection
Selection pressure is on
the MEAN of the population.
What is phylogeny?
Evolutionary history of relationships between groups of organisms
Classification shows ancestry of groups and points of divergence from a common ancestor
