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
