DNA And Genetic Diversity 9 Flashcards
Protein synthesis - TRANSCRIPTION
Occurs in nucleus
DNA uncoils by DNA helicase
Individual RNA nucleotides line up alongside DNA nucleotide bases on template strand (U-A C-G)
RNA nucleotides joined using RNA polymerase to form messenger RNA
mRNA leaves nucleus through nuclear pore
Protein synthesis - SPLICING
splicing of pre mRNA involves the removal of introns and the joining together of exons to form mRNA - post transcriptional processing
Protein synthesis - TRANSLATION
TRNA molecule with complementary anticodon to first codon on mRNA moves to ribosome bringing its amino acid
2 tRNA molecules bind at same time to mRNA
Amino acid from first tRNA molecule attached to amino acid on 2nd tRNA molecule by a peptide bind
tRNA molecule moves away from ribosome leaving amino acid and goes to college another from amino acid pool in cytoplasm
Process continues until specific polypeptide has been produced
Causes of gene mutations
Occur spontaneously during DNA replication involving a change in sequence of nucleotide bases Mutagenic agents (X-ray, uv light) increase rate
Gene mutation - deletion
Removal of one or more bases
Results in a frame shift which alters the triplets from point of deletion
Sequence of amino acids is altered from point of deletion
Protein formed is non functional
Gene mutation - substitution
Replacement of one or more bases by one or more different bases
Can result in a new triplet coding for a different amino acid with a non functional protein, or a functional protein
Or the same amino acid may be coded for due to degeneracy
Process of meiosis
During late interphase, DNA replicates, ATP builds up, protein synthesis and replication of cell organelles occur
- First meiotic division separates members of each homologous pair
- Second meiotic division separates chromatids of each chromosome
Meiosis and genetic diversity - independent segregation
Pairing and subsequent separation of a pair during 1st division is completely independent from the separation of another pair
Chromosomes randomly associate within a gamete
Meiosis and genetic diversity - crossing over
Occurs during 1st meiotic division
2 members of each homologous pair form a bivalent
Chromatids of homologous chromosomes intertwine
Chromatids are exchanged resulting in exchange of alleles which produce new combinations of alleles, RECOMBINANTS
Chromosome mutations
Arise spontaneously by chromosome non-disjunction during meiosis
Occurs when a homologous lair do not separate during 1st meiotic division
Results in gametes with one extra chromosome than normal and gametes with one less chromosome than normal
Principles of natural selection in the evolution of organisms
Variation already present due to random mutations which result in new alleles which could benefit an organism leading to increased reproductive success
Change in environment results in those with advantageous allele being selected as they are better adapted, they survive and reproduce passing on beneficial allele - differential reproductive success
Frequency of allele increases over many generations
Directional selection
Occurs when there is a change in environment which selects those organisms with alleles for a phenotype towards one extreme of a range
Eg antibiotic resistance
Stabilising selection
Selection acts against the extreme phenotypes in a population and occurs when environment remains stable and selection occurs towards organisms with a phenotype closest to mean
Eg birth weight in humans
