Genetic Diversity And Adaptation Flashcards
Describe what is a gene mutation
- change to the quantity of bases or base sequence in the DNA
- results in a change of amino acid sequence of the polypeptide. Altering tertiary structure and function
- can arise spontaneously during DNA replication
What are the two forms of gene mutation
Base substitution and base deletion
Describe base substitution
- nucleotide is replaced changing the codon
- genetic code degenerate so may result in same amino acid
- could alter amino acid, changing tertiary structure/ R group interactions
- results in a stop codon
Describe base deletion
- nucleotide removed
- alters reading frame
- all codons/amino acids altered from that point
Describe introns and exons in eukaryotes
- introns non-coding sequences of DNA
- are transcribed then spliced from pre-mRNA in the nucleoplasm
- mature mRNA left to be translated (only contain exons)
Describe how base substitution alters protein function
- alters single base, altering codon
- may encode for a different amino acid/r group
- affecting r group interactions altering polypeptide folding/tertiary structure
- polypeptide dysfunctional
Describe a silent mutation
- base substitution results in a codon that encodes for the same amino acid
- polypeptide is not affected
What are mutagenic agents
What alters the base sequence of dna
Name some mutagenic agents
- Ionic radiation (UV light, X rays)
- Asbestos
- Carcinogens (chemicals e.g. tobacco)
Describe a diploid cell
2n chromosomes. Homologous pairs of each type. Products of fertilisation.
Describe a haploid cell
n chromosomes. One of each type. Are gametes or ‘sex cells’.
What is ‘n’
Number of types of chromosomes an organism has
Describe the human life cycle
- both diploid parents produce haploid gametes through meiosis
- 2 haploid gametes fuse together to form a diploid zygote
- zygote grows by mitosis
What are alleles
Alternate versions of the same gene
- process a different nucleotide base sequence which may alter polypeptide the gene encodes for
What are homologous chromosomes
- 2 chromosomes that posses the same genes at the same gene loci
- may not posses the same alleles. Are located in diploid cells (2n)
- made up of one paternally derived male gamete and one maternally derived female gamete
Describe division one of meiosis
- homologous chromosomes pair up in synapsis
- ‘crossing over’ rearranges alleles on homologous chromosomes
-‘independent segregation’ of homologous chromosomes to produce 2 haploid cells
Describe division 2 of meiosis
- cells align single chromosomes in metaphase 2
- chromatids are separated
- produces 4 genetically non-identical haploid cells
5 differences between mitosis and meiosis
1 division / 2 divisions
Produces 2 daughter cells (2n dioloid) / produces 4 daughter cells (n haploid)
Genetically identical / genetically non-identical
Growth + repair / sexual reproduction
Only chromatids separates / 2nd division separates chromatids
Describe non disjunction
Failure to separate a pair of homologous chromosomes in meiosis 1. Gametes will either have an extra chromosome or one missing
Define genetic diversity
Total number of different alleles in a population
Define a population
A group of individuals of the same species that live in the same place and can interbreed to produce fertile offspring
Name 5 sources of genetic variation
- random mutation
- crossing over
- independent segregation
- random fertilisation
- random breeding
Describe natural selection
- reproductive successes of individuals affect allele frequency in populations
- random mutations of genes result in new alleles
- may result in a selective advantage over others
- individuals better adapted and more likely to survive and breed successfully when faced with particular selective pressures
- advantageous alleles passed onto the next generation
- over many generations these will increase in frequency within a population
- less advantageous allies decrease in frequency
Describe directional selection in bacteria
- antibiotics act as a selective pressure
- spontaneous, random gene mutation
- new protein produced
- increased resistance to an antibiotic
- resistant bacteria survive and reproduce by binary fission
- susceptible bacteria die
- frequency of resistant bacteria increases
- population ‘normal distribution’ curve shifts in direction of population becoming more resistant
