Genetic Diversity and Natural Selection Flashcards
what is a mutation
random change in a DNA base sequence
explain how a mutation may lead to a non functioning protein
- mutation changes the primary structure
- this may change the position of the hydrogen, ionic and disulphide bonds
- this changes the tertiary structure of the protein
what are the 3 different types of mutation
- substitution
- deletion
- addition
what is a subsitition mutation
changing only one base in the DNA triplet
expan why not all base substitutions cause a change in the primary structure
- the genetic code is degenerate
- a substitution may code for the original amino acid to be coded
explain how a substitution mutation could effect the ploypeptide produced
- the substitution may result in the formation of a stop codon. This could make the polypeptide much shorter in length
what are addition and deletion mutations
when DNA bases are added or deleted within the sequence
addition and deletion mutation leads to a ……
frame shift
what is a frame shift
the alteration of the base triplets and codons downstream from the mutation
explain how deletetion and addition mutations affect the polypeptide produced
- frame shift
- chages the primary structure
- changes the tertiary structure
what are mutagenic agents
increase the rate of gene mutations
wat are 3 mutagenic agents and give examples
- high energy radiation - x rays, uv light
- carcinogens - nitrous acid converting cytosine to uracil
- biological agents - viruses
what does meiosis produce
daughter cells that are genetically different from each other
- how much DNA replications take place during meiosis
- how much divisions take place during meiosis
- 1
- 2
what are the 2 divisions in meisis referred to as
meiosis 1 and meiosis 2
meosis produces ……… cells
4 haploid
give two differences between mitosis and meiosis
- meiosis produces 4 geneticaly different cells, mitosis produces 2 genetically identical cells
- meiosis produces haploid cells, mitosis produces diploid
- meiosis involves 2 divisions, mitosis involves 1
explain the process of meiosis one
- homologus chromosomes pair
- crossing over occurs at chiasmata
- cell divides into two. Homologus chromosomes seperate randomly (independant segregation)
what are homologous chromosomes
pairs of chromosomes with the same genes at same loci
what happens prior to meiosis
DNA replicates during interphase by semi conservative replication
what are the 2 processes during meiosis one that lead to genetic variation
- independant segregation
- crossing over
explain what happens during meiosis 2
- sister chromatids are pulled apart and move to opposite poles of the cell
- each cell divides, producing 4 haploid cells
diagram of meosis
describe how the process of meiosis results in haploid cells
(4 marks)
- DNA replication
- Two divisions
- seperation of homologous chromosomes
- seperation of sister chromatids
- produces 4 halpoid cells
give one way that genetic variation is increases which doesnt take place in meiosis
random gametes fuse during fertilisation
explain the process of independant segregation
- during meiosis 1
- random assortment of homologous chromosomes
- each pair of homologous chromosomes is seperated and the maternal and paternal move to opposite poles
explain the process of crossing over
- homologous pairs of chromosomes associate
- chiasmata forms
- equal legths of non sister chromatids being exchanged
- new combinatio of alleles
how do mutations in chromosomes occur
non disjunction during meiosis
how does non disjunction occur
when the homologous chromosomes or chromatids do not split equally
give 3 sources of genetic diversity and variation
- random mutation
- meiosis
- random fusion of gametes
explain the process of natural selection
- random mutations can produce new alleles of a gene
- this creates variation in the phenotype
- there is selection pressure present in the environment
- oragnisms with phenotypes providing advantages are more likely to survive and reproduce
- these organisms pass on their genes
- the advantage allele frequency increases over many generations
- the frequency of disadvantage alleles decreases
what are the two types of selection
- stablising
- directional
explain the process of stablising selection
- occurs where the environment is stable
- selected pressure at both ends of the distribution
- individuals with extreme phenotype do not survive
- favours the average and more common phenotype
- more likely to survive, reproduce and pass on their favourable alleles
- allele frequency increases
- reduces variability
- reduces opportunity for evolutionary change
explain the process of directional selection
- environmental change may produce new selection pressures that favours an extreme phenotype
- these organism are more likely to survive and reproduce
- these organisms pass on their alleles for the extreme phenotype
- the advtantageous allele frequency increases over many generations
- over time selections means tis allele combination will predominate and the mean phenotype will shift towards the extreme phenotype
