Genetic Diversity Flashcards
Outline the stages of meiosis (1)
- Homologous chromosomes pair up in synapsis
- Crossing over rearranges alleles on homologous chromosomes 3. Independent segregation of homologous to produce 2 haploid cells
Outline the stages of meiosis (2)
- Cells align single chromosomes in metaphase 2 2. Chromatids are separated 3. Product is 4 haploid cells that are genetically non identical
How does meiosis produce genetically non identical daughter cells by crossing over
Crossing over: 1. synapsids occurs where homologous chromosomes pair up in meiosis 1 2. Non sister chromatids overlap forming chiasmata 3. Same section of homologous dna are exchanged by recombination 4. Due to different alleles new allele sequences are created
How does meiosis produce genetically non identical daughter cells by independent segregation
- During metaphase 1, pairs of homologous chromosomes align on the metaphase plate 2. Orientation of one pair is random with respect to another 3. Due to different maternal/paternal alleles, this can produce genetically non intentional gametes when meiosis is repeated
What are the differences between mitosis and meiosis
Mitosis has 1 division, produces 2 daughter cells which are haploid and genetically identical. and it’s function Is growth and repair. Meiosis has 2 divisions, produces 4 daughter cells that are haploid and genetically non identical (diff alleles). It is involved in sexual reproduction
What are the similarities between mitosis and meiosis
The chromosomes are dealt with independently (as in meiosis 1st division separates homologous pairs in independent seg) and only chromatids are separated (in meiosis 2nd division separates chromatids)
How can non disjunction during meiosis result in chromosomal mutation
It is failure to separate a pair of homologous chromosomes in meiosis 1, gametes either have one extra chromosome or one missing
Define genetic diversity
The total number of different alleles in a population.
Define population
A group of individuals of the same species that live in the same place and can interbreed to produce fertile offspring
Define allele
An alternative version of the same gene, possess a different nucleotide base sequences which may alter polypeptide gene codes for/ leads to phenotypic variation
List the sources of variation within a population
- Random mutation (changes to base sequences) crossover, independent segregation, random fertilisation (gametes are genetically non identical due to allele variation) and random mating
Define the mechanism of natural selection
- Random mutation of genes may result on new alleles. 3. May result in selective advantage over others 4. These individuals are better adapted and are more likely to survive and breed successfully 5. Advantageous alleles passed on to next gen 6. Over many gens the advantageous alleles will increase in frequency in pop, means less advantageous alleles may decrease in frequency
How is antibiotic resistance an example of directional selection
- Antibiotics act as selective pressure 2. Spontaneous random mutation occurs so new protein is produced which may increase resistance to antibiotic 3. Individual bacterium survives and divides by binary fission and susceptible bacteria die 4. Population of resistant bacteria increased and the populations normal distribution curve shifts in direction of pop being more resistant
How is human birth weight an example of stabilising selection
- Environmental conditions remain stable 2. Individuals closest to mean phenotype are more likely to pass on alleles to next gen 3. Individuals with more extreme phenotypes are less likely to reproduce successfully 4. Phenotypes around mean are selected for and extremes selected against
How does genetic diversity lead to adaptation in a population
Natural selection results in species being better adapted to environment through anatomical, physiological and behavioural changes
