Genetic Diversity
- Created by: ThuggieJasm
- Created on: 25-09-19 18:35
View mindmap
- 12) Genetic Diversity
- Meiosis
- Forms gametes = sex cells
- E.g. ovum, sperm, ovule and pollen grain.
- Gametes are genetically different
- Meiosis = major cause of intraspecific variation i.e. variation within the same species
- Caused by: independent segregation/ random assortment of homologous chromosome: random orientation of homologous chromosome pairs during meiosis
- Also caused by random fusion of gametes during fertilisation
- Crossing over
- 1) When homologous chromosome pairs come together, at the start of meiosis the chromatids of each pair wrap around chiasma
- 2) sections of each chromatid break off and rejoin to the chromatid of the homologous partner (crossing over)
- Causes exchange of paternal and maternal alleles - genetic recombination
- 2) sections of each chromatid break off and rejoin to the chromatid of the homologous partner (crossing over)
- 1) When homologous chromosome pairs come together, at the start of meiosis the chromatids of each pair wrap around chiasma
- During meiosis, DNA replication occurs once but nuclear division occurs twice.
- 4 daughter cells produced
- Daughter cells have 1/2 number of chromosomes found in a normal body cell i.e. haploid
- Human cells: Diploid = 46 chromosomes Haploid = 23 chromosomes
- When sperm cell joins egg cell at fertilisation, diploid number is restored
- Ensures chromosome number is kept constant from 1 generation to next
- If chromosomes don't separate properly during meiosis and both chromosomes of a pair go into the same cell, chromosome non-disjunction can occur.
- If this happens, then at fertilisation, a zygote can have an extra copy of a particular chromosome
- E.g. Down's syndrome is caused by having an extra pair of chromosome 21
- If this happens, then at fertilisation, a zygote can have an extra copy of a particular chromosome
- If chromosomes don't separate properly during meiosis and both chromosomes of a pair go into the same cell, chromosome non-disjunction can occur.
- Ensures chromosome number is kept constant from 1 generation to next
- Daughter cells have 1/2 number of chromosomes found in a normal body cell i.e. haploid
- 4 daughter cells produced
- 1) Before meiosis starts, the DNA unravels and replicates so that two copies of each chromosome i.e. chromatids are produced
- These cells are all diploid as they have the same amount of different types of genetic info (despite having more than one copy)
- 2) The DNA condenses to form double-armed chromosomes, each made from two sister chromatids. The sister chromatids are joined in the middle by a centromere
- 3) Meiosis I (first division) - the chromosomes arrange themselves into homologous pairs
- 4) These homologous pairs are then separated, halving the chromosome number
- 5) Meiosis II (second division) - the pairs of sister chromatids that make up each chromosome are separated (the centromere is divided)
- 6) Four haploid cells (gametes) that are all genetically different are produced
- 5) Meiosis II (second division) - the pairs of sister chromatids that make up each chromosome are separated (the centromere is divided)
- 4) These homologous pairs are then separated, halving the chromosome number
- 1) Before meiosis starts, the DNA unravels and replicates so that two copies of each chromosome i.e. chromatids are produced
- These cells are all diploid as they have the same amount of different types of genetic info (despite having more than one copy)
- 2) The DNA condenses to form double-armed chromosomes, each made from two sister chromatids. The sister chromatids are joined in the middle by a centromere
- 3) Meiosis I (first division) - the chromosomes arrange themselves into homologous pairs
- 4) These homologous pairs are then separated, halving the chromosome number
- 5) Meiosis II (second division) - the pairs of sister chromatids that make up each chromosome are separated (the centromere is divided)
- 6) Four haploid cells (gametes) that are all genetically different are produced
- 5) Meiosis II (second division) - the pairs of sister chromatids that make up each chromosome are separated (the centromere is divided)
- 4) These homologous pairs are then separated, halving the chromosome number
- 3) Meiosis I (first division) - the chromosomes arrange themselves into homologous pairs
- 2) The DNA condenses to form double-armed chromosomes, each made from two sister chromatids. The sister chromatids are joined in the middle by a centromere
- These cells are all diploid as they have the same amount of different types of genetic info (despite having more than one copy)
- 3) Meiosis I (first division) - the chromosomes arrange themselves into homologous pairs
- 2) The DNA condenses to form double-armed chromosomes, each made from two sister chromatids. The sister chromatids are joined in the middle by a centromere
- These cells are all diploid as they have the same amount of different types of genetic info (despite having more than one copy)
- Forms gametes = sex cells
- Genetic Diversity: No. of different alleles of genes in a population
- Alleles: variations of a gene
- Gene: A section of DNA that codes for a protein/polypeptide
- Members of the same species have the same genes, but there is still variation due to their different alleles
- E.g. Mice all have genes for fur however, there are different alleles coding for the colour of fur
- Within one species there is a set number of genes - gene pool
- The bigger the gene pool, the greater the genetic diversity
- The greater the genetic diversity, the better survival chances of that species
- Specific alleles will increase in proportion over time depending on if they cause significant (advantageous) changes in survival and reproduction
- The greater the genetic diversity, the better survival chances of that species
- Genetic diversity = variation
- The bigger the gene pool, the greater the genetic diversity
- Causes of genetic variation: - mutation. - meiosis - random fusion of gametes (during fertilisation)
- Mutations = asexual
- Change in the sequence of bases. It can cause a change in characteristics
- If the sequence of bases is altered, this can change the sequence of amino acids
- The change in the primary structure (amino acid chain) causes a change in the tertiary structure as the hydrogen, ionic and disulphide "bridge" bonds form in different places
- This results in a loss/reduction in functioning proteins because the active site shape changes so is no longer complementary to the substrate and therefore less/no enzyme-substrate complexes can form
- The change in the primary structure (amino acid chain) causes a change in the tertiary structure as the hydrogen, ionic and disulphide "bridge" bonds form in different places
- If the sequence of bases is altered, this can change the sequence of amino acids
- Types of mutations include: substitution, insertion and deletion
- Substitution: one base is substituted with another, e.g ATGCCT becomes ATTCCT (G is swapped for T)
- The degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA base triplet.
- This means that not all substitution mutations will cause a change in the amino acid sequence of the protein - some substitutions will still code for the same amino acid
- The degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA base triplet.
- Deletion: one base is deleted, e.g. ATGCCT becomes ATCCT (G is deleted
- Substitution mutations won't always lead to a change in the amino acid sequence but deletions will
- The deletion of a base will change the number of bases present, which will cause a shift in all the base triplets after it.
- Substitution mutations won't always lead to a change in the amino acid sequence but deletions will
- Substitution: one base is substituted with another, e.g ATGCCT becomes ATTCCT (G is swapped for T)
- Change in the sequence of bases. It can cause a change in characteristics
- Meiosis & random fusion of gametes = sexual
- Mutations = asexual
- Investigating genetic diversity
- Frequency of measurable and/or observable characteristics
- Before modern tech - careful detailed observations of the anatomy and physiology of different individuals
- Comparing mRNA
- Since mRNA is made using a DNA strand template, species with a more recent common ancestor will have a more similar DNA base sequence and therefore a more similar mRNA sequence. Differences in mRNA base sequence can arise as a result of mutations
- immunological techniques
- Antibodies that are specific to antigens from a particular species e.g humans, can be mixed with antigens from a different species e.g. chimpanzees to see if they are also complementary. If the antigens (proteins) of one or two species are similar there will be many antigen-antibody complexes formed which suggests they are closely related and share a recent common ancestor
- comparing the base sequence of DNA
- Members of the same species have similar sequencesDNA
- Over time, random mutation can cause genetic variation
- Species that have closer evolutionary relationships and share more recent common ancestors have similar sequences of DNA
- Over time, random mutation can cause genetic variation
- Members of the same species have similar sequencesDNA
- Frequency of measurable and/or observable characteristics
- Genetic bottlenecks reduce genetic diversity
- 1) A genetic bottleneckis an event that cause a bug reduction in a popualtione.g. when a large number of organisms within a population die without reproducing
- E.g. Northern Elephant Seals: Northern elephant seals were hunted by hams in the late 1800s. Their original populations reduced to around 50 seals who have since produced a populationof around 170,000. This new populationhas very little genetic diversity compared to the southern elephant seals who never suffered such a reduction in numbers
- The founder effect is a type of genetic bottleneck
- This is when just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool
- The frequency of each allele in the new colony might be very different to those in the original populations.g. a rare allele in the old colony may be very common in the new one which may cause a higher incidence of genetic disease
- The founder effect can occur due to migration leading or geographical separation or if a new colony is separated from the original population for another reason e.g religion
- E.g. The Amish: The Amish population of North America are all descended from a small number of Swiss who migrated there. The population shows little genetic diversity. They have remained isolated from the surrounding population due to their religious beliefs, so few new allele s have been introduced. The population has an unusually high incidence rate of certain genetic disorders
- The founder effect can occur due to migration leading or geographical separation or if a new colony is separated from the original population for another reason e.g religion
- The frequency of each allele in the new colony might be very different to those in the original populations.g. a rare allele in the old colony may be very common in the new one which may cause a higher incidence of genetic disease
- This is when just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool
- 1) The survivors reproduce and a larger population is created from a few individuals
- Meiosis
Similar Biology resources:
Teacher recommended
Comments
No comments have yet been made