Genetic Diversity Flashcards
What are genetic mutations?
A change in the DNA base sequence leads to the formation of a new allele.
Where can mutations occur?
Changes to the DNA base sequence usually happen due to mistakes during DNA replication. Changes to the chromosomes usually happen due to the chromosome not separating correctly during meiosis.
What type of base sequence mutations are there?
- Substitution: A DNA base is swapped for another.
- Deletion: A base is removed.
- Addition: A base is added.
How can a substitution mutation have no effect on an organsim?
- The new base triplet could code for the same amino acid as the old triplet meaning there will be no change to the amino acid sequence. This means the hydrogen, ionic and disulfide bonds will form in the same place and the tertiary structure of the protein produced won’t change. This is because the genetic code is degenerate.
- If a new amino acid is coded for, but the bonds form in the same place, the tertiary structure of the protein won’t change.
- If the change happens in a recessive gene.
How can addition and deletion mutation hurt an organism?
They cause a frameshift meaning a completely different amino acid sequence is coded for. This means the bonds form in a different place and the tertiary structure of the protein produced will change. If the protein is an enzyme, the shape of the active site will change, meaning the substrate will no longer be able to fit into it and form an E-S complex.
What kind of chromosome mutations are there?
- Polyploidy: When organisms have more than two pairs of chromosomes.
- Non-disjunction: This is where homologous chromosomes fail to separate correctly during meiosis. This leads to gametes having 1 or 3 chromosomes instead of two.
How do mutations lead to genetic diversity?
They create new alleles.
Meiosis and Genetic Diversity
What is the purpose of meiosis?
To form gametes that are genetically unique and have a haploid number of chromosomes so that when gametes fuse during fertilisation the zygote has the right number of chromosomes.
What are the two stages of meiosis and what happens during each one?
- Meiosis 1: The separation of homologous chromosomes and genetic crossing over.
- Meiosis 2: The separation of chromatids and independent assortment.
Describe what happens during genetic crossing over.
- The homologous chromosomes pair up and form a bivalent.
- The chromatids of each chromosome wrap around each other and form a chiasmata.
- The chromatids break off at the chiasmata and rejoin on a chromatid on the sister chromosome.
Describe what happens during independent assortment.
The separation of maternal and paternal chromosomes in gametes is completely random.
How does meiosis lead to genetic diversity?
Genetic crossing over and independent segregation create new combinations of alleles.
How does sexual reproduction lead to genetic diversity?
The female and male gametes that fuse are decided randomly, and this creates new combinations of alleles possible.
What is the difference between mitosis and meiosis?
- Mitosis produces genetically identical daughter cells and Meiosis produces genetically unique cells.
- Mitosis produces two daughter cells and Meiosis produces 4 daughter cells.
- Mitosis produces diploid cells and Meiosis produces haploid cells.
- Mitosis has 1 cell division and Meiosis has 2.
- Mitosis is used for growth and repair and Meiosis is used for the production of gametes.
- Mitosis is used for asexual reproduction and Meiosis is important for sexual reproduction.
Genetic Diversity and Natural Selection
Define genetic diversity.
The total number of different allleles in a population.
Why is genetic diversity important?
It causes variation between organisms of the same species, which means that if there is a change in their environment, the whole species won’t be ripped off, as some of them will have characteristics that allow them to survive and reproduce.
Describe how the process of natural selection works.
- There is variation in characteristics within a species and more genetic variation arises due to random mutations.
- Individuals with alleles that code for traits that make them more likely to survive to reproduce and pass that advantageous gene on to their offspring.
- Their offspring will also have a higher survival and reproduction rate and will be able to pass on that gene to the next generation.
- Over time the frequency of that allele will increase until almost all the members of the population have the gene.
What is a stabilising selection?
When natural selection favours organisms have alleles that code for average phenotypes. For example, the ideal human birth weight is an average weight as very small babies die early as they can’t thermoregulate, and large babies are hard to give birth to, and that may cause the baby and mother harm.
What is a directional selection?
When natural selection favours organisms have alleles that code for an extreme phenotype.
What are selection pressures?
External factors that affect the ability of an organism to survive and reproduce and drive natural selection.
How does predation affect selection?
Predation means that natural selection will favour the prey that has characteristics that help them not get eaten, such as camouflage or high speed.
How does climate change affect selection?
Climate change means that natural selection will favour the organisms that have characteristics that allow them to survive in the new climate.
