Genetic diversity and adaptation

• When do mutations occur?

  Generally when DNA is replicated they are completely random and spontaneous, occur rarely and often cause a change in the specific sequence of amino acids.
• What are the 2 types of gene mutations?

  Base deletion and base substitution
• Describe base deletion and how it affects the sequence.

  A nucleotide is lost form the normal DNA sequence, whole base sequence shifted to the left by one base. Means different amino acids will be coded for as alters the triplet code, so these amino acids will form bonds in different places affecting the tertiary structure making the protein non-functional.
• Describe base deletion and how it affects the sequence?

  A nucleotide in DNA molecules is replaced by another nucleotide, will result in a different amino acid being included in amino acid chain, changing bonds and tertiary structuremaking.
• How does the degenerate code affect base substitution?

  As there are triplets that code for the same amino acid in some cases after base substitution the same amino acid will still be coded for so the amino acid sequence will remain unchanged and the protein will be functional.
• What are mutagenic agents and what are some examples?

  They are environmental factors that can increase the rate of mutation.

  Examples: toxic chemicals, high energy radiation, ionising radiation.
• What happens when mutation rate increases above normal level?

  The body’s natural mechanisms that identify and repair DNA mutations become ineffective.
• What are the 2 types of chromosome mutations?

  Changes in whole sets of chromosomes or changes in the number of individual chromosomes. Both occur spontaneously.
• Describe mutations that involve changes in whole sets of chromosome?

  It occurs when organisms have 3 or more sets of chromosomes rather than usual 2(polyploidy) it occurs mostly in plants.
• Describe the chromosome mutation that changes number of individual chromosomes?

  individual homologous pairs fail to separate during meiosis.

  Non-disjunction - usually results in gamete having one more or fewer chromosomes. On fertilisation with a normal gamete all body cells have one more or less than normal chromosome number.
• What are sister chromatids?

  Sister chromatids are identical copies of a single chromosome that are joined together by a centromere, they are genetically identical.
• What are homologous chromosomes?

  Homologous chromosomes are pairs of chromosomes that have the same genes in the same order, but may have different versions of those genes, they determine the same characteristics but may have different alleles.
• How do you calculate the number of possible combinations for each daughter cell after meiosis?

  2^n

  where n is the number of pairs of homologous chromosomes

  This only takes into account independent assortment segregation
• What is the number of possible chromosome combinations from 2 parents?

  (2^n)^2
• What is a diploid and a haploid cell?

  Diploid: full set of chromosomes

  Haploid: half set of chromosomes
• What is the importance of meiosis?

  If each gamete had full set of chromosomes then cell produced at fertilisation would have double this number. Meiosis therefore allows number of chromosome to remain constant and introduce genetic diversity. When 2 haploid cells fuse at fertilisation diploid number of chromosomes is restored.
• What is the process of meiosis?

  The first division(meiosis 1) homologous chromosomes pair up and chromatids wrap around eachother, equivalent positions of these chromatids may be exchanged in crossing over. By the end of this division homologous pairs have been separated.

  Meiosis 2 - chromatids are further apart, and 4 haploid cells are produced.
• What is a benefit of meiosis in terms of genetic variation?

  It increases genetic variation that may lead to adaptations that improve survival chances.
• What causes genetic variation in meiosis?

  Independent segregation of homologous chromosomes

  Crossing over
• Describe how independent segregation increases genetic variation?

  Each chromosomes lines up alongside homologous partner, randomly. One of each pair goes into daughter cell.

  Pairs are lined up at random so combination of chromosomes of maternal and paternal origin go into daughter cell at meiosis 1, this increases variation.
• How does fertilisation produce variation in offspring?

  Gametes fuse randomly, each gamete is genetically different, so there is variety. When gametes come from 2 different parents there is more variety.
• Describe the process of crossing over?

  When chromosomes line up alongside eachother, chromatids become twisted around eachother. Tensions are created and portions of chromatids break off. Broken regions may join chromatids of homologous partner at equivalent portions. In recombination broken off portions re combine this increases variation.
• Where does meiosis take place?

  In the reproductive organs (ovaries and testes) of organisms.
• What is the difference between meiosis 1 and meiosis 2?

  Meiosis 1 involves the separation of homologous chromosomes, while meiosis 2 involves the separation of sister chromatids.

  Meiosis 1 also involves crossing over
• How does the process of crossing over increase genetic variation?

  A new combination of alleles is created, independent assortment causes genetic variation of maternal and paternal alleles. Chromosomes are re-shuffled in any combination.
• What are the differences between mitosis and meiosis?

  Mitosis produces diploid cells and meiosis produces haploid cells. In mitosis 2 genetically identical daughter cells are produced, but in meiosis 4 genetically unique daughter cells are produced. Mitosis involves one division of sister chromatids, whereas meiosis involves division of homologous pair then sister chromatids. Mitosis does not involve independent assortment or crossing over.
• What is the definition of genetic diversity?

  The total number of different alleles in a population.
• What is the definition of a gene pool?

  The total number of alleles in a particular population at a specific time.
• What is the definition of a population?

  A group of individuals of the same species that live in the same place and can interbreed.
• What increases the chances of survival?

  Greater number of different alleles means more genetic diversity, more genetic diversity means increased chance that a characteristic will suit new environmental conditions.
• What is the definition of allele frequency?

  The number of times an allele occurs within a gene pool.
• Describe the process of natural selection.

  Mutations occur resulting in new allele, in certain environments the allele will be advantageous, the individuals that posses this allele will be more likely to survive, greater reproductive success, will live long to breed and pass on advantageous allele. New offspring posses advantageous allele will survive will others who don’t more likely die. Over time allele frequency of advantageous allele increase and others decrease.
• What are the 3 types of adaptations?

  Structural(anatomical), physiological, behavioural.

  Adaptations make it more likely an organism will survive in particular environments
• What are 2 events that reduce genetic diversity?

  Genetic bottle neck

  Founder effect
• Describe genetic bottle neck.

  A catastrophic event causes a big reduction in population and change environment, only those adapted to survive reproduce. Genetic diversity decreases along with allele frequency of non-advantageous alleles.
• Describe the founder effect.

  A few organism go somewhere to start a new coming, they reproduce amongst themselves as only a small number of different alleles in initial population. It causes rare alleles to become more common and genetic disorders are more likely.
• What do the founder effect and genetic bottle neck do?

  They reduce genetic diversity, which leads to increased genetic drift, random changes in allele frequencies.
• What is selection?

  The process where organism that are better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to.
• What is a normal distribution curve?

  Most characteristics are affected by more then one gene these are more influenced by environment, the environment produced individuals that vary about the mean, this variation is plotted on a distribution curve.
• What are the 2 types of selection?

  Stabilising selection and directional selection.