Genetic Information and Diversity

1. A change in the base sequence of DNA.
2. That creates a new allele.

1. DNA helicase.
2. Breaks the hydrogen bonds between the bases in the two strands.
3. One DNA strand acts as a template.
4. Free floating RNA nucleotides are attracted to exposed bases on the DNA strand.
5. The attraction is according to the base pairing rule, with Uracil being used instead of Thymine. A pairs with U, G pairs with C.
6. RNA polymerase joins adjacent nucleotides.
7. Phosphodiester bonds form between adjacent nucleotides.
8. The pre-mRNA that is formed is spliced by spliceosomes to remove introns.

1. mRNA attaches to ribosome.
2. The ribosome covers 2 codons.
3. Ribosome moves to start codon.
4. Codon on mRNA binds to an anticodon on tRNA.
5. Each tRNA brings a specific amino acid.
6. The sequence of codons on the mRNA determines the order of the amino acids.
7. Formation of peptide bonds / amino acids joined by condensation reactions.
8. Amino acids join together with the use of ATP.
9. First tRNA released.
10. Ribosome moves along the mRNA until the polypeptide has been formed/ until a stop codon is reached, at which point it detaches from the chain.

1. It brings a specific amino acid to the ribosome.
2. When its anticodon binds to the codon on mRNA.

1. The energy used from ATP hydrolysis is used to attach the amino acid to tRNA.
2. The energy used from ATP hydrolysis is used to form the peptide bonds between adjacent amino acids.

1. mRNA is larger (1000s of nucleotides) than tRNA (80 nucleotides)
2. mRNA has a single helix shape, tRNA has a clover shape.
3. mRNA doesn’t contain hydrogen bonds, tRNA doesNote: One mark scheme counted points 2 and 3 in the same marking point, so go with point 1 and 2 or point 1 and 3.

1. The mutation is in an intron.
2. A silent mutation occurs so the same amino acid is coded for.
3. An amino acid is changed but there is no effect on tertiary structure.
4. The new allele is recessive so does not influence phenotype (in a heterozygous person)

1. It occurred in meiosis, in the production of a gamete.
2. A single zygote will be produced from this gamete.
3. The zygote will divide by mitosis, which produces genetically identical cells, meaning all cells in the body will be clones of this zygote.

1. First, DNA replication occurs during interphaseNote: Clearly it is a good idea to mention this, even if it’s technically not part of meiosis.
2. The first division separates homologous chromosomes.
3. The second division separates sister chromatids.
4. This produces 4 haploid nuclei.

1. Homologous chromosomes arrange randomly at the middle of the cell.
2. Producing different combinations of maternal and paternal chromosomes.
3. This creates genetic variation.
4. And halves the chromosome number.Note: notice that halving the chromosome number is listed as a function of independent segregation itself.

1. Homologous pairs of chromosomes associate and form a bivalent.
2. Chromosomes in the bivalent twist around each other and a chiasma forms.
3. Equal lengths of chromatids/ alleles are exchanged.
4. A new combination of alleles is formed in each non-sister chromatid. (This shows that it's important to talk about alleles being exchanged, not genes).

1. Crossing over.
2. Independent segregation of homologous chromosomes.
3. Mutations.
4. Random Fertilisation, which produces a new combination of alleles.

Note: epigenetics is not a cause of genotypic diversity, but is a cause of phenotypic diversity.

1. In meiosis.Note: it is important to mention this, as it is what causes all body cells to have the mutation.
2. Chromosome(s) are not separated.

1. It can happen to multiple chromosomes (even ALL of them), causing cells to have up to double the number of correct chromosomes.
2. It usually happens in meiosis 1, so always talk about ‘chromosomes’ not separating.Note: this note was made to address two misconceptions I had, but I thought it would be useful to include.

1. A genetic bottleneck, which is caused when the population size is rapidly reduced, shrinking the gene pool.
2. Inbreeding.
3. The population starting from a small number of individuals, which is called the founder effect.
4. A small current population size.

Note: all four of these reduce the number of different alleles and create a smaller gene pool.

1. It produces new combinations of alleles.
2. Due to the new maternal and paternal chromosome combinations it produces.Note: ‘random fertilisation’ is the same as the ‘random fusion of gametes’

1. A mutation results in a new allele.Note: always mention it is a ‘mutation’ that results in a new ‘allele’ (not a gene).
2. Those with the allele have X trait.
3. These individuals with X trait are more likely to survive and reproduce.
4. This causes directional selection.
5. Increasing the frequency of the allele in the population over many generations.

1. They contain smaller groups within larger groups.
2. There is no overlap between groupsNote: this definition is tested a LOT.

1. It accounts for both the number of species and proportion of individuals in each species.
2. Making it useful as there may be many members of some species.

1. More plant species.
2. More, different food sources.
3. More habitats.

1. DNA sequencing is now used.
2. This means species can be analysed more accurately.
3. Rather than just relying on observations.

1. Having them reproduce and seeing if the offspring are fertile.
2. Comparing base sequence of DNA/ order of amino acids in polypeptides.

1. Fossil record.
2. Evolutionary history (phylogeny)
3. Biochemical differences (DNA, proteins)
4. Homologous features (can name a specific feature)
5. Karyotype (number and form of chromosomes)Note: I feel like mentioning behaviour like mating calls and the appearance of embryos is also worth doing if it's a long question. However, for ones where you have to just state 2 or 3, stick to biochemical and homologous features.

1. The base sequence of DNA.
2. The base sequence of mRNA.
3. The sequence of amino acids.

1. Mutations change the base sequence of DNA.
2. This causes changes in amino acid sequence.
3. These mutations build up over time.
4. More mutations and more differences in amino acid sequence indicated species are more distantly related.
5. The more distantly related species will have a less recent common ancestor.

1. Bones.
2. Skin.
3. Preserved remains.

1. Microscopy.
2. The resolution of an optical microscope is too low to distinguish the species of bacteria based on their flagella.
3. Artefacts may be mistaken for flagella.
4. The flagella may be at an angle so not visible.
5. The flagella may be difficult to stain so not visible Flagella.
6. Flagella are fragile so may be broken or missing.
7. Not all bacteria have flagella.