Genetic diversity as a result of mutations or during meiosis

• Describe the possible effects on the primary structure of a substitution mutation

  -No effect if new triplet codes for the same amino acid due to the degenerate nature of the genetic code

  -Altered if new triplet codes for a different amino acid so there is a different sequence

  -Shortened if new triplet codes for an early stop codon
• Describe the effect of a deletion mutation

  This causes a frameshift where all triplets, and so, all amino acids are different from the point of deletion onward. So the protein has a different amino acid sequence
• Why does the overall structure and function of a protein that a gene codes for, change when a mutation occurs?

  -The mutation changes the DNA base sequence

  -This changes the mRNA base sequence

  -This changes the amino acid sequence

  -Hydrogen, ionic bonds and disulphide bridges form in different places, so the protein has a different tertiary structure
• What are the causes of mutations?

  -Mutations occur spontaneously during DNA replication when the wrong base forms a base pair and DNA polymerase joins the nucleotide to the next one

  -Mutagenic agents, such as high ionising radiation and some chemicals can increase the chances of mutations by damaging the structure of DNA, so it needs to be repaired more often, which increases the chance of a mutation occurring
• Define a proteome

  All the proteins that a cell can produce
• Define a genome

  All the genes on the DNA molecule in the cell
• Define a homologous chromosome

  Same genes but may have different alleles
• Define a haploid cell

  Cells with only one copy of each chromosome
• Define a diploid cell

  Cells with two copies of each chromosome
• Describe the process of meiosis

  -The diploid cell undergoes DNA replication during interphase and each chromosome becomes two identical sister chromatids and a centromere

  -In the 1st meiotic division, the homologous chromosomes pair up and separate, forming two haploid daughter cells

  -In the 2nd meiotic division, the sister chromatids in each chromosome separate , forming four haploid daughter cells
• What are the two reasons meiosis is important?

  -Produces cells with half of the genetic information so this maintains the chromosome number from one generation to the next

  -Produces cells with genetic variation
• What are the sources of genetic variation?

  -DNA mutations

  -Independent segregation

  -Crossing over

  -When gametes meet, fertilisation is random
• Describe the process of independent segregation

  -In meiosis 1, the homologous chromosomes pair up, each one forming a bivalent

  -The homologous chromosomes can reshuffle into a random position

  -Each daughter cell receives a random combination of maternal and paternal chromosomes

  -This creates new combinations of alleles in the gametes
• Describe the process of crossing over

  -In meiosis 1, the homologous chromosomes pair up, each one forming a bivalent

  -Non sister chromatids cross over each other, forming a chiasma

  -This creates tension which causes equal lengths of non sister chromatids to be exchanged

  -This creates new combinations of alleles in the gametes
• Compare meiosis and mitosis

  -Mitosis produces 2 daughter cells but meiosis produces 4 daughter cells

  -Mitosis goes through 1 division event but meiosis goes through 2

  -Meiosis produces haploid cells but mitosis produces diploid cells in humans

  -Meiosis forms genetically non-identical daughter cells but mitosis produces genetically identical daughter cells

  -In meiosis, the homologous chromosomes pair up on the equator to form a bivalent but in mitosis, they also pair up but in a random order
• Describe the two types of nondisjunction-chromosomal mutations

  -During the 1st meiotic division, a pair of homologous chromosomes didn't separate

  -During the 2nd meiotic division, a pair of sister chromatids didn't separate

  In both, a gamete inherits an abnormal number of chromosomes
• Describe the 3 points to the human life cycle

  -When the chromosome number doubles, fertilisation has occurred

  -When the chromosome number remains the same, mitosis has occurred

  -When the chromosome number halves, meiosis has occurred

  Other organisms with a different life cycle than this are called unfamiliar life cycles