2C

• Cystic fibrosis:

  • mutation is in the gene coding for the CFTR protein
  • CFTR protein doesn’t function correctly
  • reduced transport of chloride ions out of the cell
  • water leaves mucus to go into cell due to osmosis
  • thick sticky mucus
• mutation - permanent change in the DNA of an organism
• A mutation can occur doing cell mitosis and cell meiosis.
• A mutation of a base leads to a different amino acid which leads to a different protein that is not specific to its function.
• point mutation - change in a single base in the DNA code
• base substitution - a base in a gene is substituted for another
• base deletion - a base is completely lost from the sequence, can cause frame shift
• base insertion - an extra base is added, can cause frame shift
• chromosomal mutations - changes in the positions of whole genes within the chromosomes
• whole-chromosome mutations - the loss or duplication of a whole chromosome
• Mutations cause variation in an organism:

  • silent - different codon, same amino cid, no effect
  • mis-sense - different amino acid, different protein
  • non-sense - adds a stop codon, protein is too short
• Mis-sense mutations can be positive, neutral, or harmful. If the mutations leads to a new superior protein, it can create a reproductive advantage which is positive. If the mutation does not improve or worsen the chances of survival, it is neutral. If the mutation occurs in a protein that is important to the function of a cell, it is harmful.
• Mutations in gametes can be inherited e.g. thalasseamia, cystic fibrosis
• Mutations in somatic cells are not inherited, and often cause cancer. However, most mutations have no effect because they occur in the non-coding part of DNA, or the code is degenerate.
• Sickle Cell disease:

  • base substitution in one base in one codon changes Glu to Val
  • haemoglobin molecules to stick together
  • do not carry oxygen efficiently
  • causes severe pain and sometimes death
• Mutations can happen to any cell at any time, but they usually occur during the copying of DNA for cell division. Mutagens e.g. X-rays, chemicals, increase the rate of mutation.
• phenotype - physical traits expressed as a result of the interactions of the genotype with the environment
• genotype - genetic make-up of an organism with respect to a particular feature
• locus - site of a gene on a chromosome
• alleles - versions of a gene
• Chromosomes are arranged in homologous pairs, with 23 from the mother and 23 from the father.
• Gene - segment of DNA that codes for a specific protein
• homozygote - both alleles coding for a particular characteristic are the same e.g BB or bb
• heterozygous - the two alleles coding for a particular characteristic are different e.g. Bb
• dominant - characteristic which is expressed in the phenotype regardless whether the individual is homozygous dominant or heterozygous for that allele
• recessive - characteristic which is expressed in the phenotype only when the individual is homozygous recessive
• True breeding is when 2 homozygous individuals are crossed, so all of their offspring have identical alleles and show the same characteristic in their phenotype e.g. BB x bb -> Bb. If 2 heterozygous individuals are crossed, the offspring will include homozygous dominant, homozygous recessive, and heterozygous e.g. Bb x Bb -> BB, Bb, bb.
• Punnet square:

  • parental phenotype (white fur x black fur)
  • parental genotype (bb x BB)
  • gametes (b, b, B, B)
  • square diagram + phenotype
  • offspring genotypes (Bb)
  • offspring phenotypes (grey fur)
• F1 generation is when the parents were both homozygous for the same allele, so all offspring are heterozygous and have the same phenotype of the dominant allele e.g. Bb. F2 generation is the offspring of the F1 generation, where the recessive allele can become visible again as the offspring are varied e.g. BB, Bb, Bb, bb.
• In order to find out whether an individual is homozygous dominant or heterozygous, a test cross is used. A test cross is repeatedly breeding an individual with a homozygous recessive individual. If all of the offspring are identical i.e. F1 generation, then the individual is homozygous dominant. However, if any of the offspring is homozygous recessive, then the individual is heterozygous. Until an offspring is recessive, it is impossible to be sure that the individual is homozygous dominant.
• codominance - in heterozygotes, where both alleles in a gene are fully expressed in the phenotype
• Blood types:

  Ia + Io -> A

  Ia + Ia -> A

  Ib + Io -> B

  Ib + Ib -> B

  Io + Io -> O

  Ia + Ib -> AB
• Organisms to use for genetic experiments:

  • cheap
  • easy to grow
  • short life cycle
  • large number of offspring
  • clear distinguished characteristics
• Genetic pedigree diagrams show the inheritance of a trait in a family over a long period of time. It highlights the carriers of the recessive phenotype. It can be used to predict carriers of the mutations, and to decide whether or not to conceive.
• autosomes - chromosomes which carry information about the body but do not determine the sex of an individual
• Females are homogametic because they have 2 X chromosomes. They produce gametes of only type of sex chromosome : X.
• Males are heterogametic because they have an X and Y chromosome. They produce gametes with different types of sex chromosomes : X or Y.
• Genes carried on the X chromosome are sex-linked, because they will always be expressed in a male offspring, regardless whether the allele is dominant or recessive, because there is no corresponding allele on the Y chromosome. If the gene is mutated, the male offspring will be affected the mutation, whereas the female offspring won't be.
• Red-Green colourblindness:

  • gene to see colour on X chromosome is mutated
  • recessive mutation
  • more common in men due to sex-link
• Haemophilia:

  • genes coding for blood clotting components on X
  • clotting factor (VIII) is missing
  • blood clots don't form leading to blood loss
  • can be fatal