inheritance and evolution

• how many chromosomes does a human gamete contain?

  23
• how many chromosomes does a normal human cell contain?

  46
• where does meiosis take place?

  reproductive organs
• structure of DNA


  polymer made up of nucleotides , double helix , each nucleotide is made up of a base, phosphate group and sugar molecule
• what is a gene?

  small section of DNA on a chromosome
• what is a genome?

  entire genetic material of an organism
• benefits of understanding the human genome?

  help us search for genes that are linked to a disease , help us understand and treat inherited disorders , trace human migration patterns
• what is a phenotype?


  the characteristics an organism has as a result of their genotype
• Each set of three bases (known as a codon or triplet) codes for a single  amino acid
• 1. The sequence of bases in DNA determines the sequence of amino acids in the chain.
  2. The chain of amino acids (a 'polypeptide'), then folds up to form a protein.
  3. Different sequences of amino acids lead to proteins with different shapes.
  4. This allows different proteins to carry out different functions.
• A copy of the DNA is made, but is now mRNA.

  The copy moves to the ribosome into to the cytoplasm. Amino acids are connected together in a specific order at the ribosomes to create a specific protein molecule. It is then folded into the correct unique shape. This is very important, as it allows the protein to do their jobs, such as enzymes or hormone
• How is mRNA different to DNA?

  mRNA is shorter than DNA and is single stranded
• Why does a gene of DNA have to be copied to mRNA (transcription)?

  DNA is too large to leave the nucleus
• what is a mutation?

  a change in the base sequence of DNA
• what can increase the risk of mutations?

  carcinogens and ionising radiation
• what happens in a substitution mutation?

  One base in the sequence is replaced with a different base 
• what happens in an insertion mutation?

  an extra base is added into the sequence
• is cystic fibrosis a dominant or recessive condition?

  recessive
• what is polydactyly?


  an inherited disorder where a baby is born with extra fingers or toes
• what causes polydactyly?

  a dominant allele
• what is cystic fibrosis caused by?

  recessive allele of the gene for cystic fibrosis
• what is cystic fibrosis?

  a disorder of the cell membranes which results in thick, sticky mucus to build up in the lungs and digestive system 
• embryo screening

  cells are extracted from the embryo to screen for the potential of containing the gene for an inherited disorder
• • Antenatal testing is used to analyse an individual's DNA or chromosomes before they are born. This testing is offered to couples who may have an increased risk of producing a baby with an inherited disorder, but it can't detect all the risks of inherited disorders.
• • Neonatal testing known as the new born blood spot test involves analysing a sample of blood that is taken from pricking a baby's heel. It detects genetic disorders in order to treat them early.
• • Pre-implantation genetic diagnosis (PGD) is used on embryos before implantation. Fertility drugs stimulate the release of several eggs.The eggs are collected and fertilised in a Petri dish. This is known as in vitro fertilisation (IVF). Once the embryos have reached the eight-cell stage, one cell is removed.
  • The cells are tested for the disorder causing alleles. Embryos that don't contain the disorder allele are implanted into the uterus.
• advantages of embryonic screening

  reduce overall suffering since fewer people will have health problems , save lots of money
• disadvantages of embryonic screening

  Discrimination

  • There is the potential that defining the desirability of an embryo based on their genetic make-up could promote discrimination.
  • i.e. people born without the use of screening could be considered second-class citizens.
  • If mismanaged, this technology could become a way for parents to select the most desirable embryo as their child-to-be.
  • The embryos that are not used are destroyed. This can be considered unethical or against religious views.
• Which scientist devised the laws of inheritance?

  Gregor Mendel
• Gregor Mendel (1822-1884) studied the inheritance of different characteristics in pea plants. He found that when he bred red-flowered plants with white-flowered plants, all the offspring produced red flowers. If he bred these plants with each other, most of the offspring had red flowers, but some had white. This was because the allele for red flowers is dominant, and the allele for white flowers is recessive. One of Mendel's observations was that the inheritance of each characteristic is determined by 'units' that are passed on to descendants unchanged.
• what are alleles?

  alternative forms of the same gene
• natural selection 


  fittest individuals selected to survive
• evolution


  inheritance of certain characteristics in a population over multiple generations could lead to a change in the whole species and the development of a new species
• theory of evolution shows how all living species evolved from simple life forms which were first developed more than 3 billion years ago
• Darwin's theory of evolution has been proved by antibiotic resistance and fossil records
• evolution- the natural selection of genetic changes that give rise to the phenotypes that are most suited for the environment
• An individual's characteristics are determined by both the genes they inherit, and the environment they're exposed to. This means that both contribute to the variation between organisms. Often the genes and environment will interact to create further variation. 
• mutations generally have no effect but are occasionally harmful, and very occasionally beneficial
• Describe a series of events that might result in zebras evolving to run more quickly.

  Zebras that run faster are more lively to survive so are more likely to reproduce and pass on their advantageous alleles which repeats over multiple generations so the advantageous allele spreads throughout the population, until the species has 'evolved' to run faster
• Jean-Baptiste Lamarck's early theory of evolution suggested that organisms could acquire new traits during their lifetime, and that these traits could be passed to their offspring.