Inheritance variation and evolution

• What is sexual reproduction?

  -Involves fusion of male and female gamete

  -Gametes are formed by meiosis

  -Produce genetically different offspring

  -Gamete contains 23 chromosomes (half of what a normal cells contains)
• What is asexual reproduction?

  -Involves one parent and no fusion of gamete.

  -Only mitosis involved (cell divides into two)

  -Genetically identical offspring (clones)
• How does mieosis halve the number of chromosomes in gametes?

  When a cell divides to form gametes:

  • Copies of genetic information are made
  • The cell divides twice to form four gametes, each with a single set of chromosomes
  • All gamete are genetically different from each other
• How does fertilisation restore the full number of chromosomes?

  • Gametes (male and female) join at fertilisation and restore normal number of chromosomes
  • The new cell divides by mitosis, to make a copy of itself.
  • Embryo develops and these cells start to differentiate ---> into different types of specialised cells that make up a whole organism
• What are the advantages of sexual reproduction? 


  • Produces variation in the offspring
  • If the environment changes, variation gives a survival advantage by natural selection
  • Natural selection can be sped up by humans in selective breeding to increase food production
• What is mieosis? 


  • form of cell division involved in formation of gametes in reproductive organs
  • chromosomes number is halved
  • Involves 2 divisions
• What must occur prior to meiosis?

  Interphase- copies of genetic information being made
• What happens during first stage of meiosis?

  • Chromosomes pairs line up along cell equator
  • Pair of chromosomes are separated and move to opposite poles of the cell (side is random which creates variation)
  • Chromosomes number is halved
• What happens during second stage of meiosis?

  ● Chromosomes line up along the cell equator.

  ● The chromatids are separated and move to opposite poles of the cell.

  ● Four unique haploid gametes are produced.
• Why is meiosis important for sexual reproduction? (2)

  ● It increases genetic variation.

  ● It ensures that the zygote formed at fertilisation is diploid.
• Describe fertilisation and its resulting outcome

  Gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis (which increases the number of cells).

  As the embryo develops, cells differentiate.
• What are the advantages of sexual reproduction?

  It creates genetic variation in offspring, increasing the probability of a species adapting to and surviving environmental changes.

  Natural selection can be speeded up by humans in selective breeding to increase food production.
• Describe disadvantages of sexual reproduction?

  ● Two parents are required. This makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyles.

  ● More time and energy is required so fewer offspring are produced.
• What is asexual reproduction?

  ● Type of reproduction.

  ● Involves mitosis only.

  ● Produces genetically identical offspring known as daughter cells.
• Describe advantages of sexual reproduction

  ● Only one parent is required.

  ● Lots of offspring can be produced in a short period of time, enabling the rapid colonisation of an area and reducing competition from other species.

  ● Requires less energy and time as do not need a mate.
• What are the disadvantages of sexual reproduction?

  No genetic variation which reduces species being able to adapt to environmental changes
• Describe the circumstances in which Malarial parasites reproduce sexually and asexually

  Sexual reproduction in the mosquito.

  Asexual reproduction in the human host
• Describe the circumstances in which fungi reproduce sexually and asexually

  Asexual reproduction by spores.

  Sexual reproduction to give variation
• Describe circumstances in which plants reproduce sexually and a sexually

  Sexual reproduction to produce seeds.

  Asexual reproduction by runners (e.g. strawberry plants) or bulb division (e.g. daffodils)
• What is DNA? 


  A double-stranded polymer of nucleotides, wound to form a double helix.

  The genetic material of the cell found in its nucleus.
• Define genome


  The entire genetic material of an organism
• Why is understanding the human

  genome important?

  The whole human genome has been studied and is

  important for the development of medicine in the future.

  ● Searching for genes linked to different types of disease.

  ● Understanding and treating inherited disorders.

  ● Tracing human migration patterns from the past.
• What is a chromosome?


  A long, coiled molecule of DNA that carries genetic information in the form of

  genes.
• How many chromosomes do human body cells have?

  46 (23 pairs)
• How many chromosomes do human gametes have?

  23
• Define gene


  A small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein.
• What are the monomers of DNA?

  Nucleotides
• What are DNA nucleotides made up of?

  ● Common sugar

  ● Phosphate group

  ● One of four bases: A, T, C or G
• State the full names of the four bases

  found in nucleotides

  ● Adenine

  ● Thymine

  ● Cytosine

  ● Guanine
• Describe how nucleotides interact to

  form a molecule of DNA

  ● Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand.

  ● Base connected to each sugar.

  ● Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds.
• Explain how a gene codes for a protein

  ● A sequence of three bases in a gene forms a triplet.

  ● Each triplet codes for an amino acid.

  ● The order of amino acids determines the structure (i.e. how it will fold) and function of protein formed
• Why is the ‘folding’ of amino acids important in proteins such as enzymes?

  The folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate.
• What is protein synthesis?

  The formation of a protein from a gene.
• What are the two stages of protein

  synthesis?

  1. Transcription

  2. Translation
• What does transcription involve?

  The formation of mRNA from a DNA

  template.
• Outline transcription 


  1. DNA double helix unwinds.

  2. RNA polymerase binds to a specific base sequence of non-coding

  DNA in front of a gene and moves along the DNA strand.

  3. RNA polymerase joins free RNA nucleotides to complementary bases

  on the coding DNA strand.

  4. mRNA formation complete. mRNA detaches and leaves the nucleus.
• What does translation involve?

  A ribosome joins amino acids in a specific order dictated by mRNA to form

  a protein.
• Outline translation 


  1. mRNA attaches to a ribosome.

  2. Ribosome reads the mRNA bases in triplets. Each triplet codes

  for one amino acid which is brought to the ribosome by a tRNA

  molecule (carrier molecule).

  3. A polypeptide chain is formed from the sequence of amino

  acids which join together.
• What is a mutation? 


  A random change in the base sequence of DNA which results mostly in no change to the protein coded for, or genetic variants of the protein (slight alteration but appearance and function remain).

  Mutations occur continuously.
• Describe the effect of a gene mutation in coding DNA

  ● If a mutation changes the amino acid sequence, protein

  structure and function may change (an enzyme may no longer

  fit its substrate binding site or a structural protein may lose its

  strength).

  ● If a mutation does not change amino acid sequence, there is no

  effect on protein structure or function.