Ecology + inheritance, variation and evolution

• What is sexual reproduction?

  ● Type of reproduction. ● Involves the production of gametes by meiosis. ● A gamete from each parent fuses to form a zygote. ● Genetic information from each gamete is mixed so the resulting zygote is unique.
• What are gametes?


  ● Sex cells (sperm cells and egg cells in animals, pollen and egg cells in flowering plants). ● Haploid (half the number of chromosomes).
• What is meiosis?


  ● Form of cell division involved in the formation of gametes (non-identical haploid cells) in reproductive organs. ● Chromosome number is halved. ● Involves two divisions.
• What must occur prior to meiosis?

  Interphase - copies of genetic information are made during this process.
• What happens during the first stage of meiosis?

  ● Chromosome pairs line up along the cell equator. ● The pair of chromosomes are separated and move to opposite poles of the cell (the side to which each chromosome is pulled is random, creating variation). ● Chromosome number is halved.
• What happens during the 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 is the advantage of sexual reproduction? (biology only)

  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 the disadvantages of sexual reproduction (2) (biology only)

  ● 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? (biology only)

  ● Type of reproduction. ● Involves mitosis only. ● Produces genetically identical offspring known as daughter cells.
• Describe the advantages of asexual reproduction (3) (biology only)

  ● 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 is the disadvantage of asexual reproduction? (biology only)

  No genetic variation (except from spontaneous mutations) reducing the probability of a species being able to adapt to environmental change.
• 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 the circumstances in which plants reproduce sexually and asexually

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

  23 chromosomes
• 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? (biology only)

  Nucleotides
• What are DNA nucleotides made up of? (biology only) ● Common sugar ● Phosphate group ● One of four bases: A, T, C or G
• State the full names of the four bases found in nucleotides (biology only)

  ● Adenine ● Thymine ● Cytosine ● Guanine
• Describe how nucleotides interact to form a molecule of DNA (biology only) (higher only)

  ● 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 (biology only)

  ● 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? (biology only) (higher only)

  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? (biology only) (higher only)

  The formation of a protein from a gene.
• What are the two stages of protein synthesis? (biology only) (higher only)

  1. Transcription 2. Translation
• What does transcription involve? (biology only) (higher only)

  The formation of mRNA from a DNA template.
• Outline transcription (biology only) (higher only)


  Outline transcription (biology only) (higher only) 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? (biology only) (higher only)

  A ribosome joins amino acids in a specific order dictated by mRNA to form a protein.
• Outline translation (biology only) (higher only)

  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? (biology only) (higher only)


  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 (biology only) (higher only)

  ● 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.
• What is non-coding DNA? (biology only) (higher only)

  DNA which does not code for a protein but instead controls gene expression.
• Describe the effect of a gene mutation in non-coding DNA (biology only) (higher only)

  Gene expression may be altered, affecting protein production and the resulting phenotype.
• What are alleles?


  Different versions of the same gene.