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Genome - the entire genetic material of an organism.

Eukaryotes and Prokaryotes

Chromosome - a thread-like structure of DNA that carries genetic information in the form of
genes.

Gene - a length of DNA that codes for a particular protein.

Allele - one of a number of different versions of a gene.

Genotype - the genetic makeup of an organism, consisting of all the alleles present.

Phenotype - the observable features of an organism as a result of the expression of
• particular alleles of the gene and interaction with the environment.

Cells can be viewed using a light microscope to study their structure.

Plant and animal cells are
known as eukaryotic cells as they contain a nucleus and membrane-bound organelles such as
ribosomes and mitochondria.

Plasmids are circular loops of DNA that are
found in the cytoplasm of the cell. In eukaryotes, DNA is stored in the nucleus.

Bacteria are known as prokaryotes as they do not contain these.
Genetic material in prokaryotes is stored in plasmids.

How is genetic information inherited?

Inheritance - the transmission of genetic information from parents to offspring.

Gamete – a reproductive cell which carries one half of each chromosome pair.During fertilisation, two gametes fuse to create a full set of chromosomes. Egg and
sperm cells are examples of gametes.

Homozygous - an organism containing two identical alleles of a particular gene.

Heterozygous - an organism containing two different alleles of a particular gene.

Dominant allele – a dominant allele, if present in an organism, is always expressed in
the phenotype and will mask recessive alleles.

Recessive allele – recessive alleles are only expressed in the phenotype in the
absence of a dominant allele.

Genetic engineering

  1. The desired gene is located in the DNA of an organism. This gene is isolated and
    removed from the organism using enzymes.
  1. The gene is replicated and placed into a vector, e.g a plasmid.
  1. The gene is inserted into a bacterium cell using the vector.
  1. Successfully modified cells are selected.

Benefits

Crops can be modified to improve yield by becoming resistant to frost, diseases

Crops can be modified to provide scarce nutrients.

Knowledge of the human genome can help improve medicines and vaccines

Genetic testing can be used to inform individuals about family planning and
healthcare

Risk

loss of biodiversity, contamination of wild species through
crossbreeding,

Long term health impacts of consuming genetically modified food products are not
known.

This could lead to ‘designer
babies’ and is a highly contentious topic.

Protein Synthesis

Protein synthesis is the process of making proteins from amino acids. Each amino acid is coded for
by three nucleotides on a DNA strand.

  1. A messenger RNA (mRNA) strand is made from a section of DNA which holds the code to a
    particular gene. mRNA is similar to DNA and is also made of nucleotides.

This occurs in the
nucleus. A mRNA copy is necessary as DNA is too large to leave the nucleus.

  1. The mRNA exits the nucleus and travels through the cytoplasm to a ribosome, which is the
    site of protein synthesis.
  1. The ribosome uses the mRNA strand as instructions to join amino acids together in a
    specific order, which produces a particular protein.