you and your genes 

what is the genome and what does it do?

eukaryotes and prokaryotes

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

Plant and animal cells are eukaryotic cells containing a nucleus (that stores DNA) and membrane-bound organelles such as ribosomes and mitochondria.

Bacteria are prokaryotic cells as they do not have a nucleus or membrane-bound organelles. The genetic material in prokaryotes is stored in plasmids (circular loops of DNA that are found in the cytoplasm)

characteristics

most characteristics of an organism are determined by the genome. allele (different versions of a gene) produce different characteristics.

some alleles are dominant so they will be expressed if present in the genome. characteristics can also be influenced by external factors as the organism interacts with the environment for example skin colour can be influenced by the intensity of light.

DNA

DNA acts like instructions, allowing the cell to carry out certain key processes. for example DNA allows protein synthesis where amino acids are bonded together to make proteins.

proteins are extremely important as they maintain the structure as well as carry out reactions and transport molecules

DNA is a polymer made up of many nucleotide monomers bound together in a chain. nucleotides form two long strands which wind around each other to form a double helix.

mutations

mutations are genetic changes which result in a change in the sequence of DNA bases (nucleotides). These changes occur due to a variety of factors including exposure to some chemicals and ionising radiation. if the mutation occurs at a particular allele in DNA this allele may be altered, changing how it functions. this is how new alleles are formed, resulting in genetic variation, as altered alleles produce different proteins which can influence the phenotype.

how is genetic information inherited?

single gene inheritance

an offspring inherits characteristics from both their mother and their father. two sets of genes are inherited - one from each. if the mother and father pass down the same allele for example blue eyes, the offspring will have two of the same alleles for this trait (homozygous).

if two separate alleles are passed down for example if the mother has blue eyes but the father has brown eyes, the offspring will have two different alleles for this gene (heterozygous).

alleles can be dominant or recessive. a dominant allele is always expressed if present whereas the recessive allele is only expressed in the absence of the dominant allele.

most characteristics are determined by multiple genes, meaning most characteristics are not passed on through single-gene inheritance.

sex determination

all humans have 23 pairs of chromosomes in their DNA. one of these pairs is used to determine gender. the sex chromosomes in males are called XY. the sex chromosomes in females are called XX,

when gametes are produced, they carry one-half of each chromosome pair. egg cells from the mother always carry the x chromosome. the sperm can carry either the x or y chromosome.

genetic engineering
  • the desired gene is located in the DNA. the gene is isolated and removed from the organism using enzymes.
  • the gene is replicated and placed into a vector for example a plasmid
  • the gene is inserted into a bacterium cell using the vector
  • successfully modified cells are selected.
benefits of genetic engineering
  • Crops can be modified to improve yield by becoming resistant to frost, diseases and herbicides. E.g. some strawberries have been genetically engineered to become frost-resistant by inserting an anti-freeze gene found in arctic fish.
  • Crops can be modified to provide scarce nutrients. E.g. Golden rice is a genetically modified variety of rice that produces beta-carotene, which is converted into vitamin A in the body. Areas which lack dietary vitamin A grow this rice to prevent vitamin A deficiency, which can lead to blindness and death.
  • Knowledge of the human genome can help improve medicines and vaccines as specific genes and alleles associated with a particular disease can be targeted.
  • Genetic testing can be used to inform individuals about family planning and healthcare as genetic screening can show any diseases they could have and determine whether the individual is a carrier of a disease which may be inherited by their children.
risks of genetic engineering
  • genetically modified crops can have a number of negative impacts on the environment, including loss of biodiversity, contamination of wild species through crossbreeding and leading to herbicide-resistant weeds. Genetically modified crops are also more expensive.
  • The long-term health impacts of consuming genetically modified food products are not known.
  • Genetic testing means that embryos can be screened to find out their characteristics or if they have any inherited diseases or disabilities. This could lead to ‘designer babies’ and is a highly contentious topic.

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