Starting questions

Question 1

• D1.3.4 - Gene mutation can be caused by mutagens and by errors in DNA replication or repair.
  Include examples of chemical mutagens and mutagenic forms of radiation.

• D1.3.5 - Randomness in mutation.
  Mutations can occur anywhere in the base sequences of a genome, although some bases have a higher probability of mutating than others. No natural mechanism is known for making a deliberate change to a particular base with the purpose of changing a trait.

• D1.3.6 - Consequences of mutation in germ cells and somatic cells include inheritance of mutated genes in germ cells and cancer in somatic cells.

• D1.3.7 - Mutation is a source of genetic variation.
  Gene mutation is the original source of all genetic variation. Although most mutations are either harmful or neutral for an individual organism, in a species they are in the long term essential for evolution by natural selection.

Discussion questions

1. g
    
2. vv
    
3. vb
    

Types of Mutations

Mutations come in a variety of types. Two major categories of mutations are germline mutations and somatic mutations.

Germline mutations

• occur in gametes (the sex cells), such as eggs and sperm.
• they can be transmitted to offspring,
• cause every cell in the offspring to carry those mutations.

Somatic mutations

• occur in other non-gamete cells of the body.
• have little effect on the organism, because they are confined to just one cell and its daughter cells.
• cannot be passed on to offspring.

Figure 1. Germline vs. somatic mutations. Germline mutations are found in one or more of the parental gametes and thus subsequently affect all of the cells of the offspring. Somatic mutations arise in a non-gamete cell of the affected offspring and therefore are present in only 1 area or tissue type and are not in the offspring's gametes . 

Image source: Genetics of Common and Rare Diseases Vol 8 - 2020 | https://doi.org/10.3389/fped.2020.579591

Neutral mutations

The majority of mutations have neither negative nor positive effects on the organism in which they occur. These mutations are called neutral mutations. Examples include silent point mutations, which are neutral because they do not change the amino acids in the proteins they code.

Many other mutations have no effects on the organism because they are repaired before protein synthesis occurs. Cells have multiple repair mechanisms to fix mutations in DNA.

Beneficial Mutations

Some mutations — known as beneficial mutations — have a positive effect on the organism in which they occur.

They generally code for new versions of proteins that help organisms adapt to their environment.

If they increase an organism’s chances of surviving or reproducing, the mutations are likely to become more common over time. There are several well-known examples of beneficial mutations.

Here are two such examples:

1. Mutations have occurred in bacteria that allow the bacteria to survive in the presence of antibiotic drugs, leading to the evolution of antibiotic-resistant strains of bacteria.
2. A unique mutation is found in people in Limone,  a small town in Italy. The mutation protects them from developing atherosclerosis, which is the dangerous buildup of fatty materials in blood vessels despite a high-fat diet.

Harmful Mutations

Mutations are random changes in DNA.  They may result in the production of a protein that does not function normally, or at all. Such mutations are likely to be harmful. Harmful mutations may cause genetic disorders or cancer.

• A genetic disorder is a disease, syndrome, or other abnormal condition caused by a mutation in one or more genes, or by a chromosomal alteration. An example of a genetic disorder is cystic fibrosis. A mutation in a single gene causes the body to produce thick, sticky mucus that clogs the lungs and blocks ducts in digestive organs.
• Cancer is a disease in which cells grow out of control and form abnormal masses of cells (called tumors). It is generally caused by mutations in genes that regulate the cell cycle. Because of the mutations, cells with damaged DNA are allowed to divide without restriction.

Mutations create genetic variation

***

Further reading

This is a great article about some useful human mutations

https://bigthink.com/surprising-science/evolution-is-still-happening-beneficial-mutations-in-humans/

2. Explore Beneficial mutations in humans - The Big Think
3. Find out more about Specific human genetic disorders - Human genome research institute