Mutations
Every time a cell copies its DNA, it does so with astonishing accuracy, but not perfectly: every now and then an error creeps in. These errors, called mutations, are almost always irrelevant or harmful, but they are also the source of the variation that makes evolution possible.
What a mutation is
In a culture of identical bacteria treated with penicillin, almost all of them die straight away, but one colony survives and multiplies thanks to a new defence that did not exist in its parent cells: where does a new biological characteristic come from if nobody has introduced any external genes?
Explain what a mutation is and when mutations usually occur (errors in DNA copying or the action of external agents).
Explain what a mutation is and when mutations usually occur (errors in DNA copying or the action of external agents).
Distinguish between a mutation that occurs in a somatic cell (for example, a skin cell) and one that occurs in a germ cell: which of them can be passed on to offspring?
Distinguish between a mutation that occurs in a somatic cell (for example, a skin cell) and one that occurs in a germ cell: which of them can be passed on to offspring?
Point mutations: substitution, insertion and deletion
Name three mutagenic agents, physical or chemical, and briefly explain how they act on DNA.
Name three mutagenic agents, physical or chemical, and briefly explain how they act on DNA.
Most mutations have no consequences. Explain two reasons why many mutations go unnoticed (DNA repair systems and features of the genetic code).
Most mutations have no consequences. Explain two reasons why many mutations go unnoticed (DNA repair systems and features of the genetic code).
Explain the relationship between the accumulation of mutations in genes controlling the cell cycle and the development of cancer.
Explain the relationship between the accumulation of mutations in genes controlling the cell cycle and the development of cancer.
Chromosomal mutations and causes of mutations
When the cells of a newborn baby with Down syndrome are observed under the microscope, 47 chromosomes are found instead of the usual 46: how do genetic faults arise that do not change a single letter of the code, but huge blocks of DNA?
Mutations are said to be "the raw material for evolution". Reason why, without mutations, there would be no new genetic variation for natural selection to act upon.
Mutations are said to be "the raw material for evolution". Reason why, without mutations, there would be no new genetic variation for natural selection to act upon.
A patient who has had a melanoma successfully removed from their back raises two concerns during a medical appointment: 1. "I am worried that I have passed this mutation…
A patient who has had a melanoma successfully removed from their back raises two concerns during a medical appointment:
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"I am worried that I have passed this mutation on to my newborn child."
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"Since they have already removed my tumor and my skin is tanned and weathered, I am now immune and no longer need to use sunscreen."
Refute both statements with well-founded arguments:
- a) Justify why their child will not inherit this melanoma, distinguishing between mutations in somatic cells and in germ cells.
- b) Explain why it is biologically false that skin becomes "immune" to cancer, detailing the relationship between cumulative ultraviolet radiation, mutations in proto-oncogenes or tumor suppressor genes, and the loss of cell cycle control.
Look at the diagram illustrating the genetic and cellular change in sickle cell anemia. Imagine that during genetic screening, two individuals are identified with…
Look at the diagram illustrating the genetic and cellular change in sickle cell anemia. Imagine that during genetic screening, two individuals are identified with mutations in that same codon (GAA):
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Person A: undergoes a silent point mutation where GAA changes to GAG (which also codes for glutamic acid).
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Person B: undergoes the deletion of the first base (the G is lost), altering the reading frame.
- a) Reasonably predict the phenotype of person A at the cellular level, explaining which feature of the genetic code prevents them from developing sickle cell anemia.
- b) Compare the expected cellular and functional impact on person B with the case of sickle cell anemia shown in the diagram. Justify why a single-nucleotide deletion is typically biologically more destructive to the protein than the point substitution shown.