Although most cases of cancer are sporadic, certain inherited alleles can increase an individuals lifetime risk. One example of this are certain alleles of the BRCA gene that occur in families with a history of breast cancer. Answer the following questions. In your answer please use numbering to indicate you answers to each question 1. Affected individuals are typically heterozygous for the risk allele, which is considered to be inherited in a dominant pattern. Use basic language to describe what this means (2 marks) 2. The BRCA gene encodes a protein that repairs DNA damage. The risk allele encodes a non-functional version of that protein. Is the mutation best described as affecting a tumour suppressor gene or a proto-oncogene and why? (2 marks) 3. Not all carriers of the risk allele develop cancer, but individuals with a family history of cancer have a greater risk. Is this observation best described in terms of penetrance or expressivity and why do differences in family history mean that individuals with the same BRCA genotype can have different risk? (2 marks)
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When we say that affected individuals are typically heterozygous for the risk allele and that it is inherited in a dominant pattern, it means that a person has two different versions of the BRCA gene, one normal and one risk allele. The risk allele is dominant, Show moreā¦
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Sri K.
The pedigree that follows shows the inheritance of various types of cancer in a particular family. Molecular analyses (descrihed in subsequent chapters) indicate that with one exception, the cancers occurring in the patients in this pedigree are associated with a rare mutation in a gene called $B R C A 2$. a. Which individual is the exceptional cancer patient whose disease is not associated with a $B R C A 2$ mutation? b. Is the $B R C A 2$ mutation dominant or recessive to the normal $B R C A 2$ allele in terms of its cancer-causing effects? c. Is the $B R C A 2$ gene likely to reside on the X chromosome, the Y chromosome, or an autosome? How definitive is your assignment of the chromosome carrying $B R C A 2 ?$ d. Is the penetrance of the cancer phenotype complete or incomplete? e. Is the expressivity of the cancer phenotype unvarying or variable? f. Are any of the cancer phenotypes associated with the $B R C A 2$ mutation sex-limited or sex-influenced? g. How can you explain the absence of individuals diagnosed with cancer in generations I and II?
Madhur L.
The risk of developing breast and/or ovarian cancer is greatly increased if men or women inherit a deleterious (harmful) mutation in the BRCA1 gene, because a loss of heterozygosity (LOH) event can lead to cancer. The normal BRCA1 gene codes for a tumor suppressor. True or False? The following could lead to cancer in cells of a person who inherited a mutant copy of BRCA1? Provide explanation if possible. T/F The wild type allele of BRCA1 gene has a nonsense mutation near the start codon. T/F Chromosomal non-disjunction leads to loss of the chromosome with the BRCA1 wild type allele T/F Gene duplication of the BRCA1 wild type allele T/F Wild type BRCA1 allele is moved from euchromatin to heterochromatin T/F A loss of function mutation occurs in a repressor protein for the BRCA1 gene T/F A gain of function mutation makes a hyperactive wild type BRCA1 protein
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