GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Chromosome Abnormalities
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Example Questions
Example Question #1 : Chromosomes
Which of the following choices might occur due to a chromosomal translocation?
Abnormal expression of genes located in the translocated region
All of these could result from a chromosome translocation
Gene fusions
Formation of non-functional genes that were functional before the translocation event
All of these could result from a chromosome translocation
All of the given choices describe potential outcomes of chromosomal translocations. A translocation event occurs when recombination occurs between non-homologous chromosomes. The result is two chromosomes, each with genetic material from two different sets of genes that are generally kept separate.
Being present in a new environment may affect the expression of a gene (either an increase or decrease). Also, it is possible for translocations to occur in the middle of genes. The result of this could be newly formed non-functional (broken) genes or gene fusions between two coding regions that were originally separate. These alterations of gene expression have been implicated in many human diseases, including various cancers.
Example Question #2 : Chromosomes
Which chromosome abnormality affects chromosome 21?
Turner syndrome
Down syndrome
Klinefelter syndrome
Williams syndrome
Cri-du-chat syndrome
Down syndrome
Down syndrome is also referred to as trisomy 21. In about one in every 900 births, the child has an extra copy of the 21st chromosome.
Klinefelter syndrome is the result of a male being born with two X chromosomes and one Y chromosome. A deletion on the short arm of chromosome 5 causes Cri-Du-Chat syndrome; these children have respiratory problems and distinctive facial features. Williams syndrome is the result of genetic material missing from chromosome 7—in particular the gene for elastin, which causes disorders of the circulatory system and heart. A missing or incomplete X chromosome causes Turner syndrome. People who have Turner syndrome develop as females.
Example Question #2 : Chromosomes
In the human population, what is the chance that a baby is born with a chromosomal abnormality (due to aneuploidy, deletions, or translocations)?
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Example Question #157 : Molecular Biology And Genetics
Nearly half of all spontaneously aborted pregnancies are due to chromosomal abnormalities. This includes aneuploidy (an excess or loss of 1+ chromosomes), deletions (a loss of a piece of a chromosome), and translocations (the transfer of one chromosome piece to another).
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