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Explain why small deletions and duplications are less
likely to have a detrimental effect on an individual’s phenotype than large
ones. If a small deletion within a single chromosome happens to have a
phenotypic effect, what would you conclude about the genes in this region?
Small deletions and duplications affect fewer genes so it may not affect it phenotypically. It would conclude that a gene or several genes in that region are required to produce a normal phenotype.
Two chromosomes have the following order of genes:
Normal: A B C centromere D E F G H I
Abnormal: A B G F E D centromere C H I
Does the abnormal chromosome have a pericentric or paracentric inversion? Draw a sketch showing how these two chromosomes would pair during prophase of meiosis I
- It has pericentric inversion because genes were transferred across the centromere.
Two phenotypically normal parents produce a phenotypically abnormal child in which chromosome 5 is missing part of its long arm but has a piece of chromosome 7 attached to it. The child also has one normal copy of chromosome 5 and two normal copies of chromosome 7. With regard to chromosomes 5 and 7, what do you think are the chromosomal compositions of
There is a balance translocation in chromosome 5 and 7 in one of the parents. Segregation of translocated chromosomes during meiosis caused the offspring to inherit an imbalanced translocation.
Which of the following types of chromosomal changes would you expect to have phenotypic consequences? Explain your choices.
A. Pericentric inversion
B. Reciprocal translocation
D. Unbalanced translocation
A deficiency and an unbalanced translocation are more likely to have phenotypiceffects because they create genetic imbalances. For a deficiency, there are too few copies ofseveral genes, and for an unbalanced translocation, there are too many.
Aneuploidy is typically detrimental, whereas polyploidy is sometimes beneficial, particularly in plants. Discuss why you think this is the case.
It may be related to genetic balance. In aneuploidy, there is an imbalance in geneexpression between the chromosomes found in their normal copy number versus those thatare either too many or too few. In polyploidy, the balance in gene expression is stillmaintained.
A woman who is heterozygous, Bb, has brown eyes. B (brown) is a dominant allele, and b (blue) is recessive. In one of her eyes,
however, there is a patch of blue color. Give three different explanations for how this might have occurred.
- A mutation occurred during early embryonic development that cause the phenotype. mitotic nondisjunction is one explanation where the two chromosomes carrying the b
- allele went to one cell and the two chromosomes carrying the B allele to the
- daughter cell. Another explanation is
- the loss of the chromosome that was carrying the B allele. The last possibility
- is the deletion of the B allele.
What is a G band? Discuss how G bands are useful in the analysis of the chromosome structure.
- G bands are the dark bands of the chromosomes after geimsa staining. The G bands indicated the parts of the DNA that are much constricted which are the genes
- that are not expressed. It can also be used to distinguish chromosome structures and detect changes in chromosome structure.