Download INSERT A-3c

Answers to Thinking Critically Questions
Mader: Inquiry into Life, Twelfth Edition
Chapter 26
1. Why would expectant parents want to undergo fetal genetic testing if they know that
regardless of the findings they plan to have the baby?
Explanation/Answer: The knowledge that they are having a child with a genetic
disorder will enable the parents to make plans for raising this child, including finding
proper medical attention and a support network. The knowledge that their child does not
have a genetic disorder may enable them to worry less for the remainder of the
pregnancy.
2. Why are there no viable trisomies of chromosome 1?
Explanation/Answer: Chromosome 1 is the largest of the human chromosomes and
contains many, many genes. Extra copies of this chromosome prove fatal because of the
many genes that are affected.
3. Why can a person carrying a translocation be normal except, for the inability to have
children?
Explanation/Answer: If all of the DNA is present and the breakage for the translocation
did not occur within a gene, then the phenotype of the individual can be normal.
However, when that individual’s sex cells undergo meiosis, some of the resulting
gametes will not contain the normal amount of DNA. Some gametes will have too much
while others have too little. This may result in spontaneous abortions of any child formed
from these gametes.
4. Certain genetic disorders involve a change in a gene’s DNA, but the amino acid
sequence of the protein encoded by the gene is unchanged. How can this result in a
genetic disorder?
Explanation/Answer: DNA mutations can be in regions that regulate the expression of
the gene, not just in the protein coding sequence of the gene. With a regulatory mutation,
the protein encoded by the gene may be overexpressed or not expressed at all, or may be
expressed at an inappropriate time. Any of these could lead to a genetic disorder.
5. In a genomic comparison between humans and yeast, what genes would you expect to
be similar?
Explanation/Answer: Genes that would be very similar between humans and yeast
would involve proteins that are necessary for all eukaryotic species and are therefore
highly conserved. Such proteins might be involved in glycolysis, the cytoskeleton, etc.