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Biomorph Challenge 3 Answer Key 1. ABO blood types result from 3 possible alleles: i, IA and IB in most populations. The blood types that result from the pairing of alleles is as follows:
Thus, we have 3 alleles (versions of the gene), 6 genotypes (arrangement of alleles) and 4 phenotypes (physical result of genes). a. If a person with O blood type marries a person with AB blood type, what is the % chance that they could produce a child with blood type AB? b. A child with blood type A? c. If the person with O blood type marries a person with genotype IA IA or IB i, their offspring may have which possible genotypes and phenotypes? Predicted % occurance? d. Which combination of parent blood genotypes would have the greatest variety possible in their offspring. Illustrate your thinking process. O
blood type = ii Possible
combinations: i IA, i IB, i IA, i IB
= 2 i IA and 2 i IB IBi
is one parent and ii is the other parent, possible combinations
are: Or
if you combine outcomes from both possibilities: Either comparison is acceptable. d. Would get the greatest variety if the parents were not homozygous in any allele. So…. IAi and IAIB would give: IAIA and IAIB and IAi and IBi = four different genotypes, Three phenotypes: 50% type A, 25% type AB and 25% type B Another possibility So…. IBi and IAIB would give: IBIA and IBIB and IAi and IBi = four different genotypes, Three phenotypes: 50% type B, 25% type AB and 25% type A Another possibility So…. IAi and IBi would give: IAIB and IAi and IBi and ii = four different genotypes, Four phenotypes: 25% type AB, 25% type A, 25% type B and 25% type O This combination gives the most variety in phenotype AND genotype 2. a. From the information you can find in the text of Galapagos, draw the family tree of the captain von Kleist and his brother. Define and include an appropriate genotype designation for each person. b. What do you think would happen in the unlikely event of a person inheriting the gene for Huntington’s disease from both his parents? c. Consider a hypothetical sister of Adolf and Sigfried. What are the possible genotypes for her and what chance does she have of having the disease? d. You are a genetic counselor, and you are visited by a young person whose father died of Huntington’s disease who was planning to marry someone who did not have the disease in her family. What would you advise them and why? A DNA test now exists to detect whether one carries the Huntington allele. How would this change your advice? 2a. Family von Kleist Grandmother (paternal) Grandfather (paternal) Carrier (Aa) healthy (aa)
Father (of Sigfired and Adolf) Mother Carrier (Aa) – died of disease healthy (aa)
Sons Sigfried Adolf (Captain) Carrier (Aa) healthy (aa)
b. My theory is that an AA person dies shortly after birth, or does not live until birth. Thought process is that since it is dominant and only one allele is needed to get the disease, double dominant would be lethal. Other well-explained answers are possible. c. A sister of Sigfried and Aldolf. could be either Aa or aa, with 50% chance of either genotype. d. Without the DNA test the potential father could be Aa or aa. He is marrying an aa. Cross Aa with aa and you get 50% (or 2/4) Aa and 50% (or 2/4) aa (see parts a and b). If you cross aa with aa, you get 100% (or 4/4) aa. Combining those two possibilities you get Aa = 2 out of 8 or 25% and aa = 6 out of 8 or 75%. How to advise them? Without the test, you see the above percentages, only 25% chance of having a child with the disease. Some would consider that percentage too high to chance. Some would consider it a low percentage and also consider that quality of life is good until after middle age. Accept reasonable discussion. With the DNA test, you would know what genotype the potential father is and thus know whether there is a 50% chance of having a child with the disease or a 0% chance of having a child with the disease. How to advise them? If the potential father is a carrier (will certainly develop the disease), can they live with the fact that their child with have a 50% chance of having the disease? Is adoption a possibility? Artificial insemination? Other options… If the potential father does not have the disease, now he has no doubts about his future (with respect to the disease) and practically complete assurance that the child will not have the disease.
1
in 1000 carry the gene. What is p, the allele frequency? [Note: Answers that assumed q = virtually 1.0 will be accepted, for this problem only. This estimate works for this problem, but with other numbers or formulas it doesn't work.] Old version: 1 in 1000 carry the gene. How many carry the gene? Answer 1/1000. 4. Retinitis pigmentosa is an X-linked disease causing blindness. Selena was blind from this disease, because her mother was a carrier, her father was normal. What did the author get wrong? (Look up in OMIM.) What chance does she have of passing on the disease? Actually,
recent discoveries show that dominant and autosomal versions exist: If Selena has the gene defect on BOTH X chromosomes, then all her daughters will be carriers, and all her sons will have the disease. If Selena has the gene defect on only ONE X chromosome, then there is a 50% chance her daughter will carry the trait, and 50% chance that a son will have the disease. 5. Akiko had especially hairy skin, a condition called hypertrichosis. Based on the description in the book, and information you find in OMIM, what genetic trait do you think she might have had and why? (Various answers possible.) Lots
of answers possible. 6. Researchers have identified an allele of a gene that confers resistance to HIV virus, the cause of AIDS. The allele is a version of the CCR5 gene that has part of its sequence deleted (allele CCR5-delta 32). The CCR5-delta 32 allele is present at a frequency of 0.10 in the Caucasian population of the United States. Persons who are homozygous recessive (aa) show virtually complete resistance to HIV, and those who are heterozygous (Aa) have 78% lower risk of HIV infection. Those who are homozygous dominant (AA) have no resistance to HIV. Find the percentages of the US Caucasian population that exhibit the 3 possible phenotypes.
0.1 allele frequency for the mutant gene which is recessive. * The shell of
a tortoise The
shell of a tortoise develops based on a program directed by the genes
of the tortoise. At the same time, the strength and thickness of the
shell depend upon the nutrition of the tortoise, the amount of protein
and calcium in its diet. Too high protein results in an overgrowth of
shell: Spoken
language requires genes for development of the "voice box"
as well as speech processing areas of the brain. Thus, humans can speak
but chimpanzees cannot. However, the precise language that one speaks
depends entirely on the culture in which one is raised. A Chinese baby
adopted in the USA will speak perfect English, whereas a USA baby raised
in China will speak perfect Chinese. All human beings have the genetic
potential to speak all human languages (although that potential is rapidly
modified by cultural environment, from birth onward). [See opening of book for full answers, which you would need on the test.] Each scientific hypothesis is presented with evidence against it, to be considered and argued by the scientists. Each religious hypothesis, such as that Noah's ark put them there, is simply stated as such, with no evidence for or against. That is because religious beliefs are taken on faith, whereas scientific beliefs are based on material evidence. Scientific beliefs can be disproven; or they can be shown to represent reality based on a widespread consensus of evidence. |