Traits caused by multiple factors January 2009

1. Traits caused by multiple factorsJanuary 2009

2. Polygenic and multifactorial traits

3. The Scottish Crop Research Institute is conducting research on potato texture. You work at this company and need to figure out how many genes are important for potato texture. • You cross a true-breeding potato with the roughest texture to a true-breeding potato with the smoothest texture and then self the F1 progeny. When you examine the F2 potatoes you discover 7 phenotypic classes of potato texture. How many genes determine texture in potatoes? • A. 1 • B. 2 • C. 3 • D. 4 • E. 5

4. During Wednesday’s snow storm you noticed individuals wandering around campus in shorts and sandals. Despite your alarm, you consider the possibility that cold insensitivity is genetically determined. You spend some time counting the frequency of these extremely cold- insensitive individuals. You find that they occur at a frequency of 1 in 256 people. Using an additive allele model, how many genes control cold-insensitivity? 1 2 3 4 5

5. Question: You’ve been sent into a corn field to examine cob size. After measuring hundreds of cobs, you determine that there a 9 phenotypic classes. How many genes contribute to this quantitative trait?A. 1 B. 2 C. 3 D. 4 E. 5How often (on average) would you encounter a cob in the shortest size class?A. 1/16 B. 1/64 C. 1/256 D. 1/512

6. Heritability

7. The same inbred group of chickens Free-range Barn-raised # eggs # eggs Egg size Egg size Heritability of a trait is the relative amount of phenotypic variance that is due to genetic variance. In which case is heritability larger? free-range Barn-raised

8. You have the same inbred group of chickens and you raise them in 2 different conditions Barn Free-range # eggs # eggs Egg size Egg size Heritability of a trait is the relative amount of phenotypic variance that is due to genetic variance. In which case is heritability larger? Free-range Barn The heritability is equal in both conditions Cannot be determined

9. You have the same inbred group of tomato plants and you raise them in 2 different conditions Field Greenhouse # eggs # eggs Fruit size Fruit size Heritability of a trait is the relative amount of phenotypic variance that is due to genetic variance. In which case is heritability smaller? Greenhouse Field The heritability is equal in both conditions Cannot be determined

10. While all tumors involve the accumulation of mutations, it is not clear for several tumor types if there is a heritable genetic component to tumor development. One such tumor is found in the adrenal gland. You study adrenal gland tumors in twins (both identical and fraternal) raised in the same environment and find that identical twins are significantly more likely to both have adrenal gland tumors when compared with fraternal twins (typically 1 sibling has a tumor and the other does not). Which of the following statements is a reasonable conclusion from this result? Adrenal glad tumors are primarily caused by environmental factors Adrenal glad tumors are primarily caused by genetic factors Adrenal glad tumors are caused by an equivalent amount of environmental and genetic factors Adrenal glad tumors are not caused by environmental or genetic factors

11. You think genes contribute to cocaine abuse, so you compare abusers of cocaine to their monozygotic twins, dizygotic twins, full siblings, and adopted siblings. If genes contribute to the tendency for cocaine abuse, then which of the following statements is false?A. Dizygotic twins and siblings will share the cocaine abuse trait at approximately equal rates B. Monozygotic twins will be more likely to share the cocaine abuse trait when compared to siblingsC. Siblings will be more likely to share the cocaine abuse trait when compared to adopted siblingsD. Monozygotic twins and dizygotic twins will share the cocaine abuse trait at approximately equal rates

12. QTL Mapping

13. You are interested in studying obesity. You have found a large number of obese people and have determined the alleles of many, many molecular markers that they carry on each chromosome. You discover that the allele frequency (how often you see a particular allele) for all of the molecular markers on Chromosome 1 is the same in obese patients as it is in the general population. What does this result tell you about potential mutations on Chromosome 1 contributing to obesity? A. There are likely multiple mutations on Chromosome 1 contribute to obesity B. There is likely one mutation on Chromosome 1 contributes to obesity C. There are likely no mutations on Chromosome 1 contribute to obesity

14. LOD Scores

15. 1 2 1 2 2 1 3 4 5 6 Human linkage mapping One person for this autosomal dominant trait in generation III is recombinant - who? A) 1 B) 2 C) 5 D) 6

16. I. B1B3 B2B4 1 2 II. B1B2 B3B4 B1B4 B1B4 B1B2 B3B2 2 3 4 5 6 1 Here is a pedigree showing another autosomal dominant disease but with fewer generations. If person II-1 is non-recombinant, who else in generation II is non-recombinant? II-3 and II-4 only II-2, II-5, and II-6 only II-2, II-3, II-4, and II-5 only II-2, II-3, II-4, and II-6 only

17. A scientist studying VRS (Viagra resistance syndrome) has reported that he has found a marker with a maximum LOD score of 22 at θ= 0.45 in a population on a small island. Upon reading the article which statement below are you likely to say: Big deal! Even with such a high LOD score, in terms of recombination distance the VRS gene is located far away (greater than 40 map units) from the marker so it is virutally unlinked. B) That is kind of cool… That is a high LOD score and in terms of recombination distance, the VRS gene is located at a medium distance (between 10-40 map units) from the marker C) Wow! That is such a high LOD score that the marker must be right next to (within 10 map units) the VRS gene. D) I am totally impressed! A LOD score of 22 means that there is 22:1 odds the marker and gene are linked.