Question 1: In Drosophila melanogaster, eyeless (ey) is a recessive trait in which the eyes are tiny or absent. The ey locus is found on chromosome 4. Monosomy and trisomy for this very small chromosome are compatible with survival and fertility. A trisomic wild-type male with the genotype ey+ ey ey is crossed to an ey+ ey female. Assuming random segregation of chromosomes into gametes, determine the chromosome constitution and phenotypic ratios in the offspring.
Question 2: The following DNA fragment was isolated from the beginning of a gene.
C C C T A C G C C T T T C A G G T T
G G G A T G C G G A A A G T C C A A
Determine which strand is transcribed, indicate the polarity of the two DNA strands, and then give the sequence of bases in the resulting mRNA and its polarity.
Question 3: The space probe HEA1 returns to earth following a trip to the planet Tantoun. Analysis of samples from this planet reveals that proteins are composed of 16 different amino acids, while DNA contains only two bases: rosine (R) and ziadine (Z).
a) What is the minimum codon size in this genetic code? Explain your reasoning.
b) How many of the codons in this minimum genetic code will contain at least two Zs? Explain your reasoning.
Question 4: In unit I we have examined various mechanisms of non-Mendelian inheritance.
Please write a short essay (300-400 words) in which you compare and contrast the following mechanisms. Be sure to include how each deviates from simple Mendelian inheritance.
- Maternal effect
- Maternal inheritance
- Genomic imprinting
- Trinucleotide repeat diseases
Question 5: Consider two mice that are heterozygous for insulin-like growth factor 2.
From the cross Igf2 Igf2m X Igf2 Igf2m ....
a) What genotypic ratio would be expected?
b) What phenotypic ratio would be expected?
Question 6: Rh is the most complex of the blood group types, involving at least 45 different antigens. The most clinically important antigen, D or RhO, is encoded by the gene RhD which is found on chromosome 1. Individuals that are Rh-positive have either one or two RhD genes, whereas the Rh-negative phenotype is caused by the absence of the RhD gene. (The antithetical allele d does not exist, however the letter "d" is used to indicate the D-negative phenotype). For the purpose of this homework, we will simplify things. Assume that the Rh blood group has only two alleles: the Rh-positive allele (D) and the Rh-negative allele (d).
Erythroblastosis fetalis (EF) is a condition that causes the mother's red blood cells to attack those of the baby as if they were any foreign invaders. It is referred to as hemolytic anemia of the newborn. It is caused by anti-Rh antibodies from the mother which pass through the placenta and attack fetal blood cells that happen to be Rh-positive. Babies that are at risk for this condition are those with Rh-positive blood, whose mothers are Rh-negative (dd).
Consider a population under Hardy-Weinberg equilibrium, where the frequency of the Rh-negative allele, d, is 0.3. What is the frequency of crosses that could potentially produce children with erythroblastosis fetalis?
Question 7: ABO blood type is studied in a Lebanese population, and these allele frequencies are determined.
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f(IA)
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0.30
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f(IB)
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0.15
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f(IO)
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0.55
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What are the frequencies of the various genotypes and various phenotypes in this population? Assume Hardy-Weinberg equilibrium.