Practise AP Biology 6.7 questions by linking mutation types and DNA variation to protein function, phenotype, horizontal gene transfer and natural selection.
A particular genetic disorder results from a single change in the amino acid sequence coded for in a gene. Parts of the sequence in normal and mutated genes are shown below. Normal: TAC CTC GTG GAC TGA GGT CTC Mutated: TAC CTC GTG GAC TGA GGT CAC
Second Base
Based on the codon chart above, which of the following amino acid changes is most likely found in the mutated protein?
Figure 1. A pedigree of three generations of a family that have a high frequency of a particular genetic condition
Glu → Val
Val → Glu
Glu → Pro
Pro → Val
The ald gene of fruit flies encodes the ALD protein, which is associated with both the
centromeres of chromosomes and protein filaments produced during meiosis. In the absence
of functional ALD proteins, gamete-producing cells enter anaphase I before homologous
chromosomes are correctly aligned. As a result, the gametes produced do not contain the
correct numbers of chromosomes.
Scientists generated four mutations in the ald gene: ald1, ald3, ald23, and del, which was
a deletion of the gene. To study the role of the ALD protein in meiosis, scientists used
gameteforming metaphase cells from groups of flies with different ald genotypes. Some of the
flies were homozygous for the wild-type allele of ald: WT/WT. Other flies were heterozygous for
different ald alleles: WT/del; ald1/del; ald3/ald23; ald23/del. The scientists measured the percent
of metaphase cells that contained ALD-associated filaments (Figure 1A) and the amount of ALD
protein produced by each of the cell types (Figure 1B).
Figure 1. (A) The average percent of gamete-forming metaphase cells that contained
filaments associated with ALD and (B) the amount of ALD protein produced by each
cell type. A thicker band indicates a greater amount of ALD protein.
Based on Figure 1A, identify the fly genotype in which the average percent of metaphase
cells with ALD-associated filaments is close to 12\%.
Based on Figure 1B, describe the difference in ALD protein production between gamete-
forming metaphase cells of flies with the genotype ald3/ald23 and flies with the genotype
ald23/del.
Scientists hypothesize that gamete-forming metaphase cells can produce a normal amount
of ALD-associated filaments even when they produce about half as much ALD protein as
the wild-type cells produce. Use the data in Figures 1A and 1B to support the scientists'
hypothesis.
For gamete-forming metaphase cells of the W T / del and ald1/del flies, explain why the
phenotypes observed in Figure 1A differ even though the amount of ALD protein produced
(Figure 1B) does not.
The EPAS1 gene in human populations encodes a transcription factor activated in low-oxygen conditions, such as those found in high altitude (mountainous) regions. Researchers collected DNA from several populations of modern humans, including Han, Yoruban, Luhya, and Tibetan. They also collected DNA from the fossils of Denisovans, a prehistoric population. The researchers sequenced the most common EPAS1 allele in each population and determined the specific pattern of variations, called single nucleotide polymorphisms (SNPs), at six positions in each population (Table 1).
The EPAS1 gene shows strong indications of positive selection in Tibetans, a population located in a mountainous region in Asia. Describe how the specific EPAS1 gene SNP pattern shown above became common in the Tibetan population.
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Figure 1. Effect of increasing concentrations of atovaquone on the growth of P. falciparum
