Illustrate how the five basic human eye colors can be explained by a model using two genes (A and B), each of which has two alleles (A and a, B and b)
What will be an ideal response?
In this model, human eye color is determined by different combinations of alleles of two genes interacting to synthesize and deposit melanin in the iris. If two genes control a trait and each has a dominant and a recessive allele, there are five phenotypic classes in the F2, each of which is controlled by four, three, two, one, or zero dominant alleles. The F2 ratio of 1 : 4 : 6 : 4 : 1 results from the genotypic combinations that produce each phenotype. At one extreme is the homozygous dominant (AABB) genotype with four dominant alleles; at the other extreme is the homozygous recessive (aabb) genotype with no dominant alleles. The largest phenotypic class (6/16) has six genotypic combinations. Combinations of alleles result in small differences in eye color.
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Australia, Antarctica, and South America represent fragments of
a. Australasia. b. Laurasia. c. Gondwanaland. d. Eurasia. e. Amerasia.
Huntington's disease is caused by:
a. a rare recessive allele. b. a repeat of a nucleotide triplet in a gene. c. a monosomic condition. d. a dominant X-linked allele. e. a deletion of part of chromosome 4.
The maltose operon contains genes that code for proteins that catabolize the disaccharide maltose. Similar to the Lac operon, which is only efficiently transcribed in the presence of lactose, the maltose operon is only efficiently transcribed in the presence of maltose. How might induction of the maltose operon in response to maltose be achieved?
A. Maltose causes an activator to bind an operon with an inefficient promoter. B. Maltose removes an activator from an operon with an inefficient promoter. C. Maltose causes a repressor to bind an operon with an efficient promoter. D. Maltose removes a repressor from an operon with an efficient promoter. E. Maltose causes an activator to bind an operon with an efficient promoter.
Unlike DNA, which typically forms a helical structure, different molecules of RNA can fold into a variety of three-dimensional shapes. This is largely because ___________________
(a) RNA contains uracil and uses ribose as the sugar. (b) RNA bases cannot form hydrogen bonds with each other. (c) RNA nucleotides use a different chemical linkage between nucleotides compared to DNA. (d) RNA is single-stranded.