1. Operons (Circle all correct choices.) a. are found in eukaryotes only b. can

Question

1. Operons (Circle all correct choices.) a. are found in eukaryotes only b. can be controlled by repressors c. contain a DNA sequence called a promoter d. are normally active at all times e. contain genes 2. Neurofibromatosis (a condition where tumor-like growths develop over the body) is an autosomal dominant trait. Of 65 people who are heterozygous for neurofibromatosis, 39 have neurofibromatosis and 26 are normal. What degree of penetrance does neurofibromatosis show? a.090 b, 40% C. 60% d, 100%-dominant alleles always determine phenotype. 3. When the F1 generation of a monohybrid (one gene) Mendelian cross is allowed to self-fertilize (an F1 XFI cross), the observed genotypic ratio of the progeny should be a. 3:1 b. 9:3:3:1 d. 3:2 4. If a heterozygous individual is test crossed to a recessive parent, the progeny will a. all resemble the dominant parent b. show equal numbers of dominant and recessive phenotypes c. all resemble the recessive parent d. resemble the dominant parent 75% of the time 5. Which type of rRNA is found in the small subunit of an E coli ribosome? a. 23S rRNA b. 5S rRNA c. 16S rRNA d. both (a) and (b) e. all of the above

Explanation / Answer

Ans 1- operons

B, C and E are correct choices, while A and D are wrong ones.

Because only prokaryotes have operons and not eukaryotes hence A is incorrect option.

Operons can be switched on only when needed hence it is not normally active all the times.

Ans 3- C is the correct option

Because 25% offsprings have dominant genes, 50% are heterozygous and rest 25% are recessive. Hence the ratio is 1:2:1 genotypically.

While it is 3:1 phenotypically as only dominant phenotype is expressed in heterzygous condition. Hence option A is incorrect.

9:3:3:1 is the phenotypic ratio in F2 generation of dihybrid cross. hence option B is incorrect.

Ans 4- B

In test cross the parent is crossed with a recessive genotypic individual. If heterozygous individual is test crossed then:

Rr X rr

Rr, Rr, rr, rr

The above two type of genotype results and hence the phenotype will be equal no.of dominant and recessive type. Here the genotypic and phenotypic ratio will be 1:1

All phenotypes are dominant if dominant individual is test crossed hence option A is incorrect.

All phenotypes are recessive if recessive individual is test crossed. Hence option C is incorrect too.

and 75% of progeny resembles the dominant parent in back cross not in test cross. Hence option D is also incorrect.

Ans 5- C is the correct option

E.coli is a prokaryote which has 70S ribosome composed of two subunits: one large 50S having 23S and 5S rRNA and another small 30S subunit having 16S rRNA.

Hence option A, B, D and E are incorrect.

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