Examen de Genética UAB 2022 · Primer Parcial (Octubre 2022)

Which of the following scientists is not recognized for performing experiments designed to disprove the theory of spontaneous generation?

The developmental concept of epigenesis was historically opposed to:

Which researcher demonstrated experimentally that organisms contain an active substance capable of transferring biological genetic characteristics (the transforming principle)?

Question 4 (Cytosine deamination consequence)

Deamination of cytosine generates uracil. If this damage is left unrepaired prior to the arrival of the DNA replication fork, what permanent base-pair substitution will be introduced into the synthesized DNA?

Substitution of the original C-G pair by:

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Question 5 (Chi-square monohybrid cross)

In an experiment with pea plants starting from two true-breeding lines (one with smooth seeds and the other with wrinkled seeds), an $F_2$ generation gave the following counts: 684 plants with smooth seeds and 198 with wrinkled seeds. Under the null hypothesis of a standard monohybrid cross with full dominance of smooth over wrinkled seeds, the calculated $\chi^2$ value yields a $p$-value between:

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Question 6 (Definition of mutation)

Which of the following alterations does not constitute a mutation?

Question 7 (Type of sequence mutation)

What kind of mutation is revealed by comparing these two sequences?

5'-CTGCCACGTATATAGGC-3'

5'-CTGCCAGGTATATAGGC-3'

Question 8 (Biological cycles statements)

Assess the validity of the following statements:

a.

Zygotes in diplontic life cycles are diploid, whereas zygotes in haplontic life cycles are haploid.

b.

In organisms with a diplohaplontic (haplodiplontic) cycle, spores are diploid and gametes are haploid.

Question 9 (Adenine calculation in dsDNA)

A double-stranded DNA (dsDNA) molecule is 7,904 bp long and has a G-C content of 37%. How many adenine (A) bases are present in this DNA molecule?

Question 10 (Length of dsDNA fragment)

What is the approximate physical length of a 9,762 bp B-DNA duplex fragment?

Question 11 (Base ratios in nucleic acids)

Which of the following ratios, if significantly different from 1, indicates that a DNA sample is not double-stranded?

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Question 12 (Number of telomeres in metaphase)

How many telomeres are present in a somatic pig cell ( Sus scrofa, $2n = 40$) during mitotic metaphase?

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Question 13 (Complete turns of B-DNA helix)

Approximately how many full helical turns are expected in a dsDNA molecule with a length of $3.4\text{ }\mu\text{m}$?

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Question 14 (Eukaryotic and prokaryotic chromosomes)

Which of the following characteristics is shared between eukaryotic and prokaryotic chromosomes?

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Question 15 (Dihybrid cross with lethal alleles)

In mice ( Mus musculus), a dominant allele at one locus produces yellow coat color and is lethal when homozygous, whereas the wild-type allele produces agouti color. At an independently assorting locus, a dominant allele results in a short tail and is also embryonic lethal when homozygous, whereas the recessive allele produces normal-length tails. If two mice with yellow coats and short tails are mated, what fraction of their viable progeny will display both yellow coats and short tails?

Question 16 (Maternal centromeres in anaphase)

Somatic cattle cells have 60 chromosomes ($n = 30$). During mitotic anaphase in an embryonic cell, how many centromeres of maternal origin are present?

Question 17 (Telomerase activity in cell types)

In which of the following cell types would you expect to find active telomerase enzyme?

Question 18 (Allelic dominance in alternation of generations)

In plants exhibiting an alternation of generations, in which phase can the dominance relationship between two alleles of the same gene be directly observed?

Question 19 (Sex determination in poultry)

What type of sex-determination mechanism operates in birds and poultry?

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Question 20 (Probability of PTC non-taster offspring)

The inability to perceive the bitter flavor of phenylthiocarbamide (PTC) is inherited as an autosomal recessive trait relative to the taster allele. If two heterozygous parents have a family of 6 children, what is the probability that at least one child will be unable to taste PTC?

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Question 21 (Haploinsufficiency in seed color)

The wild-type allele governing pea endosperm color produces green seeds. A newly isolated allele yields yellow seeds. When a pure-breeding green pea plant is crossed with a pure-breeding yellow plant, all F 1 individuals produce yellow seeds. What does this reveal about this gene and the yellow allele?

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Question 22 (Dominance relationships and environment)

Evaluate the accuracy of the following two statements:

a.

The dominance relationship between two alleles of a gene can vary depending on environmental conditions.

b.

In an allelic series of a single locus, an allele can be dominant to some alleles and recessive to others.

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Question 23 (RNA hairpin secondary structure)

An RNA molecule contains the following sequence fragment:

5'-... AUUAGCAGGU CGACCUCAUC-3'

The sequence underlined and in bold ( AUUAGCAGGU) pairs intramolecularly to form the stem of a hairpin loop when the RNA folds back on itself. How must the sequence continue immediately downstream from the loop to form this base-paired double-helix stem?

Question 24 (Segregation probability of paternal chromosomes)

In Drosophila melanogaster ($2n = 8$), what is the probability that a gamete produced by a female will contain the centromeric region of exactly one chromosome inherited from her father?

Question 25 (Degrees of freedom with incomplete dominance)

When testing an $\mathrm{F}_2$ generation of a monohybrid cross involving two alleles with incomplete dominance using a chi-square ($\chi^2$) test of goodness-of-fit, how many degrees of freedom must be used?