Mastering Bio Questions

haploid cell

A cell with a single chromosome set is called a haploid cell. Organisms with this type of cells are haploid organisms.

During meiosis, segments of nonsister chromatids can trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis. During what phase of meiosis does recombination occur?

Segments of nonsister chromatids trade places during prophase I, resulting in recombination.

The chromosome theory of inheritance is based upon which of the following sets of observations?

The chromosome theory of inheritance is supported by the fact that genes do segregate and genes and chromosomes do come in pairs. Also, many genes assort independently of one another.

Phylogeny

The evolutionary history of a species or group of related species.

Which population would be most likely to undergo relatively rapid allopatric speciation?

The new population is geographically isolated from others and is small (reproductively), both of which tend to promote allopatric speciation.

Imagine that a mutant strain of Drosophila undergoes crossing over at half the normal rate. How would a genetic map prepared for this mutant differ from a genetic map prepared for a normal (wild type) fly?

The order of genes would be the same in both strains, but the distances measured between genes in the mutant would be half those of the wild type. Because map distances are based on the frequency of recombination, reducing recombination frequency by half will reduce the apparent distance between genes by half (the actual distance in DNA base pairs is the same, only the estimate of this distance based on recombination frequency is reduced).

A diploid cell in a plant undergoes chromosome duplication but fails to divide properly, initiating a tetraploid (4n) branch. This branch produces a 4n flower. What can happen next?

The tetraploid (4n) flower produces 2n gametes and may then be able to self-pollinate to produce fertile 4n offspring.

Transitional forms

Transitional forms represent a link between ancestral and descendant groups; they possess features of both groups

Although in humans there are 22 pairs of autosomal chromosomes, only three different chromosomal trisomies are commonly seen in newborns. Of the remaining 19 autosomes, many trisomies have not been seen in newborns. Why not?

Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried. Unfortunately, these trisomies do occur and are commonly observed in spontaneously aborted embryos and fetuses.

convergent evolution

can produce similarities in body form when similar environments and natural selection have favored similar adaptations.

The existence of rare XY individuals who are phenotypically normal women was instrumental in learning about human sex determination. Maleness is determined by the SRY gene found on the Y chromosome. How is it possible to be an XY woman?

d) The SRY locus of the Y chromosome is deleted.If SRY is deleted, the Y chromosome would still be present, but development would occur along the female path.

During anaphase I, __________.

homologous chromosomes separate and migrate toward opposite poles

Mechanical isolation

is a form of reproductive isolation that prevents two different species from interbreeding with one another.

Gametic isolation

is a type of prezygotic barrier where the gametes (egg and sperm) come into contact, but no fertilization takes place.

Temporal isolation

is an evolutionary mechanism that keeps individuals of different species from interbreeding, even if they live in the same environment.

Behavioral isolation

is reproductive isolation based on the behavior of species in the context of mating rituals and signals.

Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from the cross PpRr × PpRr are expected to have white flowers and wrinkled seeds?

1/16 Pp × Pp would produce 3/4 purple and 1/4 white. Rr × Rr would produce 3/4 round and 1/4 wrinkled. (1/4)(1/4) = 1/16 would have white flowers and wrinkled seeds.

Assume that in cattle a spotted coat is dominant to an even coat, short horns are dominant to long horns, and the traits for coat type and horn length assort independently. In a cross between cattle that are each heterozygous for both traits, what proportion of their offspring are expected to have long horns?

1/4

Three characteristics assort independently in one species of insect: Red eyes (R) are dominant to black eyes (r). Blue wings (B) are dominant to white wings (b). Green bodies (G) are dominant to yellow bodies (g). A cross is made between two heterozygous insects (RrBbGg). What is the probability that the offspring will be homozygous dominant for all three characteristics?

1/64 The likelihood that the offspring will be homozygous dominant for any particular characteristic is 1/4 and can be determined using a Punnett square. The likelihood that the offspring will be homozygous dominant for all three characteristics can be determined using the rule of multiplication (1/4 × 1/4 × 1/4).

High levels of LDL cholesterol in the bloodstream can be the result of familial hypercholesterolemia, an inherited condition that displays incomplete dominance. In a family with a severely affected father and an unaffected mother, what percentage of their children are expected to have higher than normal blood cholesterol?

100% Individuals with two copies of the hypercholesterolemia allele suffer from severe hypercholesterolemia. However, if you inherit only one copy of this allele, you would still inherit the predisposition to have higher-than-normal blood cholesterol levels.

The 4% born with sickle-cell disease are homozygous for the sickle hemoglobin allele, so q2 = 0.04 and q = 0.2. Because p = 1 - q, p = 0.8, and the heterozygotes would be equal to 2pq, or 0.32.

32% The 4% born with sickle-cell disease are homozygous for the sickle hemoglobin allele, so q2 = 0.04 and q = 0.2. Because p = 1 - q, p = 0.8, and the heterozygotes would be equal to 2pq, or 0.32.

Meiosis starts with a single diploid cell and produces

4 haploid cells

In Labrador retrievers, a common breed of dog, black coat is dominant to chocolate, normal vision is dominant to progressive retinal atrophy (PRA), and normal hip joint is dominant to hip dysplasia. All these genes assort independently. Two dogs that are heterozygous for alleles of all three genes are crossed. Using rules of probability (not a Punnett square), what is the chance that the first pup born to these dogs will be chocolate, have normal vision, and have normal hip joints?

9/64 The chance is given by the product of the individual probabilities (chances) of obtaining a chocolate, normal vision, normal joint pup from parents heterozygous for each of these traits, or 1/4 × 3/4 × 3/4 = 9/64.

In theory, when a nondisjunction for chromosome 18 occurs during meiosis I, four gametes can be produced. If these gametes are fertilized with unaffected gametes from the second parent, what observations would you make concerning the resulting embryos?

A nondisjunction that occurs in the first meiotic division will result in one daughter cell having two copies of chromosome 18. This will be trisomic upon fertilization. The other daughter cell will have no copies of chromosome 18 and will contain a single copy of chromosome 18 upon fertilization, a condition known as monosomy.

A postzygotic reproductive barrier

A postzygotic reproductive barrier is a mechanism that reduces the viability or reproductive capacity of hybrid offspring.

A prezygotic reproductive barrier

A prezygotic reproductive barrier is a mechanism that prevents fertilization from occurring

Under some conditions, heterozygotes have greater reproductive success than homozygotes. What is this called?

An example of heterozygote advantage is the protection from malaria conferred by sickle-cell hemoglobin. The frequency of the sickle-cell allele is generally highest in areas where malaria is a major cause of death, such as West Africa, because heterozygotes are protected from the most severe forms of malaria.

Which example below presents a misconception about how antibiotic resistance develops?

Antibiotics have no effect on viruses, so this is one common misconception. More importantly, antibiotic resistance arises over several bacterial generations as resistant bacteria flourish and vulnerable strains die out. Although they are usually rare, the resistance traits are often present before the antibiotic is first used.

What is the difference between a benign tumor and a malignant tumor?

Benign tumors do not metastasize; malignant tumors do. Malignant tumors spread from their site of origin to other parts of the body.

In the laboratory, cancer cells fail to show density-dependent inhibition of growth in cell culture. What is one explanation that could account for this?

Cancer cells continuously secrete growth factors--> cell culture medium In this case, the cells would stimulate their own growth and grow far more extensively than normal cells dependent on the limiting amounts of growth factor present in the medium.

In Morgan's testcross of a gray-bodied, long-winged heterozygous female Drosophila with a homozygous recessive black-bodied, vestigial-winged male, the following offspring were obtained: 965 gray body, long wing; 944 black body, vestigial wing; 206 gray body, vestigial wing; 185 black body, long wing. Focusing only on the recombinant classes (gray body, vestigial wing and black body, long wing), the numbers of offspring of each type are similar (206 and 185). What accounts for the similar number of offspring of each recombinant phenotype?

Crossing over between chromosomes is reciprocal, so whenever a recombinant chromosome of one type is produced, there's a recombinant of the opposite type that is also produced. Every time a recombinant chromosome of one type is produced, there is a complementary type of recombinant chromosome that is also produced

Meiosis differs from mitosis in that _____ only occurs in meiosis.

Crossing over, the exchange of corresponding segments between nonsister chromatids of homologous chromosomes, only occurs during meiosis.

During prophase I of meiosis,

Homologous chromosomes stick together in pairs during prophase I.

You suspect that a serious developmental disorder is due to a chromosome abnormality and prepare a karyotype from an affected individual. In analyzing the karyotype, how could you distinguish trisomy from a chromosome structural defect such as a duplication?

In trisomy there would be one extra chromosome; in a duplication, the number of chromosomes would be normal, but one chromosome would have two copies of a portion of the chromosome. Trisomy means three copies of a chromosome; duplication involves a repeated segment of one chromosome.

In breeding pure-breeding large and small strains of mice, you cross individuals of each strain and note that their offspring are intermediate in size. Two models (explanations) to account for this result are (1) that body size in these strains is due to one gene with alleles that show incomplete dominance and (2) that body size is a polygenic trait. How could you distinguish between these models?

Intercross the F1 and see if the F2 contains three size classes (consistent with the incomplete dominance model) or if there is a range of sizes (consistent with the polygenic model).

Consider the photograph of a karyotype. This is _____.

Karyotypes, ordered displays of a person's chromosomes, are useful in identifying chromosomal abnormalities.

Why are lethal dominant alleles so much more rare than lethal recessive alleles?

Lethal dominant alleles are harmful whether they are carried in homozygous or heterozygous form, so there is always strong selection against these alleles. The ability of lethal recessive alleles to "hide" from selection in heterozygotes accounts for their prevalence relative to dominant alleles, which are always visible to selection.

Which would be a good example of intrasexual selection?

Male elephant seals use their huge bodies to batter each other in battles for access to mates. This is selection for traits (size, skill in fighting) that enhance an individual's ability to compete with members of the same sex and thereby secure mating opportunities.

How did the 1977 drought on Daphne Major cause evolutionary change in the medium ground finch population?

Medium ground finches with large and deep beaks had higher survival rates during the drought.

Trisomy for most autosomes is fatal, yet trisomy or even tetrasomy (four copies) of the X chromosome is not. What is the explanation for this difference?

Only one copy of the X chromosome is functional within any given cell, regardless of the total number of X chromosomes.

The original source of all genetic variation is __________.

mutation

Of the choices listed below, which contributes the most to genetic variation among individuals in most prokaryote species?

mutation In prokaryotes, which are haploid with a single allele for each gene, mutations immediately have their full effect. Since their generation times are very short, new mutations can proliferate rapidly.

Habitat isolation

occurs when habitat preferences lower the probability of mating between individuals associated with differing habitats.

During anaphase II, __________.

sister chromatids separate and migrate toward opposite poles

Sympatric speciation occurs

when populations of a species that share the same habitat become reproductively isolated from each other. This speciation phenomenon most commonly occurs through polyploidy, in which an offspring or group of offspring will be produced with twice the normal number of chromosomes. polyploidy in plants; habitat differentiation in animals

If the two characteristics that Mendel looked at in his dihybrid cross of smooth yellow peas with wrinkled green peas had been controlled by genes that were located close together on the same chromosome, then the F2 generation __________.

would have deviated from the 9:3:3:1 phenotypic ratio that is predicted by the law of independent assortment If the two characters are located on the same chromosome, they will not segregate independently.