Genetics Exam Two Learning Curves

Pure lines are among the essential tools of genetics. You can obtain expressed recessive traits only when you have fully pure (homozygous) lines. Pure lines are also an important resource for research. Suppose we start with a population of individuals that are all A/a (heterozygous) and allow them to self. According to Mendel's first law, after eight generations of selfing, what is the proportion of heterozygotes?

(1/2)^8

The unit of mapping (1 m.u.) is defined as a recombinant frequency of _____ percent. Map distances are roughly additive.

1

For the cross AabbCcDdEe × AaBbCcddEe, what is the overall probability of obtaining progeny of genotype aabbccddee?

1/256

Imagine you are studying F2 pea plants. You derive these plants by crossing pure green pea plants with pure yellow pea plants, and then selfing the resulting F1 generation. What proportion of plants in this F2generation would be considered pure-bred plants that produce only yellow peas?

1/4

When two organisms that are heterozygous at the same locus are crossed, ___ of the progeny will be homozygous recessive.

1/4

Monique is rolling an eight-sided die. What is the probability that the die will land on 4 two times in a row?

1/64

Coat color in mice is determined by two alleles acting at a single locus: B is dominant and results in mice with black coats, and b is recessive and results in mice with white coats. In a litter of 12 mice, nine are black (B) and three are white (b/b). What is the penetrance of the B coat color allele?

100 percent

A Punnett square for a dihybrid cross has _____ boxes representing the various gametic fusions.

16

Green pea color is recessive. If two heterozygous pea plants are crossed, what is the ratio of green to yellow offspring?

1:3

A single crossover generates _____ reciprocal recombinant products.

2

You are working with two genes in banana plants: fruit color (g) and plant height (t). Yellow fruit color and tallness are dominant and are the result of wild-type g+ and t+ alleles, respectively. You cross two pure lines and then perform a testcross with the F1 dihybrid females. The 700 F2 progeny show these genotypes: 265 are g+ · t+, 278 are g · t, 76 are g+ · t, and 81 are g · t+. What is the recombinant frequency of the two genes?

22.4 percent The recombinant genotypes are heterozygous; 76 are g+ · t, and 81 are g · t+; (76 + 81)/700 = 22.4 percent.

You wanted to draw a linkage map for three genes in the impala (A, B, C) that you suspect are linked. You have done a three-point testcross and found that in the 800 progeny of the cross, 290 are a · b · c, 270 are A · B · C, 94 are a · B · C, 88 are a · B · c, 32 are a · b · C, 19 are A · B · c, 2 are A · b · C, and 5 are A · b · c. From these data, you can conclude that the genes are linked and that _____ is the distance between A and B.

23.6 map units Add up all the progeny that contain A and b or a and B (recombinant types). The total should be 189, which divided by the total, 800, is 23.6 percent.

You are interested in the inheritance of two autosomal genes in a type of screech owl. These genes determine feather color (gray or red, governed by the alleles g+ and g) and ear tuft length (short or long, determined by the alleles e+ and e). You cross two pure breeding lines of owls and let the F1 generation (g+/g· e+/e) intercross. The F2 progeny deviate from the expected Mendelian ratio, so you cross a dihybrid F1female with a tester male. Of the 1000 progeny, 264 are (g+ · e+), _____ are (g · e), 236 are (g · e+), and 220 are (g+ · e).

280

You perform a dihybrid cross between two plants that have traits expressing a simple dominance relationship. Then, you self the F1 generation and analyze the progeny. How many degrees of freedom do you have for your chi-square test?

3

If an individual has two heterozygous gene pairs, how many genetically different gametes can be formed?

4

A cross between two distinct mutants has mutations in different genes on different chromosomes. The mutation for a melanistic griffon, g+, is on one chromosome, and the mutation for elongated canines (sabertooth), t+, is on another chromosome. So the cross is: g+; t × t+;g. What will be the frequency of the two octad types?

50% g+; t and t+; g, 50% g; t and g+;t+.

How many different kinds of gametes can be produced by an individual with the genotype AABbCCddEeFf?

8

In a three-point testcross, _____ gamete genotypes are possible.

8

The genetics of eye color is not yet fully understood. There are multiple pigments and interaction between alleles at play, but we will look at a simplified example. In Europeans, B is dominant and results in brown eyes, while b is recessive and results in blue eyes. In individuals with the BB genotype, 85 percent have brown eyes, 14 percent have green eyes, and 1 percent have blue eyes. What is the penetrance of the Bpigment allele?

85 percent

Assuming Mendel's second law is correct, what is the expected segregation ratio for traits in a dihybrid cross?

9:3:3:1

The gene that plays a primary role in maleness is the:

SRY gene.

What occurs during mitosis?

Separation of chromosomes

A chi-square test comparing observed and expected progeny is carried out, and the probability (p) value associated with the calculated chi-square value is 0.062. What does this p = 0.062 value represent?

The difference between observed and expected numbers is significant, warranting further study.

The reasons an organism might have a particular genotype and not express the corresponding phenotype include all of these EXCEPT: -The influence of other interacting genes. -The subtlety of the mutant phenotype. -The influence of the environment. -The influence of lethal alleles.

The influence of lethal alleles.

What does it mean when two genes are linked?

The two genes are on the same chromosome.

What are centromeres?

They are regions of DNA. Centromeres are regions of DNA on which the orderly reproduction of living organisms absolutely depends, and they are of great interest in genetics.

A scientist is constructing a physical map for chromosome 4 in bats. He identifies a bat gene that is 99 percent similar in sequence to a gene in mice and rats. What can he conclude?

This genetic sequence was likely present in a common ancestor of bats, mice, and rats. Furthermore, this gene likely has a similar function in all three animals.

A cross of parents with unknown genotypes produces progeny with a phenotypic ratio of 1:1:1:1:1:1:1:1. What type of cross is this?

Trihybrid testcross with unlinked genes

In Neurospora, an MII segregation pattern observed in the ascospores of an octad is indicative of:

a crossover event in the chromosomal region between the centromere and the gene locus being studied.

The standard genetic test for linkage is _____.

a dihybrid testcross

Dominance is determined by the way alleles are expressed in:

a heterozygote.

The group of haploid cells resulting from meiosis is called:

a tetrad

What is the definition of a hypostatic gene?

A gene that is suppressed by the effect of another gene at a different locus.

A researcher is studying two alleles, a wild type and a mutant, of a gene in cats. She determines that the wild-type allele is haplosufficient. What does this mean?

A haploid dose of the wild-type allele can result in a cat with a wild-type phenotype. "Haplo-" means a haploid dose (one), and sufficient refers to the ability of that single dose to produce the wild-type phenotype.

START OF CH 5 LEARNING CURVE _____ measures the degree to which a given allele is expressed at the phenotypic level.

Expressivity

A family tree or pedigree can be used to show the inheritance of mutant genes. Which of these is true regarding a pedigree? -Horizontal lines connecting a mating pair to their offspring. -Vertical lines connect a mating pair. -Filled squares or circles indicate an affected individual. -Squares are females and circles are males.

Filled squares or circles indicate an affected individual.

Which of these is true of Neurospora? -Mutant Neurospora are defective for some normal synthetic step. -Neurospora is a type of photosynthetic bacteria. -Mutant Neurospora can use its cellular biochemistry to synthesize all of its cellular components. -Neurospora is a diploid organism.

Mutant Neurospora are defective for some normal synthetic step.

Assume that the results of intercrossing mutants $, £, and ¥ are as shown: white $ × white £ → F1, all white white $ × white ¥ → F1, all blue white £ × white ¥ → F1, all blue

Mutants $ and £ must be caused by alleles of one gene, but ¥ must be caused by a mutant allele of another gene.

A line of pure pea plants with purple flowers is crossed with a pure line of pea plants with white flowers. The purple allele is dominant (P), and the white allele is recessive (p). What proportion of progeny has white flowers?

None

Some forms of Alzheimer's disease have been linked to mitochondrial DNA. If your paternal grandmother has the disease, what are the chances that you will inherit it?

Not very likely at all. Transferal of mtDNA is matrilineal, so you would inherit it only if your maternal grandmother has the disease.

_____ that contain mixtures of two genetically distinct chromosomes often show segregation of the two types into the daughter cells after one or more cell divisions. This process is called cytoplasmic segregation.

Organelle populations

Which of these is the correct order of generations? -F1, F2, and P -F2, P, and F1 -F1, P, and F2 -P, F1, and F2

P, F1, and F2 Parental generation (P), first filial generation (F1), second filial generation (F2) is the correct order of generations.

_____ and _____ measure the differences in gene expression, or phenotype, when environmental or genetic backgrounds vary.

Penetrance; expressivity

You have crossed a red flowering plant with a white flowering plant. You know that red (R) is dominant to white (r). The F1 plants all have red flowers. The genotype of the red flowering parent is:

R/R. This flower would be red, because it is homozygous for the dominant trait.

_____ is a process in which a mutation-bearing chromosome may by chance increase in frequency in the population within the cell.

Random genetic drift

The units of distance on a physical map are the numbers of DNA _____; for convenience, the _____ is the preferred unit.

bases; kilobase

START OF CH 2 LEARNING CURVE If you were to isolate any somatic cell (i.e., any cell except a gamete) from the human body, this cell would contain _____.

both sex chromosomes and autosomes

In the first step of crossing over, _____ strand(s) of a chromatid break(s) in the _____ location.

both; same

The gene comes in two forms called _____.

alleles

When two independently derived recessive mutant alleles producing similar recessive phenotypes fail to complement, they must be:

alleles of the same gene.

Cytoplasmic segregation differs from nuclear segregation in many ways except:

alleles on organelle chromosomes can be segregated into separate cells in a number of successive cell divisions.

A testcross is a cross between a fully recessive parent and an individual with _____ genotype.

an unknown (i.e., H/?)

Two mutations that are individually benign, _____ when united in the same genotype.

can become lethal Such synthetic lethals can point to some type of normal gene interaction in the wild type.

At the beginning of mitosis, the sister chromatids remain joined together at a special chromosomal region called the:

centromere

A(n) _____ is a statistical test used to check results against expectations.

chi-square test

START OF CHAPTER 4 LEARNING CURVE What are the visible manifestations of crossovers?

chiasmata

A _____ conformation in a dihybrid occurs when the two wild-type alleles are on the same homolog (i.e., represented as the genotype ++/ab).

cis

The _____ test allows a researcher to determine whether two recessive mutations are from different genes or are alleles of the same gene.

complementation

To determine whether mutations occur at the same or different loci, one could use a ___ test.

complementation

Beadle and Tatum methodically analyzed pairs of mutants using a(n) _____.

complementation test

At the onset of mitosis in somatic cells, the chromosomes _____ and _____ to form daughter units called chromatids.

condense; duplicate

Sometimes the effect of gene interaction is that one gene masks (hides) the effect of another gene at a different locus, a phenomenon known as _____.

epistasis

Mendel's law of equal segregation states that during meiosis the two alleles for a gene move into gametes:

equally, with one allele going to one gamete.

Genes necessary to the survival of an organism are called _____ genes.

essential

mtDNA _____, so it has been most useful in plotting recent evolution such as the evolution of humans and other primates.

evolves relatively rapidly

The _____ genes are, the more closely their recombinant frequencies approach 50 percent.

farther apart The farther apart the genes are, the more likely that a crossover will take place and the higher the proportion of recombinant products will be.

Both male and female dihybrids exhibiting independent assortment will generate _____ types of gametes each.

four

Both male and female dihybrids exhibiting independent assortment will generate _____ types of gametes, in a _____ ratio.

four; 1:1:1:1

Mendel's law of independent assortment states that different gene pairs assort independently during _____formation.

gamete

Molecular markers can help in the process of locating:

genes of interest.

Homozygous pure lines are important research tools that allow geneticists to maintain a source of any given _____.

genotype

In a testcross, the ratio of phenotypes in the progeny reflects the gametic _____ of the nontester parent.

genotypes

The Punnett square is a useful tool for graphically displaying the _____ outcomes of their random union.

genotypic and phenotypic

The greater the distance between the linked genes, the _____ the chance of crossovers in the region between the genes, and the _____ the proportion of recombinants that would be produced.

greater; greater

In _____, the genotypes of the products of meiosis (spores) are directly observed in the haploid organisms that arise from each spore through mitotic cell division. A ratio of 1:1:1:1 is diagnostic of _____ in a dihybrid meiocyte.

haploids; independent assortment

A researcher is studying a gene affecting bone development in mice. He notices that mice carrying a single mutant allele of this gene demonstrate several bone defects, especially in the skull and ribs. Thus, the researcher could classify this gene as:

haploinsufficient

The genes in the differential portion of the Y chromosome are called _____, meaning that they do not have copies on any other chromosome.

hemizygous

The interaction of several additive _____ genes can, by themselves, result in a bell-shaped curve with their _____ acting as metric "doses."

heterozygous; alleles

Women show _____ for the same autosomal loci than men.

higher recombinant frequencies Women show higher recombinant frequencies for the same autosomal loci than men.

In a diploid cell, chromosomes are in pairs (there are n pairs); the two members of a pair are called:

homologs

An organism with two identical alleles is called a:

homozygote

Y-linked genes:

how direct father-to-son transmission and are typically related to maleness traits.

Some hybrids between genetically different pure lines show _____.

hybrid vigor

A(n) _____ gene is suppressed by the effect of another gene at a different locus.

hypostatic

All of the plants used by Mendel were from pure breeds so, considering the phenotype, the offspring produced by those plants were:

identical

Both male and female dihybrids exhibiting _____ will generate four types of gametes.

independent assortment

Mendel's law of independent assortment has its physical basis in the:

independent segregation of alleles during meiosis

For _____, the probability of a multigene genotype or phenotype can be obtained by multiplying the probabilities of the genotype or phenotype for each of the individual genes.

independently assorting genes

After the sister chromatids are separated into daughter cells, they become:

individual chromosomes

The sum rule states that the probability of either one or the other of two mutually exclusive events occurring is the sum of their:

individual probabilities

Interference is an interaction in which crossovers _____ each other.

inhibit

Organelle genes are very closely spaced and, in some organisms, organelle genes can contain untranslated segments called _____.

introns

Red-green color blindness is more often seen in males than in females because:

it is a recessive X-linked trait and males only have one X chromosome.

Garrod's observations of alkaptonuria raised the possibility that the cell's chemical pathways were under the control of a _____ set of _____ genes.

large; interacting

A mutation that reduces functionality of a protein is called a _____ mutation.

leaky Leaky mutations reduce the level of enzyme function but do not render them completely nonfunctional.

The recombinant (i.e. nonparental) genotypes seen in the progeny of Morgan's fly testcrosses occur in approximately equal frequency and makeup _____ of the progeny's genotypes.

less than 50 percent

Recombination between _____ can be used to map their distance apart on a chromosome.

linked genes

Epistasis is inferred when a mutant allele of one gene _____ the expression of a mutant allele of another gene and _____ its own phenotype instead.

masks; expresses

In haploids, the genotypes of the products of _____ (spores) are directly observable in the haploid organisms that arise from each spore through mitotic cell division. A ratio of 1:1:1:1 is diagnostic of independent assortment in a _____.

meiosis; dihybrid meiocyte

The process by which somatic cells divide to increase their number is called:

mitosis

A type of dominance is determined by the _____ functions of the alleles of a gene and by the _____ level of analysis.

molecular; investigative

A heterozygote for a single gene (such as A/a) is sometimes called a:

monohybrid

Parental genotypes, which would be classified as nonrecombinant, were seen in _____ of the progeny resulting from Morgan's testcrosses in flies, as certain alleles tend to be inherited together.

more than 50 percent

Human mitochondrial diseases are passed to offspring by:

mothers only

It has been possible to introduce some extinct organisms into evolutionary trees using _____ sequences obtained from their remains, such as skins and bones in museums.

mtDNA

One key finding is that the "root" of the human _____ tree is in Africa, suggests that Homo sapiens originated in Africa and from there dispersed throughout the world.

mtDNA

An alligator farmer is studying his newest hatchlings. He knows that alligators, in nature, are normally brown or green; however, he has discovered a rare albino alligator among his hatchlings. This lack of pigmentation would be considered a _____ phenotype in alligators.

mutant

The heritable variants observed in a species that differ from wild type are called _____, individual organisms having some abnormal form of the trait.

mutants

RrYyPpIiggAass × rrYyPPIiGgAass, assuming complete dominance, and "kinds" means different combinations of alleles.Using this information, what fraction of the offspring from these plants will have white petals?

none of them

A researcher has mated two Neurospora with different genotypes, resulting in a ZW × zw cross. She examines the resulting tetrad, which contains cells with the genotypes Zw and zW. This tetrad would be classified as a:

nonparental ditype.

During meiosis, _____ may either cross over by chance, producing recombinants, or not cross over at all, resulting in no recombinants being produced.

nonsister chromatids In some meioses, nonsister chromatids cross over by chance in the chromosomal region between these genes, and recombinants are produced.

From C/c × C/c, _____ of the progeny will be c/c.

one-fourth

From b/b × B/b, _____ of the progeny will be b/b.

one-half

Most _____ inherited from the female because the _____ contributes the bulk of the cytoplasm, whereas the _____ contributes essentially none.

organelles are; egg; sperm

Pure lines of plants or animals are made through repeated generations of _____.

selfing Pure lines of plants or animals are made through repeated generations of selfing. (In animals, selfing is accomplished by mating animals of identical genotype.)

The arginine biosynthetic pathway is as follows: precursor → ornithine → citrulline → arginine. The three arginine mutants of Beadle and Tatum are named arg-1, arg-2, and arg-3. The arg-1 mutant grows with treatment of ornithine, citrulline, or arginine. The wild-type arg-1 gene codes for an enzyme that:

converts a precursor molecule to ornithine.

_____ results from the breakage and reunion of DNA. Two parental chromosomes break at the same position, and then each piece joins up with the neighboring piece from the other chromosome.

crossover

A _____ is the breakage of two DNA molecules at the same position and their _____ in two reciprocal recombinant combinations.

crossover; rejoining

Cells that contain mixtures of mutant and normal organelles are called:

cytohets

Both parents contribute equal amounts of _____ to the zygote, but essentially all the _____ are all contributed by the female parent.

nuclear genes; organelles and cytoplasm

The DNA sequence of alleles of a gene must have at least one _____ difference.

nucleotide If the nucleotide sequence of an allele changes as the result of a rare chemical "accident," a new mutant allele is created.

An allele with a mutation that renders it completely nonfunctional (i.e., it cannot produce a functional protein) is called a _____ allele.

null

If there are ____ mutations in genes in both duplicate systems, then a faulty system will have no backup, and the individual will lack essential function and die.

null

A researcher has mated two types of Neurospora, one with a D allele and the other with a d allele. He observes four different octads with ascospores in these orders: octad 1, DDddDDddDD; octad 2, DDDDdddd; octad 3, ddDDDDdd; and octad 4, DDddddDD. Which of these octads does NOT represent an MII segregation pattern?

octad 2

If two genes are on different chromosomes, the gene pairs are separated by a _____. If they are on the same chromosome, the alleles on one homolog are written adjacently and are separated from those on the other homolog by a _____. Please choose the correct answer from the following choices, and

semicolon; slash Gene pairs on different chromosomes are separated by a semicolon, when written, and by a slash when on the same chromosome.

The chromosomes that determine whether an individual is male or female are:

sex chromosomes

In haploids, meiosis takes place at one special stage of the life cycle when two haploid cells unite to form a transient diploid meiocyte. This cell union is a type of:

sexual union

A researcher is studying a group of genes that all appear to function in the same pathway. These genes encode proteins that are involved in multiple phosphorylation events, and when this pathway is activated, the result is the transcription of a specific target gene. These genes are most likely involved in a _____pathway.

signal-transduction

Metabolism is:

the general set of chemical reactions taking place in an organism

The probability of obtaining at least one success is the probability of all possible outcomes (this probability is 1) minus:

the probability of total failure

If a medical disorder runs in the family, a pedigree analysis can be undertaken to predict:

the probability that a certain disorder will affect the offspring of a couple in that family.

A 9:7 F2 ratio suggests interacting genes in _____; absence of either _____ function leads to absence of the end product of the pathway.

the same pathway; gene

What does cross-pollination involve?

the transfer of pollen with a brush from one plant to another plant's stigma

When two genes are located together on the same chromosome:

their alleles do not always assort independently

Genes for different traits that assort independently of each other during meiosis are based on the fact that:

they are on different homologous chromosome pairs

A researcher is studying fur color in golden retrievers. The general category of fur color in these dogs could also be referred to as a _____. If a dog had cinnamon-colored fur, this could be called the dog's fur _____.

trait, character, or property; phenotype The general category of fur color is a trait, while the specific color is the phenotype.

A _____ conformation in a dihybrid occurs when the two dominant or wild-type alleles are on different homologs.

trans

In haploids, meiosis takes place at one special stage of the life cycle when two haploid cells unite to form a:

transient diploid meiocyte.

Meiosis has _____ nuclear division(s) that results in four daughter cells with _____ the number of chromosomes of the progenitor cell (meiocyte).

two; half The DNA is copied before the first division, but not copied before the second division, resulting in haploid cells.

Several human diseases arise from a mutation that causes a nonfunctional enzyme in a specific pathway. Phenylketonuria is one such disease. Its mutation results in the inability to convert phenylalanine to:

tyrosine

Obtaining a map of gene positions on the chromosomes is an endeavor that has occupied thousands of geneticists for the past 100 years. All of these are ways that gene maps are used, EXCEPT:

understanding why nucleotides undergo mutations

You are working with two genes in sea slugs: the presence or absence of a skirt (s) and spotting (d). Presence of a skirt and dorsal spotting are both dominant wild-type alleles. You cross two pure lines and then perform a testcross with the F1 females. The 700 F2 progeny show these genotypes: 265 are s+ · d +, 278 are s · d, 76 are s + · d, and 81 are s · d+. Are these genes linked? If yes, what is the conformation of the alleles in an F1dihybrid?

yes; cis

Which of these statements regarding forward genetics is FALSE? -A researcher performing a forward genetics experiment would begin by trying to induce random multiple-gene mutations (e.g., through radiation exposure) in normal organisms. -Forward genetics can be used to identify genes involved in determining a specific property, such as eye color in fruit flies or coat color in mice. -Forward genetics requires that a researcher have access to both mutant and wild-type organisms. -One of the last steps in a forward genetics experiment could be to determine the sequence of a mutated gene.

A researcher performing a forward genetics experiment would begin by trying to induce random multiple-gene mutations (e.g., through radiation exposure) in normal organisms.

If you knew only that the individual with the genotype AaBbDdEe had the dominant phenotype for traits A, B, D, and E, which of these crosses would test the hypothesis that all these loci were on different homologous chromosome pairs?

AaBbDdEe × aabbddee

Which statement is FALSE regarding the cytoplasmic segregation process? -In chloroplasts, it is a common mechanism for producing variegated plants. -In cytohets, a type of cytoplasmic segregation can be detected. -Alleles on organelle chromosomes in asexual cells cannot show cytoplasmic segregation. -Cytoplasmic segregation is not a mitotic process.

Alleles on organelle chromosomes in asexual cells cannot show cytoplasmic segregation.

Which of these is TRUE of Beadle and Tatum's experiment? -Beadle and Tatum analyzed pairs of mutants using the chi-square test. -Beadle and Tatum used a haploid organism called Neurospora. -Beadle and Tatum cooked cells to produce auxotrophic mutants. -Beadle and Tatum used mutants that were able to synthesize all of its cellular components.

Beadle and Tatum used a haploid organism called Neurospora.

_____ is a type of inheritance in which heteroplasmons divide asexually, resulting in either the mutant or normal organelle DNA type in each daughter cell.

Cytoplasmic segregation

What factor(s) contribute(s) to continuous variation?

environment and genotype

Vitamin D-resistant rickets is an X-linked dominant disorder. If an affected female and unaffected male produce two female children, one of whom is affected, what is the genotype of the mother?

D/d If the mother is heterozygous for the dominant disorder, half of her children will be affected and the other half unaffected.

If D and R represent two linked molecular marker loci, where D is a locus with a simple DNA sequence difference, and R is a locus showing variable numbers of tandem repeats, what will the recombinants for this cross be? D1 R1/D2 R2 × D3 R3/D3 R3

D1 R2/D3 R3 and D2 R1/D3 R3

_____ means that one gene copy does not have enough function to produce a wild-type phenotype.

Haploinsufficient

_____ means that one gene copy has enough function to produce a wild-type phenotype.

Haplosufficient

A doctor isolates hemoglobin from a patient and runs this sample on an electrophoretic gel. She notices that two hemoglobin bands are present, one near the top of the gel and the other near the bottom. The doctor concludes that the patient's genotype is:

Hb^A/Hb^S

Annie is breeding angelfish to sell at the fair. She is crossing rainbow-striped angelfish with zebra-striped angelfish. Zebra-striped angelfish are the wild type, while rainbow-striped angelfish are relatively rare. She soon notices that almost all of the rainbow-striped angelfish are male. When she crosses a male rainbow-striped angelfish with a female zebra-striped angelfish, their offspring are either all zebra-striped, or all the females are zebra-striped and half the males are zebra-striped. What type of trait is rainbow-stripe color in angelfish?

X-linked recessive

The gene for a disorder that affects only males is most likely on:

Y chromosome

Green pea color is recessive. If a heterozygous pea plant is crossed with a pure yellow pea, what will the genotypes of four offspring be on average?

Y/Y, Y/y, Y/Y, Y/y Half the offspring will be heterozygous and half will be homozygous dominant when a pure yellow pea is crossed with a heterozygous pea plant.

Recombination maps:

depict the distances between genes on the same chromosome in map units.

A double heterozygote such as A/a · B/b is sometimes called a:

dihybrid

For a _____ exhibiting independent assortment, the testcross ratio is 1:1:1:1.

dihybrid

START OF CH 3 LEARNING CURVE The testcross is a useful tool for _____, where the phenotypes and genotypes of gametes cannot be observed directly.

diploids

The frequency of recombinants is assumed to be proportional to the _____ of two loci on the chromosome; hence, recombinant frequency becomes the _____.

distance apart; mapping unit

Crossovers between sister chromatids:

do occur but are rare and do not produce new allele combinations. Crossovers between sister chromatids occur but are rare. They do not produce new allele combinations, so they are not usually considered.

During Mendel's experiments, _____ alleles resulted in visible phenotypes when at least one copy was present.

dominant

During Mendel's experiments, the alleles that were visible in heterozygotes (i.e., that resulted in an observable phenotype, such as yellow seeds) were:

dominant

The arginine biosynthetic pathway is as follows: precursor → ornithine → citrulline → arginine. The three arginine mutants of Beadle and Tatum are named arg-1, arg-2, and arg-3. The arg-2 mutant does not grow with ornithine treatment but does grow with citrulline or arginine treatment. Where in the pathway does the defective enzyme of arg-2 mutants occur?

ornithine → citrulline Beadle and Tatum made a key breakthrough when they discovered that the auxotrophs for each of the three loci differed in their response to the structurally related compounds ornithine and citrulline; arg-2 occurs between ornithine and citrulline.

Gregor Mendel undertook the first analysis of single-gene inheritance using traits he found in pea plants. All of these traits make peas a good subject of study EXCEPT: -many traits (i.e., seed color and shape, plant height, flower color) could be studied. -mutants were used in horticulture and easy to acquire. -pea plants can grow to be quite large. -they produced many seeds or progeny.

pea plants can grow to be quite large

Genetics can be used to predict either the unknown genotypes of parents by using _____ of progeny, or progeny phenotype ratios from parents of known genotype.

phenotype ratios

Gene interaction can be inferred from the _____ of double mutants.

phenotypes

In genetics, the chi-square test is commonly used to assess whether or not the number of observed individuals with certain _____ are an acceptable fit to an expected _____ ratio.

phenotypes; Mendelian

The interacting genes underlying hereditary continuous variation are called _____.

polygenes

Beadle and Tatum first irradiated Neurospora cells to _____ and then tested cultures grown from ascospores for interesting _____ relevant to biochemical function.

produce mutations; mutant phenotypes

The _____ rule is used to determine the probability of observing both outcome A and outcome B. The _____ rule is used to determine the probability of observing either outcome A or outcome B.

product; sum The product rule is used to determine the probability of observing both outcome A and outcome B. The sum rule is used to determine the probability of observing either outcome A or outcome B.

To estimate how many progeny plants need to be grown to stand a reasonable chance of obtaining the desired genotype, first calculate the _____ of progeny that is expected to be of that genotype.

proportion

Although the great majority of genes encode _____, some are known to encode _____ that have special functions.

proteins; functional RNAs

A double mutant in which one of the mutations is a suppressor is called a:

pseudorevertant

The chi-square test is simply a way of _____ the various deviations expected by chance if a hypothesis is true.

quantifying

During Mendel's experiments, _____ alleles resulted in visible phenotypes only when two copies were present.

recessive

A 9:3:4 phenotypic ratio in the progeny of a dihybrid cross is diagnostic for:

recessive epistasis

When the presence of two recessive alleles (the homozygous genotype) inhibits the expression of an allele at a different locus, it is known as:

recessive epistasis.

Which of these is NOT a reason that an organism may show incomplete penetrance? -environmental influence -unspecified gene interactions -recombination -inability to measure phenotype accurately

recombination

Pure lines are generated through repeated selfing, which _____ the proportion of heterozygotes by half and results in a(n) _____ proportion of homozygotes with each generation.

reduces; increased

A researcher has crossed two types of Neurospora, one with an E allele and another with an e allele. She observes a resulting octad that has ascospores with genotypes in this arrangement: E, E, e, e, E, E, e, e. This is an example of a _____ pattern.

second-division segregation (MII)