genetics recombination

Which of the following best explains why siblings can have different traits despite having the same parents?
A. Genes always mutate randomly
B. Meiosis produces diploid gametes
C. Alleles segregate independently and recombine during gametogenesis
D. DNA is not passed down from both parents

Alleles segregate independently and recombine during gametogenesis

What event restores the diploid number of chromosomes in a zygote?
A. Mitosis
B. Meiosis
C. Fertilization
D. Crossing over

Fertilization

Mendel’s Law of Independent Assortment is best demonstrated during:
A. DNA replication
B. Mitosis
C. Meiosis I
D. Fertilization

Meiosis I

If gene A and gene B are located far apart on the same chromosome, what is the likely outcome during meiosis?
A. They will be inherited together 100% of the time
B. They will never recombine
C. They will assort independently due to high recombination rates
D. They will mutate more frequently

They will assort independently due to high recombination rates

Which structure directly determines phenotype according to Mendelian genetics?
A. Proteins
B. Enzymes
C. Genes or alleles
D. Chromatin

Genes or alleles

During fertilization, haploid gametes fuse to form a ______ zygote.

diploid

Each parent contributes ______ of the genetic material to the offspring.

half

The ______ the distance between two genes on a chromosome, the greater the chance they will be separated during recombination.

greater/farther

True or False: Recombination is more likely to occur between genes that are close together on a chromosome

false

True or False; Genes are located on specific chromosomes

true

What would be the most direct evidence that two genes are linked?
A. Equal frequency of all offspring phenotypes in a test cross
B. Greater number of recombinant offspring than parental types
C. Higher frequency of parental combinations than recombinants
D. Total suppression of recombination

Higher frequency of parental combinations than recombinants

Why are recombinant offspring less frequent than parental types when genes are closely linked?
A. They are more likely to die during development
B. Crossing over is more frequent between closely linked genes
C. Crossing over is less likely between closely linked genes
D. Mutation rates increase in closely linked genes

Crossing over is less likely between closely linked genes

In a test cross, what result would you expect if two genes are unlinked?
A. Parental combinations dominate
B. Recombinant types are completely absent
C. Equal frequency of all four phenotypes
D. Only two phenotypes appear

Equal frequency of all four phenotypes

Which of the following configurations indicates that mutant alleles are on the same homologous chromosome?
A. AB/ab
B. Ab/aB
C. ab/AB
D. aB/Ab

ab/AB

If two genes are located far apart on the same chromosome, what is likely to occur?
A. No recombination
B. Complete linkage
C. High recombination frequency
D. Equal expression of dominant alleles

High recombination frequency

Linked genes do not follow Mendel’s law of ______ because they do not always assort independently.

independent assortment

A test cross typically involves a heterozygous individual and a ______ recessive individual.

homozygous

The recombination frequency between two genes provides an estimate of their ______ on a chromosome.

distance

True or False: A 1:1:1:1 ratio in a test cross indicates that the genes are likely linked.

false

True or False: The closer two genes are on a chromosome, the more likely they will be separated by crossing over.

false

Which of the following statements best describes complete linkage?
A. Genes are inherited independently because they are on different chromosomes
B. Genes recombine frequently because they are far apart
C. Genes are so close together that recombination rarely or never separates them
D. Genes are located on mitochondrial DNA and inherited maternally

Genes are so close together that recombination rarely or never separates them

What does the presence of significantly more parental-type offspring than recombinants in a test cross indicate?
A. Genes are on different chromosomes
B. There was no crossing over
C. Genes are tightly linked
D. The test cross was not valid

Genes are tightly linked

Which of the following would likely have a recombination frequency close to 50%?
A. Two tightly linked genes
B. Two genes far apart on the same chromosome
C. Genes that are completely linked
D. Genes that are always inherited together

Two genes far apart on the same chromosome

In a trans (repulsion) configuration, which genotype arrangement is correct?
A. ab/AB
B. Ab/aB
C. AB/AB
D. ab/ab

Ab/aB

Genes in a ______ configuration have both mutant or both wild-type alleles on the same chromosome.

cis

True or False: Recombination frequency can never exceed 50%.

true

True or False: Genes that are located on the same chromosome are always linked.

false

What is recombination?

Crossing over — the exchange of DNA from one homologue chromosome to another  

True or false: a lower recombination frequency suggests that the genes that farther apart or even on different chromosomes

false

True or false: a higher recombination frequency suggests that the genes that closer together (more tightly linked)

false

true of false: When genes are linked, parental combinations appear more frequently than recombinant (nonparental) combinations  

true

What is expected with independent assortment (genes are unlinked)?

you’d expect to see equal numbers of all allele combinations in the offspring  (1:1:1:1)

What conclusion can be drawn from a test cross that produces more parental-type offspring than recombinants?
A. Independent assortment is confirmed
B. The genes are on different chromosomes
C. The genes are linked
D. The traits are codominant

The genes are linked

What does a recombination frequency of 18% between two genes indicate?
A. The genes are completely unlinked
B. The genes are very tightly linked
C. The genes are moderately linked and 18 map units apart
D. The genes are on different chromosomes

The genes are moderately linked and 18 map units apart

Why is the expected phenotypic ratio 1:1:1:1 if the genes assort independently?
A. Both parents are homozygous
B. The offspring have equal chances of inheriting any combination of alleles
C. Crossing over is completely suppressed
D. All offspring are genetically identical

The offspring have equal chances of inheriting any combination of alleles

True or False: The fly genotype GN/gn indicates that gray body and normal wings are on the same chromosome.

true (an example of cis configuration)

Which formula correctly calculates recombination frequency?
A. Total parental types ÷ total progeny
B. Total number of dominant phenotypes ÷ total progeny
C. Sum of recombinant types ÷ sum of all progeny
D. Sum of heterozygotes ÷ total progeny

Sum of recombinant types ÷ sum of all progeny

What recombination frequency would indicate that two genes are unlinked?
A. Less than 10%
B. Greater than 75%
C. Exactly 50%
D. Between 1% and 25%

Exactly 50%

Which of the following best defines a linkage group?
A. All dominant genes in an organism
B. All alleles for a single trait
C. All genes located on a single chromosome
D. All genes expressed during development

All genes located on a single chromosome

What can be inferred if two genes have a recombination frequency of 15%?
A. They are located on different chromosomes
B. They are completely unlinked
C. They are located close together on the same chromosome
D. They are alleles of the same gene

They are located close together on the same chromosome

Why do genes on different chromosomes exhibit a recombination frequency of 50%?
A. They are tightly linked
B. They never recombine
C. They assort independently during meiosis
D. They are always inherited together

They assort independently during meiosis

Genes that show independent assortment are either on nonhomologous chromosomes or far apart on the same chromosome, and thus are considered ______.

unlinked

Which of the following best explains why recombination frequency remains the same regardless of cis or trans configuration?
A. Recombination only occurs in cis configuration
B. Physical distance between genes doesn't influence recombination
C. Configuration affects recombination machinery directly
D. Recombination frequency is determined by physical distance, not initial allele arrangement

Recombination frequency is determined by physical distance, not initial allele arrangement

What role does the physical distance between genes play in recombination?
A. Greater distance means lower recombination rate
B. Greater distance increases the likelihood of recombination
C. Distance is irrelevant if genes are in cis configuration
D. Distance matters only when genes are unlinked

Greater distance increases the likelihood of recombination

Which of the following statements about the cis and trans configurations is true?
A. They determine the recombination rate
B. They affect initial allele combinations, not recombination frequency
C. They only apply to genes on different chromosomes
D. They occur after recombination events

They affect initial allele combinations, not recombination frequency

Why is recombination frequency considered a reliable estimate of gene distance?
A. Because recombination occurs randomly across the chromosome
B. Because it is directly proportional to the phenotypic dominance
C. Because it reflects the likelihood of crossing over based on gene proximity
D. Because it varies with allele dominance

Because it reflects the likelihood of crossing over based on gene proximity

Although cis/trans configuration affects the starting combination of alleles, it does not affect the ______ of recombination.

frequency

Which of the following is true about cis and trans configurations in relation to recombination frequency?
A. Cis results in more recombination than trans
B. Trans eliminates recombination entirely
C. The recombination frequency is the same in both
D. Only cis can produce recombinant offspring

The recombination frequency is the same in both

The frequency of recombination is not a fixed value, but rather depends on the specific ______ being studied.

genes

True or False: The proportion of recombinant offspring remains the same in both cis and trans configurations.

true

How does gene linkage affect the expected phenotypic ratio in a dihybrid cross?
A. It reinforces the 9:3:3:1 ratio
B. It causes the ratios to shift, with some combinations overrepresented and others underrepresented
C. It causes complete dominance in all traits
D. It increases the frequency of double recombinants

It causes the ratios to shift, with some combinations overrepresented and others underrepresented

Which of the following would be most underrepresented in a dihybrid cross involving linked genes?
A. Parental phenotypes
B. Dominant-only phenotypes
C. Recombinant phenotypes
D. Homozygous dominant genotypes

Recombinant phenotypes

n a typical dihybrid cross with independently assorting genes, what ratio of offspring is expected?
A. 3:1
B. 9:3:3:1
C. 1:1:1:1
D. 1:2:1

9:3:3:1

If a dihybrid cross between two heterozygotes results in an excess of parental-type offspring, what does this suggest?
A. The genes are on different chromosomes
B. Dominance is incomplete
C. The genes are linked
D. Independent assortment is occurring

The genes are linked

The typical 9:3:3:1 phenotypic ratio in a dihybrid cross assumes that genes are ______.

unlinked

When two genes are linked, the occurrence of ______ recombination events becomes especially rare.

double

True or False: Double crossover events can occur but are typically less frequent than single crossover events.

true

Which of the following correctly describes a centimorgan (cM)?
A. A physical length of 1,000 base pairs
B. The distance between genes that always recombine
C. A unit equal to 1% recombination frequency
D. A measure of gene dominance

A unit equal to 1% recombination frequency

What is the purpose of using recombination frequencies in gene mapping?
A. To identify dominant alleles
B. To determine gene expression patterns
C. To estimate physical distances between genes on a chromosome
D. To calculate mutation rates

To estimate physical distances between genes on a chromosome

If two genes have a recombination frequency of 7%, how far apart are they on a genetic map?
A. 0.7 cM
B. 7 map units
C. 70 map units
D. 0.07 map units

7 map units

What is the primary purpose of performing multiple two-point crosses in gene mapping?
A. To determine allele dominance
B. To identify recombination hotspots
C. To establish the relative order and distance of genes on a chromosome
D. To measure mutation frequency

To establish the relative order and distance of genes on a chromosome

If Gene A and Gene B are 5 cM apart, and Gene B and Gene C are 10 cM apart, what would a likely arrangement be if Gene A and Gene C are 15 cM apart?
A. A – C – B
B. C – A – B
C. A – B – C
D. B – C – A

A – B – C

What outcome in a two-point cross would suggest the genes are very close together?
A. Recombination frequency close to 50%
B. No recombinant offspring detected
C. A recombination frequency around 25%
D. Very few parental types in the offspring

No recombinant offspring detected

Recombination data from two-point crosses can be used to determine both the relative ______ and ______ of genes on a chromosome.

order; distance

Why do double crossovers complicate the mapping of genes that are far apart?
A) They increase the overall recombination frequency beyond 50%
B) They restore the original parental arrangement, masking recombination events
C) They always produce lethal offspring
D) They only occur during mitosis, not meiosis

They restore the original parental arrangement, masking recombination events

Which genetic cross is especially useful for detecting double crossover events?
A) Monohybrid cross
B) Two-point cross
C) Three-point cross
D) Backcross

Three-point cross

When is the chance of double crossovers between two genes considered highly unlikely?
A) When the genes are located on different chromosomes
B) When the recombination frequency is above 50%
C) When the recombination frequency between genes is below 10%
D) When the genes are in trans configuration

When the recombination frequency between genes is below 10%

If two genes have a recombination frequency of 25%, what can be inferred about the likelihood of double crossovers?
A) Double crossovers are unlikely
B) Double crossovers are likely and may mask some recombination events
C) No recombination occurs
D) Genes must be on different chromosomes

Double crossovers are likely and may mask some recombination events

Double crossovers occur when two separate crossover events happen between the same pair of ______ chromosomes.

homologous

The effects of two crossovers can cancel each other out, leaving offspring with ______ type allele combinations.

parental

ouble crossovers can cause the recombination frequency to ______, leading to an underestimate of the actual genetic distance.

decrease

True or False: Double crossovers can make genes appear closer together than they actually are.

true

In a three-point cross, the two most frequent gamete types are usually:
A) Double recombinant gametes
B) Single recombinant gametes
C) Nonrecombinant (parental) gametes
D) Gametes with new mutations

Nonrecombinant (parental) gametes

The term "linkage phase" refers to:
A) The distance between genes on a chromosome
B) Whether alleles are in cis or trans configuration in a heterozygous parent
C) The probability of a crossover occurring between two genes
D) The order of genes on a chromosome

Whether alleles are in cis or trans configuration in a heterozygous parent

Which gene’s allele changes in a double crossover event in a three-gene system?
A) The first gene
B) The middle gene
C) The last gene
D) All three genes

The middle gene

If the rarest offspring class in a three-point cross has alleles differing only in the middle gene from parental types, what does this indicate?
A) No crossover occurred
B) A single crossover between the first and second gene
C) A double crossover involving the middle gene
D) Independent assortment of the genes

A double crossover involving the middle gene

In the cis configuration of alleles, the dominant alleles are located:
A) On opposite homologous chromosomes
B) On the same chromosome
C) Randomly distributed
D) Only in recombinant gametes

On the same chromosome

The two rarest classes of offspring in a three-point cross identify the ______ crossover gametes.

double recombinant

Identifying double recombinant offspring is essential for determining the correct ______ of three genes.

order

Why can double crossovers lead to underestimation of genetic distances between genes?
A) Because double crossovers increase the observed recombination frequency
B) Because double crossovers restore parental allele combinations, masking recombination
C) Because double crossovers only occur in mitosis, not meiosis
D) Because double crossovers create new mutations that confuse the data

Because double crossovers restore parental allele combinations, masking recombination

If double crossovers are not accounted for, geneticists might conclude that:
A) Genes are farther apart than they really are
B) Genes are closer together than they really are
C) Genes assort independently
D) The genes are not linked

Genes are closer together than they really are

Double crossovers occur more frequently when genes are ______ (closer/farther) apart on the chromosome.

farther

Which of the following best describes a linkage group?
A) A group of chromosomes inherited independently
B) A set of genes located on the same chromosome that tend to be inherited together
C) Genes that assort independently during meiosis
D) Genes that are located on different chromosomes and show no linkage

A set of genes located on the same chromosome that tend to be inherited together

When many genes per chromosome are mapped, a linkage group becomes synonymous with which of the following?
A) Gene cluster
B) Chromosome
C) Genetic marker
D) Allele group

Chromosome

Which of the following best characterizes heterochromatin?
A) Lightly stained and gene-rich
B) Visible only during cell division
C) Compact, darkly stained, and composed mainly of noncoding DNA
D) Found only in prokaryotic cells

Compact, darkly stained, and composed mainly of noncoding DNA

Which type of chromatin is more likely to contain actively transcribed genes?
A) Satellite DNA
B) Heterochromatin
C) Euchromatin
D) Mitochondrial DNA

Euchromatin

Satellite DNA is most commonly found in which region of the chromatin?
A) Introns
B) Euchromatin
C) Promoter regions
D) Heterochromatin

Heterochromatin

Which of the following becomes clearly visible only after chromosomal condensation during mitosis or meiosis?
A) Ribosomal RNA
B) Heterochromatin
C) Euchromatin
D) Centrioles

Euchromatin

What is a major distinguishing feature of euchromatin compared to heterochromatin?
A) It is transcriptionally inactive
B) It contains a higher proportion of noncoding DNA
C) It is less compact and gene-rich
D) It stains more darkly under the microscope

It is less compact and gene-rich

Compared to euchromatin, the number of genes located in heterochromatin is relatively ________.

small

________ is the chromatin form primarily responsible for active gene expression, whereas ________ is generally transcriptionally inactive.

echromatin; heterochromatin

True or False: Heterochromatin is rich in functional genes and lightly stained under a microscope.

false

True or False: Euchromatin contains most of the genes responsible for protein synthesis.

true

True or False: Heterochromatin becomes visible only after chromosome condensation during cell division.

false

True or False: Gene density is higher in euchromatin than in heterochromatin.

true

Which of the following base pairs contributes more to DNA thermal stability?
A) A-T pairs, because they form triple bonds
B) G-C pairs, due to three hydrogen bonds
C) G-C pairs, due to their smaller molecular weight
D) A-T pairs, due to their lower melting point

G-C pairs, due to three hydrogen bonds

Which of the following challenges the idea that GC content determines thermal stability in organisms?
A) The presence of repetitive elements in DNA
B) The ability of RNA to fold
C) The fact that thermophilic bacteria don’t always have high GC content
D) The number of chromosomes in mammals

The fact that thermophilic bacteria don’t always have high GC content

Which statement about the relationship between GC content and thermal stability is most accurate?
A) All organisms in hot environments have high GC content
B) Thermal stability is solely determined by hydrogen bonding
C) GC content contributes to thermal stability, but other factors also play a role
D) AT-rich regions are inherently more stable due to fewer bonds

GC content contributes to thermal stability, but other factors also play a role

The ability of DNA to remain intact at elevated temperatures is referred to as ________.

thermostability

Which structural form of DNA is more commonly associated with GC-rich regions?
A) A-DNA
B) B-DNA
C) Z-DNA
D) D-DNA

Z-DNA