Genetics and Heredity

30 questions

All types30 Multiple choice16 True / False8 Matching6

In guinea pigs, black fur ( $B$ ) is dominant over white fur ( $b$ ). If two heterozygous black guinea pigs ( $Bb$ ) are crossed, what percentage of their offspring is expected to have black fur?

25%

50%

75%

100%

Show answer & explanation

Answer: 75%

Answer

75% of the offspring are expected to have black fur.

Crossing two heterozygous parents (

Bb \times Bb

) produces genotypes in a 1 BB : 2 Bb : 1 bb ratio. Because black fur is dominant, both

BB

(25%) and

Bb

(50%) display black fur, resulting in a total expected phenotype of 75% black fur.

Step-by-Step Solution

Identify the parental genotypes and set up the monohybrid cross.

The cross is

Bb \times Bb

, where each parent contributes either a

B

b

allele.

Both parents are heterozygous, carrying one dominant allele and one recessive allele.

Construct a

2 \times 2

Punnett square to determine offspring genotype probabilities.

Genotype distribution is

1\ BB

(25%),

2\ Bb

(50%), and

1\ bb

(25%).

Combining alleles from both parents yields four equally likely outcomes.

Determine which genotypes result in the black fur phenotype.

Both

BB

(25%) and

Bb

(50%) produce black fur, totaling

25\% + 50\% = 75\%

The dominant allele (

B

) masks the recessive allele (

b

), so both homozygous dominant and heterozygous genotypes express the dominant trait.

Key Concept

Monohybrid cross and dominant versus recessive phenotypic ratios

Estimated Time:1m 0s

Question 2Question →

In guinea pigs, black fur ( $B$ ) is dominant over white fur ( $b$ ). If two heterozygous black guinea pigs ( $Bb$ ) produce an offspring with black fur, what is the probability that this offspring is heterozygous?

\frac{1}{2}

\frac{2}{3}

\frac{3}{4}

\frac{1}{4}

Show answer & explanation

Answer: $\frac{2}{3}$

Answer

\frac{2}{3}

A monohybrid cross of two heterozygous parents (

Bb \times Bb

) yields four equally likely outcomes:

1\,BB

2\,Bb

, and

1\,bb

. Because the problem specifies that the offspring has black fur, the homozygous recessive genotype (

bb

) is excluded. Among the remaining three dominant outcomes (

1\,BB

and

2\,Bb

), two are heterozygous, giving a probability of

\frac{2}{3}

Step-by-Step Solution

Determine all possible genotypes from crossing two heterozygous individuals (

Bb \times Bb

The genotypic ratio of the total offspring is

1\,BB : 2\,Bb : 1\,bb

Each heterozygous parent contributes either a dominant allele (

B

) or a recessive allele (

b

) with equal likelihood.

Apply the given condition that the offspring displays black fur (the dominant phenotype).

The recessive genotype (

bb

) is ruled out, restricting the sample space to

1\,BB

and

2\,Bb

(a total of

3

possible outcomes).

A white guinea pig (

bb

) cannot be the offspring in question because the problem states the offspring has black fur.

Calculate the probability that this black offspring possesses the heterozygous genotype (

Bb

\text{Probability} = \frac{2\text{ heterozygous outcomes}}{3\text{ total black outcomes}} = \frac{2}{3}

There are

2

heterozygous outcomes (

Bb

) out of the

3

possible dominant phenotype outcomes (

BB, Bb, Bb

Key Concept

Conditional Probability in Monohybrid Inheritance and Phenotypic Selection

Estimated Time:1m 0s

Question 3Question →

A pea plant has the heterozygous genotype $Tt$ , where $T$ represents the dominant allele for purple flowers and $t$ represents the recessive allele for white flowers. What color flowers will this plant produce?

White flowers

Purple flowers

Light pink flowers

Striped purple and white flowers

Show answer & explanation

Answer: Purple flowers

Answer

The plant will produce purple flowers because the presence of the dominant allele masks the recessive allele.

In a heterozygous individual (

Tt

), the dominant allele (

T

) masks the expression of the recessive allele (

t

). Because

T

codes for purple flowers, the plant exhibits the dominant purple flower phenotype.

Step-by-Step Solution

Identify the alleles present in the genotype

Tt

The plant carries one dominant allele (

T

for purple flowers) and one recessive allele (

t

for white flowers).

Determining the allele combination is required to deduce which trait will be physically expressed.

Apply the law of dominance.

The dominant allele (

T

) is expressed, and the recessive allele (

t

) remains unexpressed in the phenotype.

In complete dominance, an organism with at least one dominant allele will display the dominant phenotype.

Key Concept

Dominant and Recessive Alleles in Mendelian Inheritance

Estimated Time:45s

Question 4Question →

An organism that displays a dominant phenotype must possess a homozygous genotype for that specific trait.

True

False

Show answer & explanation

Answer: False

Answer

False. An organism exhibiting a dominant phenotype can possess either a homozygous dominant or a heterozygous genotype.

In complete dominance, a dominant allele masks the expression of a recessive allele. An individual can express the dominant phenotype through two distinct genotypes: homozygous dominant (having two copies of the dominant allele) or heterozygous (having one dominant and one recessive allele). Thus, displaying the dominant phenotype does not require a homozygous genotype.

Step-by-Step Solution

Distinguish between genotype and phenotype under Mendelian inheritance.

Genotype represents the specific combination of alleles (

AA

Aa

, or

aa

), whereas phenotype represents the observable physical characteristic.

To establish the relationship between genetic makeup and outward physical expression.

Identify which genotypes yield a dominant phenotype in a complete dominance system.

Both homozygous dominant (

AA

) and heterozygous (

Aa

) genotypes result in the dominant phenotype because the dominant allele masks the recessive allele.

To evaluate whether a homozygous genotype is strictly required to express the dominant phenotype.

Assess the validity of the statement.

Because heterozygous individuals (

Aa

) also express the dominant phenotype, having a dominant phenotype does not guarantee a homozygous genotype.

To determine the final true/false evaluation of the statement.

Key Concept

Dominant and Recessive Alleles in Genotype versus Phenotype Expression

Estimated Time:45s

Question 5Question →

In human sex-linked inheritance, a biological male displaying an X-linked recessive trait must have inherited the causal allele from his mother, and will inevitably pass that allele to all of his biological daughters.

True

False

Show answer & explanation

Answer: True

Answer

True

Because biological males have an

XY

genotype, they receive their single X chromosome carrying the recessive allele from their mother. When an affected male reproduces, he passes his Y chromosome to all sons and his single X chromosome carrying the mutant allele to all daughters.

Step-by-Step Solution

Analyze the chromosomal sex determination in males and females

Biological males possess

XY

sex chromosomes, while biological females possess

XX

sex chromosomes.

Understanding sex chromosome distribution is essential for tracking sex-linked allele transmission.

Determine maternal inheritance for affected males

An affected male (

X^r Y

) receives his Y chromosome from his father and his

X^r

chromosome exclusively from his mother.

The Y chromosome does not carry X-linked genes, meaning the recessive allele must come from the maternal gamete.

Determine paternal transmission to female offspring

All biological daughters receive the father's single X chromosome (

X^r

) and one maternal X chromosome.

Fathers invariably contribute their X chromosome to female offspring, making all daughters inherit the paternal allele.

Key Concept

Sex-Linked Inheritance and Hemizygosity

Estimated Time:1m 0s

Question 6Question →

In genetics, which statement correctly describes a dominant allele?

It is always the most common allele found in a population.

It is expressed in an organism's phenotype even if only one copy is inherited.

It must be inherited from both parents in order to be expressed physically.

It physically alters the nucleotide sequence of the recessive allele during reproduction.

Show answer & explanation

Answer: It is expressed in an organism's phenotype even if only one copy is inherited.

Answer

A dominant allele is expressed in an organism's phenotype even if only one copy is inherited.

A dominant allele masks the effect of a recessive allele; therefore, an organism only needs to inherit one copy to display the associated phenotype.

Step-by-Step Solution

Identify the definition of allele dominance in genetics.

Dominance refers to an allele that masks the phenotypic contribution of a paired recessive allele.

Understanding how alleles interact in heterozygous pairs allows for the prediction of physical traits.

Determine the minimum number of dominant alleles needed for phenotypic expression.

Only one copy of a dominant allele is required to display the dominant phenotype.

Because the dominant allele masks the recessive allele, an organism with either one or two dominant alleles will display the trait.

Key Concept

Dominant Alleles and Phenotypic Expression

Estimated Time:40s

Question 7Question →

In an isolated bird population, the allele for a crested head ( $C$ ) is completely dominant over the allele for a smooth head ( $c$ ). Field biologists observe that only 2% of the population possesses a crested head. A researcher mates a heterozygous crested bird with a smooth-headed bird. Which of the following identifies the expected phenotypic probability for their offspring and correctly explains the low prevalence of the dominant trait in the wild?

50% crested, 50% smooth; The

C

allele has a low frequency in the gene pool, demonstrating that dominance controls individual expression rather than population prevalence.

75% crested, 25% smooth; Because the trait is dominant, the

C

allele will inherently multiply and eventually become the most common phenotype in the population.

50% crested, 50% smooth; Dominant traits always appear in the majority of a population, meaning the 2% field observation must be scientifically inaccurate.

100% crested, 0% smooth; The dominant

C

allele completely suppresses the recessive

c

allele in the population, making the smooth-headed phenotype mathematically impossible in this cross.

Show answer & explanation

Answer: 50% crested, 50% smooth; The $C$ allele has a low frequency in the gene pool, demonstrating that dominance controls individual expression rather than population prevalence.

Answer

50% crested, 50% smooth; The

C

allele has a low frequency in the gene pool, demonstrating that dominance controls individual expression rather than population prevalence.

The correct answer accurately calculates the 50% crested and 50% smooth phenotypic ratio from a

Cc \times cc

cross. It also correctly states that dominant alleles only determine phenotypic expression in a heterozygote, not the frequency of the allele in the population's gene pool.

Step-by-Step Solution

Determine the genotypes of both parent birds based on the provided text.

The crested parent is heterozygous (

Cc

). The smooth-headed parent expresses the recessive phenotype, so it must be homozygous recessive (

cc

Genotypes are required to set up a genetic cross and predict offspring probabilities.

Calculate the expected phenotypic ratio using a Punnett square for the cross

Cc \times cc

The offspring have a 50% chance of inheriting

Cc

(crested) and a 50% chance of inheriting

cc

(smooth).

Mendelian segregation dictates that the heterozygous parent contributes the

C

allele 50% of the time and the

c

allele 50% of the time, while the homozygous recessive parent always contributes the

c

allele.

Evaluate the conceptual statements regarding the low population frequency (2%) of the dominant crested trait.

Dominance describes how alleles interact within a single organism's genotype, not how frequently that allele appears in the entire population. Therefore, a dominant trait can be rare if the dominant allele itself is rare in the gene pool.

This resolves the apparent contradiction in the prompt and eliminates options relying on the misconception that dominant traits must be common.

Key Concept

Mendelian Inheritance and Allele Frequency

Question 8Question →

In a certain animal population, an autosomal dominant trait appears in only 5% of individuals. Which statement correctly explains this observation?

Dominant alleles will inevitably increase over generations until they represent the majority of the population.

The trait must be controlled by a recessive allele because it occurs in less than half of the population.

Dominance determines phenotypic expression in heterozygotes, not how common an allele is in a population.

Dominant alleles automatically suppress and eliminate recessive alleles from the gene pool over time.

Show answer & explanation

Answer: Dominance determines phenotypic expression in heterozygotes, not how common an allele is in a population.

Answer

Dominance determines phenotypic expression in heterozygotes, not how common an allele is in a population.

Allele dominance describes how an allele manifests phenotypically in an individual organism (specifically, that a heterozygous genotype exhibits the dominant phenotype). It has no direct bearing on the allele's frequency or prevalence within the overall population gene pool, which is determined by evolutionary forces like natural selection, mutation rate, and genetic drift.

Step-by-Step Solution

Differentiate between genetic dominance and population allele frequency.

Dominance refers to the relationship between alleles at the individual/organismal level (a dominant allele masks a recessive allele in a heterozygote). Allele frequency refers to the proportion of a specific allele in the population's gene pool.

Clarifies the fundamental definition of dominance versus population prevalence.

Analyze why a dominant trait can remain rare within a population.

A dominant allele can exist at low frequency if it originally arose as a rare mutation or if it does not confer a selective survival or reproductive advantage.

Explains that population dynamics (natural selection, drift, mutation) govern frequency, not dominance.

Identify the statement that accurately reflects this biological distinction.

The statement explaining that dominance governs heterozygote expression rather than population abundance is correct.

Directly answers the stem question.

Key Concept

Distinction between allele dominance and allele frequency in population genetics

Estimated Time:1m 0s

Question 9Question →

Match each foundational genetic term on the left with its correct biological definition on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Allele matches 'An alternative version or variant form of a specific gene'; Phenotype matches 'The observable physical traits or biochemical characteristics of an organism'; Genotype matches 'The complete genetic composition or specific combination of alleles in an organism'; Chromosome matches 'A condensed cellular structure composed of DNA and proteins that carries hereditary information'.

The pairings correctly match each biological concept with its exact definition: an allele is a specific gene variant, phenotype is the expressed physical trait, genotype is the underlying allele combination, and a chromosome is the structural unit carrying DNA.

Step-by-Step Solution

Identify the definition of gene variants

Allele corresponds to 'An alternative version or variant form of a specific gene'

Genes often have different forms that code for variations of the same trait.

Differentiate between observable traits and genetic code

Phenotype corresponds to 'The observable physical traits or biochemical characteristics of an organism', while Genotype corresponds to 'The complete genetic composition or specific combination of alleles in an organism'

Genotype is the underlying DNA code, whereas phenotype is the physical manifestation of that code.

Identify the cellular structure carrying DNA

Chromosome corresponds to 'A condensed cellular structure composed of DNA and proteins that carries hereditary information'

Chromosomes are the discrete packages in which nuclear DNA is organized.

Key Concept

Foundational vocabulary of heredity and genetic organization

Question 10Question →

Match each pattern of genetic inheritance on the left with the biological scenario on the right that correctly demonstrates its mechanism.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The correct pairings are: Incomplete Dominance matches the intermediate pink snapdragon phenotype; Codominance matches the simultaneous expression of both A and B blood group antigens; Polygenic Inheritance matches continuous trait variation across multiple gene loci; and Sex-Linked Recessive Inheritance matches the higher trait incidence in hemizygous biological males.

Each genetic term matches its defining physiological and phenotypic characteristics: Incomplete dominance produces an intermediate heterozygous phenotype (pink flowers); codominance results in distinct simultaneous expression of both alleles (type AB blood); polygenic inheritance yields a continuous distribution of traits through additive effects across multiple distinct genes; and X-linked recessive traits show disproportionate male expression due to hemizygosity.

Step-by-Step Solution

Differentiate between blended and co-expressed heterozygous phenotypes.

Incomplete dominance yields an intermediate blended trait (red

\times

white

\rightarrow

pink), whereas codominance yields simultaneous, unblended expression of both alleles (AB blood type antigens).

This establishes the distinction between allelic interactions at a single gene locus.

Analyze multi-locus quantitative traits versus chromosomal location effects.

Polygenic inheritance governs continuous gradations of physical traits (such as height and skin tone) via multiple interacting genes, while sex-linked recessive inheritance explains male vulnerability due to having only one X chromosome.

This pairs the remaining systemic genetic mechanisms to their definitive biological outcomes.

Key Concept

Patterns of Non-Mendelian and Chromosomal Inheritance

Estimated Time:1m 30s

Question 11Question →

In guinea pigs, black coat color ( $B$ ) is dominant over white coat color ( $b$ ). Two black guinea pigs produce a white offspring. What is the probability that their next offspring will have a heterozygous genotype?

25%

50%

75%

100%

Show answer & explanation

Answer: 50%

Answer

50%

Because the two black parents produced a white offspring with genotype

bb

, each parent must carry and pass on a recessive

b

allele alongside their dominant

B

allele, making both parents heterozygous (

Bb

). A Punnett square of

Bb \times Bb

produces genotypes in the ratio

1\ BB : 2\ Bb : 1\ bb

. The probability of producing a heterozygous offspring (

Bb

) is 2 out of 4, or 50%.

Step-by-Step Solution

Deduce parental genotypes from offspring phenotype

Both parents have the genotype

Bb

Since white coat color is recessive (

bb

), the white offspring must inherit one recessive allele (

b

) from each parent. Because both parents display the dominant black coat, both must be heterozygous carriers (

Bb

Set up a monohybrid cross for

Bb \times Bb

Genotypic distribution is

1\ BB : 2\ Bb : 1\ bb

Crossing two heterozygous parents produces four equally likely gamete combinations:

BB

(1/4),

Bb

(2/4), and

bb

(1/4).

Calculate the probability of obtaining a heterozygous genotype

2 out of 4, which equals 50%

The question specifically asks for the heterozygous genotype (

Bb

), which accounts for 2 of the 4 outcomes (50%).

Key Concept

Determination of parental genotypes and calculation of genotypic ratios in a monohybrid cross

Estimated Time:1m 0s

Question 12Question →

In fruit flies, the allele for normal wings ( $W$ ) is dominant over the allele for short wings ( $w$ ). If two heterozygous ( $Ww$ ) flies mate, what percentage of their offspring is expected to have normal wings?

25%

50%

75%

100%

Show answer & explanation

Answer: 75%

Answer

75% of the offspring are expected to have normal wings.

In a cross between two heterozygous parents (

Ww \times Ww

), the resulting genotypic ratio is

1\ WW : 2\ Ww : 1\ ww

. Because the allele for normal wings (

W

) is dominant, both

WW

(25%) and

Ww

(50%) will have the normal-wing phenotype. Adding these together gives an expected total of 75% normal-winged offspring.

Step-by-Step Solution

Determine parent gametes and set up a Punnett square for the cross

Ww \times Ww

Each parent produces gametes with alleles

W

and

w

with equal probability (

50\%

each).

Heterozygous organisms produce two types of gametes due to the law of segregation.

Combine alleles to find the offspring genotypic ratio.

The genotypes produced are

25\%\ WW

50\%\ Ww

, and

25\%\ ww

Crossing the gametes yields

1/4\ WW

2/4\ Ww

, and

1/4\ ww

combinations.

Identify all genotypes that express the dominant normal-wing phenotype.

Both

WW

(

25\%

) and

Ww

(

50\%

) display normal wings, totaling

25\% + 50\% = 75\%

The dominant allele

W

masks the recessive allele

w

in heterozygous individuals.

Key Concept

Monohybrid cross phenotypic ratios and dominant allele inheritance

Estimated Time:45s

Question 13Question →

In humans, a biological father cannot pass an X-linked genetic trait directly to his biological son.

True

False

Show answer & explanation

Answer: True

Answer

True. A biological father contributes a Y chromosome to produce male offspring, meaning he cannot transmit an X-linked gene to his son.

The statement is true because sex determination dictates that a male offspring inherits a Y chromosome from his father and an X chromosome from his mother. Consequently, any allele located on the father's X chromosome cannot be transmitted to his male offspring.

Step-by-Step Solution

Identify the sex chromosome composition in human biological sex determination.

Biological females possess two X chromosomes (

XX

), while biological males possess one X and one Y chromosome (

XY

Sex-linked traits are governed by genes located specifically on sex chromosomes.

Determine which sex chromosome a father passes to a male child.

To produce a male child (

XY

), the father must contribute a Y chromosome, while the mother contributes an X chromosome.

If the father contributed his X chromosome, the child would be female (

XX

Evaluate the inheritance pathway for X-linked traits.

Since a son receives exclusively a Y chromosome from his father, none of the father's X-linked alleles can be inherited by the son.

Direct father-to-son transmission of X-linked traits cannot occur in standard chromosomal inheritance.

Key Concept

Sex-Linked Inheritance and Chromosomal Sex Determination

Estimated Time:45s

Question 14Question →

An organism's phenotype refers to its observable physical traits, whereas its genotype refers to its underlying genetic makeup.

True

False

Show answer & explanation

Answer: True

Answer

True

The statement is true because it accurately reflects the definitions used in genetics: phenotype represents physical expression and genotype represents genetic composition.

Step-by-Step Solution

Define the term phenotype in biological genetics.

Phenotype is the expressed physical, anatomical, or physiological trait of an organism.

Establishing the precise scientific meaning of physical expression.

Define the term genotype in biological genetics.

Genotype is the specific combination of alleles or genetic code present in an organism's DNA.

Distinguishing genetic information from outward physical traits.

Compare the provided statement with the established definitions.

The statement correctly pairs phenotype with observable traits and genotype with genetic makeup.

Confirming the validity and truth value of the assertion.

Key Concept

Genotype versus Phenotype Distinction

Estimated Time:30s

Question 15Question →

A plant inherits an allele for purple flowers ( $P$ ) from one parent and an allele for white flowers ( $p$ ) from the other. If purple is dominant over white, which flower color will the plant have?

White flowers

Light pink flowers

Purple flowers

A mix of purple and white petals

Show answer & explanation

Answer: Purple flowers

Answer

The plant will have purple flowers.

Because the purple allele (

P

) is dominant over the white allele (

p

), a plant with the heterozygous genotype (

Pp

) will display only the dominant phenotype, which is purple flowers.

Step-by-Step Solution

Determine the genotype of the offspring.

The plant inherits one dominant allele (

P

) and one recessive allele (

p

), giving it the heterozygous genotype

Pp

Each parent contributes one allele for the trait to the offspring.

Apply the rule of complete dominance to find the phenotype.

The dominant allele (

P

) completely masks the expression of the recessive allele (

p

Under standard Mendelian dominance, having at least one dominant allele produces the dominant physical trait.

Key Concept

Dominant and Recessive Allele Expression

Estimated Time:45s

Question 16Question →

In human inheritance, a father who is affected by an X-linked dominant condition will pass the disorder to 100% of his daughters and 0% of his sons, whereas a mother who is heterozygous for the same condition will pass it to approximately 50% of her offspring regardless of their biological sex.

True

False

Show answer & explanation

Answer: True

Answer

The statement is true.

The statement is completely accurate. Biological males (

XY

) pass their

X

chromosome to all biological daughters and their

Y

chromosome to all biological sons. If a male has an X-linked dominant disorder, all his daughters will receive that dominant allele (

X^D

) and express the trait. Since sons only receive his

Y

chromosome, none will inherit the X-linked condition from him. Conversely, biological females (

XX

) pass one of their two

X

chromosomes randomly to each child. A heterozygous female (

X^D X^d

) has a 1 in 2 (50%) chance of passing on the affected allele to any offspring, regardless of sex.

Step-by-Step Solution

Determine the sex chromosomes inherited from the father.

The father passes his

X

chromosome to all daughters and his

Y

chromosome to all sons.

This establishes which offspring can potentially inherit an X-linked trait from the father.

Analyze the expression of the dominant trait in the daughters.

100% of the daughters inherit the father's affected

X

chromosome and will express the condition.

A dominant trait only requires one copy of the allele to be expressed in the phenotype.

Analyze the transmission to the sons.

0% of the sons inherit the trait from the father.

Sons inherit the

Y

chromosome from the father, which does not carry the gene for the X-linked condition.

Determine the probability of inheritance from a heterozygous mother.

The mother has a 50% chance of passing the affected

X

chromosome to any given child, male or female.

During meiosis, the two

X

chromosomes segregate randomly into eggs, independently of the fertilizing sperm's sex chromosome.

Key Concept

X-linked Dominant Inheritance Patterns

Estimated Time:1m 30s

Question 17Question →

In pea plants, the allele for tall stems ( $T$ ) is dominant over the allele for short stems ( $t$ ). If a homozygous dominant ( $TT$ ) plant is crossed with a heterozygous ( $Tt$ ) plant, what percentage of the resulting offspring will be tall?

50\%

75\%

100\%

25\%

Show answer & explanation

Answer: $100\%$

Answer

100% of the offspring will be tall.

The homozygous dominant parent (

TT

) contributes a dominant allele (

T

) to every single offspring. Since the presence of just one dominant allele (

T

) is sufficient to produce the tall phenotype, 100% of the resulting offspring will be tall (50%

TT

and 50%

Tt

Step-by-Step Solution

Determine the alleles contributed by each parent's gametes.

The homozygous dominant parent (

TT

) produces only gametes with

T

. The heterozygous parent (

Tt

) produces 50% gametes with

T

and 50% gametes with

t

During meiosis, alleles segregate so each gamete carries one allele per gene.

Construct a Punnett square to find offspring genotypes.

Possible offspring combinations are

TT

(50%) and

Tt

(50%).

Combining the gametes (

T \times T \rightarrow TT

and

T \times t \rightarrow Tt

) yields the genotypic distribution.

Determine the phenotypic expression of the genotypes.

Both

TT

and

Tt

genotypes result in the tall phenotype, giving a total of

100\%

tall offspring.

The dominant allele (

T

) completely masks the recessive allele (

t

) whenever present.

Key Concept

Monohybrid cross with complete dominance where a homozygous dominant parent ensures all offspring exhibit the dominant phenotype.

Estimated Time:1m 0s

Question 18Question →

Match each genetic term with its correct biological description.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Gene pairs with 'A specific segment of DNA that contains instructions for producing a particular protein', DNA pairs with 'The double-stranded nucleic acid molecule that stores an organism's complete genetic blueprint', RNA pairs with 'The single-stranded nucleic acid molecule that delivers genetic instructions to ribosomes for protein synthesis', and Mutation pairs with 'A permanent alteration in the nucleotide base sequence of an organism's genetic material'.

Each genetic concept matches its fundamental biological definition: DNA is the double-stranded master code, a gene is a specific protein-coding segment of DNA, RNA is the single-stranded messenger for protein synthesis, and a mutation is a permanent change in the nucleotide sequence.

Step-by-Step Solution

Identify the primary storage molecule of hereditary instructions.

DNA is matched with the double-stranded nucleic acid containing the complete genetic blueprint.

Deoxyribonucleic acid serves as the primary master repository of genetic information in living cells.

Identify the individual unit of heredity that codes for proteins.

Gene is matched with the specific DNA segment carrying instructions to produce a protein.

Genes are specific sequences of nucleotides within a larger DNA molecule.

Identify the molecule responsible for transmitting instructions to ribosomes.

RNA is matched with the single-stranded nucleic acid that delivers genetic instructions for protein synthesis.

RNA transcribes instructions from DNA and aids in translation at the ribosome.

Identify the term for changes occurring in the genetic code.

Mutation is matched with a permanent alteration in the nucleotide base sequence.

Any insertion, deletion, or substitution in the DNA sequence constitutes a genetic mutation.

Key Concept

Molecular Basis of Heredity and Nucleic Acids

Estimated Time:45s

Question 19Question →

Match each fundamental genetic term with its correct biological description or definition.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Autosome corresponds to any non-sex chromosome; Gamete corresponds to a haploid reproductive cell; Allele corresponds to a variant form of a gene; Karyotype corresponds to an organized visual display of chromosome pairs.

Each biological term matches its exact definition within inheritance: autosomes are non-sex chromosomes, gametes are haploid reproductive cells, alleles are variant forms of genes, and karyotypes are visual displays of full chromosomal sets.

Step-by-Step Solution

Differentiate body chromosomes from sex chromosomes

Autosome correctly pairs with 'Any standard numbered chromosome that is not directly involved in determining biological sex'

Autosomes carry genes for general physiological traits and somatic functions rather than sex determination.

Identify the ploidy and reproductive role of sex cells

Gamete correctly pairs with 'A specialized haploid reproductive cell carrying half the standard number of chromosomes'

Gametes undergo meiotic division to reduce chromosome count by half so fertilization creates a diploid zygote.

Define the relationship between genes and their specific versions

Allele correctly pairs with 'An alternative sequence or variant form of a specific gene located at a given chromosomal locus'

A gene may have two or more functional variations in a population, which are called alleles.

Identify the diagnostic visualization technique for chromosomal analysis

Karyotype correctly pairs with 'An organized visual profile of an individual's complete set of chromosomes arranged by size and number'

A karyotype allows geneticists to visually inspect chromosome numbers, morphology, and structural integrity.

Key Concept

Core structural, cellular, and molecular terminology governing genetic inheritance and chromosome organization.

Estimated Time:1m 0s

Question 20Question →

In humans, the allele for having freckles ( $F$ ) is dominant over the allele for not having freckles ( $f$ ). If an individual inherits the heterozygous genotype $Ff$ , which physical characteristic will they display?

They will not have freckles because recessive traits are expressed more frequently in populations.

They will not have freckles because two copies of a dominant allele are required for expression.

They will have freckles because a single dominant allele is sufficient to mask the recessive allele.

They will show an intermediate blend because dominant and recessive alleles always mix equally.

Show answer & explanation

Answer: They will have freckles because a single dominant allele is sufficient to mask the recessive allele.

Answer

They will have freckles because a single dominant allele is sufficient to mask the recessive allele.

Because the allele for freckles (

F

) is dominant, an individual with the heterozygous genotype (

Ff

) only needs one copy of the dominant allele to display freckles. The dominant allele completely masks the expression of the recessive allele (

f

Step-by-Step Solution

Identify the relationship between the two alleles given in the problem.

The allele

F

(freckles) is dominant, and

f

(no freckles) is recessive.

Determining which allele is dominant establishes the rule of expression.

Determine the physical phenotype produced by the heterozygous genotype

Ff

The organism expresses the dominant trait (having freckles).

In simple Mendelian inheritance, having at least one dominant allele results in the dominant phenotype.

Key Concept

Dominant vs. Recessive Allele Expression in Heterozygous Genotypes

Estimated Time:45s

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