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Genetics and Heredity

30 questions

All types30Multiple choice16True / False8Matching6
Question 21Question →

In Mendelian genetics, what characteristic definitively identifies an allele as dominant?

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Answer: It is expressed in the phenotype whenever at least one copy is present in the genotype.

Answer

An allele is dominant if it is expressed in the phenotype whenever at least one copy is present in the genotype.
In genetics, a dominant allele is defined by its ability to determine the organism's physical phenotype even when only a single copy is inherited alongside a recessive allele. Therefore, an individual with either a heterozygous genotype or a homozygous dominant genotype will express the dominant trait.

Step-by-Step Solution

1
Define genetic dominance at the individual level
Dominance refers to the interaction between alleles of a gene in an individual, where the presence of a dominant allele masks the expression of a recessive allele.
Dominance is a biochemical expression property within a genotype, not a measure of population frequency or evolutionary fitness.
2
Determine the genotypic conditions required for expression
An organism with either a homozygous dominant genotype or a heterozygous genotype will display the dominant phenotype.
Only one copy of a dominant allele is necessary for the corresponding trait to be physically observed.
3
Distinguish dominance from population frequency and segregation laws
Dominant traits are not necessarily the most common in a population, nor do they destroy recessive alleles.
Alleles maintain their structural integrity and separate cleanly into gametes during meiosis regardless of dominance relationships.

Key Concept

Dominant alleles mask recessive alleles in heterozygous genotypes and are expressed whenever at least one copy is present.
Estimated Time:1m 0s
Question 22Question →

In humans, mature gametes produced through meiosis are diploid cells that each contain 46 individual chromosomes.

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Answer: False

Answer

False
The statement is false because human gametes (sperm and egg cells) are haploid, containing 23 chromosomes rather than the diploid count of 46 found in somatic body cells.

Step-by-Step Solution

1
Analyze the claim regarding the ploidy level and chromosome count of human gametes.
The statement asserts that human gametes (sperm and egg) are diploid and contain 46 chromosomes.
Accurate evaluation requires distinguishing between somatic body cells and reproductive cells.
2
Determine the effect of meiosis on chromosome number during gametogenesis.
Meiosis is a reductional division that halves the chromosome number from diploid (2n=462n = 46) to haploid (n=23n = 23).
This reduction ensures that when a sperm (2323) fertilizes an egg (2323), the resulting zygote receives the correct species chromosome number (4646).

Key Concept

Haploid vs. Diploid Chromosome Numbers in Gametogenesis
Estimated Time:45s
Question 23Question →

In guinea pigs, the allele for black fur (BB) is dominant over the allele for white fur (bb). If two heterozygous (BbBb) guinea pigs mate, what percentage of their offspring is expected to have white fur?

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Answer: 25%25\%

Answer

25%25\% of the offspring are expected to have white fur.
In a cross between two heterozygous parents (Bb×BbBb \times Bb), each parent contributes a recessive allele (bb) with a probability of 12\frac{1}{2}. The probability of producing a homozygous recessive offspring (bbbb) is 12×12=14\frac{1}{2} \times \frac{1}{2} = \frac{1}{4}, or 25%25\%. Since white fur is recessive, only the bbbb genotype displays white fur.

Step-by-Step Solution

1
Determine the parental genotypes and possible gametes.
Both parents have the heterozygous genotype BbBb, producing gametes carrying either allele BB or allele bb with equal probability.
Heterozygous organisms possess one dominant allele and one recessive allele for a given gene.
2
Construct a Punnett square to determine all possible offspring genotypes.
The resulting genotypic ratio is 1 BB1\ BB (25%25\%), 2 Bb2\ Bb (50%50\%), and 1 bb1\ bb (25%25\%).
Mendel's Law of Segregation states that allele pairs separate during gamete formation and recombine randomly at fertilization.
3
Determine the phenotype associated with white fur.
Only the homozygous recessive genotype (bbbb) results in white fur, representing 11 out of 44 combinations (25%25\%).
Because the black fur allele (BB) is dominant, any individual with at least one BB allele (BBBB or BbBb) will display black fur.

Key Concept

Monohybrid cross phenotypic and genotypic ratios in Mendelian inheritance
Estimated Time:1m 0s
Question 24Question →

In genetics, traits can be transmitted and expressed through various non-Mendelian and chromosomal mechanisms. Match each pattern of genetic inheritance with its defining biological description. Which description correctly pairs with each inheritance pattern?

Click a left item, then click its matching right item

Items

Incomplete dominance
Codominance
Polygenic inheritance
Sex-linked inheritance

Matches

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Answer

Incomplete dominance matches with the intermediate blended phenotype; Codominance matches with the simultaneous, distinct expression of both alleles; Polygenic inheritance matches with a single trait governed by multiple additive genes; Sex-linked inheritance matches with traits controlled by genes on sex chromosomes.
Each inheritance pattern describes a distinct genetic phenomenon: incomplete dominance produces an intermediate phenotype between two homozygotes; codominance manifests both distinct alleles simultaneously; polygenic inheritance produces continuous traits through the interaction of multiple distinct genes; and sex-linked inheritance involves transmission of traits carried on sex chromosomes.

Step-by-Step Solution

1
Differentiate between allele interaction patterns in heterozygotes
Incomplete dominance produces an intermediate blended form, whereas codominance produces simultaneous expression of both distinct parental traits.
This establishes the fundamental distinction between blending interactions and dual-expression interactions.
2
Identify multi-locus and chromosomal location mechanisms
Polygenic traits result from multiple independent genes working together on one trait, while sex-linked traits depend on gene loci located on the X or Y chromosomes.
This clarifies the difference between gene quantity effects and sex chromosome-specific transmission.
3
Pair each genetic term with its corresponding functional definition
All four inheritance patterns are accurately linked to their specific phenotypic outcomes and biological mechanisms.
Completes the matching matrix based on verified Mendelian and non-Mendelian genetics principles.

Key Concept

Complex Patterns of Heredity and Gene Expression
Estimated Time:1m 0s
Question 25Question →

In sheep, the allele for white wool (WW) is dominant over the allele for black wool (ww). If a homozygous dominant ram (WWWW) mates with a heterozygous ewe (WwWw), what percentage of the offspring is expected to display black wool?

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Answer: 0%0\%

Answer

The expected percentage of offspring displaying black wool is 0%0\%.
The homozygous dominant parent passes a dominant allele (WW) to all offspring. Because a single dominant allele is sufficient to express the dominant trait, all offspring will have white wool (50%50\% WWWW and 50%50\% WwWw), leaving 0%0\% with black wool (wwww).

Step-by-Step Solution

1
Determine the gametes produced by each parent.
The homozygous dominant ram (WWWW) produces only WW gametes. The heterozygous ewe (WwWw) produces 50%50\% WW gametes and 50%50\% ww gametes.
Alleles segregate during meiosis such that each gamete carries one allele for the trait.
2
Determine the offspring genotypes using a Punnett square.
Combining the alleles yields 50%50\% WWWW and 50%50\% WwWw genotypes.
Fertilization randomly pairs one maternal allele with one paternal allele.
3
Determine the phenotypic expression based on dominance.
Both WWWW and WwWw genotypes result in white wool because the presence of the dominant allele WW masks the recessive allele ww.
A recessive phenotype (black wool, wwww) requires two copies of the recessive allele, which cannot occur when one parent contributes only dominant alleles.

Key Concept

Dominant and recessive inheritance in monohybrid crosses
Estimated Time:45s
Question 26Question →

Two biological parents who both have type AB blood can produce a biological child with type O blood.

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Answer: False

Answer

False
The statement is false because expressing type O blood requires the homozygous recessive genotype (iiii). Parents with type AB blood have the genotype IAIBI^A I^B, which contains only the codominant IAI^A and IBI^B alleles. Because neither parent carries the recessive ii allele, they cannot produce a child with type O blood.

Step-by-Step Solution

1
Determine the genotypes of the parents from their blood phenotypes.
Both parents have the genotype IAIBI^A I^B.
The ABO blood group system exhibits codominance, meaning a person with type AB blood must have one IAI^A allele and one IBI^B allele.
2
Determine the possible allele combinations that the offspring can inherit.
The possible offspring genotypes are IAIAI^A I^A (type A), IAIBI^A I^B (type AB), and IBIBI^B I^B (type B).
Each parent can contribute either an IAI^A or an IBI^B allele during gamete formation.
3
Evaluate whether the genotype for type O blood can be produced.
A child cannot have type O blood.
Type O blood is homozygous recessive (iiii), requiring an ii allele from each parent, which neither type AB parent possesses.

Key Concept

Codominance and Multiple Allele Inheritance in ABO Blood Groups
Estimated Time:45s
Question 27Question →

An organism that possesses two identical alleles for a specific gene is described as heterozygous.

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Answer: False

Answer

False, because an organism with two identical alleles for a gene is homozygous.
The statement is false because possessing two identical alleles defines a homozygous condition. An organism is heterozygous only when it has two different alleles for that gene.

Step-by-Step Solution

1
Identify the genetic term for an individual carrying two matching alleles for a gene.
Two identical alleles represent a homozygous genotype.
The prefix 'homo-' means same, indicating that identical genetic variants were inherited from both parents.
2
Evaluate the definition of the term heterozygous.
The prefix 'hetero-' means different, describing an organism with two different alleles for a gene.
Comparing these definitions confirms that possessing identical alleles makes an organism homozygous rather than heterozygous.

Key Concept

Distinction between homozygous and heterozygous genotypes
Estimated Time:30s
Question 28Question →

In genetics, which statement correctly describes the function of a dominant allele?

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Answer: It masks the phenotypic expression of a recessive allele in a heterozygous individual.

Answer

The dominant allele masks the phenotypic expression of a recessive allele in a heterozygous individual.
In genetics, a dominant allele produces its characteristic phenotype whether an individual carries two copies (homozygous dominant) or only one copy paired with a recessive allele (heterozygous).

Step-by-Step Solution

1
Define genetic dominance
Dominance describes the relationship between two alleles where one allele masks the observable effect of the other in a heterozygous genotype.
Understanding the precise biological definition distinguishes dominance from population frequency or fitness.
2
Evaluate the mechanism of expression
An individual with one dominant and one recessive allele (AaAa) displays the dominant phenotype.
A single copy of a dominant allele is sufficient for its physical trait to appear.

Key Concept

Dominant and Recessive Alleles
Estimated Time:45s
Question 29Question →

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

Click a left item, then click its matching right item

Items

Genotype
Phenotype
Allele
Chromosome

Matches

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Answer

Genotype matches the specific genetic makeup or combination of alleles; Phenotype matches the observable physical or biochemical characteristics; Allele matches an alternative or variant form of a single gene; Chromosome matches a condensed structure of DNA and histone proteins.
Each term is accurately matched to its precise biological definition: Genotype is the organism's allele combination, Phenotype is the observable physical trait, Allele is a specific variant form of a gene, and Chromosome is the organized thread-like structure of DNA and protein.

Step-by-Step Solution

1
Differentiate between genetic code and physical expression.
Genotype corresponds to the underlying genetic makeup and allele combination, whereas phenotype represents the observable physical traits.
Genotype is the internal genetic instructions, while phenotype is the outward result.
2
Distinguish between individual gene variations and macroscopic cellular structures.
An allele is an individual variant of a gene, whereas a chromosome is the large organized package composed of DNA and proteins containing many genes.
An allele is a sub-unit of genetic sequence variation, while a chromosome is the structural vehicle for genomic DNA.
3
Pair each genetic term with its exact corresponding definition.
All four pairs are accurately aligned based on precise biological terminology.
Each definition uniquely identifies the specific level of genetic organization and function.

Key Concept

Foundational Genetics Terminology and Structural Hierarchy
Estimated Time:1m 0s
Question 30Question →

An organism displaying a dominant phenotype is crossed with a homozygous recessive individual (aaaa). If 50% of the resulting offspring exhibit the recessive phenotype, what is the genotype of the dominant parent?

Show answer & explanation

Answer: Heterozygous (AaAa)

Answer

Heterozygous (AaAa)
The correct answer is the heterozygous genotype (AaAa). Because offspring with the recessive phenotype must inherit a recessive allele (aa) from each parent, the parent with the dominant phenotype must carry at least one recessive allele (aa). Since this parent also displays the dominant trait, it must carry a dominant allele (AA), confirming its genotype as AaAa.

Step-by-Step Solution

1
Determine the required genotype of the recessive offspring.
Offspring showing the recessive phenotype must be homozygous recessive (aaaa).
Recessive traits are only physically expressed when an organism carries two recessive alleles.
2
Identify the parental origin of the alleles in the recessive offspring.
Each aaaa offspring receives one recessive allele (aa) from the homozygous recessive parent and one recessive allele (aa) from the dominant parent.
Offspring inherit exactly one allele for each gene from each biological parent.
3
Deduce the dominant parent's complete genotype.
The dominant parent must possess one dominant allele (AA) to express the dominant phenotype and one recessive allele (aa) to produce aaaa offspring, resulting in the genotype AaAa.
A test cross between a heterozygous individual (AaAa) and a homozygous recessive individual (aaaa) yields a 1:1 phenotypic ratio (50% dominant, 50% recessive).

Key Concept

Test Cross and Mendelian Allele Segregation
Estimated Time:1m 0s
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