QCM : Genetics Fundamentals: Inheritance and Variation — 11 questions

Questions et réponses du QCM

1. What best describes multiple allelism at a gene locus?

A population contains more than two possible alleles at one locus, although each individual carries only two
Two different genes interact to produce one trait
A single individual carries more than two alleles at one locus
A heterozygote shows an intermediate phenotype between two homozygotes

A population contains more than two possible alleles at one locus, although each individual carries only two

Explication

Multiple allelism means a gene has more than two allele forms in the population, but any one individual still has only two copies. The option about a single individual carrying more than two alleles is incorrect.

2. What does the term 'multiple allelism' refer to in genetics?

A gene locus having only two possible alleles in a population
A gene locus with more than two possible alleles in a population
A gene with multiple functions in different tissues
A single allele that produces multiple phenotypes

A gene locus with more than two possible alleles in a population

Explication

Multiple allelism refers to a gene locus that has more than two possible alleles within a population, allowing for greater phenotypic diversity. The other options either describe a different concept or are incorrect.

3. In a single-gene lethal-allele scenario, why can an expected 3:1 offspring ratio shift to 2:1?

One homozygous genotype is lethal and therefore missing from the observed offspring
The heterozygous genotype always dies before birth
The trait is controlled by more than one gene locus
The dominant allele becomes recessive in the next generation

One homozygous genotype is lethal and therefore missing from the observed offspring

Explication

When a homozygous lethal genotype dies, those individuals are not counted among surviving offspring, so the observed ratio changes from 3:1 to 2:1. The heterozygote is generally viable, not lethal.

4. What is the primary difference between incomplete dominance and codominance in terms of heterozygote phenotype expression?

Incomplete dominance produces a phenotype identical to one of the homozygotes, while codominance produces a new phenotype.
Incomplete dominance results in an intermediate phenotype, while codominance shows both traits simultaneously.
Incomplete dominance always results in a dominant phenotype, while codominance results in a recessive phenotype.
Incomplete dominance involves multiple alleles, whereas codominance involves only two alleles.

Incomplete dominance results in an intermediate phenotype, while codominance shows both traits simultaneously.

Explication

Incomplete dominance produces an intermediate phenotype in heterozygotes, whereas codominance results in the expression of both alleles' traits simultaneously without blending.

5. What amount of functional protein is associated with the dominant phenotype in the simple example of protein P?

No functional protein at all
Exactly 25% functional protein
At least 50% functional protein
Only 100% functional protein

At least 50% functional protein

Explication

In the example, the dominant phenotype appears when at least half of the functional protein is produced, matching the threshold idea of dominance. PP gives 100%, Pp gives 50%, and pp gives 0%.

6. What is the primary purpose of having multiple alleles at a single gene locus in a population?

To prevent mutations from occurring at the gene locus
To simplify inheritance patterns across generations
To increase genetic diversity and phenotypic variation
To ensure each individual has only two alleles per gene

To increase genetic diversity and phenotypic variation

Explication

Multiple alleles at a gene locus increase the potential for phenotypic diversity within a population, allowing for a wider range of traits. This does not restrict individuals to only two alleles nor does it prevent mutations; instead, it enhances variation.

7. How does the protein-function model connect genotype to phenotype for protein P?

Protein amount is unrelated to the visible trait
Only the recessive genotype produces a functional protein
Different genotypes produce different amounts of functional protein, which determine the phenotype
The genotype directly determines phenotype without any protein intermediate

Different genotypes produce different amounts of functional protein, which determine the phenotype

Explication

The model explains dominance through the amount of working protein produced by each genotype, linking genotype to phenotype. In the example, PP, Pp, and pp produce different functional-protein levels that correspond to different traits.

8. When was the concept of incomplete dominance first formally described in genetic studies?

In the 1950s, following the discovery of DNA structure
In the 1970s, with advances in molecular biology
In the early 1900s, around 1900-1910
During the 1920s, with the rise of Mendelian genetics

In the early 1900s, around 1900-1910

Explication

The concept of incomplete dominance was first formally described in the early 1900s, around 1900-1910, as scientists observed heterozygotes exhibiting intermediate phenotypes, which challenged the simple dominant-recessive model.

9. How does the phenotypic expression of heterozygotes in codominance differ from that in incomplete dominance?

In codominance, heterozygotes express both alleles simultaneously without blending, whereas in incomplete dominance, heterozygotes show an intermediate phenotype.
In codominance, heterozygotes do not express any phenotype, while in incomplete dominance, they show a phenotype that is a mixture of the two homozygotes.
In codominance, heterozygotes display a phenotype that is a blend of both alleles, while in incomplete dominance, they express both traits distinctly.
In codominance, heterozygotes have a phenotype identical to one of the homozygotes, whereas in incomplete dominance, they show a completely new phenotype.

In codominance, heterozygotes express both alleles simultaneously without blending, whereas in incomplete dominance, heterozygotes show an intermediate phenotype.

Explication

In codominance, heterozygotes express both alleles simultaneously, resulting in a phenotype that shows features of both traits without blending. In incomplete dominance, heterozygotes have an intermediate phenotype, blending the traits of the homozygotes.

10. Who is credited with proposing the concept of lethal alleles in genetics?

Sutton and Boveri
Gregor Mendel
Hugo de Vries
Thomas Hunt Morgan

Sutton and Boveri

Explication

Sutton and Boveri are credited with proposing the chromosome theory of inheritance, which laid the groundwork for understanding lethal alleles as gene variants that can cause death in homozygous form.

11. What is the primary effect of lethal alleles on the expected genotypic ratios in a population?

They cause all heterozygotes to die, reducing heterozygote frequency.
They eliminate homozygous individuals for the lethal allele, altering Mendelian ratios.
They increase the overall genetic diversity by introducing new alleles.
They have no effect on ratios but influence phenotype expression.

They eliminate homozygous individuals for the lethal allele, altering Mendelian ratios.

Explication

Lethal alleles cause homozygous individuals to die, which removes certain genotypes from the population and shifts expected Mendelian ratios, often reducing the frequency of homozygous genotypes.

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Single-gene variations — types?

Incomplete dominance, codominance, lethal alleles, multiple alleles.

Multiple alleles concept

More than two alleles possible at one gene locus.

Protein dominance — threshold?

≥50% functional protein causes dominant phenotype.

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