Mendelian Genetics MCQ Quiz - Objective Question with Answer for Mendelian Genetics - Download Free PDF

The correct answer is Law of Segregation does not apply in this experiment

Concept:

• Incomplete dominance is a type of gene interaction in which the dominant allele is not completely dominant over the recessive allele.
• It forms offspring with intermediate phenotype or different phenotype.

Explanation:

• Antirrhinum is commonly known as snapdragon. Flowers of Antirrhinum follow incomplete dominance.
• When red flowers (RR) are crossed with white flowers (RR), all flowers (Rr) of the F1 generation obtained are pink in color.
• The pink color obtained is due to incomplete dominance as red color is incompletely dominant on the white color.
• When flowers of the F1 generation were crossed, three types of flowers are obtained, red (RR), pink (Rr), and white (RR).
• The genotypic and phenotypic ratio is the same, that is, 1:2:1.
• The Law of segregation is applicable in case of incomplete dominance.
• The Law of segregation says that the alleles do not show any blending and that both the characters are recovered as such in the F2 generation though one of these is not seen at the F1 stage.
• So here in this case, though parental characters red and white are not seen in the F1 generation, but recovered in the F2 generation.
• Hence, the law of segregation is followed here.

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The correct answer is All of these

Explanation:

• Every gene contains the information to express a particular trait.
• Genes code for RNA and proteins that act as enzymes or metabolites.
• These enzymes and metabolites are a part of a biochemical reaction that presents a particular trait.
• DNA contains many genes → transcribed to RNA → translated to protein → RNA and protein act as enzymes and metabolites → biochemical reaction → trait expressed 
• In a diploid organism, there are two copies of each gene, i.e., as a pair of alleles.
• One allele is received from one parent (father) and another from another parent (mother).
• In a heterozygote, one allele is dominant and another is recessive.
• In presence of the dominant allele, the recessive is not able to express.
• Different alleles produce slightly different proteins, which function in different ways.  
• In dominant/recessive relationships, the recessive allele produces a non-functional protein. The dominant allele produces a functioning protein.
• In incomplete dominance, it is thought that in a heterozygote, the dominant allele is functioning properly and the recessive allele is malfunctioning.
• The normal or dominant allele produces the normal enzyme but the modified or recessive allele could be responsible for the production of –
  • the normal/less efficient enzyme, or
  • a non-functional enzyme, or
  • no enzyme at all

The correct answer is Shape of seed

Concept:

• In Gregor Mendel's classic experiments on pea plants, he observed that seeds could be either round or wrinkled. It was later found that this trait is controlled by the gene that regulates the enzyme involved in starch synthesis. When starch is synthesized normally (dominant allele "R"), the seeds are round. When there is a mutation in this gene (recessive allele "r"), it leads to less efficient starch synthesis, resulting in wrinkled seeds

Explanation:

• A single gene product may produce more than one effect. For example, starch synthesis in pea seeds is controlled by one gene.
• It has two alleles (B and b).
• Starch is synthesised effectively by BB homozygotes and therefore, large starch grains are produced.
• In contrast, bb homozygotes have lesser efficiency in starch synthesis and produce smaller starch grains.
• After maturation of the seeds, BB seeds are round and the bb seeds are wrinkled.
• Heterozygotes produce round seeds, and so B seems to be the dominant allele. But, the starch grains produced are of intermediate size in Bb seeds.

The correct answer is TTRr

Explanation:

The correct genotype of the parent plant is TTRr because when this plant is selfed (crossed with itself), it can produce the following combinations of progeny:

Parents: TTRr x TTRr

Gametes: TR, Tr

• Phenotype: Tall plants with round seeds (3):Tall plants with wrinkled seeds (1)
• Genotype: TTRR (1) : TTRr (2): TTrr (1)             

Tall plants with round seeds: These plants can have the genotypes TTRR, TTRr.

Tall plants with wrinkled seeds: These plants can have the genotypes Ttrr.

The correct answer is round and yellow

Explanation:

• The Law of Independent Assortment states that when two pairs of traits are combined in a hybrid, the segregation of one pair of characters is independent of the other pair of characters.
• When a round, green-seeded pea plant (RRyy) is crossed with a wrinkled, yellow-seeded pea plant, (rrYY) the seeds produced in the F1  generation are round, yellow (RrYy) seeds. 
• Punnet square can be effectively used to determine the independent segregation of the two pairs of alleles during meiosis and produce eggs and pollen in the F1 generation RrYy plant.
• This is an example of a dihybrid cross.
• In a dihybrid cross, the phenotypes such as round, yellow; wrinkled yellow; round, green; and wrinkled green appeared in the ratio 9:3:3:1.
• Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F1 progeny that have round, yellow (RrYy) seeds.

The cross is in the following,

Therefore, F1 generation: RrYy (Round and yellow)

Concept-

• Gregor Mendel conducted hybridization experiments on garden peas for seven years (1856-1863).
• A dihybrid cross describes a mating experiment between two organisms that are identically hybrid for two traits.
• A hybrid organism is one that is heterozygous, which means that carries two different alleles at a particular genetic position.
• Therefore, a dihybrid organism is one that is heterozygous at two different genetic loci.
• Gregor Mendel performed dihybrid crosses on pea plants and discovered a fundamental law of genetics called the Law of Independent Assortment.

Explanation-

• Mendel selected traits for dihybrid cross for his experiments-
  • Colour of cotyledons- Yellow (Y) and Green (y).
  • Seed shape - Round (R) and Wrinkled (r).

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• The phenotypic ratio produced is 9: 3: 3: 1.
• The genotypic ratio produced is 1: 2: 2: 4: 1: 2: 1: 2: 1.

Therefore the 9 types of genotype and 4 types of the phenotype are present in the mendelian dihybrid cross.

Additional Information

• Monohybrid Cross
  • Phenotypic ratio- 3: 1
  • Genotypic ratio- 1: 2: 1

The correct answer is a Dihybrid cross.

• Mendel's law of independent assortment can be demonstrated by the Dihybrid cross.

Key Points

• Mendel's law of independent assortment:
  • Independent assortment is a fundamental principle of genetics evolved by Gregor Mendel in the 1860s.
  • Mendel formulated this principle after discovering another principle known as Mendel's law of segregation, both of which govern heredity.
  • The law of independent assortment asserts that an assortment of each pair of traits is independent of the other, i.e.during gamete formation, one pair of traits segregates from another pair of traits independently. 
  • Dihybrid cross – Cross is made between a homozygous dominant parent to another homozygous recessive parent on the basis of twocharacters.
  • By using this cross, Mendel postulated the Law of Independent Assortment.

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Explanation:

• Mendel selected traits for dihybrid cross for his experiments-
  • Colour of cotyledons- Yellow (Y) and Green (y).
  • Seed shape - Round (R) and Wrinkled (r).
• The phenotypic ratio produced is 9: 3: 3: 1.
• The genotypic ratio produced is 1: 2: 2: 4: 1: 2: 1: 2: 1.
• This proved that two pairs of alleles assorted independent of each other.

Therefore, Mendel's law of independent assortment can be demonstrated by a dihybrid cross.

Additional Information 

• Monohybrid cross – Cross is made between a homozygous dominant parent to another homozygous recessive parent on the basis of one character.
  • By using this cross Mendel postulated the Law of dominance and the Law of Segregation.

The correct answer is  All of these.

Explanation-

Gregor Mendel is regarded as the "father of modern genetics" due to his groundbreaking experiments on pea plants in the mid-19th century. His studies led him to formulate the fundamental principles of heredity.

Mendel conducted his experiments with seven pairs of contrasting characters in pea plants. These are traits that exist in one of two forms. The seven characters that Mendel focused on were:

• Seed Shape: This can be either round (dominant) or wrinkled (recessive).
• Seed Color: This can be yellow (dominant) or green (recessive).
• Flower Color: This can be violet (dominant) or white (recessive).
• Flower Position: The flowers on the plant can be axial (dominant), meaning they are located along the stem, or terminal (recessive), meaning they are located at the end of the stalk.
• Pod Shape: The pod can be inflated (dominant) or constricted (recessive).
• Pod Color: The pod can be green (dominant) or yellow (recessive).
• Stem Length: The stem can be long (dominant) or short (recessive).

For his experiment, Mendel cross-fertilized plants that had different traits for the same character (e.g., a plant with round seeds and a plant with wrinkled seeds) and observed the offspring in the subsequent generations. He performed these experiments over many years and on thousands of pea plants.

Concept-

• Gene is the basic unit of inheritance.
• Genes are hereditary markers from which control various characteristics like skin colour, height, etc.
• Gene which controls more than one character is called a pleiotropic gene.
• This gene shows multiple phenotypic effects.

Explanation-

• Phenylketonuria (PKU) is one such disorder that is caused due to a single gene mutation.
• The mutation is caused in the gene encoding phenylalanine hydroxylase enzyme.
• Affected people lack this enzyme, which can convert phenylalanine to tyrosine.
• Lack of the enzyme results in accumulation of phenylalanine, which gets converted to phenylpyruvic acid.
• Phenylpyruvic acid has adverse effects on the body:
  • Mental retardation
  • Reduction of hair
  • Skin pigmentation
• Thus, we can see that a single gene mutation is causing multiple phenotypic expressions.

Additional InformationPolygenic Inheritance -

• Polygenic inheritance was first described by Nilsson Ehle.
• It is the inheritance of characters in which one character is controlled by many genes.
• Here, the intensity of character depends upon the number of the dominant alleles.
• For example, human skin colour which is spread across a gradient and not distinct.
• It is the result of the additive effect of each allele.

Concept: 

• The dihybrid cross is a cross between two different genes means a cross between two different characters.
• The set of observable characteristics of an individual like height and color is called the phenotype.
• Genotype refers to the genetic constitution of an organism.

​​Explanation:

Below is the dihybrid cross between a pea plant with yellow round (YYRR) seeds and one with green wrinkled (yyrr) seeds.

• Phenotypes obtained from the above cross are in the ratio of 9:3:3:1 -

1. Yellow round - 1 YYRR, 2 YYRr, 1 YyRR, 4 YyRr
2. Green round - 1 yyRR, 2 yyRr
3. Yellow wrinkled - 1 YYrr, 2 Yyrr
4. Green wrinkled - 1 yyrr

• Hence, the number of phenotypes is 4.

• Genotypes obtained from the above cross are YYRR, YYRr, YYrr, YyRR, YyRr, Yyrr, yyRR, yyRr, yyrr in the ratio of 1: 2: 1: 2: 4: 2: 1: 2: 1.

• Hence, the number of possible genotypes is 9.

Therefore, the correct answer is option (4).

Concept: 

• An individual set of observable characteristics like height and color is called the phenotype.
• Genotype refers to the genetic constitution of an organism.
• A Monohybrid cross is a cross involving a pair of contrasting character.

​​Explanation:

• Option 1: 
  • When a cross is done between TT (homozygous tall) and Tt (heterozygous tall), it gives the first filial generation of all tall plants.
  • Therefore, this is not the correct answer.

• Option 2: 
  • When a cross is done between Tt (heterozygous tall) and Tt (heterozygous tall), the first filial generation ratio of 3 (Tall) : 1 (Dwarf) plants is obtained.
  • Therefore, this is the correct answer.​

• Option 3: 
  • Cross between TT (homozygous tall) and TT (homozygous tall) gives the first filial generation of all tall plants.
  • Therefore, this is not the correct answer.

• Option 4: 
  • Cross between Tt (heterozygous tall) and tt (homozygous dwarf) gives the first filial generation ratio of 1 (Tall) : 1 (Dwarf) plant.
  • Here, the dwarf plants are NOT just a few, but equal the number of tall plants.
  • Therefore, this is not the correct answer.

• Co-dominance is a form of genetic inheritance where both alleles contribute equally and visibly to the phenotype of the organism. In the F1 generation, this results in offspring that display traits from both parents equally.
• For example, in the case of blood types, if one parent has type A blood and the other has type B blood, their offspring may have type AB blood, exhibiting characteristics of both A and B alleles.

• Rationale: Incomplete dominance occurs when the phenotype of the F1 generation is a blend of the parental traits, rather than a display of both. This means the offspring will show an intermediate phenotype, not clearly resembling either parent fully.

• Rationale: Pleiotropy refers to a single gene influencing multiple, seemingly unrelated phenotypic traits. It does not specifically relate to the resemblance of the F1 generation to the parents in terms of individual traits.

• Rationale: The Law of Dominance, proposed by Gregor Mendel, states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic. The dominant allele masks the recessive one, meaning the F1 generation will resemble the dominant parent more, not both parents equally.

• Among the given options, co-dominance is the correct answer because it directly describes a situation where the F1 generation shows traits from both parents equally, which is not the case with incomplete dominance, pleiotropy, or the law of dominance.

Concept:

• Drosophila melanogaster is a common fruit fly belonging to the Order Diptera.
• Drosophila melanogaster shows XX-XY mechanism of sex determination.
• The Y chromosome is longer than the X chromosome.
• The Y chromosome has a J-shaped appearance with a short arm and a long arm.
• Genes governing eye color, body type and wing type are present on the X chromosome in a Drosophila.

Important Points

• The given traits are the body color and wing type of Drosophila melanogaster.
• Both of these characters are governed by genes present on the X chromosome.
• The Y chromosome does not play a role in determining the body color and wing type in Drosophila melanogaster.

As per the question,

• Body color:
  • ​Dominant wild type - Grey-bodied (+)
  • Recessive mutant type - Yellow-bodied (y)
• Wing type:
  • ​Dominant wild type - Developed wing (+)
  • Recessive mutant type - Vestigial wing (vg)
• Male Parental Generation:
  • Phenotype - Dominant wild type grey-bodied with developed wings 
  • Genotype - (+ +)
• Female  Parental Generation:
  • ​Phenotype - Recessive mutant yellow-bodied with vestigial wing
  • Genotype - (y vg)
• (+ +) represents the genes for dominant wild-type grey-bodied and developed wings respectively on the X chromosome.
• The Y chromosome is represented as a J-shaped structure.
• For a female Drosophila melanogaster, since the phenotype is recessive mutant, both the X chromosomes need to carry the same alleles of the gene.
• (y vg) represents the genes for yellow-bodied and vestigial wings respectively on both the X chromosomes.

So the correct answer is option 2.​

The correct answer is Half of the heterozygous Ww individuals will be red-flowered.

Concept:

• Mendel's experiments with pea plants laid the foundation for our understanding of genetics. In one of his classic experiments, he crossed plants with different traits to observe how these traits were inherited by the offspring.
• In this particular case, Mendel crossed a pea plant with two dominant alleles for red flowers (WW) with a pea plant with two recessive alleles for white flowers (ww).
• The F1 generation refers to the first generation of offspring resulting from this cross.

Explanation:

• Every individual in the F1 generation will receive a W allele from the red-flowered parent: This is correct. Each offspring will inherit one allele from each parent. Since the red-flowered parent is homozygous dominant (WW), it can only pass on the W allele.
• In the course of meiosis, a heterozygous individual will form two kinds of gametes: This is correct. A heterozygous individual (Ww) will produce two types of gametes - one with the W allele and one with the w allele.
• Half of the heterozygous Ww individuals will be red-flowered: This is incorrect. All individuals in the F1 generation will be heterozygous (Ww) and will display the dominant red flower phenotype. Therefore, 100% of the F1 generation will be red-flowered, not just half.
• Ww individuals are red-flowered and are indistinguishable from the homozygous WW individuals: This is correct. The presence of even one dominant allele (W) will result in the red flower phenotype, making Ww individuals phenotypically identical to WW individuals.