Mendelian Monohybrid Cross | Heredity and Evolution | Assessment | English | Grade 10

The cross between two garden pea plants with a pair of contrasting characters is called ________.

• Monohybrid cross

• One hybrid cross

• Both option 1 and option 2

Answer explanation

The cross between two garden pea plants with a pair of contrasting characters is called monohybrid cross.

In mendelian monohybrid cross, phenotypic ratio of F₂ generation is ______.

• 3 : 1

• 1 : 2 : 1

• 1 : 3

• 2 : 1 : 2

Answer explanation

External characters of any organism such as tallness and dwarfness are called phenotypes, and the ratio of these characters is called phenotypic ratio. In the F₂ generation of monohybrid cross between garden pea plants, 3 plants were tall and 1 plant was dwarf. Hence the phenotypic ratio of F₂ generation in monohybrid cross is 3 : 1.

The garden pea plant having yellow coloured seeds was crossed with the garden pea plant having green coloured seeds and F₁ generation was produced. All plants of F₁ generation were having yellow coloured seeds. What does this mean?

• The character of green seed colour is not transferred in F₁ generation

• Green seed colour is dominant over yellow seed colour

• Yellow seed colour is recessive trait

• Yellow seed colour is dominant over green seed colour

Answer explanation

The F₁ generation produced by the cross of plant having yellow seed colour and plant having green seed colour, will have different allele for seed colour. The trait that gets expressed is called the Dominant trait while the trait that is not expressed is called the recessive trait. In F₁ generation, all plants were having yellow coloured seeds. It means that the trait of yellow seed colour is expressed and green seed colour is not expressed. Hence yellow seed colour is dominant over green seed colour and green seed colour is the recessive trait. Hence option 4 is the right answer.

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

Which one of the following can not be explained on the basis of law of dominance?

• The objects that control a particular character is called a factor

• Factors occurs in pair

• Out of one pair of factors one is dominant and other is recessive

• Alleles do not show any blending and the characters of both parents are recovered in F₂ generation

Answer explanation

According to Mendel's law of dominance, in every individual the characters are controlled by factors. Due to the involvement of two parents in sexual reproduction, factors are found in pairs. The allele in the pair of factors may be similar or different. In the pair of factors, if the two alleles are different then only one of the factors is expressed. The factor that gets expressed is called the Dominant factor/ dominant gene, while the factor that is not expressed is called the recessive trait/recessive gene. Hence option 1, option 2 and option 3 can be explained on the basis of law of dominance. Alleles do not show any blending and the characters of both parents are recovered in F₂ generation can be explained on the basis of law of segregation.

In mendelian monohybrid cross, genotypic ratio of F₂ generation is ______.

• 3:1

• 1:02:01

• 9:3:3:1

• None of these

Answer explanation

The factors or traits that regulate the traits are called genotypes. In the F₂ generation of monohybrid cross between garden pea plants is TT:Tt:Tt:tt i.e. 1:2:1.

A homozygous tall garden pea plant is crossed with homozygous dwarf garden pea plant and F₁ generation is produced. Then F₁ hybrid plant is crossed with the homozygous dwarf garden pea plant. The progeny produced by this cross will contain:

• 100% tall plants

• 70% tall plants

• 50% tall plants

• 10% tall plants

Answer explanation

Homozygous tall garden pea plant will be of genotype TT. Homozygous dwarf garden pea plant will be of genotype tt. So the plant of F₁ generation will be of genotype Tt. The character of tallness is dominant and the dwarfness is recessive. Hence in F₁ generation the garden pea plant will be tall. After that the F₁ generation garden pea plant (Tt) is crossed with homozygous dwarf garden pea plant (tt). So the progeny produced by this cross will contain 50% tall plants of genotype (Tt) and 50% dwarf plants of genotype (tt).

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

In humans the blood group B is dominant over blood group O. Sharad's blood group is B and his wife's and his daughter's blood group is O. What is the Sharad's genotype for blood group if?

• BB

• OO

• BO

• The given information is not enough

Answer explanation

It is given that in humans the blood group B is dominant over blood group O. Here Sharad's wife and Sharad's daughter has blood group O. Since blood group O is recessive, it is expressed only when the both alleles are recessive. That is the individual is homozygous. Hence for blood group the genotype of Sharad's wife and Sharad's daughter is OO. Sharad's blood group is B and B is dominant character. Hence the genotype of Sharad's blood group can be heterozygous (BO) or homozygous (BB). But here the Sharad's daughter has blood group O and it's genotype is OO. This means she has received O allele from mother and father. Hence Sharad's genotype is heterozygous for blood group and it is BO.

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2