CLASS 12 CBSE
BIOLOGY REPEATED
QUESTIONS OF UNIT VII
BY ASHMITA DASGUPTA
BTECH CSE (IoT), VIT VELLORE, 3RD YEAR
, UNIT VII : GENETICS AND EVOLUTIONS
CHAPTER 4 : PRINCIPLES OF INHERITANCE AND VARIATION
Question 1: What is a test cross? Show a monohybrid test cross using a Punnett square.
Years: 2018, 2020, 2023
ANSWER: A test cross is a genetic technique used to determine the genotype of an individual
exhibiting a dominant phenotype. This is achieved by crossing the individual with a
homozygous recessive individual. If the dominant phenotype individual is homozygous
dominant, all offspring will exhibit the dominant trait. If heterozygous, the offspring will
display a 1:1 ratio of dominant to recessive phenotypes.
Let's illustrate a monohybrid test cross using a Punnett square. Suppose we have an organism
with a dominant phenotype (T), which could be either homozygous (TT) or heterozygous (Tt),
and we want to determine its genotype. We will cross it with a homozygous recessive (tt)
individual.
, If the dominant phenotype individual is heterozygous (Tt):
Analysis of Result:
T(Dominant) t (Recessive)
Genotypic Ratio: 1:1
Tt (Dominant tt (Recessive
t (Recessive) 1. 50% Heterozygous (Tt)
Phenotype) Phenotype)
2. 50% Homozygous Recessive (tt)
Tt (Dominant tt (Recessive Phenotypic Ratio: 1:1
t (Recessive)
Phenotype) Phenotype)
1. 50% show the Dominant trait.
2. 50% show the Recessive trait.
If the dominant phenotype individual is homozygous (TT):
T(Dominant) T(Dominant) Analysis of Result:
Genotypic Ratio: 100% Heterozygous (Tt)
Tt (Dominant Tt (Dominant Phenotypic Ratio: 100% Dominant Phenotype
t (Recessive)
Phenotype) Phenotype) Key takeaway: Because the TT parent has no
recessive alleles to give, it is impossible for any
Tt (Dominant Tt (Dominant offspring to express the recessive trait (tt), no
t (Recessive)
Phenotype) Phenotype) matter what the other parent contributes.
BIOLOGY REPEATED
QUESTIONS OF UNIT VII
BY ASHMITA DASGUPTA
BTECH CSE (IoT), VIT VELLORE, 3RD YEAR
, UNIT VII : GENETICS AND EVOLUTIONS
CHAPTER 4 : PRINCIPLES OF INHERITANCE AND VARIATION
Question 1: What is a test cross? Show a monohybrid test cross using a Punnett square.
Years: 2018, 2020, 2023
ANSWER: A test cross is a genetic technique used to determine the genotype of an individual
exhibiting a dominant phenotype. This is achieved by crossing the individual with a
homozygous recessive individual. If the dominant phenotype individual is homozygous
dominant, all offspring will exhibit the dominant trait. If heterozygous, the offspring will
display a 1:1 ratio of dominant to recessive phenotypes.
Let's illustrate a monohybrid test cross using a Punnett square. Suppose we have an organism
with a dominant phenotype (T), which could be either homozygous (TT) or heterozygous (Tt),
and we want to determine its genotype. We will cross it with a homozygous recessive (tt)
individual.
, If the dominant phenotype individual is heterozygous (Tt):
Analysis of Result:
T(Dominant) t (Recessive)
Genotypic Ratio: 1:1
Tt (Dominant tt (Recessive
t (Recessive) 1. 50% Heterozygous (Tt)
Phenotype) Phenotype)
2. 50% Homozygous Recessive (tt)
Tt (Dominant tt (Recessive Phenotypic Ratio: 1:1
t (Recessive)
Phenotype) Phenotype)
1. 50% show the Dominant trait.
2. 50% show the Recessive trait.
If the dominant phenotype individual is homozygous (TT):
T(Dominant) T(Dominant) Analysis of Result:
Genotypic Ratio: 100% Heterozygous (Tt)
Tt (Dominant Tt (Dominant Phenotypic Ratio: 100% Dominant Phenotype
t (Recessive)
Phenotype) Phenotype) Key takeaway: Because the TT parent has no
recessive alleles to give, it is impossible for any
Tt (Dominant Tt (Dominant offspring to express the recessive trait (tt), no
t (Recessive)
Phenotype) Phenotype) matter what the other parent contributes.
