Assertion (A): Mendel used pea plants to study inheritance
patterns.
Reason (R): Pea plants have many contrasting characters and
show cross-pollination naturally.
Answer: (C) A is true, but R is false.
Explanation: Mendel selected pea plants due to their easily
observable contrasting traits and their ability to self-pollinate, which could
also be artificially cross-pollinated.
Assertion (A): In a dihybrid cross, the phenotypic ratio of the
F2 generation is 9:3:3:1.
Reason (R): The principle of independent assortment applies to
dihybrid crosses.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Independent assortment states that genes for
different traits segregate independently during gamete formation, resulting in
the 9:3:3:1 ratio.
Assertion (A): A test cross is used to determine the genotype
of an individual with a dominant phenotype.
Reason (R): The individual with the dominant phenotype is
crossed with a homozygous recessive individual.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A test cross involves crossing the organism with a
recessive homozygote to reveal the genotype of the dominant individual.
Assertion (A): Linkage decreases the chances of recombination
of alleles.
Reason (R): Linked genes are located on the same chromosome and
tend to be inherited together.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Linkage keeps genes together on the same
chromosome, reducing recombination.
Assertion (A): In incomplete dominance, the phenotype of the
heterozygote is intermediate between the two homozygotes.
Reason (R): In incomplete dominance, both alleles express
equally in the phenotype.
Answer: (C) A is true, but R is false.
Explanation: In incomplete dominance, neither allele is
completely dominant, and the heterozygote shows an intermediate phenotype.
Assertion (A): ABO blood grouping in humans is an example of
multiple alleles.
Reason (R): Multiple alleles are present in the population, but
an individual has only two alleles.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: ABO blood grouping is controlled by three alleles:
,
,
and .
An individual can have only two of these alleles.
Assertion (A): Haemophilia is more common in males than in
females.
Reason (R): Haemophilia is an X-linked recessive disorder.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Males have only one X chromosome, so a single
defective gene on the X chromosome causes haemophilia.
Assertion (A): A female carrier for color blindness has a 50%
chance of passing the defective allele to her sons.
Reason (R): Sons inherit their X chromosome from their mother.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A carrier female (XX)
can pass the defective allele to half of her offspring, and male children
inheriting the defective X become colorblind.
Assertion (A): Down syndrome is caused by trisomy of chromosome
21.
Reason (R): Non-disjunction of chromosomes during meiosis leads
to trisomy.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Down syndrome results from the presence of an
extra chromosome 21 due to non-disjunction.
Assertion (A): Turner syndrome individuals have 44 autosomes
and an XO sex chromosome complement.
Reason (R): Turner syndrome is caused by the absence of one X
chromosome.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Turner syndrome is a monosomy condition where
females lack one X chromosome.
Assertion (A): The sex of a child is determined by the father
in humans.
Reason (R): The sperm can carry either an X or a Y chromosome,
while the ovum always carries an X chromosome.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Male gametes determine the sex of the offspring
since they contribute either an X or a Y chromosome.
Assertion (A): Sickle cell anemia is caused by a single point
mutation in the gene coding for beta-globin.
Reason (R): This mutation leads to the substitution of glutamic
acid with valine.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Sickle cell anemia is caused by a point mutation
in the -globin
gene, resulting in abnormal hemoglobin.
Assertion (A): Mendel’s work remained unnoticed until 1900.
Reason (R): There was a lack of knowledge about chromosomes and
meiosis during Mendel's time.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Mendel's findings were rediscovered in 1900
because earlier, there was insufficient understanding of cellular mechanisms
like meiosis.
Assertion (A): Law of segregation is applicable to both
monohybrid and dihybrid crosses.
Reason (R): Law of segregation states that alleles of a gene
pair segregate during gamete formation.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The law of segregation is a universal principle
that applies to the segregation of alleles in all types of crosses.
Assertion (A): Mendel's experiments showed that traits are
inherited independently.
Reason (R): Independent assortment applies only to genes
located on different chromosomes.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Independent assortment is observed when genes are
located on separate chromosomes or far apart on the same chromosome.
Assertion (A): Polygenic inheritance results in continuous
variation.
Reason (R): Polygenic traits are controlled by multiple genes,
each contributing additively to the phenotype.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Traits like height and skin color show continuous
variation because they are influenced by multiple genes.
Assertion (A): A man with AB blood group cannot have a child
with O blood group.
Reason (R): The O blood group phenotype requires both alleles
to be recessive (ii).
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A person with AB blood group does not carry the
recessive allele ,
making it impossible to have offspring with O blood group.
Assertion (A): Phenylketonuria (PKU) is caused by the absence
of the enzyme phenylalanine hydroxylase.
Reason (R): PKU is an autosomal recessive disorder where
phenylalanine accumulates in the body.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In PKU, phenylalanine cannot be metabolized into
tyrosine, leading to its toxic accumulation.
Assertion (A): Non-disjunction of chromosomes can lead to
genetic disorders like Turner syndrome.
Reason (R): Non-disjunction results in the gain or loss of
chromosomes during gamete formation.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Turner syndrome results from the loss of one X
chromosome due to non-disjunction.
Assertion (A): The Barr body represents an inactive X
chromosome in females.
Reason (R): In females, one of the two X chromosomes is
randomly inactivated during early embryogenesis.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The inactivated X chromosome forms a Barr body to
ensure dosage compensation in females.
Assertion (A): Chromosomal theory of inheritance correlates the
behavior of chromosomes with Mendelian principles.
Reason (R): Genes are located on chromosomes, which segregate
and assort independently during meiosis.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Sutton and Boveri proposed the chromosomal theory
of inheritance based on Mendel's principles.
Assertion (A): Down syndrome is caused by an error in mitosis.
Reason (R): Non-disjunction in chromosome 21 during meiosis
leads to trisomy.
Answer: (C) A is false, but R is true.
Explanation: Down syndrome is caused by meiotic
non-disjunction, not mitotic error.
Assertion (A): Male-pattern baldness is an example of a
sex-influenced trait.
Reason (R): These traits are influenced by sex hormones but are
controlled by autosomal genes.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Male-pattern baldness depends on androgen levels,
despite being autosomal.
Assertion (A): Genes present on the same chromosome are always
inherited together.
Reason (R): The closer the genes are on a chromosome, the
lesser the chance of recombination.
Answer: (C) A is false, but R is true.
Explanation: Linked genes are often inherited together, but
crossing over can separate them.
Assertion (A): Genes located on different chromosomes segregate
independently during meiosis.
Reason (R): Independent assortment of genes results in genetic
variation in offspring.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Independent assortment of genes located on
different chromosomes during meiosis is one of the key mechanisms that
contribute to genetic variation.
Assertion (A): A heterozygous person for a dominant allele
shows the dominant phenotype.
Reason (R): A heterozygous genotype has both a dominant and a
recessive allele.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In a heterozygous individual, the dominant allele
expresses its trait even in the presence of the recessive allele.
Assertion (A): The F1 generation of a dihybrid cross always
exhibits the dominant traits.
Reason (R): In a dihybrid cross, the dominant traits are
expressed in the heterozygous F1 generation.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In a dihybrid cross involving two traits, the F1
generation typically exhibits the dominant traits due to the presence of
dominant alleles.
Assertion (A): The law of independent assortment applies to
linked genes.
Reason (R): Linked genes are located close together on the same
chromosome and are inherited together.
Answer: (C) A is false, but R is true.
Explanation: The law of independent assortment applies to genes
on different chromosomes or genes that are far apart on the same chromosome.
Linked genes do not assort independently.
Assertion (A): The appearance of a genetic disorder in the
offspring depends solely on the genotype of the parents.
Reason (R): Both parents contribute equally to the offspring’s
genotype.
Answer: (B) A is false, but R is true.
Explanation: While the genotype does play a crucial role,
environmental factors also influence the phenotype, not just the parents’
genetic contribution.
Assertion (A): X-linked recessive traits are more commonly
expressed in males than females.
Reason (R): Males have only one X chromosome, so they do not
have a second X to mask the recessive allele.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Since males have only one X chromosome, they are
more likely to express X-linked recessive traits, whereas females require two
copies of the recessive allele (one on each X chromosome).
Assertion (A): The presence of Barr bodies in females is a
result of random X-inactivation.
Reason (R): X-inactivation occurs to balance the gene dosage
between males (XY) and females (XX).
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In females, one of the X chromosomes is randomly
inactivated in each cell, forming a Barr body. This balances the gene dosage
between males and females.
Assertion (A): Cystic fibrosis is an autosomal dominant
disorder.
Reason (R): Cystic fibrosis is caused by a mutation in the CFTR
gene, which codes for a membrane protein.
Answer: (C) A is false, but R is true.
Explanation: Cystic fibrosis is actually an autosomal recessive
disorder, not dominant. The mutation in the CFTR gene causes the disorder.
Assertion (A): A monohybrid cross results in a 3:1 phenotypic
ratio in the F2 generation.
Reason (R): This ratio is due to the segregation of two alleles
for a single trait.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Mendel’s monohybrid cross leads to a 3:1
phenotypic ratio because of the segregation of alleles for a single trait.
Assertion (A): A child with blood type O can have parents with
blood types A and B.
Reason (R): The O blood type is recessive, requiring both
parents to contribute an i allele.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: For a child to have blood type O, both parents
must carry the recessive
allele, even if they have blood types A or B.
Assertion (A): Huntington’s disease is an autosomal dominant
disorder.
Reason (R): The disease manifests in individuals who inherit
just one copy of the dominant allele.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Huntington’s disease is caused by a dominant
allele, and it can affect individuals who inherit one copy of the allele.
Assertion (A): A genotype consisting of two identical alleles
is termed heterozygous.
Reason (R): Heterozygous individuals carry two different
alleles for a particular gene.
Answer: (C) A is false, but R is true.
Explanation: A genotype with two identical alleles is termed
homozygous, not heterozygous.
Assertion (A): Dihybrid crosses result in a 9:3:3:1 phenotypic
ratio in the F2 generation.
Reason (R): This ratio is due to the independent assortment of
two traits.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In a dihybrid cross, the 9:3:3:1 ratio results
from the independent assortment of alleles for two traits.
Assertion (A): Epistasis refers to the interaction between two
genes that affect a single trait.
Reason (R): One gene can mask the expression of another gene in
epistasis.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Epistasis occurs when one gene interferes with the
expression of another gene, leading to variations in the trait.
Assertion (A): The genetic basis of sex determination in humans
is XY.
Reason (R): The presence of two X chromosomes in females and
one X and one Y chromosome in males determines sex.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In humans, males are XY and females are XX. The Y
chromosome determines male sex.
Assertion (A): Mendel’s law of dominance states that one allele
may mask the effect of the other allele.
Reason (R): Dominant alleles express their effect even in the
heterozygous state.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The law of dominance explains that a dominant
allele expresses its effect even if only one copy is present in a heterozygous
individual.
Assertion (A): Genetic recombination occurs during meiosis.
Reason (R): Recombination occurs when homologous chromosomes
exchange genetic material.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Genetic recombination during meiosis occurs
through crossing over, where homologous chromosomes exchange genetic material.
Assertion (A): The phenomenon of incomplete dominance leads to
blending inheritance.
Reason (R): In incomplete dominance, neither allele is
completely dominant over the other, resulting in an intermediate phenotype.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Incomplete dominance results in an intermediate
phenotype, such as pink flowers in a cross between red and white flowers.
Assertion (A): Crossing over results in genetic variation.
Reason (R): Crossing over occurs between homologous chromosomes
during meiosis and leads to new combinations of alleles.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Crossing over during meiosis leads to genetic
recombination, creating new combinations of alleles and promoting genetic
variation.
Assertion (A): Autosomal dominant disorders are less common
than autosomal recessive disorders.
Reason (R): Autosomal dominant disorders are typically more
severe, leading to early death in many cases.
Answer: (C) A is false, but R is true.
Explanation: Autosomal dominant disorders are often more severe
but not necessarily less common than autosomal recessive disorders.
Assertion (A): In codominance, both alleles of a gene are
expressed in the heterozygous condition.
Reason (R): Codominance results in a phenotype that is a blend
of both alleles.
Answer: (C) A is true, but R is false.
Explanation: In codominance, both alleles are fully expressed
without blending, as seen in blood group AB, where both IA and IB alleles are
expressed.
Assertion (A): Mendel’s law of segregation states that alleles
do not mix or blend.
Reason (R): During gamete formation, alleles separate randomly
and independently.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The law of segregation explains that alleles for a
trait separate during gamete formation and retain their distinct identities.
Assertion (A): Linkage reduces the frequency of recombination
between two genes.
Reason (R): Genes located close together on the same chromosome
are often inherited together.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Linked genes do not assort independently and are
inherited together unless separated by crossing over.
Assertion (A): A test cross determines whether an individual
with a dominant phenotype is homozygous or heterozygous.
Reason (R): A test cross is performed by crossing the
individual with a homozygous recessive organism.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A test cross involves crossing an individual
showing the dominant phenotype with a homozygous recessive individual to
determine its genotype.
Assertion (A): Pleiotropy is a condition where a single gene
influences multiple traits.
Reason (R): The phenotypic effects of pleiotropy are due to
multiple alleles of a gene.
Answer: (C) A is true, but R is false.
Explanation: Pleiotropy occurs when a single gene affects
multiple traits, but it is not due to multiple alleles; it is the result of the
gene's diverse roles in an organism.