When two unrelated individuals or lines are
crossed, the per romance of F1 hybrid is often
superior to both parents. This phenomenon is
called :
A.
Sphcing
B.
Transformation
C.
Heterosis
D.
Metamorphosis
Correct Answer: C
Explanation:
The increased vigour displayed by the
offspring from a cross between genetically different
parents is called heterosis. Hybrids from crosses
between different crop varieties (F1
hybrids) are often
stronger and produce better yields than the original
varieties.
Study the pedigree chart of a certain family
given below and select the correct conculusion
which can be drawn for the character –
A.
The trait under study could not be colourblindness
B.
The female parent is heterozygous
C.
The parents could not have had a normal
daughter for this character
D.
The male parent is homozygous dominant
Correct Answer: B
Explanation:
The given pedigree chart shows that both the
daughters received the gene from the parents,
while son may be normal or affected. It shows
that the female parent is heterozygous.
ABO blood grouping is controlled by gene I
which has three alleles and show co-dominance.
There are six genotypes. How many phenotypes
in all are possible -
A.
five
B.
four
C.
three
D.
six
Correct Answer: B
Explanation:
The three alleles IA, IB and i of gene I in
ABO blood group system can produce six different
genotypes and four different phenotypes as shown
below :
A cross in which an organism showing a
dominant phenotype in crossed with the
recessive parent in order to know its genotype is
called -
A.
Dihybrid cross
B.
Back cross
C.
Monohybrid cross
D.
Test cross
Correct Answer: D
Explanation:
Test cross is performed to determine the
genotype of F2
plant. In a typical test cross an organism
showing dominant phenotype and whose genotype is
to be determined is crossed with one that is homozygous
recessive for the allele being investigated, instead of
self-crossing. The progenies of such a cross can easily
be analysed to predict the genotype of the test organism.
In antirrhinum two plants with pink flowers were
hybridized. The F1 plants produced red, pink and
white flowers in the proportion of 1 red, 2 pink
and 1 white. What could be the genotype of the
two plants used for hybridization ? Red flower
colour is determined by RR, and White by rr
genes -
A.
rrrr
B.
rr
C.
Rr
D.
RR
Correct Answer: C
Explanation:
The given situation is an example of
incomplete dominance where phenotype found in
F1
generation do not resemble either of the two
parents. The genotype of the two plants used for
cross will be
The incomplete dominance of dominant allele (here
‘R’) over recessive allele (here ‘r’) could be due to
mutations (insertion, deletion, substitution or inversion
of nucleotides). The mutant allele generally produces
a faulty or no product. This modification in the product
may lead to incomplete dominance of the (unmodified)
wild type dominant allele.
ABO blood groups in humans are controlled by
the gene I. It has three alleles – IA, IB
and i.
Since there are three different alleles, six
different genotypes are possible. How many
phenotypes can occur –
A.
One
B.
Two
C.
Three
D.
Four
Correct Answer: D
Explanation:
The three alleles in ABO blood groups in
humans can produce six different genotypes
and four different phenotypes.
Which one of the following cannot be explained
on the basis of Mendel's Law of Dominance?
A.
Out of one pair of factors one is dominant,
and the other recessive
B.
Alleles do not show any blending and both
the characters recover as such in F2
generation
C.
The discrete unit controlling a particular
character is called a factor
D.
Factors occur in pairs
Correct Answer: B
Explanation:
According to Mendel’s law of Dominance,
out of two contrasting allelomorphic factors
only one expresses itself in an individual. The
factor that expresses itself is called dominant
while the other which has not shown its effect
in the heterozygous individual is termed as
recessive. The option (c) in the given question
cannot be explained on the basis of law of
dominance. It can only be explained on
the basis of Mendel’s Law of independent
assortment, according to which in a dihybrid
cross, the two alleles of each character assort
independently of the alleles of other character
and separate at the time of gamete formation.
The genotype of a plant showing the dominant
phenotype can be determined
by –
A.
Pedigree analysis
B.
Back cross
C.
Test cross
D.
Dihybrid cross
Correct Answer: C
Explanation:
Test cross is the cross of an individual
with an individual having recessive phenotype.
It is used to determine the genotype of a plant
showing the dominant phenotype, that means
to determine whether the individual exhibiting
dominating characters are homozygous or
heterozygous.
Select the correct statement from the ones given
below with respect to dihybrid cross –
A.
Genes far apart on the same chromosome
show very few recombinations
B.
Tightly linked genes on the same
chromosome show very few recombination
C.
Tightly linked genes on the same
chromosome show higher recombinations
D.
Genes loosely linked on the same
chromosome show similar recombinations
as the tightly linked ones
Correct Answer: B
Explanation:
Linkage is the phenomenon of certain genes
staying together during inheritance through
generations without any change or separation due to
their being present on the same chromosome. Linked
genes occur in the same chromosome. Strength of the
linkage between two genes is inversely proportional
to the distance between the two i.e., two linked genes
show higher frequency of crossing over
(recombination) if the distance between them is higher
and lower frequency if the distance is small.
Which one of the following symbols and its
representation, used in human pedigree
analysis is correct –
A.
B.
C.
D.
Correct Answer: A
Explanation:
A record of inheritance of certain genetic
traits for two or more generations presented in the form
of a diagram or family tree is called pedigree. In a
pedigree a square represents the male, a circle the
female, solid (blackened) symbol shows the trait under
study or affected individual; unaffected or normal
individual by an open or clear symbol and a cross or
shade (of any type) in the symbol signifies the carrier
of a recessive allele. Words can also be used in place
of symbols. Parents are shown by horizontal line while
their offsprings are connected to it by a vertical line.
The offsprings are then shown in the form of a
horizontal line below the parents and numbered with
arabic numerals.
Study the pedigree chart given below :
What does it show ?
A.
Inheritance of a recessive sex-linked disease
like haemophilia
B.
Inheritance of a sex-linked inborn error of
metabolism like phenylketonuria
C.
The pedigree chart is wrong as this is not
possible
D.
Inheritance of a condition like
phenylketonuria as an autosomal recessive
trait
Correct Answer: D
Explanation:
The chart shows the inheritance of
a condition like phenylketonuria as an
autosomal recessive trait. Parents’ needs to
be heterozygous as two of their children are
known to be sufferer of the disease. It cannot
be recessive sex linked inheritance because
then the male parent would also be sufferer.
Caused by substitute of valine by glutamic
acid in the beta globin chain of haemoglobin
B.
An autosomal linked dominant trait
C.
Caused by a change in a single base pair of
DNA
D.
Characterized by elongated sickle like RBCs
with a nucleus
Correct Answer: C
Explanation:
Sickle-cell anaemia is an autosomal hereditary
disorder in which erythrocytes become sickle shaped.
It is caused by the formation of abnormal haemoglobin
called haemoglobin-S. Haemoglobin-S is formed when
6th amino acid of $\beta $-chain, i.e., glutamic acid is replaced by valine due to substitution. It occurs due to
a single nucleotide change (A $ \to $ T) in the $\beta $-globin
gene of coding strand. In the normal $\beta $-globin gene
the DNA sequence is CCTGAGGAG, while in sicklecell anaemia, the sequence is CCTGTGGAG.
Which one of the following conditions in
humans is correctly matched with its
chromosomal abnormality/linkage?
A.
Klinfelter's syndrome — 44 autosomes + XXY
B.
Colour-blindness — Y-linked
C.
Down syndrome — 44 autosomes + XO
D.
Erythroblastosis foetalis — X-linked
Correct Answer: A
Explanation:
Klinefelter's syndrome is a genetic
disorder affecting men in which an individual
gains an extra X chromosome, so that the
usual Karyotype of XY is replaced by one of
XXY. Symptoms of Klinefelter's syndrome
named after us physician H.P. Klinefelter,
include female characteristics (such as breast
enlargement).
So, the corresponding genotype will be AaBb.
Haploids are more suitable for mutation studies
than the diploids. This is because:
A.
all mutations, whether dominant or recessive
are expressed in haploids
B.
mutagens penetrate in haploids more
effectively than in diploids
C.
haploids are reproductively more stable than
diploids
D.
haploids are more abundant in nature than
diploids
Correct Answer: A
Explanation:
Haploid plants, are always pure because they
possess only one set of chromosomes. So, the
mutations are expressed very easily in haploid plants
as compared to diploid plants.
A human male produces sperms with the
genotypes AB, Ab, AB, and ab pertaining to two
diallelic characters in equal proportions. What is
the corresponding genotype of this person ?
A.
AaBb
B.
AABB
C.
AaBB
D.
AABb
Correct Answer: A
Explanation:
As sperms produced are with genotypes AB,
Ab, aB, ab (two diallelic character) the person must
be heterozygous for both genes. So his genotype will
be AaBb.
In the hexaploid wheat, the haploid(n) and
basic(x) numbers of chromosomes are :
A.
n = 21 and x = 14
B.
n = 21 and x = 21
C.
n = 7 and x = 21
D.
n = 21 and x = 7
Correct Answer: D
Explanation:
Hexaploid wheat has six sets of homologous chromosomes. In botanical nomenclature, the term "haploid" (n) refers to the number of unique chromosomes in a gamete, which in the case of hexaploid wheat is 21. The "basic" number (x) is the number of chromosomes in a single set within the organism, which in hexaploid wheat is 7, as there are six such sets (6x = 42 total chromosomes in a somatic cell).
In pea plants, yellow seeds are dominant to
green. If a heterozygous yellow seeded plant is
crossed with a green seeded plant, what ratio of
yellow and green seeded plants would you
expect in F1 generation ?
A.
9 : 1
B.
3 : 1
C.
50 : 50
D.
1 : 3
Correct Answer: C
Explanation:
Let GG ⇒ homozygous yellow seed
plant.
Gg ⇒ heterozygous green
gg ⇒ homozygous green
According to the question :
So, the ratio will be 50 : 50
Sickle cell anaemia has not been eliminated from
the African population because-
A.
It is not a fatal disease
B.
It is controlled by dominant genes
C.
It is controlled by recessive genes
D.
It provides immunity against malaria
Correct Answer: D
Explanation:
In sickle cell anaemia RBCs become
sickle shaped which are not supportive for the
growth of malarial parasite Plasmodium so it
provides immunity against malaria disease.
Crossing the F1 hybrid with a double
recessive genotype
C.
Crossing between two genotypes with
recessive trait
D.
Crossing between two genotypes with
dominant trait
Correct Answer: B
Explanation:
A cross of F1 hybrid with its recessive
homozygous parent is called the test cross. It
is done to determine the genotype of a given
plant. If the given plant has homozygous
dominant traits then on test cross it gives all
dominant trait plants but if it is heterozygous dominant than it gives dominant and recessive
phenotypes in 1 : 1 ratio.
In Mendel's experiments with garden pea, round
seed shape (RR) was dominant over wrinkled
seeds (rr), yellow cotyledon (YY) was dominant
over green cotyledon (yy). What are the
expected phenotypes in the F2 generation of the
cross RRYY × rryy ?
A.
Round seeds with yellow cotyledons, and
wrinkled seeds with yellow cotyledons
B.
Only wrinkled seeds with green cotyledons
C.
Only wrinkled seeds with yellow cotyledons
D.
Only round seeds with green cotyledons
Correct Answer: A
Explanation:
Since round seed shape is dominant over
wrinkled seed shape and yellow cotyledon is dominant
over green cotyledon so RRYY individuals is round
yellow and rryy is wrinkled green.
Phenotype is the appearance of one
organism while genotype is the gene
complement it has from its ancestors. These
genes only show their effect in phenotype but
environment also plays an important role in
this. Hence phenotype is a result of genotype
and environmental interaction.
Which one of the following is an example of
polygenic inheritance ?
A.
Skin colour in humans
B.
Pod shape in garden pea
C.
Production of male honey bee
D.
Flower colour in Mirabilis jalapa
Correct Answer: A
Explanation:
Polygenic inheritance is the inheritance
of traits which are dependent on the no.
of genes such as the skin colour of human
beings. eg. AABB is black AaBB in neither
dark nor black. AaBb is again wheatish Aabb
is light and aabb is white colour.
Both sickle cell anemia and Huntington's chorea
are-
A.
Congenital disorders
B.
Bacteria-related diseases
C.
Virus-related diseases
D.
Pollutant-induced disorders
Correct Answer: A
Explanation:
A congenital disorder is a medical condition
that is present at birth. Congenital disorders can be a
result of genetic abnormalities, the intrauterine
environment, or unknown factors. Sickle cell disease
[a group of genetic disorders caused by sickle
haemoglobin (HbS). HbS
molecules tend to clump
together, making red blood cells sticky, stiff and more
fragile and causing them to form into a curved, sickle
shape] and Huntington’s chorea (an inherited disorder
characterised by degenerative changes in the basal
ganglia structures, which ultimately result in a severely
shrunken brain and enlarged ventricles, abnormal body
movements called chorea and loss of memory) are
congenital disorders.
Fertilization of an XX egg by a normal
Y-bearing sperm
Correct Answer: B
Explanation:
Cri-du-chat syndrome, also called deletion
5p syndrome, (or 5p minus), is a rare genetic disorder.
Cri-du-chat syndrome is due to a partial deletion of
the short arm of chromosome number 5. The name of
this syndrome is French for “cry of the cat,” referring
to the distinctive cry of children with this disorder.
The cry is caused by abnormal larynx development,
which becomes normal within a few weeks of birth.
Infants with cri-du-chat have low birth weight and may
have respiratory problems. Some people with this
disorder have a shortened lifespan, but most have a
normal life expectancy.
G-6-P dehydrogenase deficiency is associated
with haemolysis of -
A.
RBCs
B.
Lymphocytes
C.
Platelets
D.
Leucocytes
Correct Answer: A
Explanation:
Glucose-6-P dehydrogenase is the
first enzyme of glucose oxidation during
Pentose Phosphate Pathway. RBC contain
haemoglobin which combines with oxygen
to form oxyhaemoglobin which gives its
oxygen for oxidation of food. In haemolysis
there is destruction of RBCs with release
of haemoglobin into plasma resulting in
jaundice. So, now RBCs cannot provide
oxygen for oxidation of food thereby causing
deficiency of G-6-P dehydrogenase.
Which of the following is not a hereditary
disease ?
A.
Cretinism
B.
Cystic fibrosis
C.
Haemophilia
D.
Thalasasemia
Correct Answer: A
Explanation:
Cretinism occurs due to hyposecretion of
thyroid hormones. Haemophilia is a sex linked
recessive trait. Cystic fibrosis is also a recessive
autosomal disorder resulting in mucus clogging in
lungs. Thalassemia involves a gene mutation in the
polypeptide chains of haemoglobin.
A man and a woman, who do not show any
apparent signs of a certain inherited disease,
have seven children (2 daughter and 5 sons).
Three of the sons suffer from the given disease
but none of the daughters are affected. Which of
the following mode of inheritance do you
suggest for this disease
A.
Autosomal dominant
B.
Sex-linked recessive
C.
Sex-linked dominant
D.
Sex-limited recessive
Correct Answer: B
Explanation:
The daughters receive one X chromosome
from the father and one X chromosome from
the mother. Since all the daughters suffer from
their father’s disease, the X chromosome
from the father must be carrying a dominant
trait.
A women with 47 chromosomes due to three
copies of chromosome 21 is characterized by -
A.
Superfemaleness
B.
Turner's syndrome
C.
Triploidy
D.
Down's syndrome
Correct Answer: D
Explanation:
A woman with 47 chromosomes due to three copies of chromosome 21 is characterized by Down's syndrome, which is Option D.
Here's a brief explanation of each option :
Option A, Superfemaleness: This term is sometimes colloquially used for a condition known as Triple X syndrome, where a female has an extra X chromosome (47,XXX instead of the typical 46,XX). It's not associated with three copies of chromosome 21.
Option B, Turner's syndrome: This is a condition where a female partially or completely lacks one of the two X chromosomes (usually represented as 45,X instead of 46,XX). It's unrelated to having an extra copy of chromosome 21.
Option C, Triploidy: This is a rare chromosomal disorder where individuals have three copies of every chromosome (69 chromosomes in total), not just an extra copy of chromosome 21.
Option D, Down's syndrome: This is the correct answer. Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It's the most common chromosome abnormality in humans.
A woman with normal vision, but whose father
was colour bind, marries a colour blind man.
Suppose that the fourth child of this couple was
a boy. This boy -
A.
May be colour blind or may be normal
vision
B.
Must have normal colour vision
C.
Must be colour blind
D.
Will be partially colour blind since he is
heterozygous for the colour blind mutant
allele.
Correct Answer: A
Explanation:
Since the woman’s father was colour
blind. She would be a carrier of the colour
blindness gene. When she marries a colour
blind man. Their progeny could be
Haemophilia is more commonly seen in human
males than in human females because -
A.
This disease is due to an X-linked dominant
mutation
B.
This disease is due to a Y-linked recessive
mutation
C.
This disease is due to an X-linked recessive
mutation
D.
A greater proportion of girls die in infancy
Correct Answer: C
Explanation:
This disease is due to an X-linked
recessive mutation. Males suffer this disorder
since they have only one X chromosome and
hence express any trait on this chromosome.
In order to find out the different types of
gametes produced by a pea plants having the
genotype AaBb, it should be crossed to a plant
with the genotype -
A.
aaBB
B.
aabb
C.
AaBb
D.
AABB
Correct Answer: B
Explanation:
A test cross involving the crossing of F1
individual with the homozygous recessive parent. It
is done to find out homozygous and heterozygous
individuals. So AaBb, should be crossed with aabb.
One of the parents of a cross has a mutation in
its mitochondria. In that cross, that parent is
taken as a male. During segregation of F2
progenies that mutation is found in -
A.
50% of the progenies
B.
1/3 of the progenies
C.
None of the progenies
D.
All the progenies
Correct Answer: C
Explanation:
Mitochondria is an organelle present in
the cytoplasm. A zygote receives its cytoplasm
from the female parent gamete. Hence in the
given question, the F2 progenies receive the
mitochondrial genome from the male parent,
so mutation is not passed to progenies.
The recessive genes located on X-chromosomes
in humans are always-
A.
Expressed in females
B.
Sub-lethal
C.
Expressed in males
D.
Lethal
Correct Answer: C
Explanation:
Males have only one X - chromosome.
Hence any gene present on the one X -
chromosome expresses itself n males. Females
have two X- chromosomes . The mutant allele
must be present on both the X-Chromosomes
to express itself phenotypically. If only one
copy of allele present, then the female only
becomes a carrier showing no external
manifestation of the gene. Sublethal condition
can never arise in males.
A male human is heterozygous for autosomal
genes A and B and is also hemizygous for
hemophilic gene h. What proportion of his
sperms will be abh :-
A.
1/16
B.
1/32
C.
1/8
D.
1/4
Correct Answer: C
Explanation:
The male human is heterozygous for
autosomal gene A and B and also hemizygous for
haemophilic gene h, then his genotype will be
AaBbXhY because haemophilia is a sex linked trait
that is present on X-chromosome. So, the total number
of gametes will be abXh, abY, ABXh, ABY, AbXh, AbY, aBXh, aBY. So the proportion of abXh sperm will be 1/8.
A normal woman, whose father was colour-blind
is married to a normal man. The sons would be :-
A.
All colour-blind
B.
75 % colour-blind
C.
All normal
D.
50% colour-blind
Correct Answer: D
Explanation:
In question, where the genotype of the other
parent is not mentioned then that should be considered
normal. Colour blindness is a recessive sex- linked
trait
(i) To find out the genotype of a woman.
Her father is colour-blind \ his genotype is XcY and
her mother is normal so her genotype is XX.
So, woman is carrier
(ii) When this woman marries normal man
$ \therefore $ 50% of the sons would be colour blind.
In a plant, red fruit (R) is dominant over yellow
fruit (r) and tallness (T) is dominant over
shortness (t). If a plant with RRTt genotype is
crossed with a plant that is rrtt
A.
75% will be tall with red fruit
B.
25% will be tall with red fruit
C.
50% will be tall with red fruit
D.
All the offspring will be tall with red fruit
Correct Answer: C
Explanation:
Since red fruit colour is dominant over
yellow fruit colour and tallness is dominant over
shortness.
Which one of the following conditions though
harmful in itself, is also a potential saviour from
a mosquito borne infectious disease ?
A.
Pernicius anaemia
B.
Thalassaemia
C.
Leukemia
D.
Sickle cell anaemia
Correct Answer: D
Explanation:
A sickle cell anaemia affected person is
more resistant to mosquito born infectious
disease because the sickle - cell shaped RBCs
are hostile to the protozoa Plasmodium.
Down's syndrome is caused by an extra copy of
chromosome number 21. What percentage of
offspring produced by an affected mother and a
normal father would be affected by this disorder ?
A.
50%
B.
100%
C.
75%
D.
25%
Correct Answer: A
Explanation:
Down’s syndrome is the example of autosomal
aneuploidy. Here, an extra copy of chromosome 21
occurs. As it is an autosomal disease, the offsprings
produced from affected mother and normal father should
be 50%.
Pattern baldness, moustaches and beard in
human males are examples of : -
A.
Sex limited traits
B.
Sex influenced traits
C.
Sex determining traits
D.
Sex linked traits
Correct Answer: B
Explanation:
Sex influenced traits are autosomal traits that
are influenced by sex. If a male has one recessive allele,
he will show that trait, but it will take two recessive
alleles for the female to show that same trait e.g. pattern
baldness, moustaches and beard in males. Sex linked
traits are those traits determining genes of which are
found on the sex chromosomes. Sex limited traits are
the traits which are expressed in a particular sex though
their genes also occur in the other sex e.g., milk
secretion in mammalian females.
Whether the egg is fertilized or develops
parthenogenetically
C.
The ratio of number of X-chromosomes to
the sets of autosomes
D.
The ratio of pairs of X-chromosomes to the
pairs of autosomes
Correct Answer: D
Explanation:
According to genic balance theory of sex
determination the ratio between the number of
X-chromosomes and number of complete sets of
autosomes will determine the sex. The X-chromosome
is believed to carry female tendency genes, while
autosomes carry male tendency genes. Both these
sets of genes start functioning and there has to be
a balance between them for an individual to become
male or female. If the ratio between X and A is 1.0
it will be a female individual and when it is 0.5, it
would be male.
Two crosses between the same pair of genotypes
or phenotypes in which the sources of the
gametes are reversed in one cross, is known as : -
A.
Reciprocal cross
B.
Reverse cross
C.
Test cross
D.
Dihybrid cross
Correct Answer: A
Explanation:
A reciprocal cross means that the same two
parent are used in two experiments in such a way that
if in one experiment A is used as the female parent
and B is used as the male parent then in the other
experiment A will be used as the male parent and B as
the female parent. Thus the sources of gametes are
reversed. When the F1
individuals obtained in a cross
is crossed with the recessive parent, it is called a test
cross. When inheritance of two pairs of contrasting
character is studied simultaeneously it is called
dihybrid cross.
The incomplete dominance of dominant allele (here
‘R’) over recessive allele (here ‘r’) could be due to
mutations (insertion, deletion, substitution or inversion
of nucleotides). The mutant allele generally produces
a faulty or no product. This modification in the product
may lead to incomplete dominance of the (unmodified)
wild type dominant allele.
What does it show ?
To find the genotype of hybrid test cross is
done.
So, the ratio will be 50 : 50
So, woman is carrier
