In Antirrhinum (Snapdragon), a red flower was crossed with a white flower and in F1 generation, pink
flowers were obtained. When pink flowers were selfed, the F2 generation showed white, red and pink
flowers. Choose the incorrect statement from the following :
A.
Ratio of F2 is ${1 \over 4}$ (Red) : ${2 \over 4}$ (Pink) : ${1 \over 4}$ (White)
B.
Law of Segregation does not apply in this experiment
C.
This experiment does not follow the Principle of Dominance
D.
Pink colour in F1 is due to incomplete dominance
Correct Answer: B
Explanation:
Inheritance of flower colour in Snapdragon is a classic example for incomplete dominance.
In a cross between true breeding red flower (RR) and true breeding white flower (rr) produced a pink flower (Rr).
When the pink coloured flower of F1 generation was selfed, F2 generation produced plants with red flowers, pink flowers and white flowers in the ratio of 1 : 2 : 1. Here, both red and white flowers were not dominant over each other. Both tried to express their traits and hence an intermediate colour of both red and white resulting in pink colour flowers. Thus, genes for flower colour in snapdragon is an exception of Mendel's first principle i.e. Law of dominance. Law of segregation is universally applicable.
The frequency of recombination between gene pairs on the same chromosome as a measure of the distance
between genes was explained by :
A.
Alfred Sturtevant
B.
Gregor J. Mendel
C.
Sutton Boveri
D.
T.H. Morgan
Correct Answer: A
Explanation:
Alfred Sturtevant explained chromosomal mapping on the basis of recombination frequency which is directly proportional to distance between two genes on same chromosome.
In domesticated fowls, sex of progeny depends on the type of sperm rather than egg.
B.
Human males have one of their sex-chromosome much shorter than the other.
C.
Male fruit fly is heterogametic
D.
In male grasshoppers, 50% of sperms have no sex-chromosome.
Correct Answer: A
Explanation:
The type of sex determination in birds is called female heterogamety and male homogamety. Thus, the sex of the progeny depends on the type of egg rather than the type of sperm. The female birds have two different sex chromosomes designated as Z and W while male birds have two similar sex chromosomes and called ZZ.
Inbreeding depression can be overcome by outcrossing
C.
Produces purelines
D.
Increases homozygosity
Correct Answer: A
Explanation:
Statement in option (a) is incorrect about
breeding. The correct form of statement is as follows
Inbreeding depression decrease the productivity.
Inbreeding refers to mating of closely related
individuals for 4-6 generation. Increasing
homozygosity due to the inbreeding results in
decrease in the variation within the group and
stabilisation of a particular type (i.e. pureline).
Continued inbreeding specially, usually reduces
fertility of animals and even their productivity.
This condition is called inbreeding depression.
Blood group of the father is ‘A’ and blood
group of mother is ‘B’. Then predict the
blood group of the progeny
A.
A, AB
B.
A, B, AB, O
C.
B, AB
D.
O, A, B
Correct Answer: B
Explanation:
(b) When blood group of father is A and of mother is B then the blood group of progeny will be A, B, AB and O.
The problem does not specify whether the parents are homozygous or heterozygous for the alleles of gene I.
Thus, the possible genotype of
parent could be :
(i) When only one parent is homozygous
(ii) When both parents are homozygous
(iii) When both parents are heterozygous
Therefore, in either of the three cases, the alleles that could be contributed from male parent is either '$\mathrm{I^A}$' or '$\mathrm{i}$' likewise the alleles that could be contributed from female parent is either '$\mathrm{I}^{\mathrm{B}}$' or '$\mathrm{i}$'.
Assertion : Down’s syndrome, Klinefelter’s
syndrome and Turner’s syndrome are
chromosomal disorders.
Reason : In Klinefelter’s syndrome females
are sterile.
A.
If both assertion and reason are true and reason is the correct explanation of assertion.
B.
If both assertion and reason are true, but reason is not the correct explanation of assertion.
C.
If assertion is true, but reason is false.
D.
If both assertion and reason are false.
Correct Answer: C
Explanation:
Assertion is true, but reason is false.
Down's syndrome, Klinfelter's syndrome and Turner syndrome are chromosomal disorders. In Klinfelter's syndrome males are sterile as individual possess 47 chromosomes ($44+\mathrm{XXY}$).
Down's syndrome It is also called 21 trisomy. It occurs due to the non-disjunction of 21 chromosome during meiosis. It is an autosomal aneuploidy caused by presence of extra chromosomes number $21,(45+\mathrm{XY}$ in male, $45+\mathrm{XX}$ in female).
Turner' syndrome It is due to monosomy. The individual has $(44+\mathrm{XO})$ instead of 46 chromosomes. The females become sterile.
Which of the following characteristics represent 'Inheritance of blood groups' in humans?
a. Dominance
b. Co-dominance
c. Multiple allele
d. Incomplete dominance
e. Polygenic inheritance
A.
b, c and e
B.
a, b and c
C.
b, d and e
D.
a, c and e
Correct Answer: B
Explanation:
IAIO, IBIO - Dominant-recessive relationship
IAIB - Codominance
IA, IB & IO - Three different allelic forms
of a gene (multiple allelism)
Select the incorrect statement(s) from the options given below with respect to dihybrid cross.
I. Tightly linked genes on the same chromosome show higher recombinations.
II. Genes far apart on the same chromosome show very few recombinations.
III. Genes loosely linked on the same chromosome show similar recombinations.
A.
I and II
B.
III and II
C.
I and III
D.
All of these
Correct Answer: D
Explanation:
Mendel’s law of independent assortment
states that when the parents differ from each
other in two or more pair of contrasting
characters, the inheritance of one pair of factor is
independent of the other. For the character to
assort independently they should be located on
separate non-homologous chromosomes. Genes
present on the same chromosome show linkage.
It means that these characters remain together
and thus less number of combinations are
formed. This phenomenon is called linkage and
such genes are called linked genes.
A normal woman whose father was colourblind, marries a normal man. What kinds of children can be expected and in what proportion?
A.
All daughters normal, $50 \%$ of sons colourblind
B.
All daughters normal, all sons colourblind
C.
$50 \%$ daughters colourblind, all sons normal
D.
All daughters colourblind, all sons normal
Correct Answer: A
Explanation:
$\begin{aligned}
X^{\mathrm{C}} X & =(50 \% \text { carrier daughters }) \\\\
X X & =(50 \% \text { normal daughters }) \\\\
X^C Y & =(50 \% \text { colourblind sons }) \\\\
X Y & =(50 \% \text { normal sons })
\end{aligned}$
Which one of the following conditions correctly describes the manner of determining the sex?
A.
Homozygous sex chromosomes (ZZ) determine female sex in birds
B.
XO type of sex chromosomes determine male sex in grasshopper
C.
XO condition in humans as found in Turner's syndrome determines female sex
D.
Homozygous sex chromosomes (XX) produce males in Drosophila
Correct Answer: B
Explanation:
XO type of sex chromosomes determine male
sex in grasshoppers. This type of sex-determination
comes under XX-XO type. It is common in
cockroaches, grasshoppers and bugs. The female
has two homomorphic sex chromosomes XX and
is homogametic. It produces similar eggs, each
with one X-chromosome. The male has one
chromosome only and is heterogametic. It
produces two types of sperms–gynosperms with X
and androsperms without X.
Other statements can be corrected as follows
In birds, the females are heterozygous and
represented as ZW.
Assertion Phenylketonuria is recessive
hereditary disease caused by body’s failure to
oxidise an amino acid phenylalanine to
tyrosine, because of defective enzyme.
Reason It is characterised by in the
presence of phenylalanine acid in urine.
A.
Both A and R are true and R is the correct explanation of A
B.
Both A and R are true, but R is not the correct explanation of A
C.
A is true, but R is false
D.
A and R are false
Correct Answer: B
Explanation:
Phenylketonuria occurs due to the deficiency
of liver enzyme phenylalanine hydroxylase which
converts phenylalanine into tyrosine. It occurs in
people who are homozygously recessive. It results
in a higher level of phenylalanine in blood, tissue
fluids and urine.
Assertion The non-allelic genes for red hair
and prickles are usually inherited together.
Reason The genes for red hair and prickles
are located on the same chromosome in close
association.
A.
Both A and R are true and R is the correct explanation of A
B.
Both A and R are true, but R is not the correct explanation of A
C.
A is true, but R is false
D.
A and R are false
Correct Answer: A
Explanation:
Genes situated in the same chromosomes are
said to be linked. All genes in a single
chromosome form a linkage group and usually
pass it into the same gamete and are inherited
together as a result of linkage. These genes do not
show independent assortment, e.g. genes for red
hair and prickles are linked genes.
Thalassemia and sickle cell anemia are caused due to a problem in globin molecule synthesis. Select the correct statement.
A.
Both are due to a qualitative defect in globin chain synthesis
B.
Thalassemia is due to less synthesis of globin molecules
C.
Sickle cell anemia is due to a quantitative problem of globin molecules
D.
Both are due to a quantitative defect in globin chain synthesis
Correct Answer: B
Explanation:
Sickle cell anaemia is caused due to point
mutation in which at the 6th position of beta globin
chain, glutamic acid is replaced by valine. Thus, it is a
qualitative defect in functioning of globin molecules.
Thalassemia is caused due to either mutation or
deletion which ultimately results in reduced rate of
synthesis of one of the globin chains that make up
haemoglobin. Hence, it is a quantitative defect in
functioning of globin molecules.
Which one from those given below is the period for Mendel’s hybridisation experiments ?
A.
1870 – 1877
B.
1857 – 1869
C.
1840 – 1850
D.
1856 – 1863
Correct Answer: D
Explanation:
The correct period for Mendel's hybridization experiments is Option D, 1856 – 1863. Gregor Mendel conducted his experiments on plant hybridization using pea plants between these years. During this period, he meticulously crossbred peas and observed the inheritance patterns of certain traits, which led to the formation of the fundamental laws of genetics, known as Mendel's Laws of Inheritance.
Among the following characters, which one was
not considered by Mendel in his experiments on
pea?
A.
Stem-Tall or dwarf
B.
Pod-Inflated or constricted
C.
Trichomes-Glandular or non-glandular
D.
Seed-Green or yellow
Correct Answer: C
Explanation:
During his experiments Mendel have
taken seven characters in a pea plant. In
which nature of trichomes i.e., glandular or
non-glandular was not considered by Mendel.
The genotypes of a Husband and Wife are IAIB and IAi.
Among the blood types of their children, how many different genotypes and phenotypes are possible?
A.
4 genotypes ; 3 phenotypes
B.
4 genotypes ; 4 phenotypes
C.
3 genotypes ; 4 phenotypes
D.
3 genotypes ; 3 phenotypes
Correct Answer: A
Explanation:
Husband × Wife
Number of genotypes = 4
Number of phenotypes = 3
IAIA and IAi = A
IAIB = AB
IBi = B
The mechanism that causes a gene to move from one linkage group to another is called
A.
crossing-over
B.
translocation
C.
duplication
D.
inversion
Correct Answer: B
Explanation:
Translocation i s a chromosomal
abnormality caused by rearrangement of parts
between non-homologous chromosomes. It may
cause a gene to move from one linkage group to
another.
Pick out the correct statements :
(a) Haemophilia is a sex-linked recessive disease.
(b) Down's syndrome is due to aneuploidy.
(c) Phenylketonuria is an autosomal recessive gene disorder.
(d) Sickle cell anaemia is an X – linked recessive gene disorder.
A.
(a), (b) and (c) are correct
B.
(a), (c) and (d) are correct.
C.
(a) and (d) are correct
D.
(b) and (d) are correct.
Correct Answer: A
Explanation:
Sickle cell disease is inherited in an
autosomal recessive pattern.
A cell at telophase stage is observed by a student in a plant brought from the field. He tells his teacher that this cell
is not like other cells at telophase stage. There is no formation of cell plate and thus the cell is contaning more
number of chromosomes as compared to other dividing cells. This would results in -
A.
Polyteny
B.
Aneuploidy
C.
Polyploidy
D.
Somaclonal variation
Correct Answer: C
Explanation:
Polyploidy is the phenomenon of occurrence
of more than two sets of chromosomes in the nucleus
of a cell. Polyploidy is more common in plants.
Polyploidy arises as a result of total non-disjunction
of chromosomes during mitosis or meiosis.
Match the terms in Column-I with their description in Column-II and choose the correct option :
Column-I
Column-II
(a) Dominance
(i) Many genes govern a single character
(b) Codominance
(ii) In a heterozygous organism only one allele expresses itself
(c) Pleiotropy
(iii) In a heterozygous organism both alleles express themselves fully
(d) Polygenic inheritance
(iv) A single gene influences many characters
A.
(a) - (ii), (b) - (iii), (c) - (iv), (d) - (i)
B.
(a) - (iv), (b) - (i), (c) - (ii), (d) - (iii)
C.
(a) - (ii), (b) - (ii), (c) - (iv), (d) - (iii)
D.
(a) - (iv), (b) - (iii), (c) - (i), (d) - (ii)
Correct Answer: A
Explanation:
Let's match the terms in Column-I with their descriptions in Column-II:
(a) Dominance: Describes a relationship between alleles of a gene, where one allele masks the expression of another allele at the same locus.
(b) Codominance: Occurs when both alleles at a locus are expressed and the phenotype is a combination or simultaneous expression of both alleles.
(c) Pleiotropy: Occurs when one gene influences multiple different phenotypic traits.
(d) Polygenic inheritance: This term refers to a situation where a single trait is controlled by more than one gene (often, many genes contribute to the phenotype).
Now we match them with the descriptions:
(a) - (ii) "In a heterozyous organism only one allele expresses itself" aligns with the concept of Dominance.
(b) - (iii) "In a heterozyous organism both alleles express themselves fully" is correct for Codominance.
(c) - (iv) "A single gene influences many characters" corresponds to Pleiotropy.
(d) - (i) "Many genes govern a single character" is the definition of Polygenic inheritance.
In a testcross involving F1 dihybrid flies, more parental-type offspring were produced than the recombinant-typeoffspring. This indicates
A.
Both of the characters are controlled by more than one gene
B.
The two genes are linked and present on the same chromosome
C.
The two genes are located on two different chromosomes
D.
Chromosomes failed to separate during meiosis
Correct Answer: B
Explanation:
If in a dihybrid test cross more parental
combinations appear as compared to the recombinants
in F2 generation, then it is indicative of involvement
of linkage. Linkage is the tendency of two different
genes on the same chromosome to remain together
during the separation of homologous chromosomes
at meiosis. During complete linkage no recombinants
are formed whereas in incomplete linkage few
recombinants are produced along with parental
combinations.
A tall true breeding garden pea plant is crossed with a dwarf true breeding garden pea plant. When the F1 plants
were selfed the resulting genotypes were in the ratio of -
When a tall true breeding garden pea plant
is crossed with a dwarf true breeding garden pea plant
and the F1 plants were selfed the resulting genotypes
were in the ratio of 1 : 2 : 1 i.e., Tall homozygous :
Tall heterozygous : Dwarf
It can be illustrated as given below:
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.
Linkage was first suggested by Sutton and Boveri
(1902-1903) when they propounded the famous
“chromosomal theory of inheritance.” Bateson and
Punnett (1906) while working on sweet pea found
that the factors for certain characters do not show
independent assortment. However, it was Morgan
(1910) who clearly proved and defined linkage on
the basis of his breeding experiments in fruit fly
(Drosophila melanogaster).
In the following human pedigree, the filled
symbols represent the affected individuals.
Identify the type of given pedigree.
A.
X-linked dominant
B.
Autosomal dominant
C.
Autosomal recessive
D.
X-linked recessive
Correct Answer: C
Explanation:
Autosomal recessive traits are the traits
which are caused by recessive autosomal genes when
present in homozygous condition. The given pedigree
can be explained as:
As the trait appears only in homozygous recessive
individuals (aa), therefore it is an autosomal recessive
trait.
A colour blind man marries a woman with
normal sight who has no history of colour
blindness in her family. What is the
probability of their grandson being colour
blind?
A.
1
B.
Nil
C.
0.25
D.
0.5
Correct Answer: C
Explanation:
When a colour blind man (XcY) marries a
normal woman (XX), all of their daughters are carriers
and all of their sons are normal, as shown in following
figure:
When the carrier daughter (XXc) is married to a normal
man, the probability of their son being colour blind is
0.25, as shown in following figure:
From above crosses, it is clear that the probability of
occurrence of colour blindness in the grandson of a
colour blind man and a normal woman is 0.25.
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A man with blood group ‘A’ marries a woman
with blood group ‘B’. What are all the possible
blood groups of their offsprings?
A.
A and B only
B.
A, B, AB and O
C.
A, B and AB only
D.
O only
Correct Answer: B
Explanation:
The man has blood group A, thus its genotype can either be IAIA or IAIO. Similarly, woman can either have IBIB, or IBIO genotype. Thus, theiroffspring can have any of the blood groups A (IAIA or IAIO), B (IBIB or IBIO), AB (IAIB) or O (IOIO).
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Multiple alleles are present
A.
on different chromosomes
B.
at the same locus of the chromosome
C.
at different loci on the same chromosome.
D.
on non-sister chromatids
Correct Answer: B
Explanation:
All alleles of a gene are situated on the
same loci of chromosome in organisms.
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How many pairs of contrasting characters in pea
plants were studied by Mendel in his
experiments?
A.
Eight
B.
Five
C.
Seven
D.
Six
Correct Answer: C
Explanation:
Seven pairs of contrasting characters were
selected in pea plant and studied by Mendel
in his experiment.
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Alleles are
A.
true breeding homozygotes
B.
different phenotype
C.
heterozygotes
D.
different molecular forms of a gene
Correct Answer: D
Explanation:
Genes are the units of inheritance and
contain the information that is required to express a
particular trait in an organism. Alternating forms of a
single gene which code for a pair of contrasting traits
are known as alleles. For example, two alleles
determine the height of pea plant (tall and dwarf).
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An abnormal human baby with ‘XXX’ sex
chromosomes was born due to
A.
formation of abnormal sperms in the father
B.
fusion of two ova and one sperm
C.
formation of abnormal ova in the mother
D.
fusion of two sperms and one ovum
Correct Answer: C
Explanation:
The abnormal baby has an extra X
chromosome, thus it must have been produced by
fusion of abnormal XX ovum with a normal X sperm.
Abnormal XX sperm is not possible because, males
have XY genotype, and if produce abnormal sperms,
then XY sperms and O sperms will be produced. If
fusion of multiple gametes have occurred (either two
ova with one sperm or two sperms with one ovum),
then the human baby will have triploid genotype not
the trisomy of sex chromosomes.
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The movement of a gene from one linkage group
to another is called
A.
inversion
B.
translocation
C.
duplication
D.
crossing over
Correct Answer: B
Explanation:
In translocation, the movement of a gene
takes place from one linkage group to another
between non-homologous chromosomes.
A human female with Turner’s syndrome
has single sex chromosome i.e., 44 + X0 (45). Such
females are called sterile females with rudimentary
ovaries. Other associated phenotypes of this condition
are short stature, webbed-neck, broad chest, lack of
secondary sexual characteristics and sterility. Thus, any
imbalance in the copies of the sex chromosomes may
disrupt the genetic information necessary for normal
sexual development.
Epistasis is the phenomenon of suppression of phenotypic expression of gene by a
nonallelic gene which shows its own effect.
A dominant epistatic allele suppresses the
expression of a nonallelic gene whether the
latter is dominant or recessive. For example,
fruit colour of Summer Squash (Cucurbita
pepo) is governed by a gene which pruduces
yellow colour in dominant state (Y-) and green
colour in recessive state (yy).
A man whose father was colour blind marries a women who had a colour blind mother and
normal father. What percentage of male children of this couple will be colour blind?
A.
50%
B.
25%
C.
0%
D.
75%
Correct Answer: A
Explanation:
Colour blindness is a X-chromosome
linked character.
Down’s syndrome is the chromosomal
disorders due to the presence of an additional
copy of the chromosome number 21 (trisomy
of 21). The affected individual is short
statured with small round head, furrowed
tongue and partially open mouth and mental
development is retarted.
Which one is the incorrect statement with regards
to the importance of pedigree analysis?
A.
It confirms that DNA is the carrier of genetic
information
B.
It helps to trace the inheritance of a specific trait
C.
It confirms that the trait is linked to one of the
autosome
D.
It helps to understand whether the trait in
question is dominant or recessive
Correct Answer: A
Explanation:
Pedigree analysis is a system of analysis by
following the movement and distribution of certain
genetic traits in many generations of a family. Pedigree
analysis cannot confirm that DNA is the carrier of
genetic information because it is an analysis system.
For DNA based experiments, molecular biology
techniques are used.
Which idea is depicted by a cross in which the F1
generation resembles both the parents?
A.
law of dominance
B.
co-dominance
C.
incomplete dominance
D.
inheritance of one gene
Correct Answer: B
Explanation:
In codominance, both the alleles are able
to express themselves independently when present
together resulting in a phenotype that is intermediate
between both the parental homozygous phenotypes,
thereby resembling both of them. E.g., roan coat colour
in cattle is a result of co-dominance of alleles for white
and red coat colour.
If both parents are carriers for thalessemia, which is an autosomal recessive disorder, what are the chances of
pregnancy resulting in an affected child ?
A.
100%
B.
25%
C.
no chance
D.
50%
Correct Answer: B
Explanation:
Genotype of carrier parents is – Aa
(male parent) × Aa (female parent)
AA → normal child (25%)
Aa → carriers child (50%)
aa → affected child (25%)
Which of the following cannot be detected in a developing foetus by amniocentesis ?
A.
Sex of the foetus
B.
jaundice
C.
Klinefelter syndrome
D.
Down syndrome
Correct Answer: B
Explanation:
Amniocentesis is a fetal sex determination
test in which amniotic fluid containing fetal cells which
surrounds the developing embryo is extracted and cells
are tested for chromosomal pattern to identify genetic
disorders, if any. Jaundice is not a chromosomal
disorder thus cannot be tested by amniocentesis.
If two persons with 'AB' blood group marry and have sufficiently large number of children, these children
could be classified as 'A' blood group : 'AB' blood group : 'B' blood group in 1 : 2 : 1 ratio. Modern technique
of protein electrophoresis reveals presence of both 'A' and 'B' type proteins in 'AB' blood group individuals.
This is an example of :
A.
Codominance
B.
Partial dominance
C.
Incomplete dominance
D.
Complete dominance
Correct Answer: A
Explanation:
ABO blood group system in human beings is an example of codominant, dominant
recessive and multiple alletes. Blood groups
are controlled by the gene I located on 9th
chromosome that has 3 multiple alleles, out
of which any two are found in a person.
In codominance both gene express it self
completely
Select the incorrect statement with regard to Haemophilia is :
A.
It is a dominant disease
B.
A single protein involved in the clotting of blood is affected
C.
It is a recessive disease
D.
It is a sex-linked disease
Correct Answer: A
Explanation:
Haemophilia is sex-linked disease which is
also known as bleeder’s disease as the patient will
continue to bleed even from a minor cut since he or
she does not possess the natural phenomenon of blood
clotting due to absence of antihaemophiliac globulin
or factor VIII (haemophilia – A) and plasma
thromboplastin factor IX (haemophilia–B, Christmas
disease) essential for it. As a result of continuous bleeding the patient may die of blood loss. It is
genetically due to the presence of a recessive sex linked
gene h, carried by X-chromosome. A female becomes
haemophiliac only when both of her X-chromosomes
carry the gene (XhXh).
However, such females
generally die before birth because the combination of
these two recessive alleles is lethal. A female having
only one allele for haemophilia (XXh) appears normal
because the allele for normal blood clotting present on
the other X-chromosome is dominant. Such females are
known as carriers. In case of males, a single gene for the
defect is able to express itself as the Y-chromosome is
devoid of any corresponding allele (XhY).
Number of genotypes = 4
As the trait appears only in homozygous recessive
individuals (aa), therefore it is an autosomal recessive
trait.
When the carrier daughter (XXc) is married to a normal
man, the probability of their son being colour blind is
0.25, as shown in following figure:
From above crosses, it is clear that the probability of
occurrence of colour blindness in the grandson of a
colour blind man and a normal woman is 0.25.
AA → normal child (25%)