UNIT TEST
TOPIC: - INHERITANCE AND
VARIATIONS
MARKS:-25 TIME:-1.30HRS.
SECTION-A
QN.1) SELECT AND WRITE THE
CORRECT ANSWER: - (04)
i) The genotypic and phenotypic ratio
are not identical in case of:
a) Incomplete
dominance. b) Monohybrid test cross
c) Dihybrid test cross. d) Complete dominance
ii) What will be the ratio of different types of gametes formed by a pea plant with YyRr
genotype?
a) 9:3:3:1. b) 1:1:1:1. c)
3:1 d) 1:1
iii) In
humans, the sex chromosome complement is
a) XX–XY b) XX–XO c) ZO–ZZ d)
ZW–ZZ
iv) Daughter of a colour blind father and normal mother marries
a colour blind person. Colour blindness in
the family shall be
a) 50% sons and 50% daughters
b)
All sons and daughters
c)
All daughters
d)
All sons
QN.2) ANSWER THE FOLLOWING: - (03)
i)
How many linkage groups are present in Drosophila melanogaster?
Drosophila shows four linkage groups.
ii) Define
euploidy.
Ans: - When the chromosome number in a cell is the exact
copy of the primary basic number then it is called as euploidy.
iii)
Give one example of complete linkage.
Ans:-X-chromosome of Drosophila male shows
complete linkage.
SECTION-B
ATTEMPT ANY FOUR: - (08)
QN.3) State
any four reasons for Mendel’s success.
Ans:-1] Selection of pea plant was important reason.
2] Mendel selected and studied single
character at a time.
3] Mendel used
principles of mathematics and statistics for interpretation of results.
4] Mendel kept his records in definite pattern which helped to
trace the characters in several generations.
5] Mendel’s luck played major role in his
success.
6] Luckily, there was no linkage or incomplete dominance in characters
selected by Mendel.
QN.4) Explain
incomplete dominance with suitable example and also state the ratio.
Ans:-1) Both the alleles or genes of
allelomorphic pair express themselves partially.
2)
One allele is unable to suppress the expression of other allele completely.
3)
Intermediate expression of character in F1 hybrid is seen.
4)
e.g. Mirabilis jalapa
QN.5) Write
an account of chromosomal theory of inheritance.
Ans: - 1) Chromosomes are present in pairs in
somatic cells.
2)
During gametogenesis homologous chromosomes pair, segregate and assort independently.
Each gamete receives only one chromosome from a pair.
3) Nucleus
of gametes contains chromosomes which carry all hereditary characters.
4)
Male and female gametes carry all hereditary traits and form the link between
parents and offsprings.
5)
Fusion of both the gametes leads to restoration of the diploid number of
chromosomes of the species.
Ans.:-1) When a single gene controls two or more
different traits, it is called as pleiotropic gene and the phenomenon is called
as pleiotropism.
2) The
phenotypic ratio is 1:2 instead of 3:1 because of the death of recessive
homozygote.
3)
The disease sickle cell anemia is caused by a gene Hbs and HbA
is the normal gene. The lethal gene is responsible for death of the bearer in
homozygous condition.
4) It
produces sickle trait in heterozygous carrier.
5) Thus,
two different expressions are produced by a single gene.
Ans :-( any two points)
|
Chromosomal disorders |
Mendelian disorders |
|
1) Caused by chromosomal abnormalities. |
1) Caused by allelic abnormalities. |
|
2) Develop due to defective synapsis and disjunction. |
2) Develop due to mutation. |
|
3) Defect can be known through amniocentesis. |
3) Defect can be predicted through pedigree analysis. |
|
4) Rarely transmitted. |
4) Transmitted into the progeny. |
QN.8) Write
a note on mechanism of sex determination in birds.
Ans.:- 1) The
mechanism of sex determination in birds is ZW - ZZ type.
2) The
male is homogametic with ZZ chromosomes and female shows heterogametic nature
with ZW chromosomes.
3) It can be represented by following chart:
SECTION-C
ATTEMPT ANY TWO: - (06)
QN.9) Describe
the structure of sex chromosomes with the help of labelled diagram.
Ans.: The two sex chromosomes are X-chromosome and Y-
chromosome. The structure can be explained as follows:
A) X - Chromosome:-
1) The X–chromosomes is sub metacentric with the
centromere located
slightly away from the middle.
2) It shows two types of segments namely,
homologous and non-homologous
chromosomes.
3) The homologous part shows identical gene loci
and cross over during
meiosis.
4) The non- homologous region carry X - linked
genes which show X - linked inheritance.
5) The X - chromosomes shows large amount of Euchromatin
and small
amount of heterochromatin.
6) X - chromosome is present
in both males and females.
7) It decides female sex of zygote.
8) The linkage shown by X - chromosome is known
as X - linkage.
9) X - chromosomes shows crisscross inheritance.
B) Y - Chromosome:
1) Y -
chromosomes is present in males and absent in females.
2) It shorter than X - chromosomes and curved at
end except humans.
3) It shows centromere at one end hence it is
acrocentric in nature.
4) It shows homologous segment which shows
crossing over during meiosis.
5) The non-homologous part do not carry same gene
loci and do not show crossing over.
6) The genes present on non-homologous part are
called as Y - linked gene and show Y -
linked inheritance
7) Y - Chromosomes contain small amount of Euchromatin
and large amount of heterochromatin.
8) The linkage shown by Y - Chromosomes is known
as Y - linkage.
9) Y - Chromosomes shows straight inheritance.
10) It determines male sex.
QN.10) Write a note on Down’s syndrome.
Ans: - 1) Down’s
syndrome is caused due to aneuploidy.
2) The
syndrome was described by John Langdon Down.
3) It
is due to trisomy at 21st chromosome due to which the genotype shows (46 + 1
=47)
4) An extra chromosome number 21 (from group G).
It results in 3 copies of 21st chromosome
instead homologous pair.
5) It occurs due to failure of separation of
chromosome or non-disjunction during meiosis.
6) It is due to trisomy represented by (2n + 1)
7) The different symptoms are as follows:
a) Typical facial features with a fold of skin
(epicanthal fold skin) over the inner
corner of eye. It results in downward slanting of eyelids.
b) Typical flat face, rounded flat nose,
protruding tongue with open mouth.
c) Mental retardation.
d) Poor skeletal development, short stature and
relatively small skull and palate is
arched.
e) Flat hand with characteristic crease which runs all the way
across the palm. (Simian crease)
QN.11) Write a note on monohybrid test cross and
also mention its significance.
Ans:-1] A cross made between
F1 hybrid and its homozygous recessive parent by considering single character is
called as monohybrid test cross.
2] It can be explained with the help of following example,
1] Pure line
varieties:-It helps in development of homozygous true breeding variety.
2] It explains the law
of dominance and law of segregation.
3] It explains
homozygous and heterozygous conditions of the individuals i.e. determine the
genotypes of the unknown plants.
4] It is easy and quick
method of obtaining exotic variety.
5] Back cross is usually used in hybridization programme due to its simple ratios.
SECTION-D
ATTEMPT ANY ONE:- (04)
QN.12) Define
inheritance. Give statements for various laws of inheritance.
Ans:- A) Inheritance :-The transmission of
genetic information from generation to generation is known as inheritance.
B) Statement of Law of Dominance:
"When
two homozygous individuals with one or more sets of contrasting characters are
crossed, the alleles (characters) that appear in F, are dominant and those
which do not appear in F, are recessive".
C)
Statement of Law of Segregation:
The
law states that "When hybrid (F1) forms gametes, the alleles segregate
from each other and enter in different gametes". The gametes formed are
pure in that they carry only one allele each (either dominant allele or
recessive allele). Hence, this law is also described as "Law of purity of
gametes".
D) Statement of Law of Independent Assortment:
The
law states that "When hybrid possessing two (or more) pairs of contrasting
factors (alleles) forms gametes, the factors in each pair segregate
independently of the other pair".
Ans.: 1) The sex linked disease in
which a person is unable to distinguish between red and green colour as both these appears him or her grey is known
as red green colour blindness.
2) The
disease develops due to recessive X - linked genes over X -chromosome.
3) It
prevents formation of colour sensitive cells in the retina necessary for distinction of red and green.
4) The
genes for normal vision (dominant) and colour blindness (recessive) are located on non homologous region of X -
chromosome and absent on Y - chromosomes.
The inheritance of characters from father to his grandson through his daughter is called as crisscross inheritance or digenic type of inheritance.
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