- There would be eighteen autosomes in the karyotype of this
animal. This is because egg is haploid and if it contains nine
autosomes and one sex chromosome then the diploid cells
of individual will contain eighteen autosomes and a pair of
sex chromosomes.
- Ligation of complimentary sticky ends is more efficient than
the ligation of blunt ends, because complementary sticky
ends can base pair with one another by hydrogen-bonding
forming a relatively stable structure for the DNa ligase to act
upon. Thus, DNa fragments with sticky ends are preferred
over DNa fragments with blunt ends to generate a chimeric
DNa molecule.
- (a) Six genotypes and four phenotypes are present in the
human population, which are as follows :
IA IA, IA i – blood group a
IB IB, IB i – blood group b
IA IB – blood group ab
i i – blood group O.
(b) The source of heroin is opium which is dried latex of unripe
capsular fruit of Papaver somniferum. Heroin is a semisynthetic
opiate formed from morphine (natural opiate) by acetylation.
It is a depressant and slows down body functions.
- Complete removal of gonads cannot be considered as a
contraceptive option because it will make the person infertile
and will lead to the unavailability of certain hormones that
are required for proper functioning of accessory reproductive
parts.
- CuT is copper releasing IuCD and LNG - 20 is hormone
releasing IuCD. Cu ions released by CuT suppress sperm
motility and fertilising capacity of sperms, whereas the
hormones released by LNG-20 make the uterus unsuitable
for implantation and the cervix hostile to the sperms.
OR
The two pairs of organs which show convergent evolution are:
(b) Wings of insects and birds
(d) Pectoral fins of sharks and flippers of dolphins
Wings of insects and birds have different basic structure but
have same function i.e., flying. Similarly, the basic structural
plan of pectoral fins of sharks and flippers of dolphins is
different but their function is same i.e., swimming. These
organs are analogous organs which indicate a similar
adaptation (flying and swimming) by unrelated groups
through modification or evolution of different parts. Thus,
they exhibit convergent evolution.
- Refer to answer 6, a and b page no. 408, `MTG Excel in Biology’.
- (a) a cross between a heterozygous pea plant with round
and yellow seeds (rryy) and a homozygous dominant pea
plant (rryy) is given as :
RY
RrYy × RRYY
Ry rY ry
RY RRYY RRYy RrYY RrYy
The number of genotypes is four and the number of
phenotypes is one i.e., round and yellow.
(b) Refer to answer 3, page no. 117, `MTG Excel in Biology’.
- When the natural selection favours small or large-sized
individuals, more individuals of that type appear in next
generation. Due to this, mean size of the population changes
towards one particular direction. This change is referred to as
directional selection and can be represented as :
Fig.:Directional selection
Conserved
EliminatedMean
(a)
EliminatedMean
(b) (c)
- (a) In a prokaryotic (bacterial) cell, transcription and
translation are coupled i.e., translation begins while the
mrNa is still being synthesised. It is because of the absence
of nucleus in a prokaryotic cell to separate the processes of
transcription and translation. both these processes occur in
the cytoplasm of a prokaryotic cell.
(b) DNa polymerase can polymerise nucleotides only in 5′ → 3 ′
direction on 3′→ 5 ′ strand because it adds them at the 3′
end. On the DNa template strand with polarity 5′ → 3 ′,
only a short segment of DNa strand can be built in 5′→ 3 ′
direction due to exposure of a small stretch of template
at one time. These short segments of DNa (called Okazaki
fragments) are later joined by means of DNa ligase forming
the lagging strand. Thus, DNa replication is discontinuous on
the template strand with polarity 5′→ 3 ′.
- (a) In amniocentesis, a small amount of amniotic fluid
is withdrawn by passing a syringe needle through the
abdominal wall and uterine wall into the amniotic sac.
In chorionic villi sampling (CVS), a catheter is inserted into
the uterus through the mother's vagina and cervix (guided
by ultrasound) to withdraw a small amount of foetal tissue
from the placenta.
(b) The rate of succession would be faster in a forest destroyed
by forest fire. It is because a forest destroyed by forest fire is
a secondarily barred area and has already built in soil organic
matter. It is biologically fertile, so underground parts, some
seed remnant species and invaders can give rise to new
community as soon as conditions become favourable.
- (a) The part labelled 'X' is generative cell which divides
mitotically to give rise to two male gametes either at the
time of dehiscence or during germination of pollen grain.
The two male gametes will take part in double fertilisation
i.e., one will fuse with egg to form zygote and the other will
fuse with secondary nucleus to form primary endosperm
nucleus which gives rise to endosperm.
(b) Oceans are low productivity ecosystems because in oceans,
productivity is limited by light which decreases with
increasing water depth.
- (a) The given figure represents subcutaneous implant.
