- according to the data given, the f 3 progeny shows a
typical Mendelian monohybrid phenotypic ratio of the
dominant and recessive phenotypes i.e., 3 : 1. It indicates
that both the parents are homozygotes, one for dominant
trait and the other for recessive trait. Thus, the genotypes
of the parents will be ee and ee. The cross between the
hybrid parents produced in f 2 generation, which resulted
in three offsprings with erect ears, and one with drooping
ears can be represented as follows:
8.(i) The purpose of the urey and Miller’s experiment was
to prove that life has originated spontaneously from non
living matter i.e. to provide experimental evidence for the
theory of abiogonesis or chemical evolution.
(ii) energy was supplied in the form of electrical discharges
from electrodes at 800°C.
(iii) The experiment was run continuously for a week.
(iv) The gases used during experiment to simulate the
primitive atmosphere were methane, ammonia, hydrogen
and water vapour.
- SCID is Severe Combined Immuno deficiency. It is a
congenital disease caused due to absence of T and
b-lymphocytes, two types of white cells necessary for
fighting infections, since birth.
It differs from aIDS in the respect that in aIDS, T-helper
cells which stimulate antibody production by b-cells are
reduced, due to viral attack while in SCID, both T and
b-cells are absent i.e., individuals are born without these
cells.
OR
Due to infection, our body temperature rises, as a result
of release of certain chemicals called endogeneous
pyrogens from damaged tissues, and the cells involved in
inflammation. When enough pyrogen reaches the brain,
the body’s thermostat is reset to a higher temperature,
allowing the temperature of the entire body to rise.
Mild fever strengthens the defence mechanism by
activating the phagocytes, and by inhibiting the growth
of microbes. a very high temperature, however, may prove
dangerous. It must be quickly brought down by giving
antipyretics or fever reducing drugs e.g. aspirin and by
applying cold packs.- Differences between primary and secondary succession
are given in the following table:
Primary
succession
Secondary succession- It occurs in an area
which has been bare
from the beginning.
Secondary succession occurs
in an area which has been
denuded recently.- Soil is absent when
primary succession
starts.
Soil is present in the area
where secondary succession
begins.- re p r o d u c t i v e
structures of any
previous community
are absent.
reproductive structures of
the previous occupants are
present in the area.- Pioneer community
comes from outside.
Pioneer community develops
partly from propagules of
previous occupants and partly
from migrants.- Seral communities
are many.
Seral communities are a few.- (i) The diagram of a fertilized embryo sac is drawn as
follows: