Lesson: Heredity and Evolution
If a
trait A exists in 10% of a population of an asexually reproducing species and a
trait B exists in 60% of the same population, which trait is likely to have
arisen earlier?
Trait B is likely to have arisen earlier because it
is present in a higher percentage of the population.
How does the creation of variations in
a species promote survival?
Variations in a species take place in response to
the changes in the environment. This enables a species to cope with new
changes. Depending on the nature of variations, different individuals would
have different kinds of advantages. For example, bacterial variants that can
withstand heat have better chances to survive a heat wave than the non-variant
bacteria. Thus, variations in a population of a species help in survival of a
species.
How do Mendel’s experiments show that
traits may be dominant or recessive?
During monohybrid cross by conducted by Mendel, one
trait did not appear in the F1 generation. However, it appeared in the F2
generation obtained by self-fertilization of the F1 generation.
From his experiment, he concluded:
a)
The
trait which appeared in all the members of F1 generation and in 75% members of
the F2 generation was a dominant trait.
b)
The
trait which did not appear in F1 generation but reappeared in 25% of F2
generation was a recessive trait.
How do Mendel’s experiments show that
traits are inherited independently?
During dihybrid
cross, Mendel crossed the pure-bred tall plants having round seeds with pure bred
short plants having wrinkled seeds. It was observed that all the F1 generation
plants were tall with round seeds. This indicated that the traits of tallness
and round seeds were dominant.
Later, the self-breeding
of F1 generation seeds yielded F2 generation. The F2 generation plants had characteristics
of tall with round seeds (9 plants), tall with wrinkled seeds (3 plants), short
with round seeds (3 plants) and short with wrinkled seeds (1 plant). The tall
wrinkled seeded and short round seeds were the new combinations. This could
develop only when the traits were inherited independently. Thus, Mendel was
able to propose the law of independent
assortment which explains independent inheritance of traits.
A man with blood group A marries a woman with blood
group O and their daughter has blood group O. Is this information enough to
tell you which of the traits blood group A or O is dominant? Why or why not?
No. This information is not sufficient to determine
which of the traits is dominant or recessive. We need data of at least three
generations whereas the given data is about two generations.
How is the sex of the child determined in human
beings?
The sex of a new-born in human is genetically
determined i.e., genes inherited from parents decide whether the new born will
be a boy or a girl. If a sperm with X chromosome fertilizes the egg, it results
in the development of a girl child. Whereas, if a sperm with Y chromosome
fertilizes the egg, it results in the development of a male child.
What are the different ways in which
individuals with a particular trait may increase in a population?
Individuals with a particular trait may increase in
a population:
·
When
a trait is acquired during the individual's lifetime
·
When
some genes governing the trait become common in a population
·
When
the trait offers some survival advantage
Why are the traits acquired during an individual’s lifetime,
not inherited?
Acquired traits do not bring any change in the
genotype of an individual. Therefore, these traits are not inherited.
Why are the small numbers of surviving
tigers a cause of worry from the point of view of genetics?
Variations are essential to the survival of a
species. The small number of surviving tigers does not allow many variations to
occur. A deadly disease or any calamity may cause death of all the tigers. Hence,
a small number of surviving tigers is a cause of worry.
What factors could lead to the rise of a new
species?
Natural selection, genetic drift and acquisition of
traits during the life time of an individual can give rise to new species.
Will geographical isolation be a major factor in
the speciation of a self-pollinating plant species? Why or why not?
In self-pollinating
plant species, pollens are transferred from the anther of one flower to the
stigma of the same flower or another flower of the same plant.
So, geographical
segregation cannot be a major factor in speciation. However, there are chances
of some environmental changes that can lead to some variations.
Will geographical isolation be a major factor in the speciation of an
organism that reproduces asexually? Why or why not?
No. Asexually reproducing organisms pass on the parent DNA to offspring
that leaves no chance of speciation. Hence, geographical isolation does not
affect much in asexually reproducing organisms. However, geographical isolation
may work as a major factor in cross-pollinated species.
Give an example of characteristics being used to
determine how close two species are in evolutionary terms.
A few ancient reptiles such as dinosaurs had
feathers. However, they could not fly with those feathers. The feathers were
used only to provide insulation in cold weather. Later, birds adapted the
feathers for flight. This means that birds are very closely related to reptiles,
as dinosaurs were reptile.
Can wings of a butterfly and wings of a
bat be considered homologous organs? Why or why not?
Wings of bats are skin folds stretched mainly
between elongated fingers. The wings of birds are a feathery covering all along
the arm. Wing of a butterfly and the wings of a bat are similar in function.
They help them in flying. Since they perform similar function and have
different origins, they are analogous organs.
What are fossils? What do they tell us about the
process of evolution?
The remains of organisms that once existed on earth
are called fossils. They tell us about the development of simple structured
organisms to complex structured organisms. They also give insights into how
evolution could have taken place in an organism to sustain themselves in a competitive
environment.
Why are human beings who look so different from
each other in terms of size, colour and looks said to belong to the same
species?
A species is a group of organisms that are capable of interbreeding to
produce a fertile offspring. In spite of wide differences in size, colour and
looks, human beings can interbreed. Hence, all of them are considered as one
species.
In evolutionary terms, can we say which among bacteria, spiders, fish
and chimpanzees have a ‘better’ body design? Why or why not?
Evolution cannot always be equated with progress or
better body designs. It does not mean that simple body designs are inefficient.
When we take complexity as a criterion, the chimpanzee is better than other
given organisms. On the other hand, if we take the ability of survival in
almost all kinds of habitat as a criterion, bacteria, having a simple body
design, are still the most cosmopolitan organisms found on earth.
Therefore, bacteria, spiders, fish and chimpanzees are all different
branches of evolution.