RC 07 - NOV 13

Evolutionary change does not take place directly on the bodies of
living beings but on the gene pool of the breed or species. The idea
of a
gene pool is central to the body of knowledge and theory that goes
under the name of the 'Neo-Darwinian Synthesis' that forms the basis
of the modern understanding of evolution. Charles Darwin, the father
of evolutionary theory, himself knew nothing of it. It was not a part
of
his intellectual world, nor indeed were genes. He was aware, of
course, that characteristics run in families, aware that offspring
tend to
resemble their parents and siblings, aware that particular
characteristics of dogs and pigeons breed true. Heredity was a central
plank of
his theory of natural selection. But a gene pool is something else.
The concept of a gene pool has meaning only in the light of Mendel's
law of the independent assortment of hereditary particles. Darwin
never knew Mendel's laws, for although Gregor Mendel, the father of
genetics, was Darwin's contemporary, he published his findings in a
German journal which Darwin never saw.

A Mendelian gene is an all-or-nothing entity. When you were conceived,
what you received from your father was not a substance, to be
mixed with what you received from your mother as if mixing blue paint
and red paint to make purple. If this were really how heredity
worked (as people vaguely thought in Darwin's time) we'd all be a
middling average, halfway between our two parents. In that case, all
variation would rapidly disappear from the population (no matter how
assiduously you mix purple paint with purple paint, you'll never
reconstitute the original red and blue). In fact, of course, anybody
can plainly see that there is no such intrinsic tendency for variation
to
decrease in a population. Mendel showed that this is because when
paternal genes and maternal genes are combined in a child (he didn't
use the word 'gene', which wasn't coined until 1909), it is not like
blending paints, it is more like shuffling and reshuffling cards in a
pack.
Nowadays, we know that genes are lengths of DNA code, not physically
separate like cards, but the principle remains valid. Genes don't
blend; they shuffle. You could say they are shuffled badly, with
groups of cards sticking together for several generations of shuffling
before
chance happens to split them.
Any one of your eggs (or sperms if you are male) contains either your
father's version of a particular gene or your mother's version, not a
blend of the two. And that particular gene came from one and only one
of your four grandparents; and from one and only one of your eight
great-grandparents.
Hindsight says this should have been obvious all along. When you cross
a male with a female, you expect to get a son or a daughter, not
a hermaphrodite. Hindsight says anybody in an armchair could have
generalized the same all-or-none principle so that it applies to the
inheritance of each and every characteristic. Fascinatingly, Darwin
himself was glimmeringly close to this, but he stopped just short of
making the full connection.

1

What is this passage about?

1) The concept of genes and how they combine was unknown when the
theory of evolution was propounded.
2)
The idea of how genes combine in a gene pool is central to
evolutionary theory, but was unknown to its proponent, Charles
Darwin.
3) Though Charles Darwin came up with evolutionary theory, he missed
out on explaining how genes and the gene pool work.
4)
Charles Darwin, the father of evolutionary theory, himself did not
understand how genes work, and it was left to later
scientists to fill in the gaps.


2

When you cross a male with a female, you expect to get a son or a
daughter, not a hermaphrodite.' What is the point that the author is
trying to make with this statement?

1) It is obvious that hermaphrodites are born only when the process of
combining male and female genes goes wrong.
2)
It should be clear how genes work based on the fact that maleness and
femaleness are distinct traits that do not mix in
offspring.
3)
Darwin should have understood the principles on which genes work based
on the fact that male and female genes do not
blend.
4) None of the above.

3

The passage given below is followed by a set of questions. Choose the
most appropriate answer to each question.
Which of the following can be inferred about Charles Darwin from this passage?


1) He did not know German.
2) He had no idea that genes worked on an all-or-none principle.
3) He was aware of the importance of heredity in evolutionary processes.
4) All of the above.


4

The passage given below is followed by a set of questions. Choose the
most appropriate answer to each question.
If you were to interview the author, which follow-up question would you ask him?

1) How did the concept of genes help in understanding heredity?
2) Are Darwin's and Mendel's ideas still relevant to modern biology?
3) How is the concept of the gene pool important to evolutionary theory?
4) Does the inheritance of gender differ from the inheritance of other traits?