1) The document discusses heredity and evolution, including the accumulation of variation during reproduction and its effects over generations. 2) It covers Mendel's experiments which established the rules of inheritance and traits being passed from parents to offspring. 3) Evolution occurs as generations accumulate subtle variations, with some helping organisms survive and pass on their traits while others do not, not impacting survival.

1. HERIDITY AND
EVOLUTION
BY:- RAJAT KUMAR
X-A

2. INTRODUCTION
 We have seen that reproductive processes give rise to new individuals that
are similar, but subtly different and how some amount of variation is
produced even during asexual reproduction. And the number of successful
variations are maximized by the process of sexual reproduction.
 Here we will study
 The mechanism by which variations are created and inherited.
 The long-term consequences of the accumulation of variations are also an
interesting point to be considered.

3. ACCUMULATION OF VARIATION
DURING REPRODUCTION
 Inheritance from the previous generation provides both a common basic
body design, and subtle changes in it, for the next generation.
 The second generation will have differences that they inherit from the first
generation, as well as newly created differences.

4. Creation of diversity over succeeding
generations
 This figure represent the
situation if single individual
reproduces, as happens in
asexual reproduction. If one
bacterium divides, and the
resultant two bacteria divide
again, the four generated
bacteria would be very similar.
There would only very minor
differences between them,
generated due to small
inaccuracies in DNA copying.

5. HEREDITY
 The most obvious outcome of the reproductive processes still remains the
generations of individuals of similar design.
 The process by which traits and characteristics are reliably inherited from
the parents to offspring is called heredity.
 A trait is a particular characteristic— anatomical, biochemical or
behavioral—that is the result of gene–environment interaction.

6. INHERITED TRAITS
 We are all unique. Even though we share some characteristics with our
peers and our family members, every one of us has a unique combination
of traits.
 Some traits are controlled by genes that pass from parent to child. Others
are acquired through learning. But most are influenced by a combination
of genes and environmental factors. Below are some examples of variable
traits that are easy to observe.

7. Here is an example
If earlobes hang free, they are detached.
If they connect directly to the sides of
the head, they are attached. Earlobe
attachment is a continuous trait: while
most earlobes can be neatly categorized
as attached or unattached, some are in-
between.

8. RULES FOR THE INHERITENCE OF TRAITS- MENDAL’S
CONTRIBUTION
 The rules for inheritance of such traits in human beings are related to the
fact that both the father and the mother contribute practically equal
amount of genetic material to the child.
 This means that each trait can be influenced by both paternal and maternal
DNA. Thus for each there would be two versions in each child.

9. GREGOR JOHANN MENDEL
(1822–1884)Mendel was educated in a monastery
and went on to study science and
mathematics at the University of
Vienna. Failure in the examinations for
a teaching certificate did not suppress
his zeal for scientific quest. He went
back to his monastery and started
growing peas. Many others had
studied the inheritance of traits in peas
and other organisms earlier, but
Mendel blended his knowledge of
science and mathematics and was the
first one to keep count of individuals
exhibiting a particular trait in each
generation. This helped him to arrive at
the laws of inheritance that we have
discussed in the main text.

10. MENDEL’S CONTRIBUTION
 Mendel worked out the main rules of such inheritance, and it is interesting
to look at some of his experiments from more than a century ago.
 Mendel blended his knowledge of science and mathematics and was the
first one to keep count of individuals exhibiting a particular trait in each
generation.
 This helped him to arrive at the laws of inheritance

11. MENDEL’S FIRST EXPERIMENT
Mendel took pea plants with Parent (P) different
characteristics – a tall plant and a short plant, TT
(Tall) tt (Short)
Mendel observed that, when peas with more
than one trait were crossed, the progeny did not
always match the parents. This is because
different traits are inherited independently – this
is the principle of independent assortment. For
example, he cross-bred pea plants with round,
yellow seeds and plants with wrinkled, green
seeds. Only the dominant traits (yellow and
round) appeared in the F1 progeny, but all
combinations of trait were seen in the self-
pollinated F2 progeny.

12. HOW DO TRAITS GET EXPRESSED?
 Cellular DNA is the information source for making proteins in the cell. A section
of DNA that provides information for one protein is called the gene for that
protein.
 We know that plants have hormones that can trigger growth. Plant height
canthus depend on the amount of a particular plant hormone. The amount of
the plant hormone made will depend on the efficiency of the process for making
it. Consider now an enzyme that is important for this process. If this enzyme
works efficiently, a lot of hormone will be made, and the plant will be tall. If the
gene for that enzyme has an alteration makes the enzyme less efficient, the
amount of hormone will be less, and the plant will be short.
 Thus, genes control characteristics, or traits.

13. MENDEL’S ANOTHER EXPERIMENT
Mendel chose to cross a pea plant that was homozygous and dominant for round
(RR), yellow (YY) seeds with a pea plant that was homozygous and recessive for
wrinkled (rr), green (yy) seeds, represented by the following notation:
RRYY x rryy
Organisms in this initial cross are called the parental, or P generation. The offspring
of the RRYY x rryy cross, which is called the F1 generation, were all heterozygous
plants with round, yellow seeds and the genotype RrYy.
Next, Mendel crossed two plants from the F1 generation. This step is the dihybrid
cross, and it is represented as:
RrYy x RrYy
Mendel observed that the F2 progeny of his dihybrid cross had a 9:3:3:1 ratio and
produced nine plants with round, yellow seeds, three plants with round, green
seeds, three plants with wrinkled, yellow seeds and one plant with wrinkled, green
seeds. From his experiment, Mendel observed that the pairs of traits in the parental
generation sorted independently from one another, from one generation to the
next.

14. SEX DETERMINATION
Different species use very different strategies for determining the sex of newborn
individuals. Some rely entirely on environmental cues. Thus, in some animals, the
temperature at which fertilized eggs are kept determines whether the animals
developing in the eggs will be male or female. In other animals, such as snails,
individuals can change sex, indicating that sex is not genetically determined.
However, in human beings, the sex of the individual is largely genetically
determined. In other words, the genes inherited from our parents decide whether
we will be boys or girls. But so far, we have assumed that similar gene sets are
inherited from both parents.

15. SEX DETERMINATION IN HUMAN BEINGS
In human beings sex is determined by the chromosomes . The
explanation lies in the fact that all human chromosomes are
not paired. Most human chromosomes have a maternal and a
paternal copy, and we have 22 such pairs. But one pair, called
the sex chromosomes, is odd in not always being a perfect
pair. Women have a perfect pair of sex chromosomes, both
called X. But men have a mismatched pair in which one is a
normal-sized X while the other is a short one called Y. So
women are XX, while men are XY.
The sex of the children will be determined by what they
inherit from their father. A child who inherits an X
chromosome from her father will be a girl, and one who
inherits a Y chromosome from him will be a boy.

16. EVOLUTION
 Evolution is change in the heritable
traits of biological populations over
successive generations. Evolutionary processes give
rise to diversity at every level of biological
organizations including the levels of species,
individual organisms

17. Consider a group of twelve red beetles. They live, let us assume, in some
bushes with green leaves. Their population will grow by sexual
reproduction, and therefore, can generate variations
SITUATION 1
SITUATION 2
SITUATION 3

18.  a) Some variations help organisms to survive :-
 Eg :- There are some beetles living in green bushes. They increase their numbers by
reproduction. Crows can easily see the red beetles and they are eaten by the crows.
During reproduction due to some variation some green beetles are produced instead of
red beetles. The green beetles are not visible to crows and are not eaten by them. Then
gradually the population of the red beetles decreases and the population of the green
beetles increases. This variation has helped the organisms to survive.
 b) Some variations do not help organisms to survive :-
 Eg :- During sexual reproduction a colour variation occurs in red beetles and some
blue beetles are produced instead of red beetles. Both the red and blue beetles are visible
to crows and are eaten by them. Then the population of both red and blue beetles
decreases. This variation has not helped the organisms to survive
 c) Aquired traits cannot be passed from one generation to the next :-
 Eg :- If the population of beetles increases and plants are affected by diseases, then
the food available for the beetles decreases and their body weight also decreases. If after
a few years the availability of food increases then the body weight of the beetles also
increases. This acquired trait cannot be passed from one generation to the next because
there is no change in their genetic composition.

19. ACQUIRED AND INHERITED TRAITS

20.  Consider another example of how an individual cannot pass on to its progeny
the experiences of its lifetime. If we breed a group of mice, all their progeny will
have tails, as expected. Now, if the tails of these mice are removed by surgery in
each generation, do these tailless mice have tailless progeny? The answer is no,
and it makes sense because removal of the tail cannot change the genes of the
germ cells of the mice.
 Therefore the experiences of an individual during its lifetime cannot be passed
on to its progeny, and cannot direct evolution. Change in non-reproductive
tissues cannot be passed on to the DNA of the germcells. Therefore the
experiences of an individual during its lifetime cannotbe passed on to its
progeny, and cannot direct evolution.

21. CHARLES ROBERT DARWIN (1809-1882)
 Darwin formulated his hypothesis
that evolution took place due to
natural selection.
 But he did not know the mechanism
whereby variations arose in the
species.
 Evolution is the change in the
inherited traits of a population of
organisms through successive
generations.
 This change results from interactions
between processes that introduce
variation into a population.

22. SPECIATION
 Speciation is the evolution of new species. It occurs when a population of
interbreeding individuals is spit up into separate populations. These
separate population then continue to evolve independent of each other.
Over time, they may become spate species and be unable to breed with
the population from which they were initially separated. For animals they
reproduce without sex, species are defined by arbitrary decisions based on
how genetically distinct groups have become. Speciation can occur if a
geographic barrier prevents gene flow between two population of same
species.

23. EVOLUTION AND CLASSIFICATION
 Evolution: Most of the life forms that wee see today have arisen from the
accumulation of changes in the bodydesign of ancient organisms. This
slow change in the body design of an organism over a long period of time
is termed as evolution.
 Classification allows things to be identified and categorized on the basis of
structure and function of an organism, and accordingly, we can refer to
them as primitive or advanced organisms.

24. HOMOLOGOUS ORGANS
Homologous organs :- are organs
which are similar in structure but
different in functions.
Eg :- The fore limbs of amphibians,
reptiles, birds, and mammals have
similar structures but different
functions. Frog (amphibian) uses its
fore limb to raise the front of the body.
Lizard (reptile) uses its fore limb for
walking and running. Birds fore limbs
are modified as wings for flying.
Mammals use the fore limbs for
grasping, walking, running, swimming,
flying etc. This shows evolutionary
relationship.

25. ANALOGOUS ORGANS
Analogous organs :- are organs
which are different in structures
but similar in functions.
Eg :- The wings of butterfly, bird
and bat have different
structures but similar functions.
This shows evolutionary
relationship.

26. Fossils
Fossils :- are the remains of organisms
which lived long ago.
From the study of fossils we can know
their structures and the time period in
which they lived. The fossils of complex
and recent organisms are found closer to
the surface of the earth and the fossils of
simpler organisms are found deeper inside
the earth. The age of fossils can be
determined by Radio Carbon Dating. The
study of fossils show evolution of simpler
forms into complex forms and their
evolutionary relationship.

27.  Evolution of complex organs and thus of complex organisms has
happened in stages. Let us take the example of evolution of eyes. Planaria
is the first animal which shows ‘eye’ like structure. The dark spots on
planaria are light sensitive spots but a planaria cannot distinguish between
two different objects. Eyes of insects are compound eyes which are made
up of thousands of optical surfaces. Eyes of higher animals are simple eyes
which are composed of a single lens. Most of the animals cannot
differentiate among colours. Depth perception is also weak in many
animals. Human eyes are the most advanced; because humans can
recognize colours and have very good depth perception.
EVOLUTION BY STAGES

28.  i) Evolution of eyes :- The eyes of planaria are just eye spots to detect light. It
developed gradually into a complex organ in higher animals.
 ii) Evolution of feathers :- Feathers were first developed in dinosaurs and used
for protection from cold. Later birds used them for flying.

29.  iii) Evolution by artificial selection :- Humans cultivated wild cabbage for over 2000 years
and produced different vegetables from it by artificial selection.
 Eg :- Cabbage – by selecting short distance between the leaves.
Cauliflower – by selecting sterile flowers.
Kale – by selecting large leaves
Kholrabi – by selecting the swollen stem
Broccoli – by arresting flower growth

30. EMBRYOLOGY

31. EVOLUTION VS PROGRESS:
 Evolution does not mean progress in every case. This can be proved by
example of bacteria. Bacteria are the simplest and one of the oldest
organisms on the earth. Their simple body design does not make them
weak from any angle. Bacteria are known to survive some of the harshest
climates; like craters of volcanoes and sulfur springs. Many animals have
certain features which hamper even their routine activities. For example; the
branch-like horns of antelope are a handicap for them. When an antelope
runs for its life; there are times when its horns get entangled in branches or
bushes. This results in the death of the antelope. Colorful feathers of a male
peacock are very good when it comes to attract a female. But because of its
conspicuous feathers, it can be easily spotted by a predator. Because of its
bulky feather it cannot fly away to safety.

32. Human Evolution
 The modern humans are called Homo sapiens. Many
scientific investigations have shown that the modern
humans evolved in Africa. They migrated towards
north; in due course of time and settled near what is
known as the Mediterranean Sea. When the ice age
ended, melting of ice resulted in the in water level.
The humans migrated in different directions from
that area. One branch went to the western Asia, then
to the Indian Peninsula and finally to Australia. From
the Indian Peninsula, branch migrated towards China
and subsequently to the North America. From North
America, the humans migrated to the South
America. From the Mediterranean Sea, the second
branch migrated towards Europe; where they are
believed to replace the Neanderthals.

33. THE END