4. heredity and evolution

 We have discussed how
some amount of variation
is produced even during
asexual reproduction.

 And the number of
successful variations are
maximised by the process
of sexual reproduction.

 The mechanism by which
variations are created and
inherited. (Heredity).

 The long-term consequences
of the accumulation of
variations are also an
interesting point to be
considered. (Evolution).

 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.

 This process continues….

 If there were a population of
bacteria living in temperate
waters, and if the water
temperature were to be increased
by global warming, most of these
bacteria would die, but the few
variants resistant to heat would
survive and grow further.

 Some of the variations might
be so drastic that the new DNA
copy cannot work with the
cellular apparatus it inherits.

 Such a newborn cell will simply
die.

 Some DNA copies that would
not lead to such a drastic
outcome. Surviving cells are
similar, but cleverly different
from each other.

 This inbuilt tendency for
variation during reproduction is
the basis for evolution

 Accumulation of Variation during Reproduction

 Variation is useful for the survival of species over time.

 Questions NCERT Page No. 143 (Q No. 1 and 2)

 1. 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?

 2. How does the creation of variations in a species
promote survival?

 Surviving cells are similar, but
cleverly different from each
other.

 The process by which traits and
characteristics are reliably inherited
from the parents to offspring.

 A trait is a particular characteristic—
anatomical, biochemical or
behavioural—that is the result of
gene–environment interaction.

 Free and attached earlobes are two variants found
in human populations.

 This means that each trait can
be influenced by both paternal
and maternal DNA.

 Thus, in each child, for each trait
there will be two versions
(Allele), one inherited from each
parent.

 An allele is two or more forms of
the DNA sequence of a particular
gene.There are two types--

 Heterozygous –

If the two alleles for a trait are
different (Tt)

 Homozygous –

If the two alleles for a trait are the
same (TT)

 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

 The rules of heredity determine the process by which
traits and characteristics are reliably inherited.

 The rules of heredity determine the process by which
traits and characteristics are reliably inherited.

 Read NCERT Page No. 142-146

 Write a brief biography of Gregor Johann Mendel
(1822–1884)

 The process by which traits and
characteristics are reliably
inherited from the parents to
offspring.

 This means that each trait can
be influenced by both paternal
and maternal DNA.

 Thus, for each trait there will be
two versions in each child.

 Mendel took pea plants with
Parent (P) different characteristics –
a tall plant and a short
plant,

TT (Tall) tt (Short)

TT (Tall) tt (Short) Linkage of two genes located
on same chromosome

T t

Tt (all)
First Generation (F1)

 The progeny of the
TT X TT parental plants were,
of course, all tall.

TT (all are tall)

Tt X Tt
First Generation
F1 X F1

?

Tt X Tt Sperm
First Generation T t
F1 X F1

T Since both the genes are carried on
the sane chromosome they do not
separate from each other at
Egg meiosis, F1 Progeny produces only
t two types of gametes.

Tt X Tt
First Generation
F1 X F1

T Sperm t
TT Tt
T Tall Tall
Egg
Second Generation
Tt tt
t Tall Short
(F2)

Phenotype - the way an organism looks, Examples: Tall or Short
Genotype - the gene combination of an organism, Ex:- TT, Tt, tt

TT Tt
Tall Tall
Tt tt
Tall Short

 Were the tall plants in the
Tt (all) F1 generation exactly the
First Generation (F1) same as the tall plants of
the parent generation?

Tt (all)  But only the tallness trait
was expressed in F1.
First Generation (F1)
 These two may be
identical, or may be
different, depending on the
parentage.

 The trait that is observed in the
offspring is the dominant trait
(uppercase)

TT Tt  Traits like ‘T’ are called dominant
traits,

 The trait that disappears in the
Tt tt offspring is the recessive trait
(lowercase)

 While those that behave like ‘t’
are called recessive traits.

 Rules for the Inheritance of Traits
(Incase of single trait)

 In the F1 Progeny all were tall plants

 In the F2 Progeny all were not tall (ratio 3:1)

Questions NCERT Page No. 147 (Q No. 1), Page 144

1. How do Mendel’s experiments show that traits may be
dominant or recessive? Explain with diagram.

2. What experiment would we do to confirm that the F2
generation did in fact have a 1:2:1 ratio of TT, Tt and tt
trait combinations?

TT (Tall) tt (Short)

T t

 Were the tall plants in the F1
Tt (all) generation exactly the same as
First Generation (F1) the tall plants of the parent
generation?

Parent (P)

Round: R Wrinkled: r
Green: y Yellow: Y

Segregation of two
hypothetical genes
located on different
chromosome

Sperm
RY Ry rY ry

RY

Ry Since the chromosomes segregate
independently at meiosis, the F1
Progeny give rise to four different
rY types of gametes.

Egg
ry

Sperm
RY Ry rY ry

Round Yellow Round Yellow Round Yellow Round Yellow
RY RRYY RRYy RrYY RrYy
Round Yellow Round Green Round Yellow Round Green
Ry
RRYy RRyy RrYy Rryy

Round Yellow Round Yellow Wrinkled Yellow Wrinkled Yellow

rY RrYY RrYy rrYY rrYy
Egg Wrinkled Yellow Wrinkled Green
Round Yellow Round Green
ry
RrYy Rryy rrYy rryy

Find Genotypic Ratio RY Ry rY ry

--------------------------- Round Yellow Round Yellow Round Yellow Round Yellow
RY RRYY RRYy RrYY RrYy
Round Yellow Round Green Round Yellow Round Green
Ry
RRYy RRyy RrYy Rryy

Round Yellow Round Yellow Wrinkled Yellow Wrinkled Yellow

rY RrYY RrYy rrYY rrYy

Round Yellow Round Green Wrinkled Yellow Wrinkled Green
ry
RrYy Rryy rrYy rryy

 Rules for the Inheritance of Traits
(Incase of dual traits)

 In the F1 Progeny all were Round, Yellow

 In the F2 Progeny Ratio (9:3:3:1)

Questions NCERT Page No. 147 (Q No. 2 and 3)

1. How do Mendel’s experiments show that traits are
inherited independently?

2. 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?

Round Yellow Round Yellow Round Yellow Round Yellow

RRYY RRYy RrYY RrYy

TT Tt Round Yellow

RRYy
Round Green

RRyy
Round Yellow

RrYy
Round Green

Rryy

Tt tt Round Yellow Round Yellow Wrinkled Yellow Wrinkled Yellow

RrYY RrYy rrYY rrYy

Round Yellow Round Green Wrinkled Yellow Wrinkled Green

RrYy Rryy rrYy rryy

 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.

More efficient Less efficient
enzyme / Protein enzyme / Protein

More
Hormone
? Less
Hormone

Taller Shorter

More efficient Less efficient
enzyme / Protein enzyme / Protein

More
Hormone
G Less
Hormone

Taller Shorter

 This means that each
pea plant must have two
sets of all genes (Allele),
one inherited from each
parent.

 An allele is two or more
forms of the DNA
sequence of a particular
gene.

 Each gene set is present in the body cell as separate
independent pieces, each called a chromosome.

 Thus, each cell will have two copies of each chromosome,
one each from the male and female parents.

 Every germ cell will take one chromosome from each pair
and these may be of either maternal or paternal origin.

 When two germ cells combine, they will restore the normal
number of chromosomes in the progeny, ensuring the
stability of the DNA of the species.

 They reproduce sexually

 They have two distinct,
male and female, sex cells
called gametes

 Their traits are easy to
isolate.

 They can be crossed easily.

 A section of DNA that provides information for one protein
is called the gene for that protein.

 In the Mendelian experiments both parents must be
contributing equally.

 Formation of single set of genes by the each germ cell

 Selection of pea plants.

Read NCERT Page No. 142 to 146

 The two alleles for a
trait must separate
when gametes are
formed

 A parent randomly
passes only one allele
for each trait to each
offspring

 The genes for different
traits are inherited
independently of each
other.

Factors of temperature

Change of sex.

Factors of inherited sex chromosome

Normal Human Chromosome, Total 23 pairs (46)

Paternal Copy Maternal Copy

22 pairs of Autosomes (44)

1 pair Sex Chromosome (XY) 1 pair Sex Chromosome (XY)

Male Female

 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.

 Thus a father is responsible
for giving birth of a boy or a
girl, not mother.

 The human sperm cell is
haploid.

 The human ovum cell
is also haploid.

 The two alleles for a trait must separate when
gametes are formed

 The genes for different traits are inherited
independently of each other.

 Sex determination in human

Questions NCERT Page No. 147 (Q No. 4)

4. How is the sex of the child determined in human beings
with diagram?

 We learnt that the
chromosomes in the nucleus
of a cell contain information
for inheritance of features
from parents to next
generation in the form of DNA

 If the information is
changed, different proteins
will be made. Different
proteins will eventually lead
to altered body designs.

 This creates two copies of
the DNA in a reproducing
cell, and they will need to
be separated from each
other.

 DNA copies separate, each
with its own cellular
apparatus.

 Effectively, a cell divides to
give rise to two cells.

 The DNA copies generated will be similar, but may not be
identical to the original. This inbuilt tendency for variation
during reproduction is the basis for evolution.

Analyse variations in the red beetles population

Situation 1

Situation 2

Situation 3

Frequency of certain genes in a population changed
over generations. natural selection is directing
Situation 1 evolution in the beetle population. It results in
adaptations in the beetle population.

Accidents in small populations can change the
frequency of some genes in a population, even if they
Situation 2 give no survival advantage. It provides diversity
without any adaptations.

Changes in body without any genetic variations, due to
environmental factors, but it is not evolution. Changes in the
Situation 3 non-reproductive tissues caused by environmental factors
are not inheritable.

 A basic event in reproduction is the creation of a DNA copy
which bring variation.

 Variation may be by survival due to natural selection, may
be accidental or may be due to environmental situations

Variations in the red beetles population

Situation 1

Situation 2

Situation 3

 Changes in the non-
reproductive tissues
caused by environmental
factors are not inheritable.

 Changes in the body
without any genetic
variations, due to
environmental factors, but
it is not evolution.
Situation 3

ACQUIRED TRAITS INHERITED TRAITS

 These are those characters,  These are those characters,
received by an organism in received by an organism
his/her life time due to from his/ her ancestors
different conditions. through GENES.

 Ex:- Due to an accident a  Ex:- Tall and Short height,
man had lost his leg, Attack Eye colour, skin colour,
of Polio. body structure, general
characters etc.

 When change in reproductive tissues pass (as a new trait) on
to the progeny (DNA of the germ cells), evolutions come.

 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?

 It makes sense because
removal of the tail
(acquired trait) cannot
change the genes of the
germ cells of the mice.

 Acquired trait can not pass
on to the next generation.

 So, it is important to
inherit GENES to bring
evolution.

 This is the reason why the
ideas of heredity and
genetics that we have
discussed earlier are so
essential for understanding
evolution.

 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.

Mendel’s experiments give us
the mechanism for the
inheritance of traits from one
generation to the next.

Darwin’s theory of evolution
tells us how life evolved from
simple to more complex forms.

Formation of Earth

Simple Inorganic molecules

Simple organic molecules

Complex organic molecules

Artificial atmosphere, NH3, CH4, H2S (No O2) over water

Bellow 100 o C , Electrical sparks-lightning

15% of Carbon (C) from Methane get converted

Simple organic molecules Amino Acids- Protein

Formation of Protoplasm

Simple Cell

 Acquired and Inherited Traits

Changes in the specialised reproductive tissues
of germ cells bring variation.

 Evolution comes with inheritance.

 Origin of life.

Read NCERT Page 149-150, NCERT Exercise Q No. 1,2,3 (Page 149)

1. What are the different ways in which individuals with a
particular trait may increase in a population?

2. Why are traits acquired during the life-time of an individual not
inherited?

3. Why are the small numbers of surviving tigers a cause of worry
from the point of view of genetics?

 But this does not properly explain formation of new species.

Both they belong to the same population, so
here speciation does not occur.

Genetic flow in each sub-population brings variations

Natural selection in each sub-population

Variation is combined with geographical isolation, then

Change in the DNA & number of chromosomes, thus

Germ cells of the two groups cannot fuse with each other.

 Characteristics are details of
appearance or behaviour; in
other words, a particular
form or a particular function.

Cell

Prokaryotic Eukaryotic

Unicellular Unicellular Multicellular

Monera Protista Fungi Planate Animalia

 We can thus build up small
groups of species with
recent common ancestors.

A common ancestor

 Tracing common ancestors
back in time leads us to the
idea that at some point of
time, non-living material
must have given rise to life.

 Speciation-Formation of new species.

 Characteristics are details of appearance or
behaviour; in other words, a particular form or a
particular function.

 The more characteristics two species will have in
common, the more closely they are related.

 A hierarchy is developing that allows us to make
classification groups

Read NCERT Page 150-152, NCERT Exercise Q No. 1,2,3 (Page 151)

1. What factors could lead to the rise of a new species?

2. Will geographical isolation be a major factor in the peciation of a
self pollinating plant species? Why or why not?

3. Will geographical isolation be a major factor in the speciation of
an organism that reproduces asexually? Why or why not?

 Excavating and Time-dating

 Studying fossils,

 Determining DNA sequences

 Characteristics in different
species would be similar because
they are inherited from a common
ancestor. It is known as
homologous characters.

 Characteristics in different species
would be different in body design
but have a common look and truly
derived from two different
ancestors. It is known as
analogous characters.

 Fossils are the preserved
remains of animals, plants, and
other organisms from the
remote past.

 The fossil record is life’s
evolutionary epic that unfolded
over four billion years as
environmental conditions and
genetic potential interacted in
accordance with natural
selection.

 Digging the soil and finding
layers of soil and rock particles.

 By detecting the ratios of
different isotopes of the same
element in the fossil material.

 Homologous characters

 Analogous characters.

 Fossils are the preserved remains of animals, plants,
and other organisms from the remote past

Read NCERT Page 153-155, NCERT Exercise Q No. 2,3 (Page 156)

2. Can the wing of a butterfly and the wing of a bat be
considered homologous organs? Why or why not?

3. What are fossils? What do they tell us about the process of
evolution?

Extra Question: Explain the formation of fossils.

 Fossils are the preserved
remains of animals, plants, and
other organisms from the
remote past.

 The fossil record is life’s
evolutionary epic that unfolded
over four billion years as
environmental conditions and
genetic potential interacted in
accordance with natural
selection.

 Complex organs may have
evolved because of the survival
advantage of even the
intermediate stages.

 Organs or features may be
adapted to new functions during
the course of evolution.

 For example, feathers are
thought to have been
initially evolved for warmth
and later adapted for flight.

 If that is the case, then
comparing the DNA of different
species should give us a direct
estimate of how much the DNA
has changed during the
formation of these species.

 Complex organs may have evolved because of the
survival advantage of even the intermediate stages.

 Organs or features may be adapted to new functions
during the course of evolution.

 Changes in DNA during reproduction are the basic
events in evolution

Read NCERT Page 153-155, NCERT Exercise Q No. 1 (Page 156)

Give an example of characteristics being used to determine how
close two species are in evolutionary terms.

Extra Question: Write a short note on Molecular phylogeny.

 Evolution cannot be said to
‘progress’ from ‘lower’ forms
to ‘higher’ forms.

 Rather, evolution seems to
have given rise to more
complex body designs even
while the simpler body
designs continue to flourish.

 A new species has emerged. It
will all depend on the
environment.

 It is just that natural selection
and genetic drift have together
led to the formation of a
population that cannot
reproduce with the original
one.

 Rather, both human beings
and chimpanzees have a
common ancestor a long time
ago.

 That common ancestor is
likely to have been neither
human or chimpanzee.

 Instead, the two resultant
species have probably
evolved in their own separate
ways to give rise to the
current forms.

 There is no biological basis
to the notion of human
races.

 Study of the evolution of
human beings indicates that
all of us belong to a single
species that evolved in
Africa and spread across the
world in stages.

 EVOLUTION SHOULD NOT BE EQUATED WITH ‘PROGRESS’

 Human Evaluation

Read NCERT Page 156-158, NCERT Exercise Q No. 1, 2 (Page 158)

NCERT Exercise Q No. 1 to 12 (Page 159)

4. heredity and evolution

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