4. heredity and evolution

Chapter 9Heredity and Evolution

We have seen that reproductive processes give rise to new individuals that are similar, but

subtly different.

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.

In this chapter, we shall be studying…

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).

Concept no. 1

Accumulation of Variation during Reproduction

Creation of diversity over succeedinggenerations

Inheritance from the previous generation

Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation.

Now think about what would happen when this new

generation will reproduces.

Variation in second generation during reproduction

The second generation will have differences that they inherit from the first generation.

This process continues….

Concept no. 2

Variation is useful for the survivalof species over time.

Do all these variations in a species have equal chances of surviving in the environment?

Obviously not…..

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.

Drastic variations may not survive

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 variations may survive for long time

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

Let us recall…..

Accumulation of Variation during Reproduction

Variation is useful for the survival of species over time.

Prep Work….

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?

Concept no. 1

We learnt……Accumulation of Variation during

Reproduction

Creation of diversity over succeedinggenerations

Concept no. 2

We also learnt…..Variation is useful for the survival

of species over time.

Drastic variations may survive for long time

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

Organisms look similar because their body designs are similar

If body designs are to be similar, the blueprints for these designs should be

similar

Heredity at its most basic level involves inheritance of traits

Concept no. 3

Heredity

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.

but even if the body designs are same, there could have some variations in it

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

Concept no. 4

Equal Contribution of both the parents to form a particular trait.

Both the Parents contribute equal amounts of genetic

material to the child

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.

Allele

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)

Gregor Johann Mendel (1822–1884)

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

Let us recall…..

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

Prep Work….

Read NCERT Page No. 142-146

Write a brief biography of Gregor Johann Mendel

(1822–1884)

Concept no. 3

We learnt about heredity

Heredity

Concept no. 4

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

Concept no. 5

Rules for the Inheritance of Traits

(Incase of single trait)

Cross Pollination

Mendel took pea plants with different characteristics –

a tall plant and a short plant,

Parent

(Tall)

(Short)

In the F1 Progeny all were tall plants

Tt (all)

First Generation

(Tall)

(Short)

Linkage of two genes located on same

chromosome

Were the tall plants in the F1 generation exactly the same as the tall

plants of the parent generation?

First Self pollination between two tall parental plants.

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

TT (all are

Second Self pollination between two tall plants of F1 progeny

Tt X Tt

Generation

F1 X F1 ?

Formation of 2 different types of gametes during second self pollination (F1 X F1)

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

Tt X Tt

First Generation

F1 X F1

In the F2 Progeny all were not tall

Tt X Tt

Generation

F1 X F1

TTTall

TtTall

ttShortSecond

Generation

Phenotypic Ratio (3 : 1)Genotypic Ratio (1:2:1)

TTTall

TtTall

ttShort

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

Mendel went for F2 Progeny through self pollination to find the answer of this

question…..

Were the tall plants in the F1 generation exactly the same as the tall plants of the parent generation?

Tt (all)

First Generation

material to the offspring (F1)

But only the tallness trait was expressed in F1.

These two may be identical, or may be different, depending on the parentage.

Tt (all)

First Generation

Dominant traits and Recessive traits

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

Traits like ‘T’ are called dominant traits,

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

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

Let us recall…..

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

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

Prep Work….

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?

Concept no. 5 We learnt….

Were the tall plants in the F1 generation exactly the same as the tall plants of the parent generation?

Tt (all)

First Generation

(Tall)

(Short)

Tt X Tt

Generation

F1 X F1

TTTall

TtTall

ttShortSecond

Generation

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

Traits like ‘T’ are called dominant traits,

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

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

Concept no. 6

(Incase of dual traits)

Cross Pollination

Parent

Round: R Green: y

Wrinkled: rYellow: Y

In the F1 Progeny all were Round, Yellow

Segregation of two hypothetical genes located on different chromosome

Formation of 4 different types of gametes during self pollination (F1 X F1)

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

In the F2 Progeny all were not Round, Yellow

Round Yellow

RrYyRound Yellow

Round Green

Round Yellow

Round Green

Round Yellow

Wrinkled Yellow

Round Yellow

Round Green

Wrinkled Yellow

rrYyWrinkled

In the F2 Progeny Phenotypic Ratio (9:3:3:1)

Round Yellow

RrYyRound Yellow

Round Green

Round Yellow

Round Green

Round Yellow

Wrinkled Yellow

Round Yellow

Round Green

Wrinkled Yellow

rrYyWrinkled

ryFind Genotypic Ratio

---------------------------

Let us recall…..

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)

Prep Work….

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?

Concept no. 3

We learnt about heredity

Heredity

Concept no. 4

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

Concept no. 5 We learnt….

Tt X Tt

Generation

F1 X F1

TTTall

TtTall

ttShortSecond

Generation

Concept no. 6We also learnt

(Incase of dual traits)

In the F2 Progeny all were not Round, Yellow

Round Yellow

RrYyRound Yellow

Round Green

Round Yellow

Round Green

Round Yellow

Wrinkled Yellow

Round Yellow

Round Green

Wrinkled Yellow

rrYyWrinkled

Round Yellow

RrYyRound Yellow

Round Green

Round Yellow

Round Green

Round Yellow

Wrinkled Yellow

Round Yellow

Round Green

Wrinkled Yellow

rrYyWrinkled

Concept no. 7

Mechanism of Heredity Work

Basic Concept of Gene

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.

Who is responsible for the efficiency of protein?

More efficient enzyme / Protein

More Hormone

Less Hormone

Taller Shorter

Less efficient enzyme / Protein

Genes control characteristics, or traits.

More Hormone

Less Hormone

Taller Shorter

Equal contribution of both the parents

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.

Formation of single set of genes by the each germ cell

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.

Concept no. 8

Selection of Pea Plants

Why did Mendel select pea plant?

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.

Let us recall…..

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.

Prep Work….

Read NCERT Page No. 142 to 146

Concept no. 9

Mendelism

Law of Segregation

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

Law of Independent Assortment

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

Concept no. 9

Sex Determination

Factors of inherited sex chromosome

Change of sex.

Factors of temperature

Different species use very different strategies

Factors of inherited sex chromosome

Normal Human Chromosome, Total 23 pairs (46)

22 pairs of Autosomes (44)

Paternal Copy

Maternal Copy

1 pair Sex Chromosome (XY)

MaleFemal

1 pair Sex Chromosome (XY)

Sex determination in human

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.

Can you guess how many chromosomes are there in a sperm cell ?

Sperm has 23 chromosomes (22 + X) or (22 + Y)

The human sperm cell is haploid.

Now you may guess total number of chromosomes in a ovum

Ovum has 23 chromosomes (22 + X)

The human ovum cell is also haploid.

Can you guess how many chromosomes are there in a zygote and what is its’ type?

Zygote has 46 (23 pair chromosomes),is diploid

(23 haploid sperm + 23 haploid ovum)

Let us recall…..

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

Prep Work….

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

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

DNA (Deoxyribo Nucleic Acid) molecules

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

The DNA in the cell nucleus is the information source for making proteins

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

altered body designs.

Genes control characteristics, or traits.

More Hormone

Less Hormone

Taller Shorter

Cells use chemical reactions to build copies of their DNA

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

Concept 10

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

variation

DNA copying is accompanied by the creation of an additional

cellular apparatus

DNA copies separate, each with its own cellular apparatus.

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

Variation during reproduction is the basis for evolution

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.

Let us analyse a situation

Population of red beetles in the green bushes

Situation 1

Situation 2

Situation 3

Analyse variations in the red beetles population

Population of red beetles in the green bushes

Situation 1

Situation 2

Situation 3

Frequency of certain genes in a population changed over generations. natural selection is directing 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 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 non-reproductive tissues caused by environmental factors are not inheritable.

Let us recall…..

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

Prep Work….

Read NCERT Page No. 147-148

Concept 10we learnt……

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

Variation during reproduction is the basis for evolution

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.

We analyzed a situation

Can you say why don’t we consider situation 3 as a matter of evolution?

Situation 1

Situation 2

Situation 3

Variations in the red beetles population

Variations without any genetic change

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

Concept 11

Acquired and Inherited Traits

ACQUIRED TRAITS

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

Ex:- Due to an accident a man had lost his leg, Attack of Polio.

INHERITED TRAITS

These are those characters, received by an organism from his/ her ancestors through GENES.

Ex:- Tall and Short height, Eye colour, skin colour, body structure, general characters etc.

Changes in the specialised reproductive tissues of germ cells bring variation

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

Let us analyse another situation

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 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.

Concept 12

Evolution comes with inheritance

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

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.

According to Darwin…

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.

Concept 13

Origin of life

Mendelism ,Darwinism

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.

J.B.S. Haldane, a British scientist 1929

Simple Inorganic molecules

Formation of Earth

Simple organic molecules

Complex organic molecules

Stanley L. Miller and Harold C. Urey Experiment conducted in 1953Artificial 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

Let us recall…..

Acquired and Inherited Traits

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

Evolution comes with inheritance.

Origin of life.

Prep Work….

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?

We had studied about…..

Situation 1

Situation 2

Situation 3

Variations in the red beetles population

The changes are small, even though they are significant-micro evolution

But this does not properly explain formation of new species.

New species do not form in the following picture, because……

Both they belong to the same population, so here speciation

does not occur.

Concept 14

Speciation-Formation of new species

Genetic flow in each sub-population brings variations

Variation is combined with geographical isolation, then

Natural selection in each sub-population

Change in the DNA & number of chromosomes, thus

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

Concept 15

Evolution and classification

What is meant by ‘characteristics?

Characteristics

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

Cellular difference brings new Classifications

Prokaryotic

Eukaryotic

Unicellular

Multicellular

Unicellular

Planate

Animalia

Monera

FungiProtis

The more characteristics two species will have in common, the more closely

they are related.

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

A common ancestor

A hierarchy is developing that allows us to make classification

groups

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.

Biosphere

Ecosystem

Community

Population

Individual

Organ System

Organs

Tissue

Let us recall…..

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

Prep Work….

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?

Concept 14We learnt…

Speciation-Formation of new species

Genetic flow in each sub-population brings variations

Variation is combined with geographical isolation, then

Natural selection in each sub-population

Change in the DNA & number of chromosomes, thus

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

Concept 15We learnt…

Evolution and classification

Cellular difference brings new Classifications

Prokaryotic

Eukaryotic

Unicellular

Multicellular

Unicellular

Planate

Animalia

Monera

FungiProtis

The more characteristics two species will have in common, the more closely

they are related.

A common ancestor

Biosphere

Ecosystem

Community

Population

Individual

Organ System

Organs

Tissue

Concept 16

Tools of Tracing Evolutionary Relationships

Excavating and Time-dating

Studying fossils,

Determining DNA sequences

Homologous characters.

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

Analogous 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.

Concept 17

Fossils (from Latin fossus, literally "having been dug up")

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.

How do we know how old the fossils are?

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.

Let us recall…..

Homologous characters

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

Prep Work….

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.

Concept 16We studied….

Tools of Tracing Evolutionary Relationships

Can you recall homologous characters?

Homologous characters.

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

Can you recall analogous 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.

Concept 17

We learnt about Fossils (from Latin fossus, literally "having been dug up")

What are fossils?

Fossils

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

What do we learn from fossils?

Fissile is a missing link

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.

Concept 18

Evolution by Stages

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.

Evolution by Stages

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

Evolution by Stages

Concept 19

Another way of Tracing Evolutionary Relationships

Changes in DNA during reproduction are the basic events in evolution

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.

Let us recall…..

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.

Prep Work….

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.

Concept 18we learnt …

Evolution by Stages

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

Concept 19We also learnt…

Another way of Tracing Evolutionary Relationships

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.

Concept 20

EVOLUTION SHOULD NOT BE EQUATED WITH ‘PROGRESS’

Evolutionary trend

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.

Multiple branches possible at each and every stage of evolution

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.

It is not true that human beings have evolved from chimpanzees.

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.

Concept 20

Evolution in Human

All humans are a single species.

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.

Let us recall…..

EVOLUTION SHOULD NOT BE EQUATED WITH ‘PROGRESS’

Human Evaluation

Prep Work….

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

ratio of tt

thesame tt

tt trait combinations

thett tt offspring

thefirst generation

asfirst generation f1

f1 progeny

tt talltt shortt t

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