1. Heredity and Evolution
BY,
Mrs. SABEENA HASHIM

2. Reproduction give rise individuals that are similar but not identical.
variation is very less in those organisms that under goes asexual reproduction. example sugar cane (stem cutting)- less variation, variation is not visible.
In case of animals and human beings variation is more because of sexual reproduction and variations are visible.
Long term consequences of the accumulation of variations gave rise to evolution of organisms.
These changes were inherited and give rise to enormous diversity of organisms on the earth
INTRODUCTION

3. ACCUMULATION OF VARIATION DURING REPRODUCTION:
During reproduction, characters are inherited or transmitted from one generation to the other, i.e from parents to the offspring.
There are two aspects- a) inheritance of basic body structure; b) inheritance of suitable changes (variation) that enable the organisms for better adaptation.
variations are produced in organisms whether they reproduce asexually or sexually. the variations produced in organisms during succesive generations get accumulated in the organisms and pass on to more and more individuals of each generation.
diagram-9.1 pg. no 142.
fig 9.1 which represents situation where a single bacterium reproduces. the original organisms i. e the bacterium divides and produces two similar bacteria with few changes. These bacteria divide and reproduce. four individual bacteria are produced,i.e two from each. these four bacteria will be similar but there would be minor differences.( due to error in DNA copying).
In case of sexually reproducing organisms show greater variations will be generated.
Depending on the nature of variations different organisms will have different kinds of advantages. example- bacteria that can withstand heat will survive better in a heat wave.in further generations of bacteria the variation of more heat resistance will go on accumulating and will ultimately develop a high heat resistant variety of bacteria.
ACCUMULATION OF VARIATION DURING REPRODUCTION:

5. Heredity is the transmission of characteristics from one generation to the other generation.
The rules heredity determine the process by which traits and characteristics are reliable inherited.
HEREDITY

6. Branch of biology that deals with the study of heredity and variation.
GENETICS

7. Any differences in traits between individuals of a species caused either through genetic or environmental factors is variation.
VARIATION

8. The recognisable features of an organisms are called traits or characters.

9. RULES OF HEREDITY Inherited traits:
Inheritance is a phenomenon by which living organisms transmit their characters from one generation to the other generation.
Inherited traits are controlled by genetic materials of individuals obtained from parents.
example- free and attached ear lobe, roller and non roller tongue.
RULES OF HEREDITY

10. RULES FOR THE INHERITANCE OF TRAITS- MENDELS CONTRIBUTIONS:
The rules for inheritance of traits in human beings are related to the fact that both father and mother contribute practically equal amounts of genetic material to the child.
GREGOR JOHANN MENDEL (father of genetics) worked on the garden pea plant (Pisum sativa L.). Mendel used a number of contrasting characters of garden peas- round/ wrinkled seeds, tall/ short plants, white/violet flowers and so on. he took pea plants with different characteristics, produced progeny from them and calculated the percentage of inheritance.
RULES FOR THE INHERITANCE OF TRAITS- MENDELS CONTRIBUTIONS:

11. WHY DID MENDEL SELECT GARDEN PEA PLANT?
These plants have short life cycle.
Very easy and convenient to raise, maintain, and handle these plants.
Pea flowers are bisexual.
The pant shows several distinct and easily detectable contrasting traits.
Artificial cross pollination is possible due to large reproductive organs.
WHY DID MENDEL SELECT GARDEN PEA PLANT?

12. In order to understand the pattern of inheritance of a single pair of contrasting characters (tall/ short), Mendal crossed two different pure breed pea plants. he noted he occurrence of the trait in the first generation or F1 progeny- no medium -height plants. All plants were tall. The offspring produced in F1 generation resembled only one .parental traits.
Mendel then crossed the tall plants generation among themselves and found that both tall and short plants were obtained in F2 generation in the ratio of 3:1{ phenotypic ratio} (75% tall and 25% short ).This indicates that both the tallness and shortness traits were inherited in the F1 plants but, only the tallness trait was expressed.
3:1- phenotypic ratio.
(1;2;1- genotypic ratio).
TT, Tt- Tall plant. (dominant trait)
tt- short plant ( recessive trait)
Fig no- 9.3
MONOHYBRID CROSS

14. DOMINANT TRAIT- the trait which expresses itself in hybrid.
RECESSIVE TRAIT- the trait which does not express itself physically and remains unexpressed due to presence of of dominant trait is called recessive trait.
F1 GENERATTION: The generation resulting immediately from a cross of the first set of parents.
F2 GENERATION: offspring's resulting from a cross of the members of F1 generation.

15. It involves the inheritance of two pairs of contrasting contrasting characters at the same time by crossing between two organisms of species.
Mendel did the experiment in the following way;
1. He crossed pure line plants having round yellow seeds with pure line plants having wrinkled green seed.
2. In F1 generation, he obtained only round and yellow seeds, i.e the characters of only one of the parent( dominant).
3. He raised the plants from seeds of F1 generation and allowed self pollination to obtain F2 generation.
4. In F2 generation, four types of combinations of shape and colour of seeds appeared.
DIHYBRID CROSS

16. F2 progeny showed new mixtures, four types of combinations of shape and colour of seeds appeared. i.e. Round yellow seeds, round green seeds, wrinkled yellow, wrinkled green.
The combinations obtained were in a definite phenotypic ratio i.e 9:3:3:1
9-round yellow,3-round green, 3- wrinkled yellow, 1-wrinkled green.
On the basis of the results of dihybrid cross Mendal concluded that, though the two pairs of original characteristics combine in the FA2 generation, they separated and behaved independently in subsequent generations.
Thus it shows that traits are independently inherited.
FLOW CAHET PG. NO145.

18. MECHANISM OF HEREDITY- HOW DO TRAITS GET EXPRESSED
DNA- Is the information source for making proteins in the cell.
GENE- A segment of DNA that provides information for one protein is called gene for that protein. It is a unit of inheritance.
We know that plants have hormones that can trigger growth. Plant height can thus depend on the amount of a particular plant hormone. The amount of a particular plant hormone made will depend on the efficiency of the process for making it.
Consider now an enzyme that is important for this process for making it. 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 that makes the enzyme less efficient, the amount of hormone will be less and the plant will be short, thus genes control characteristics or traits.
MECHANISM OF HEREDITY- HOW DO TRAITS GET EXPRESSED

19. CHROMOSOMES: Are long thread-like structures which contain heredity information of the individual and thereby the carrier of genes.
In sexual reproduction, both the parents contribute equal amount of genetic material to the progeny.
Each cell will have two copies of each chromosome, one each from the male and female parents. Every germ cell will take one chromosomes from each pair and these may be either maternal or paternal in origin.
When the male and female germ cells combine during fertilization, there occurs rest0ration of normal number of chromosomes in the progeny, ensuring the stability of the DNA of the species.

20. It is the mechanism through which sex of a individual is determined.
In some organisms sex determination entirely depend on environmental cues.
In some animals, the temperature at which fertilized eggs are kept determines whether the animal developing in the eggs will be male or female.
In animals like snails, individuals can change sex, indicating that sex is not genetically determined.
SEX DETERMINATION.

21. In human beings, the sex of the individual is largely genetically determined. In other words, the genes inherited from parents determines the sex of an individual.
Each cell in human beings consists of 46 chromosomes or 23 pairs of chromosomes. 22 pairs of chromosomes are found common in both males and females. These are autosomes. The 23rd pair of chromosomes in human beings takes part in sex determination and thus is termed as sex chromosomes or allosomes.
In females 23rd pair of chromosomes consists of same chromosomes represented as X, whereas in males the 23rd pair of chromosomes consists of two different chromosomes represented as X and Y. So women are XX, while men are XY.
During fertilization, the egg cell fuses with sperm cell, resulting in the formation of the zygote. If the egg cell carrying an X chromosomes fuses with the sperm carrying X chromosomes, the resulting child would be a girl. If the egg cell carrying an X chromosomes fuses with the sperm carrying Y chromosomes, the resulting child would be a boy. thus sex of the children will be determined by what they inherit from their father.
FIG 9.6,PG.NO-146.

23. The gradual changes resulting in the formation of new forms from pre-existing forms over a long period of (millions of year) is called as evolution.
EVOLUTION.

24. Let us study an illustration to find out the cause of variation.
Variation is caused due to error in DNA copying as well as due to sexual reproduction.
Let us study an illustration to find out the cause of variation.
Consider a group of 12 red beetles they live small bushes with green leaves. Their population will grow by sexual reproduction and therefore can generate variations. There are predators which feed on these beetles and regulate their population.
Lets consider some of different situations that can develop in this beetle populations.

25. SITUATION: 1 Colour variations arises during reproduction.
So that there is one beetle that is green in colour instead of red.
His colour change can be passed to its progeny, so that all its progeny beetles are green.
Crows cannot see green- coloured beetles on green leaves of the bushes and therefore cannot eat them, while progeny of red beetles continues to be eaten. As a result, there are more and more green beetles than red beetles.
SITUATION: 1

26. SITUATION: 2 Colour variation arises and results in blue beetles.
Passes it to its progeny.
So all progeny are blue.
Crow can see both red and blue beetles on the green bushes and can eat them.
As the population expands, initially there are few blue beetles but most are red.
At this point an elephant comes by and stamps on the bushes where the beetles live.
This kills most of the red beetles.
By chance, the few beetles that have survived are mostly blue.
Beetle population slowly expands again but now, the beetles in the population are mostly blue.
SITUATION: 2

27. EXPLANATION: SITUATION 1: APPEARANCE OF FAVOURABLE VARIATIONS.
The variation became more common because it gave a survival advantage.
It was naturally selected which directs the evolution.
The natural selection in this was exerted by the crows
The more crows, more red beetles are eaten and more the proportion of green beetles in the population.
Thus natural selection directed evolution of green beetles.
THE PHENOMENON WHERE IN THE WILD, THE NATURE SELECTS TRAITS FAVOURABLE TO THE SPECIES IN THE ENVIRONMENT IS CALLED NATURAL SELECTION.
Expalined by Charles Darwin.
EXPLANATION:
SITUATION 1:

28. EXPLANATION: SITUATION 2:
APPEARANCE OF UNFAVOURABLE VARIATIONS.
Here colour change gave no survival advantage.
Instead it was simply a matter of accidental survival,
So accident in small population can change the frequency o some gene in a population even though there was no survival advantage. This is called genetic drift. Which provides diversity without any daptation.
GENETIC DRIFT- THE ELIMINATION OF THE GENES OF CERTAIN TRAITS OR CHARACTERS FROM A SMALL POPULATION DUE TO DEATH OR MIGRATION OF MEMBRES OF THAT POPULATION.
Genetic drift can occur in small isolated population.
It may lead to fixing of unfavorable feature and loss of beneficial feature in a population.
EXPLANATION:
SITUATION 2:

29. Bushes on which beetles feed, suffer from a disease and the amount of leaf material (food) for the beetle is reduced.
As a result average weight of adult beetles decreased.
After few years, when the plant disease is eliminated, the beetles further gain weight due to availability of adequate food.
Thus lack of food doesn’t bring any genetic change, hence character cannot be inherited.
SITUATION: 3

31. ACQUIRED AND INHERITED TRAITS
In sexually reproducing organisms, the germ cell are made in specialised reproductive tissues.
For example if the weight of the beetle is reduced because of starvation, that will not change the DNA of the germ cells. Low weight is not a trait that can be inherited by the progeny of a starving beetle., that is not an example of evolution, since the change is not inherited over generations.
Change in non reproductive tissues(somatic cells) cannot be passed onto the DNA of the germ cells.
Experiences of an individual during its lifetime cannot be passed on to its progeny and cannot direct evolution.
Example- removal of tails from mice by surgery.
ACQUIRED AND INHERITED TRAITS

32. ACQUIRED TRAIT INHERITED TRAIT
The trait which are developed in the organisms during their lifetime and are not inherited by the next generation.
These are somatic variations.
These are not transmitted to the successive generations.
Example- low body weight.
INHERITED TRAIT
The traits which are passed from one generation to the next generation through DNA in the germ cells are called inherited traits.
These are genetic variations.
they are transmitted to the successive generations.
Example- free and attached ear lobes, eye colour, skin colour etc.

33. Charles Darwin Evolution of species by natural selection.
Origin of life.

34. A species is a group of similar organisms which are capable of interbreeding and producing fertile offspring.
The process of formation of new species from already existing species is called speciation.
Formation of new species can be said to have happened only when they are reproductively isolated.
REPRODUCTIVE ISOLATION: It is a process which prevents the population of two different groups from interbreeding.
It is necessary for speciation to occur, that the gene pool of a section of population should separate from the rest, resulting in stoppage of gene flow and accumulation of variants, some of which do not allow it to interbreed with original parent population.
SPECIATION

35. MECHANISM OF SPECIATION
Suppose there is a widespread population of beetle on a mountain range.
Beetle population becomes large and spreads over the entire mountain.
Sub-population of beetles are formed as beetles do not travel much.
Beetles reproduce within the sub population (no new species formed)
MECHANISM OF SPECIATION

36. A beetle migrates from sub-population to another(either due to its own will or by dropping by crow
Migrant beetle reproduces with the individual of new sub- population.
Genes enter in the new population( partial gene flow- no new species formed).
Two sub-population of beetles separated by a large river( geographical isolation)
Isolation of sub population ( level of gene flow becomes minimum, genetic drift occurs, variations accumulates in the sub population.

37. Natura selection operates differently in different population and creates differences in the genetic constitution of two sub-population.
Members of two sub- populations cannot reproduce (DNA changes and germ cells of two groups cannot fuse).
New species formed.

38. FACTORS RESPONSIBLE FOR SPECIATION. 1, Genetic drift. 2
FACTORS RESPONSIBLE FOR SPECIATION. 1, Genetic drift. 2.Severe change in the DNA(mutation). 3.Migration. 4.Geographical isolation- cant be a major factor in self pollinating plants and in asexually reproducing species.

39. GEOGRAPHICAL ISOLATION
It is the most common reason for reproductive isolation and speciation.
It prevents interbreeding among the individuals of a species due to which there in no gene flow between separated group of population.
geographical isolation is brought about by geographical barriers like mountain range, big desert, valley, river etc.
It may also be achieved by migration of some individuals to a geographically different areas.
GEOGRAPHICAL ISOLATION

40. EVOLUTION AND CLASSIFICATION
The evolutionary relationships can be determined by the methods of classification.
classification- is the system of arrangement of organisms in certain similarities and differences and placing them in hierarchy that reveals their relationship.
During classification, individuals showing certain similarities and differences and placing them in hierarchy that reveals their relationship.
CHARACTERSTICS- characteristics are details of appearance or behavior in other words, a particular form or function.
Example- four limbs in human beings, photosynthesis in plants etc.
EVOLUTION AND CLASSIFICATION