Key Points - Heredity and Evolution

Genetics: Branch of science that deals with Heredity and variation.
Heredity: It means the transmission of features/ characters/ traits from one generation to the next generation.
Variation: The differences among the individuals of a species/ population are called variations.

MENDEL AND HIS WORK ON INHERITANCE
Gregor Johann Mendel (1822&1884): Started his experiments on plant breeding and hybridisation
Mendel fi was known as Father of Genetics
Plant selected by Mendel: Pisum sativum (garden pea). Mendel used a number of contrasting characters for garden pea.

TABLE OF CONTRASTING CHARACTERS. (SEVEN PARTS)
CHARACTER - DOMINANT - RECESSIVE - TRAIT - TRAIT
Flower colour
Purple
White
Flower position
Axial
Terminal
Yellow
Green
Seed colour
Round
Wrinkled
Seed shape
Inflated
Constricted
Pod shape
Green
Yellow
Pod colour
Tall
Dwarf
Height of plant
Seven pairs of contrasting characters in Garden
Pea
Mendels Experiments: Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time)
Monohybrid Cross:
Cross between two pea plants with one pair (monohybrid cross) contrasting characters
Example: Tall / Short Plants.

- PARENT GENERATION
·
Dwarf plant
Tall plant
·tt
T
TT
T
GAMETES
Tt
F1 GENERATION (first filal generation)
SELF POLLINATION
Tt (F1) Tt
All tall plants
· Tt (F1)
GAMETES
T
 t
TT
F2 GENERATION (Second Final
TALL
Gneration
Phenotypic ratio
Phenotypic ratio
T
E
Tt
Tt
 tt
TALL
TALL
SHORT
3:1
1:2:1

8. X-Science
- 82
X-Science
- TT tt
Both dominant gene
Both recessive gene
Tt
Pure or conditon
One dominant, one recessive gene
 homozygous
Hetrozygous condition.
[Hybrid]
Phenotypic ratio: 3:1
Genotypic ratio: 1:2:1
Phenotype fi
Physical appearance [Tall or Short]
Genotype fi
Genetic make up [TT, Tt or tt]
Observations:

1. All F1 progeny were tall (no medium height plant (half way characteristic)

2. F2 progeny ¼ were short

3. Phenotypic ratio F2 -  3:1
Genotypic ratio F2 -  1:2:1

Conclusions:

1. TT and Tt both are tall plants while tt is a short plant.

2. A single copy of T is enough to make the plant tall, while both copies have to be 't' for the plant to be short.

3. Characters/Traits like 'T' are called dominant trait (because it express itself) 't' are recessive trait (because it remains supressed)

Dihybrid Cross: A cross macle between two plants having two pairs of contrasting characters is called dihybrid cross.

PARENT
GENERATION
GAMETES
ROUND
GREEN SEEDS
WRINKLED
·
YELLOW SEEDS
RRYY fl
RY
 rryy fl ry
F1
RrYy
[round, yellow]

8. X-Science
- ·
F1
RY
Ry rY ry fl
Selfing F1fi
Rr Yy
F1
·Rr Yy
RY
Ry rY ry
G
A
H
E
T
E
S
RY
RY
RRYY
Ry
RRYy
 rY
RrYy
 ry
RrYy
 flRy
RRYy
RRyy
RrYy
Rryy
 rY
RrYY
RrYy
 rrYY
 rrYy
 ry
RrYy
Rryy
 rrYy
 rryy
F2
PHENOTYPIC RATIO:
Round, yellow
Round, green
Wrinkled, yellow
Wrinkled, green
GENOTYPIC RATIO:
RRYY
RRYy
RrYY
RRyy
RrYy
Rryy rrYY rrYy rryy
;
:
:
:
:
:
:
:
:
:9
:3
:3
:1
1
2
2
1
4
2
1
2
1
RATIO: 1: 2: 2: 1: 4: 2: 1: 2: 1

Observations:

1. When RRYY was crossed with rryy in F1 generation all were Rr Yy round and yellow seeds.

2. Self pollination of F1 plants gave parental phenotype + two mixtures (recombinants) Round wrinkled, green yellow: seeds plants appeared in the ratio of 9:3:3:1
Conclussions:

1. Round and yellow seeds are DOMINANT characters

2. Occurence of new phenotypic combinations show that genes for round and yellow seeds are inherited independently of each other.

Sex Determination
Phenomenon of decision or determination of sex of an offspring

FACTORS
Responsible for Sex Determination
Environmental
In some animals the temperature at which the fertilised eggs are kept decides the gender.
Genetic
In some animals like humans gender or individual is determined by a pair of chromosome called sex chromosome
 eg. in Turtle
XX -  Female
XY -  Male
Sex Chromosomes: In human beings there are 23 pairs of chromosome. Out of these 22 chromosomes pairs are called autosomes and the last pair of chromosomes that help in deciding gender of that individual are called sex chromosome.
XX -  female
XY -  male
Sex determination in Human beings
PARENTS:
FATHER
XY
GAMETES (Reproductive cells)
Zygote formed after fusion of gametes
X
MOTHER
XX
Y
X
XX
FEMALE
XX
FEMALE
50% probability of a female child
X
XY
MALE
XY
MALE
50% probability of a male child
This shows that half the children will be boys and half will be girls. All children will in herit an X chromosome from their mother regardless whether they are boys or girls. Thus sex of children will be determined by what they inherit from their father, and not from their mother.

8. X-Science
- Evolution

SITUATION-I
Group of red beetles
Colour variation arises during reproduction
All beetles red except one that is green
One beetle Green
Reproduction
Crows feed on red beetle
Progeny beetles green
No. of beetles reduces
Crow could not feed on green beetles as they got camouflaged in green bushes
Number of green beetles increases
Situation 1: Green beetles got the survival advantage or they were naturally selected as they were not visible in green bushes. This natural selection is exerted by crows resulting in adaptations in the beetles to fit better in their environment

SITUATION-II
Group of red beetles
Reproduction
All beetles are red except one that is blue
Reproduces
One blue beetle
Reproduces
Number of red beetle increases
No. of blue beetle increases
Crows can see both blue and red beetles and can eat them
Number reduces but still red beetles are more and blue ones are few
Suddenly elephant comes and stamps on the bushes
But now beetles left are mostly blue.

- Situation 2: Blue beetles did not get survivals advantage. Elephant suddenly caused major havoc in beetle population otherwise there number would have been considerably large.
From this we can conclude that accidents can change the frequency of some genes even if they do not get survival advantage: This is called genetic drift and it leads to variation.

Mechanism of Heredity
Characters or traits of an organism are controlled by the genes

A Section of DNA (cellular)
Gene
Provides information
For synthesis of Proteins
Proteins controls a character
Example:
Gene T
Gene t
 responsible for synthesis of efficient enzyme (Protein) responsible for synthesis of less efficient enzyme

8. More production of growth hormone
Less production of growth hormone
Results in
Tall
Plants
Results in short
Plants
X-Science
- Genetic drift. It leads to diversity without any adaptation

SITUATION-III
Group of red beetles
Habitat of beetles (bushes)
Suffer from plant disease
Average weight of beetles decreases due to poor nourishment
No of beetles kept on reducing
Later plant disease gets eliminated
Number and average weight of the beetles increases again

Situation 3: No genetic change has occured in the population of beetle. The population gets affected for a short duration only due to environmental changes
Acquired and Inherited Traits
Acquired Traits
Inherited Traits

1. These are the traits which are developed in an individual due to special conditions

1. These are the traits which are passed from one generation to the next.

2. They cannot be transferred to the progeny

2. They get transferred to the progeny.

3. They cannot direct evolution

3. They are helpful in evolution.
 eg. Low weight of starving beetles.
 eg. Colour of eyes and hair

- Speciation
Micro evolution: It is the evolution which is on a small scale. eg. change in body colour of beetles.
Speciation: it is the process of formation of new species.
Species: A group of similar individuals that along to a population that can interbreed and produce ferrite off spring.
Geneflow: It is exchange of genetic material by interbreeding between populations of same species or individuals

WAYS BY WHICH SPECIATION TAKES PLACE
Speciation takes place when variation is combined with geographical isolation.
Gene flow: occurs between population that are partly but not completely seperated
Sub Population
X1 (local)
Interbreeding
[Reproduction]
Gene flow
Sub Population
X1 (migrant)
Variation in
Local population
Genetic Drift
It is the random change in the frequency of alleles (gene pair) in a population over successive generations.
*Natural Selection: The process by which nature selects and consolidate those organisms which are more suitably adapted and posesses favorable variations

POPULATION Z
Sub Population
Z1
GEOGRAPHICAL BARRIER
ISOLATION (River, Mountain)
Sub Population
Z2
Over many-many generations

8. Results in Accumulation of different variations in
Sub population Z1 and Z2
Genetic drift
Natural selection
Sub population Z1 and Z2 incapable of interbreeding
Reproductive
Barrier
Formation of
Formation of new Species 1 new Species 2
Genetic drift takes place due to a) Severe changes in the DNA b) Change in number of chromosomes
Evolution and classification
Both evolution and classification are interlinked.

1. Classification of species is reflection of their evolutionary relationship.

2. The more characteristic two species have in common the more closely they are related.

3. The more closely they are related, the more recently they have a common ancestor.

4. Slmilarities among organisms allow us to group them together and to study their characteristic

- Tracing Evolutionary Relationships (Evidences of Evolution)

I. Homologous Organs: (Morphological and anatomical evidences. These are the organs that have same basic structural plan and origin but different functions.
Example:
Forelimb of Horse
Winds of bat
Paw of a cat
 (Running) (flying) (walk/scratch/attack)
Same basic plan, different functions

II. Analogous Organs: These are the organs that have different origin and structural plan but same function example:
Design different
Wings of bat fi elongated fingers with skin folds same function ie. flight
Wings of bird fi
Feathery covering along the arm

III. Fossils: (Palaeontological evidences)
The remains and relics of dead organisms of the past.
Example: i)
Fossil of wooly mammoth
 ii) Archeopteryx (fossil bird) iii) Dead insect caught in hot mud.

FOSSILS ARE PRESERVED TRACES OF LIVING ORGANISMS
Eg. AMMONITE
-Fossil invertebrate
TRILOBITE
- Fossil in vertebrate
KNIGHTIA
- Fossil fish
RAJASAURUS
- Fossil dinosaur skull

- AGE OF THE FOSSILS i.
Deeper the fossil, older it is.
II. Detecting the ratios of different of the same element in the fossil material ie Radio-carbon dating.
[C-(14) dating)
Recent

1. ...........................

2. ...........................

3. ...........................

4. ...........................

5. ..........................

6. ..........................

Older
Evolution by stages
Evolution takes place in stages ie bit by bit over generations.
I.
Fitness advantage
Evolution of Eyes
Evolution of complex organs is not sudden it occurs due to minor changes in DNA, however takes place bit by bit over generations. enough to
Flat worm has rudimentary eyes give fitness advantage
Insects have compound eyes
Humans have binocular eyes
II. Functional Advantage
Evolutions of feathers
Feathers fi provide insulation in cold weather but later they might become useful for flight.
Example:
Dinosaurs had feathers, but could not fly using feathers. Birds seem to have later adapted the feathers to flight.
Artificial Selection:
Humans have been a powerful agent in modifying wild species to suit their own requirement through out ages by using artificial selection. eg (i) Wild cabbage the dissimilar looking structures have evolved from a common ancestral design. (ii)
Wheat (many varieties obtained due to artificial selection)

- WILD
CABBAGE
KALE

CABBAGE with larger leaves with short distance between the leaves
BROCCOLI
KOHL RABI
CAULIFLOWER
Has sterile flowers
Arrested flower development
With Swollen parts

Molecular Phylogeny:

- It is based on the idea that changes in DNA during reproduction are the basic  events in evolution
- Organisms which are more distantly related will accumulate greater  differences in their DNA

- Human Evolution
Tools to Study Human Evolutionary Relationship
Excavating
Time dating
Fossils
Determining
DNA
Sequences

Although there is great diversity of human forms all over the world get all humans are a single species

GENETIC FOOTPRINTS OF HUMANS
Hundreds/thousand of years ago
Earliest members arose in Africa
East Asia
South Africa
Africa
Philippines
Island of
Indonesia
West
Asia
Central
Asia
Australia
Eurasia

- They did'nt go in a single line
- They went forward and backward
- Moved in and out of Africa
- Sometimes came back to mix with each other.

...........................................................................................................
Question Bank
Very Short Answers (1 Mark)

1. Define variation

2. What is monohybird cross?

3. What is dominant trait.

4. What are genes?

5. Define Homologous organs

6. If an individual has XX chromosome [22+XX] will that individual be male or female.

7. Which plant Mendel had choosen for his experiments.

8. How do Mendel's experiment show that traits may be dominant or recessive?

9. Define analogous organs? Give example.

Short Answers (2 Marks)

1. Differentiate between acquired and Inherited traits? Give example of each.

2. Explain what are fossils? How the age of fossils be determined

3. What is speciation? What factors lead to formation of a new species.

4. Explain the mechanism of sex determination in humans.

5. Differentiate between homologous and analogous organs. by giving examples.

6. Define inheritance. What are the units of inheritance

7. What is genetic drift? How it contributes to the formation of new species

8. Explain monohydrid cross by taking tall and dwarf plants. Mention the phenotypic and genotypic ratio of F1 and F2 off springs.

Long Answer (5 Marks each)

1. Explain the process of artificial selection by taking the example of wild cabbage plant.

2. Explain about the human evolution.