HBSE 10th Class Science Notes Chapter 9 Heredity and Evolution

Haryana State Board HBSE 10th Class Science Notes Chapter 9 Heredity and Evolution Notes.

Haryana Board 10th Class Science Notes Chapter 9 Heredity and Evolution

Accumulation of Variation During Reproduction

During reproduction, the offspring inherit two things from their previous generation. They are –
1. A common basic body design and
2. Some fine (i.e. minor) variations. This way with each new generation born, the variations get accumulated.
Parental generation (P): The first set of parents crossed is called parental generation. The parental generation is denoted by ‘P’.

First generation (F1): All the offspring born from the first set of parents crossed are said to be belonging to the First generation. The First generation is denoted by F1

HBSE 10th Class Science Notes Chapter 9 Heredity and Evolution

Second generation (F2): All the offspring born from the F1 generation are said to be belonging to the Second generation. The Second generation is denoted by F2.

Heredity:

  • Heredity means the transmission of characters from parents to offsprings. For example, eggs laid by a sparrow will hatch sparrow and not any other bird. Similarly, a dog gives birth only to pups.
  • Thus, in this sense, it can be said that heredity is the continuity of features from one generation to another. This is the essence of heredity.

Rules for the Inheritance of Traits – Mendel’s Contributions

There are two versions for each trait in each child –
In a sexual reproduction, the father, as well as the mother, contributes equal amounts of genetic material to the child.

Mendel’s contribution in the field of inheritance of characteristics:
Mendel studied garden pea plants for the expression of a character. The character under study was ‘the height of plants’. Mendel took pure tall plants (TT) and pure short plants (tt).

Cross-pollination between parent (P) generation plants:
On performing cross-pollination between TT – pure tall plants and tt – pure short plants, all the plants of F1 generations were as tall as TT of P generation.

Self-pollination of (a) Tall Parental Generation plants and (b) F1 generation plants:
(a) The new plants produced by the self-pollination of Tall i.e. TT Parental Generation plants were all tall.
(b) The new plants produced i.e. the second (F2) generation plants by the self-pollination of F1 generation plants were a mix of tall and short plants. 75% of the plants were tall and 25% of the plants were short. This means the ratio of tall : short plant in the F2 generation was 3:1.

HBSE 10th Class Science Notes Chapter 9 Heredity and Evolution

How do these Traits get Expressed?

In plants as”well as organisms, the characters (traits) get expressed due to specific reactions. These reactions take place with the help of enzymes. When a specific gene undertakes synthesis of a specific protein it results in expression of a specific character.

Sex determination:

  • In sexual reproduction, the mechanism to determine the sex of an organism is known as sex determination. In human beings, the sex is determined by genes located on the chromosomes.
  • In humans, each cell contains 23 pairs of chromosomes.
  • In females, the 23rd pair contains two similar ‘X’ sex chromosomes i.e. the 23rd pair is ‘XX’. In males, the 23rd pair contains one ‘X’ sex chromosome and one ‘Y’ sex chromosome i.e. the 23rd pair is ‘XY’.

Sex of the foetus:
If a sperm carrying ‘X’ chromosome fuses with the ‘X’ chromosome of female egg i.e. if ‘XX’ combination occurs, female will be produced. If a sperm carrying ‘Y’ chromosome fuses with the ‘X’ chromosome of female egg, i.e. if ‘XY’ combination occurs, male will be produced.

HBSE 10th Class Science Notes Chapter 9 Heredity and Evolution

Evolution

Natural selection:
Natural selection is a central concept of evolution. In general terms it is also called ‘survival of the fittest’. Natural selection can be considered as the one ‘selected by nature’.

Genetic drift:
The sudden and random change in the gene frequency that occurs by chance in a small population is known as genetic drift.

Acquired and Inherited Traits

Evolution:

  • Evolution is the sequence of gradual changes, which have taken place over millions of years in primitive plants and animals from which new species are formed.
  • All the varieties of organisms, which we see around us, have evolved from some ancestors that lived on this earth long time ago.

Acquired traits:
Acquired trait means a trait or characteristic of an organism that it has not inherited but has developed in response to the environment. For example, if an organism starves for some time and reduces its weight, then it is called acquired trait.

Inherited trait:
A trait of an organism, which is caused by a change in its DNA, is known as inherited trait.

Variation:
Any difference that occurs between cells, individual organisms, or groups of organisms of any species either by genetic differences or by the effect of environmental factors on the expression of the genetic potential is called variation.

Acquired variation:
An acquired characteristic (variation) is a change which is acquired not due to heredity but due to response to the environmental factors.

HBSE 10th Class Science Notes Chapter 9 Heredity and Evolution

Acquired variation may occur in the function or structure of an organism caused after birth due to reasons such as disease, injury, accident, repeated use or misuse, or other environmental factors.

Speciation:
The process of evolution of new species that occurs when members of similar population no longer interbreed to produce fertile off spring is known as speciation.

Reasons of speciation:
Geographical isolation, changes in DNA, change in number of chromosomes, gene cells of two isolated groups of populations, which cannot fuse with each other, etc.

Evolution and Classification

How are organisms classified?

  • Classifying organisms by grouping them in certain way helps us to study them properly.
  • One of the basic methods of classifying the organisms is on the basis of similarities they possess. A characteristic means a particular type of appearance (form) or behaviour (function).

Example:
We humans have four limbs (two hands and two legs) and it is our appearance (form characteristic. Plants perform photosynthesis is a behavioral (function) characteristic.

Tracing Evolutionary Relationships

Evidence for evolution:
Certain significant sources which provide proofs for evolution are called evidences for evolution. The main ones are:

Evidences through homologous organs: Those organs that have same internal structure but different functions are called homologous organs. For example, the basic design of internal structure of bones of forelimbs of a frog, lizard, bird, bat and man is same, even though these organs perform different functions.

Evidence through analogous organs: Those organs, which have different designs but similar appearance and carry out similar functions are called analogous organs. For example, wings of insects and birds have different structures but perform similar functions.

Evidence through fossils: The remains of dead organisms buried under the earth for millions of years are known as fossils. By studying these fossils, scientists learn how organisms evolved over time.

HBSE 10th Class Science Notes Chapter 9 Heredity and Evolution

Evolution by Stages

Evolution of eyes:
The eyes of animals have been created in stages after many generations. First of all, eye was formed in planaria (flat-worm) which was in the form of a simple spot. Gradually, it became a complex organ.

Evolution of cabbage:
Wild cabbage is the ancestor of cabbage, broccoli, cauliflower, kohlrabi and kale varieties. These varieties have evolved from wild cabbage because farmers performed artificial selection on the wild cabbage and the varieties produced from it. Today, all the said varieties look different from their ancestor i.e. wild cabbage.

Evolution Should Not be Equated With ‘Progress’

Actually, no real ‘progress’ has taken place in the idea of evolution. The only progressive trend that is seen in evolution is that with time more and more complex body designs have emerged. This does not mean that the older designs were inefficient. Many older and simpler designs still survive.

Human Evolution: Research suggests that all the humans have evolved from a single species called Homo sapiens and initially belonged to Africa.

Leave a Comment

Your email address will not be published. Required fields are marked *