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1. Changes in the frequency of genes in small populations, due to accidents is known as “Genetic drift”.’ 

2. Let us consider a colour variation occurred in red colour beetles which are living on green coloured leaves of bushes. 

3. It results in “blue” colour beetles instead of ‘red’ colour beetles and passed its colour to its progeny.

4. Initially in the population, there are few blue beetles, but most are red. 

5. Imagine at this point, an elephant comes by and stamps on the bushes where the beetles live. 

6. This kills most of the beetles but by chance a few beetles survived are mostly blue.

7. Again the beetle population slowly increases, but in the beetle population most of them are in blue colour. 8. Thus genetic drift provides diversity in the population.

Change in the frequency of genes in small populations is called genetic drift.

Recessive gene: Gene that produces its characteristic phenotype only when its allele is identical.

Genetic drift: It is the change ¡n the frequency of genes in a small population.

1. Any group of population of an organism has variations and all members of group are not identical. 

2. Variations maybe passed from parent to offspring through heredity. 

3. The natural selection over abundance of offspring leads to a constant struggle for their survival in any population. 

4. Individuals with variations that help them to survive and reproduce tend to live longer and have more offsprings than organisms with less useful features. 

5. The offsprings of survivors inherit the useful variations, and the same process happens with every new generation until the variation becomes a common feature. 

6. As the environment changes, the organism within the environment adapt and changes to the new living conditions.

7. Over a long period of time, each species of organism can accumulate so many changes that it becomes a new species, similar to but distinctly different from the original species. All species on the earth arise in this way. 

8. Evolution is a slow and continuous process that involves several thousands of generations.

1. Evolution takes place through the accumulation of new characters or variations in a species of organisms. 

2. Accumulation of variations occurs only when new characters are passed on from one generation to other and much more new characters are added to the pre-existing once. 

3. So this happens oVer a kirig period of time, sometimes several generations may pass. 

4. Hence it happens in a slow and steady manner. 

5. It is not just about change but producing something new and different. 

6. It is about the formation of new species and their adaptation to their environments.

1. Variations which are beneficial are selected by nature and passed from parents to offspring through heredity. 

2. The same process happens with every new generation until the variation becomes common feature. 

3. As the environment changes, the organism within environment adopts and changes to the new living conditions. 

4. Over a long period of time, each species of organisms can acuumulate so many changes that it becomes a new species. 

5. Thus evolution of organisms took place from common pre-existing ancestors.

D) James Douglas

(B) Female, Male

i) Phenotypic ratio 3 : 1 

ii) Two heterozygous plants – (Yy, yY)

1. Evolution is a continuous and comprehensive process. 

2. If it does not take place, there is no formation of new species. 

3. Variations do not take place and hence desirable traits are not developed. 

4. All the Earth would be with the primitive species without any changes.

1. What is human evolution? 

2. When were early man like forms appeared on land? 

3. When did the fossil of the homosapiens appeared on earth? 

4. Where did the early man lived? 

5. Where can we trace the earliest members of the human race homosapiens? 

6. When do some of our ancestors left Africa? 

7. How the residents of Africa migrated to other places? 

8. Why did the residents of Africa migrated to other places?

9. Are all humans evolved from single ancestor?

• Each human cell contains 23 pairs of chromosomes out of which 22 pairs of chromosomes are autosomes.
• 1 pair of chromosomes are called allosomes or sex chromosomes. 
• Gametes produced by women will be with only ‘X’ chromosomes.
• Gametes produced by man will be of two types one with X chromosomes and the other with Y chromosomes.
• If the sperm carries the X chromosome and fertilizes the ovum with the X chromosome, the resultant baby will have XX condition. So the baby will be a girl.
• If the sperm carries the Y chromosome and fertilizes the ovum with the X chromosome, the resultant baby will have XY condition. So the baby will be a boy.

The nitrogen bases present in DNA are adenine, guanine, thymine and cytosine.

The expanded form of DNA is Deoxyribo Nucleic Acid.

1. In the struggle for existence, only the fittest can survive.
2. Darwin published his famous book The origin of species’ in 1859. 
3. The small changes within the species are called Micro Evolution.
4. The changes beyond the species are called Macro Evolution.

(C) Embryology

(C) phenotype

Nature influences whether the organism should survive or perish in nature. 

(B) A. R. Wallace

(C) Charles Lyell

(D) Jean Lamarck

C) the acquired traits passed onto its progeny

(D) Length and thickness of stem

In the inheritance of more than one pair of characters, the factors for each pair of characters assort independently of the other pairs. This is known as Law of independent assortment.

Law of dominance states that among a pair of alleles for a character only one expresses itself in the first generation, as one of the alleles is dominant over the other.

The factors which are responsible for the character or trait of an organism, are now named genes.

During sexual reproduction, one factor from each parent is taken to form a new pair in the offspring.

Crossing yellow and green seeds produced all yellow seeds because yellow is the dominant factor.