Science [5 marks Questions]

	Acquired Traits	Inherited Traits
1.	Development: The traits develop during life time of an individual.	The traits are obtained from the parents.
2.	Nature: They are somatic variations.	They are genetic variations.
3.	Cause: Acquired traits develop due to direct effect of environment, use and conscious efforts.	The traits develop due to mutations and reshuffling of genetic material.
4.	Fate: They die with the death of the individual. Ex. Muscular body of a wrestler.	They are passed on to the next generation. Ex. Fused and free ear lobes.

Acquired characters are acquired due to individual’s response to external stimuli. These traits develop because of constant exposure to a certain stimulus and the resultant response by the individual. Let us take the example of a certain cricketer who is an excellent batsman. He could become an excellent batsman because of several reasons. Some of them could be; his keen interest in the game, timely support from his family and friends, proper coaching at the right age and timely selection in the cricket team. All the cricketing ability could be acquired by him because of the way he responded to all the challenges and opportunity. But this does not mean that the son of this cricketer would become an excellent cricketer; because cricketing ability is not an inheritable character.
In fact, acquired characters just alter the phenotype of an individual. It has no effect on genotype. A character can only be inheritable when it changes the genotype of individual. Hence, acquired characters are not inherited.

Mendel chose Garden Pea or Edible Pea (Pisum sativum) as his experimental material because of:

1. Easy availability of detectable contrasting traits of several characters.
2. Flower structure normally allows self fertilization but cross fertilization can also be carried out easily.
3. Annual nature of the plant.
4. Formation of a large number of seeds by each plant.
5. Requirement of little care except at the time of cross breeding.

Humans follow XX - XY mechanism of sex determination. Human females have forty-six chromosomes arranged in twenty two homologous and homomorphic autosomes and two copies of X chromosomes as sex chromosomes (44 + XX). They do not play significant role in sex determination of child.
Males have twenty-two homomorphic pairs and one heteromorphic pair, the XY pair (44 + XY). Fertilization of egg (22 + X) with sperm carrying 22 + X chromosomes gives female child (44A + XX). Fertilization of egg (22 + X) with sperm carrying 22 + Y chromosomes gives male child (44A + XY). Only daughters indicate fusion of egg with sperms carrying 22 + X chromosomes every time.

All the human races appear to be different but they have a large number of common characters. The list of common characters can be very long but we can make a shorter list:

• Similar size of brain.
• Bipedal locomotion Hair of body.
• Ability to handle tools.
• Ability to communicate using language.
• Highly complex social behavior.
• Same body design.

All these characters show a common ancestry for all human races. Moreover, the fact that all human beings are able to interbreed keeps them under the same species.

Fossils are remains or impressions of past organisms that are found in the rocks. Fossils of lower strata belong to early periods while those of upper strata are of later periods. Arranging the fossils stratumwise will indicate the occurrence of different forms of life at different times. It is found that the early fossils generally belong to simple organisms. Complexity and elaboration increased gradually with evolution. Evolution has never been linear or straight. A number of variants or branches appeared, some of which were more complex while others were less complex. Fossils indicate the path of evolution of different groups.They can indicate the phylogeny of some organisms, e.g, Horse, Elephant.
Some fossils have characteristics intermediate between two groups, e.g., toothed bird Archaeopteryx. They indicate how one group has evolved from another.

It depends on our perspective through which we try to evaluate evolution. If complexity in body design is the parameter to define evolution, then human beings are more evolved than bacteria. Bacteria are unicellular while human beings are multicellular. Bacteria show cellular level of organization, while human beings show organ system level of organization. In terms of complexity human beings are definitely highly evolved compared to bacteria.But when we compare the ability of survival, then situation is quite opposite. Human beings are living in almost every part of the earth but they can live only on land. Moreover, in extreme environmental conditions, human beings make artificial facilities to counter the adverse conditions. This means their body is not adapted to withstand extreme climatic conditions. Bacteria, on the other hand, are known to be present almost everywhere on earth. They are known to live even in some of the harshest conditions; like Sulphur spring, crater of volcano, etc. Bacteria can survive in highly acidic environment and they can survive extreme temperatures. From this angle, bacteria can be considered as more evolved than human beings.

Yes, geographical isolation of individuals of a species leads to speciation. Splitting of existing species into two new species followed by their geographical isolation brings about reproductive isolation. Populations of a species get separated into two groups by accumulation of genetic variations in them. These newly formed groups are then isolated by any geographical barrier.
Reproductive isolation is absence of interbreeding between members of different species. Geographical barriers prevent interbreeding between two groups. This in turn causes isolation of gene pool of section of population from rest; inhibits gene flow (spread of genes between populations) and thereby leads to formation of new species.

The apparent structures in an organism, are termed morphological structures. Morphological structures can be easily seen by all us. Molecular structure is about the structure of biomolecules which are the integral components of organisms.
We see lot of diversity all around us. This diversity is possible because of diversity in morphological structures. This shows that morphological structures are least stable. Life which began as simple forms on the earth in now composed of many complex forms.
But despite all the evolution which have taken place through millions of years, the structure biomolecules remains the same. A DNA is same in a human and in a mouse. A protein has same structure in a bird and in a fungi. So, the molecular basis of life has not changed through all these years. This shows that evolution has exhibited a greater stability of molecular structure when compared with morphological structure.

Basic Features of Inheritance:

1. Unit Characters: An organism is made of a large number of characters, each of which behaves as a unit.
2. Genes: Characters are controlled by genes.
3. One Gene-One Character: A single gene generally controls one character.
4. Location of Genes: Genes are located on chromosomes.
5. Alleles: A gene may have two or more forms called alleles. They represent different traits of a character.
6. Paired Alleles: An individual possesses two alleles of every gene. The two may be similar or dissimilar.
7. Dominance: Where there are two different forms or alleles of the gene, generally one expresses its effect. It is called dominant allele. The other which does not express its effect in presence of dominant allele, is called recessive allele.
8. Segregation: The two alleles separate at the time of gamete formation. A gamete has only one allele or form of the gene.
9. Independent Assortment: The alleles of different genes located on separate chromosomes behave independent of one another.
10. Pairing: Fusion of gametes during fertilization, brings together the two forms of a gene in the zygote.

1. Round yellow (RRYY)
2. Round yellow (RRYY), Round yellow (RrYy), Round green (RRyy), Round green (Rryy), wrinkled yellow (rrYY), wrinkled yellow (rrYy), wrinkled green (rryy).

3. Wrinkled green (rryy)
4. Round yellow (RrYy)