DNA sequences are used for studying human evolution. There is no biological basis to the idea of human races. All human beings are a single species but there is a great diversity of human forms and features across the earth. The earliest members of human species Homo sapiens are traced from Africa.
The evidences in support are as follows:
1.Common body plan, structure, physiology and metabolism.
2.Constant chromosome number
3. Common genetic blue print
4. Free inter-breeding

(a) Yes.
(b) Geographical isolation prevents gene flow between populations of a species whereas asexual reproduction generally involves only one individual. Slowly the separated individuals will reproduce among themselves and generate new variations. Geographical isolation gradually leads to genetic drift. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

(a) Fossils help to trace the racial history of organisms.
(b) They help to measure the geological time.
(c) Older fossils lie at the depth and young fossils are at the upper surface of the earth. Complex organisms are present at top and simple organisms are present at the bottom.
(d) Fossil like-Archaeopteryx-show the link between two different types of species.

From this study, we cannot make any inference whether light eye colour trait is recessive or dominant, because as both the parents have light colour eye, all the children will definitely have light colour eye (though certain variations may occur).

Classification of organisms is based on relative similarities and differences in their internal and external structures. Similarities among organisms will allow us to group them and study the groups and classify them. Some basic characteristics will be shared by most organisms. The more characteristics the two species will have in common, the more closely they are related. The more closely they are related, the more recently they have had a common ancestor. So we can say that classification of a species is in fact a reflection of their evolutionary relationship.

When organisms (plants or animals) die, their bodies will decompose by the action of micro-organisms in the presence of oxygen, moisture etc.
Sometimes in the lack of such conditions (oxygen, moisture, etc.), their body does not decompose completely and is preserved as fossil with the passage of time in the rocks  In many cases the soft parts of the organism get decomposed and hard parts (like bones etc.) become fossil. Sometimes even the soft parts (like leaf etc.) remain preserved as fossils in the form of their impressions inside the rocks.
Methods to determine the age of fossils:
1. Relative method: The fossils which we find in layers closer to the surface of the earth are more recent; the fossils which are found in deeper layers are older.
2.Carbon dating: Fossils were once living objects and all living objects, contain some carbon-14 atoms which are radio-active.When a living object dies and forms fossil, its carbon -14 radioactivity goes on decreasing gradually.The age of the fossil is found by comparing the carbon -14 radioactivity left in the fossil with the carbon -14 radioactivity present in the living objects today.

50%

The organisms resulting due to crossing over and exchange of gene segments are known as offspring.

It is the process of transmission of characters from the parents to their offspring.

It is believed that features in dinosaurs might have provided insulation in cold weather but later on became useful for flights in birds.

Yes, geographical isolation can lead to speciation. Due to geographical isolation, the members of two sub groups may not be able to interbreed as a result of genetic drift. Natural selection also operates differently in these subgroups. This leads to speciation.

RrYy (Round yellow).

(a) No
(b) Though animals have a vast diversity in structures they, do not have a common ancestry. This is because common ancestry may limit the extent of diversity. As many of these diverse animals inhabit the same habitat, their evolution by geographical isolation and speciation is also not likely.

Human females have two X chromosomes. At the time of gamete formation, one X chromosome enters each gamete. Hence all the gametes possess an X chromosome.

Female baby

(a) No, she should not take the medicine.
(b) Of course she should visit a doctor to get information.
(c) She is having 50% chances of having a male child as 50% sperms carry Y chromosome and 50% X chromosome.

No, depending on the nature of variations different individuals have different kinds of advantages. However, when a drastic 'Change occurs in environment only those organism in the population will survive which have an advantageous variation in that population to survive in changed environment.