Expression of these traits:
- Inside the cell, It is cellular DNA which provides information for making proteins.
- Gene of the protein is the section of DNA which provides information about that protein.
- The Traits of a particular organism depend upon the amount of particular hormones present.
- The amount of hormones produced will depend upon the efficiency of the process of production.
- Gene has the main role in making these hormones, If there is any alteration in gene then there will be variation in traits.
- In human beings, the gene for each trait is present as separate independent pieces which are called a chromosomes.
- Each cell have two copies of each chromosome, one each from the male and female parents.
- To know about the gender or sex of the offspring is said to be sex determination.
- There are several factors which are responsible for sex determination, but two main factors are mainly seen, One is environmental factor and the other one is Genetic factor.
- In some animals, the temperature at which the fertilized eggs are kept decides the sex of their offspring. Turtle has the same mode.
- In humans and many animals the sex or gender of offspring is determined by a pair of chromosomes. They are called sex chromosomes.
Sex determination in human beings:
- Human beings have 23 pairs of chromosome.
- In these 23 pairs of chromosomes, 22 pairs are called autosomes.
- The last pair of chromosomes help in deciding the gender of an individual and this chromosome is sex chromosome.
- The sex chromosome in female is ‘XX’ and that in male is ‘XY’.
- All the offspring inherit ‘X’ chromosome from mother either children is boy or a girl.
- The sex of children totally depends on the chromosomes what they inherit from their father, not what they get from their mother.
- Evolution is simply the change inherited to the next generation from previous one in biological population over a long period of time (millions of years).
- As we already know that life on this earth is evolved from a single unicellular organism.
- Every organisms present on this earth is said to be evolved from single ancestor.
- No genetic change can occur in a particular niche for a short period.
- Only due to environmental change, the population gets affected.
Acquired and Inherited Traits:
|These traits are acquired
during lifetime mainly from
|These traits are inherited
from generation and passed
to the next generation.
|It doesn’t bring changes in
the DNA of germ cell.
|Genes of inherited traits are
present in DNA of germ cell.
resistance to environmental
|Example: Eye colour, Face
colour, hair colour etc.
- The process by which new species originates is said to be speciation.
- A group of organisms which have similar characters, also they can breed among themselves are said to be species.
- If two groups of the same species are anyway prevented from interbreeding for many generations then speciation can occur.
- Thus speciation covers a major part in heredity and evolution.
Speciation takes place by following ways:
- Gene flow: It takes place between population that are partially but not completely separated.
- Genetic drift: It takes place due to either severe change in DNA or change in number of chromosomes.
- Natural selection: Nature selects the organisms best suited under adaptable conditions and favorable variations. As, nature selects the best.
- Geographical isolation: When a group of species are separated due to geographical barriers such as mountain, river etc. so that gene flow stops in separate groups of population.
Evolution and Classification:
- The modern system of classification is based on evolutionary relationship also, they are called phylogenetic classification.
- When two species have similar characteristics then they are also closely related. This leads better to the fact that both must have same ancestor.
- These similarities among organisms allows us to group them together also helps in studying each group characteristics wholly.
- The kingdom appears as highest taxa, while the species appears as the lowest taxa.
- Heredity and evolution go hand in hand.
Evidence of Evolution:
Everyday archeologists find a new evidence that proves evolution has taken place on this earth. To make it easy for research as well as studies they have classified something:
Organs having common design but serve different functions in different animals. Homologous organ provides evidence for evolution as we identify wheather they are derived from the same ancestor.
Example: Forelimbs of all tetrapods i.e. forelimb of horse (running), wings of bat (flying), paw of cat (attack) etc.
Organs which have different design but serve a common function in different animals are said to be analogous organs.
Example: Wings of birds and wings of bat are examples of a pair of analogous organs.
The preserved remains of animals or plants or other organisms from past (min. 10,000 years) are called fossils. Fossils gives idea about many extinct animals and also give vision of how the evolution could have taken place.
Example: Ammonite: Fossil and Trilobite – invertebrate.
Evolution by stages:
Everything on this earth took time to evolve stage by stage from simple to complex.
Let’s understand the evolution of eyes:
- Planaria is the first animal which shows ‘eye’ like structure, but they can’t differentiate between two objects.
- Insect’s eyes are compound eyes which are made up of thousands of optical surfaces.
- In higher animals we see that they have simple eyes which are composed of a single lens, also most animals can’t differentiate between colours.
- Now come to human eyes, they are most advanced, easily we can identify colours and also have depth perception.
- The scientific name of modern human beings is Homo-sapiens.
- Scientists proved that Homo sapiens have evolved in Africa. They migrated from there towards north.
- After being a great diversity of humans on this earth but till today humans are single species.
- Excavation, time-dating, studying fossils, as well as determining DNA sequences are the tools that have been used for studying human evolution.
- People moved forwards and backwards, with groups sometimes separating from each other, sometimes coming back to mix with each other, even moving in and out of Africa.
- Thus heredity and evolution in human are in core study.