8th Class Science Human Reproduction Heredity and Evolution

       Heredity and Evolution

Heredity is the transmission of the characters of the parents to their offspring from one generation to the next. The characteristics include physical, physiological and psychological behavior of the organisms. Gregore Mendel carry out his experiment with the pea plant, as they show many contrasting traits, that were easy to track through the generations. In his first experiment, he considered only one trait, such as, height, colour, shape of the seed, etc. This is known as monohybrid. According to him, the genotype is made of certain structure, which controls the inheritance of all traits. The different expression of the gene is called alleles, in which each trait is represented by a letters. According to law of inheritance, all the traits have separate entities by themselves, which are controlled by the genes. The genetic material is a nucleoprotein called chromatin. It is made up of DNA and protein.

             Variation

It is defined as the difference among individuals of the species. There are two types of variations, such as, somatic and non-inheritable. Variation helps the organisms to adapt to the changing conditions. The different theories of evolutions are:

            Organic Evolution

Evolution is regarded as the gradual development of more complex species from the pre-existing simpler species. This takes place over the millions of years, which is clear from the evidences of fossils. According to the theory of organic evolutions, continuous use of an organ results in well developed organs and less used or unused organ over a long period of time will result in disintegration of the organ. For example, the giraffes were forced to extend their neck, and stretch their legs to reach higher vegetations. There are many evidences of evolutions; study of fossils of plants and animals helps us to understand the theory of evolutions. The geological distribution of organisms on the earth is also an important part of study. The embryological study of the organisms also helps to study the evolution theory.

         Heredity is the transmission of character from one generation to the next. The genotype is made of certain structure, which controls the inheritance of all traits. The different expression of the gene is called:

(a) Genotype

(b) Alleles     

(c) Phenotypes

(d) Inheritance

(e) None of these

Answer: (b)

       Variation is defined as the difference in the organisms, which arises from one generation to the next. The variation which arises in the organism is either due to the genetic mapping or due to the external conditions. The traits, which the organisms develop due to the external conditions are called:

(a) Inherited traits

(b) Desired traits

(c) Acquired traits

(d) Mixed traits

(e) None of these

Answer: (c)

• During the entire life time, a female oyster produces 100 million young ones and a hen lays 19 dozen eggs in a year.
• A disease called cirrhosis is more prominent in men without hair on his chest.
• The number of bacteria on each feet of human is about one trillion.
• The amount of heat given of by our body in thirty minutes can boil half a gallon of water.
• The teeth in human starts growing six month before the baby are born.

• Reproduction enables the organisms to live generation aftergeneration. It is normally of two types; sexual and asexual. Asexual reproduction does not involve male and female organisms, while the sexual reproduction involves both the male and female. The offspring formed in asexual reproduction are normally identical, and are referred as clones. Unicellular organisms reproduce by asexual method.
• Sexual method involves the formation of gametes. It is a very complex process and takes longer time. Organisms may be bisexual in which both male and female sex organ are present. Plants can also reproduce by sexual method. Both male and female sex organ may present in the same plant or may present on different plant. The transfer of pollen is of two types: self pollination or cross pollination. In flowering plants, after fertilization, ovary develops into fruit and ovules mature into seeds. Inside the mature seeds is the progenitor of the next generation, called the embryo..