Question

notes for chapter heredity and evolution

Answer 1

Heredity and Evolution

Heredity: The passing of traits from the parents to offspring is called heredity. This is heredity which is responsible for many commonly observable facts; like siblings looking similar in overall appearance.

Genotype: The complete set of genes in an organism’s genome is called genotype.

Phenotype: The observable characters in an organism make the phenotype. Phenotype is a result of genotype’s interaction with the environment. Due to this reason, many phenotypes are not inheritable.

Acquired Traits: Traits; which are acquired due to interaction with the environment; are called acquired traits. Acquired traits are not inheritable. For example; if a boxer develops bulging biceps, it does not mean that his son would be borne with bulging biceps.

Inheritable Traits: Traits; which can be expressed in subsequent generations; are called inheritable traits. Such traits bring a change in the genotype of the organism and hence become inheritable.

Accumulation of Variations During Reproduction:

Asexual reproduction involves a single parent and is hence not ideal ideal for facilitating variations. Some minor variations do occur due to inaccuracies in DNA replication. But the quantum of variations would be too little and would take too many years to show effect.

Sexual reproduction, on the other hand, is ideal for facilitating variations because two parents are involved in it. The offspring’s genotype is contributed by two parents and hence chances of variations are very high.

Rules of Inheritance

Gregor Johann Mendel conducted experiments on pea plants and proposed the rules of inheritance; based on his observations. Mendel observed that characters are often present in pairs. A pair of contrasting characters is called allele.

Possible Reasons of Pea Plants Used by Mendel:

Pea can be termed as biennial plant, i.e. two generations of a pea plant can grow in a given year. This means that Mendel could get enough time to observe a larger number of generations.Many easily identifiable and contrasting characters are present in pea plants.Cross pollination can be easily induced in pea plants.

Monohybrid Cross: The cross in which just two contrasting characters are studied is called monohybrid cross. Mendel did monohybrid cross for his first experiment. He selected a pair of contrasting characters for that experiment.

Let us take the example of cross between tall plants and short plants. The figure; given here shows the results of this experiment.

TT represents the genotype of tall plant and tt represents the genotype of short plants. In the F2 generation, all plants were tall but their genotype was Tt; which means they were not pure tall plants. This could be established by the appearance of the character of shortness in the F2 generation; in which most of the plants were tall and some of the plants were short. This experiment showed that the character of shortness of recessive in F1 generation and hence could not be observed. The ratio of number of tall plants to that of short plants in F2 generation was 3 : 1.

Answer 2

hey there..
here is a link hope it helps u


http://www.dronstudy.com/book/heredity-and-evolution-chapter-notes/