Lesson: Heredity and Evolution

A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as:

(a) TTWW

(b) TTww

(c) TtWW

(d) TtWw

(c)

An example of homologous organs is:

(a) Our arm and a dog’s fore-leg

(b) Our teeth and an elephant’s tusks

(c) Potato and runners of grass

(d) All of the above

(b)

In evolutionary terms, we have more in common with:

(a) A Chinese school-boy

(b) A chimpanzee

(c) A spider

(d) A bacterium

(a)

A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light-coloured eye trait is dominant or recessive? Why or why not?

This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. But the study gives the data of only two generations.

How are the areas of study $—$ evolution and classification $—$ interlinked?

Classification is based on similarities and differences amongst organisms.

Two species are more closely related if they have more characteristics in common. It means that they have a more recent ancestor. With subsequent generations, variations make organisms more different than their ancestors.

This proves that we classify organisms according to their resemblance, which is similar to creating an evolutionary tree.

Also, the modern system of classification is otherwise called phylogenetic classification. This means it is based on evolutionary relationships. Hence, evolution and classification are closely related.

Explain the terms analogous and homologous organs with examples.

Homologous organs are the organs that have same basic structural design and origin but have different functions.

Example: The forelimbs of humans and the wings of birds

Analogous organs are the organs which have different basic structural design and origin but have similar functions.

Example: The wings of birds and insects.

Outline a project that aims to find a dominant coat colour in dogs.

Dogs have a variety of genes that govern coat colour. A dog inherits one gene from each of his/her parents and the dominant gene gets expressed in the phenotype. Let us take one parent with black coat (B) and the other parent with brown coat (b).

Situation 1: Crossing to get the F1 generation.

In F1 generation, all the offspring’s will be heterozygous (Bb). Since black (B) is dominant, all the offspring’s will be black. However, they will have both B and b alleles.

Situation 2: Crossing the heterozygous pups to get the F2 generation.

The F2 generation will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offspring’s.

Explain the importance of fossils in deciding evolutionary relationships.

Fossils are preserved traces of living organisms.

Important features of fossils:

(a) Fossils help in determining the sequence of appearance of a particular character in a particular group of species.

(b) Fossils help in establishing evolutionary traits among organisms and their ancestors.

(c) Fossils help in establishing the time period in which a particular species lived.

What evidence do we have for the origin of life from inanimate matter?  

An experiment done by Miller and Urey established that life originated from inanimate matter. In their experiment, they replicated conditions which may have existed during the early years of the origin of Earth. In that experiment, inorganic substances gave rise to amino acids. As we know, amino acids make up protein molecules and support life in its basic form. Therefore, it adequately suggests that life originated from inanimate matter.

Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

During sexual reproduction, genotype of a progeny is contributed by two different individuals. This results in various permutations and combinations.

Whereas in case of asexual reproduction, only very small variations pass on to the progeny. This is mainly due to inaccuracies in DNA copying.

Thus, offspring of asexual reproduction are more or less genetically similar to their parents. Therefore, there are more chances of variations during sexual reproduction than during asexual reproduction. Due to this reason, the evolution in sexually reproducing organisms proceeds at a faster pace than in asexually reproducing organisms.

How is equal genetic contribution of male and female parents during fertilisation of a progeny?

Human female has two X sex chromosomes and male has one X and one Y sex chromosome. During fertilization, the male gamete (haploid) fuses with the female gamete (haploid). This results in formation of the diploid zygote. The zygote gets 50% of genes from each parent. Thus, equal genetic contribution is ensured from the male and female parents during fertilization.

Only those variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not? 

Yes. We agree with the statement. All variations do not have an equal chance of surviving in the environment. The chances of surviving depend on the nature of variations. There are many variations which help an individual to survive. But there are certain variations which may not be beneficial, yet they are inherited through subsequent generations.

For example, the colourful plumage of peacock helps a peacock in finding a suitable mate but it is also eye-catching for its predators.