Q: 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:

The appearance of the recessive trait in F1 generation (dwarfism) confirms the presence of one recessive allele in the dominant parent and makes it heterozygous for plant height (Tt). Since all F1 generation has a violet flower, the dominant parent is homozygous for flower color. If the dominant parent was double heterozygous (TtWw), the F1 generation would exhibit recessive traits of both plant height and flower color. But all F1 generation exhibits violet flowers which confirm that the dominant parent is homozygous for flower color. Thus the correct answer is option C.

Question 1

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:

Accepted Answer

The appearance of the recessive trait in F1​ generation (dwarfism) confirms the presence of one recessive allele in the dominant parent and makes it heterozygous for plant height (Tt). Since all F1​ generation has a violet flower, the dominant parent is homozygous for flower color. If the dominant parent was double heterozygous (TtWw), the F1​ generation would exhibit recessive traits of both plant height and flower color. But all F1​ generation exhibits violet flowers which confirm that the dominant parent is homozygous for flower color. Thus the correct answer is option C.

Question 2

An example of homologous organs is:

Accepted Answer

Our arm and a dog's foreleg is the example of homologous organs.

Question 3

In evolutionary terms, we have more in common with:

Accepted Answer

In terms of evolution, organisms belonging to the same species have more in common than organisms belonging to different species of the same genus or different genus. We have more in common with a Chinese school-boy because both belongs to the same species of Homo sapiens, and thus, share a common ancestor.

Question 4

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 eye colour trait is dominant or recessive? Why or why not?

Accepted Answer

Unless we know the genotype of these variants of the trait, it is not possible to tell which is dominant or recessive. At least, three-generation are required to come to any conclusion about the genotype of a particular trait.

Question 5

How are the areas study of evolution and classification interlinked?

Accepted Answer

Organisms are classified into various groups on the basis of similarities and dissimilarities they share amongst each other. The more characteristics two species have in common, more closely they are related to each other. The closeness of two species indicates a common ancestor between them. Thus, classification of species is a reflection of their evolutionary relationship.

Question 6

Explain the terms analogous and homologous organs with examples.

Accepted Answer

The structures that share a similarity in terms of their morphology, genetics, anatomy, embryology, may or may not have similar function but have the same origin are called as homologous organs. For example, the forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar. The structures that look similar superficially and are dissimilar anatomically but does the similar functions are called as analogous structures. For example, the wings of birds and insects.

Question 7

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

Accepted Answer

Coat colour in dogs is governed by a variety of genes. At least 11 genes have been identified that influence the colour of coat in a dog. A dominant gene is a gene that is expressed in both homozygous as well as heterozygous conditions, whereas recessive gene is only expressed in homozygous condition.Let us consider, one parent is homozygous black (BB) and another parent is homozygous brown (bb). Cross between the two parent produces the offspring with the genetic make-up: Bb. Now we don't know whether Black is dominant or brown is dominant. By observing the off-springs produced are we can say which one is a dominant trait. If the F1​ generation comprisess of black we can say black is dominant and if it is brown then we can say brown is dominant.

Question 8

Explain the importance of fossils in deciding evolutionary relationships.

Accepted Answer

Fossils are the remains or impression preserved of prehistoric plant or animal embedded in rock. Fossils provide us with the knowledge of animals and plants that lived hundreds of years ago which are now extinct. It helps us to compare the animals that lived during prehistoric times with its present descendants. They provide the missing link in the study of evolution. They are helpful in providing information while forming a sequence of the organisms in the pathway of evolution.

Question 9

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

Accepted Answer

Miller-Urey experiment provided evidence for the origin of life from inanimate matter. In the experiment, they created an atmosphere containing molecules like ammonia, methane and hydrogen sulphide, but no oxygen. This atmosphere was similar to the atmosphere present during the primitive Earth. Temperature was maintained constant at 100oC and sparks were passed through the mixture to stimulate lightning. After a particular time, certain amount of the carbon from methane had been converted to simple compounds of carbon like amino acids. Amino acids are the precursors of the proteins and proteins are the molecules that support the life in basic form.

Question 10

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?

Accepted Answer

Sexual reproduction results from the fusion of gametes produced by male and female. Sexual reproduction causes more viable variations because:i) There might be an error in the copying of DNA, though the event is rare.ii)Segregation of chromosome of maternal and paternal origin at the time of gamete formation is random.iii) There is an exchange of genetic material between homologous chromosomes during formation of gametes.In case of asexual reproduction, variation is significantly less since only a single parent is involved. Very small changes occur due to inaccuracies during DNA copying that pass on to the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually reproducing organisms.

Question 11

How is the equal genetic contribution of male and female parents ensured in the progeny?

Accepted Answer

Genetic material in most organisms is present in pairs of chromosomes. Gametes in the sexually reproducing organisms are formed by the process of meiosis during which half of the genetic material goes into each gamete. When the gametes from male and female parents fuse with each other during sexual reproduction, the normal complement is restored. Half of the genetic material comes from the female and half from the male.

Question 12

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

Accepted Answer

It is agreeable that only variations that confer an advantage to an individual organism will survive in a population. All variation does not necessarily provide an equal chance of survival to an organism in the environment. Survival chances highly depend on the nature of variations. For example- variation leading to the increase of heat-resistant bacteria is beneficial to the bacteria for its survival when it finds itself in a condition where suddenly there is an increase in the temperature of its habitat above the optimum temperature required for survival.

Question 13

The result of a dihybrid cross between two individuals is recorded as :Choose the correct option for A, B, C and D :

Accepted Answer

The dihybrid cross between round green plant and wrinkled yellow plant is shown as :

Question 14

Can the wing of butterfly and the wing of a bat be considered homologous organs? Why or why not?

Accepted Answer

No, though the function of wing in both the cases is same but their structural plan and origin is different.

Question 15

In a monohybrid cross between tall pea plants denoted by TT and short pea plants denoted by tt, Preeti obtained only tall plants denoted by Tt in the F1 generation. However, in F2 generation she obtained both tall and short plants. Using the above information explain the law of dominance.

Accepted Answer

GivenBy this information, it is clear that in F1, when the genotype of tall plant Tt, they appear tall. This clearly means that when both the genes are present the effect is that of only ' T ', which is dominant. The recessive gene is unable to express itself in presence of a dominant gene. According of Law of Dominance, a single copy of dominant trait is enough for its expression.

Question 16

Explain the importance of fossils in deciding evolutionary relationships.

Accepted Answer

Study of fossils helps us to know as to how characters/features have evolved in different groups of organisms. We also can find out which organism evolved earlier.

Question 17

Why are triats acquired during the life-time of an individual not inherited?

Accepted Answer

Any change in non-reproductive tissues cannot be passed on to the DNA of the germ-cells. Therefore, the traits acquired during life-time of an individual are not inherited.

Question 18

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 eye colour trait is dominant or recessive? Why or why not?

Accepted Answer

On the basis of population study whicever trait is more prevalent is the dominant one. In this case, the study says that light eye coloured children have light eyed parents. This clearly shows that it is a recessive trait so that both parents give the recessive gene for the child also to be homozygous recessive.

Question 19

How do Mendel's experiments show that traits are inherited independently?

Accepted Answer

When a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in F1 all the plants have round yellow seeds. However, in F2 generation all the traits appear independently.Result:Round Yellow =9Round Green =3Wrinkled yellow =3Wrinkled Green =1.

Question 20

(a) Why do we say that homozygous plants produce pure progeny?(b) Define heterozygous.(c) Explain how the process of speciation takes place.

Accepted Answer

(a) Homozygous plants, whether for dominant or recessive trait have both identical genes for that trait. Thus, they always produce similar gametes resulting in pure breeding plants.(b) When the two chromosomes in the homologous pair are different i.e., one is dominant and other recessive, such a pair is said to heterozygous.(c) Let us study the example of beetles. Let the original beetle population be red. if due to variation a agreen beetle was produced it would have survival advantage over red beetle. Thus, green beetles would be naturally selected, and will grow in number.If few of these green beetles move to some other area, adapt to changed environment and after few generations, would vary greatly from the original population of red beetles. These two populations may not be able to interbreed due to accumulation of variation.Thus, due to Natural Selection and Genetic Drift, a new species of beetles is formed.

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