CHAPTER 9.
HEREDITY AND EVOLUTION
PAGE No: 143
1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exist in 60% of the same population. Which trait is likely to arisen earlier ?
The trait B is likely to be arisen earlier.The population of trait B is much greater than the population of A.
Trait A is a new trait which only spread to only 10% of the population by reproduction.
2. How does the creations of variations in a species promote survival?
Sexual reproduction give rise to subtle variations in new individuals. Hence different variant emerges in the species. The variant which are suitable to the environment will survive and the others will perish.
If the environment in which the organism lives get drastically altered, the organisms cannot survive .But if there are some variants which can survive in the changed environment, these organism would reproduce and continue the species
Example : The bacteria living in water would die due to increase in temperature because of global warming. But the variants which can resist high temperature would survive.
If the environment in which the organism lives get drastically altered, the organisms cannot survive .But if there are some variants which can survive in the changed environment, these organism would reproduce and continue the species
Example : The bacteria living in water would die due to increase in temperature because of global warming. But the variants which can resist high temperature would survive.
PAGE No: 147
1. How do Mendel's experiments show that traits may be dominant or recessive?
In the F2 generationThe traits which are present in 75% of the individuals are dominant and the traits which are present in 25% of the individuals are dominant
2. How do Mendel's experiments show that traits are inherited independently?
Mental crossed contrast characters of two traits of pea plants. The F1 progeny showed only the dominant characters. But in the F2 progeny the traits from the parents as well as new traits where shown. This shows that the traits are inherited independently
This happens during the gamete formation where the genes separates independently
3. A man with blood group A marries a woman with blood group O and there daughter has a blood group O. Is this information enough to tell you which of the traits blood group A or blood group O is dominant? Why or whynot?
From the information given we cannot conclude whether the blood group A or blood group O is dominant.
Either can be possible because each individual carries two factors. Recessive charactor will only appear when the two traits are similar. Here two cases arrise
Case 1
Blood group A is dominant and blood group O is recessive
Here father is AA or AO and mother is OO
When A is considered to be dominant over O , the combinations such as AO, OO,AO, AO,AO,AO,AO and OO
Since two of the combinations are OO, the daughter can have blood group O
Case 2
Blood group O is dominant and blood group A is recessive
Here father is AA and mother is OA or OO
When O is considered to be dominant over A , the combinations such as OA,OA,OA,AA,OA,OA,OA and AA
Since six of the combinations are OA, the daughter can have blood group O
Either can be possible because each individual carries two factors. Recessive charactor will only appear when the two traits are similar. Here two cases arrise
Case 1
Blood group A is dominant and blood group O is recessive
Here father is AA or AO and mother is OO
When A is considered to be dominant over O , the combinations such as AO, OO,AO, AO,AO,AO,AO and OO
Since two of the combinations are OO, the daughter can have blood group O
Case 2
Blood group O is dominant and blood group A is recessive
Here father is AA and mother is OA or OO
When O is considered to be dominant over A , the combinations such as OA,OA,OA,AA,OA,OA,OA and AA
Since six of the combinations are OA, the daughter can have blood group O
4. How is the sex of the child determined in human beings?
In human beings 23 pairs of chromosome are present. Out of that 22 pairs are the characters of the parents other than sex chromosome The 23rd pair is called the sex chromosome.
Woman have XX chromosome as sex chromosome and it is perfectly matched.
Men have XY chromosome as sex chromosome , and it is mismatched as Y chromosome is shorter than X chromosome .
All the children inherit from there mother regardless of whether they are boys or girls. This means that the sex of the child will be determined from what they inherit from there father.
A child who inherits a X chromosome from the father will be a girl and the child who inherits a Y chromosome from the father will be a boy.
Woman have XX chromosome as sex chromosome and it is perfectly matched.
Men have XY chromosome as sex chromosome , and it is mismatched as Y chromosome is shorter than X chromosome .
All the children inherit from there mother regardless of whether they are boys or girls. This means that the sex of the child will be determined from what they inherit from there father.
A child who inherits a X chromosome from the father will be a girl and the child who inherits a Y chromosome from the father will be a boy.
PAGE No: 150
1. What are the different ways in which individuals with a particular trait may increase in a population ?
When a variation occurs and it results in the better survival of the organism in a existing environment. These traits will be selected naturally. Hence more individuals with that particular trait will increase in a population.2. Why are traits acquired during the life time of an individual not inherited?
The traits acquired during the life time is known as acquired characters.
These characters are not inherited because these affects the somatic cells and not the germ cells .Hence the change in character cannot be passed to next generation. Thus the acquired characters would die with the death of the person
Example : The scar that a soldier gets in a battle field
These characters are not inherited because these affects the somatic cells and not the germ cells .Hence the change in character cannot be passed to next generation. Thus the acquired characters would die with the death of the person
Example : The scar that a soldier gets in a battle field
3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
If some natural calamity occurs , since they are limited in numbers they would get killed and extinct.
Moreover since there are less numbers, they breed among themselves and there is less chances for variations.
If a deadly disease affect the tiger all the tigers may die as there would be less variation in the genotype to survive the disease
Moreover since there are less numbers, they breed among themselves and there is less chances for variations.
If a deadly disease affect the tiger all the tigers may die as there would be less variation in the genotype to survive the disease
PAGE No: 151
1. What factors could lead to the rise of a new species ?
The factors which affects the rise of new species are1. Genetic Variation
2. Natural selection
3. Reproductive isolation.
4. Speciation
2. Will geographical isolation be a major factor in the speciation of a self pollinating plant species? Why or why not?
No.
As the plant is self pollinating it would be less affected by geographical isolation.
In contrast in a cross pollinated species,geographical isolation is a major factor which would result in the accumulation of variations.
As the plant is self pollinating it would be less affected by geographical isolation.
In contrast in a cross pollinated species,geographical isolation is a major factor which would result in the accumulation of variations.
3. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
No.
Asexually reproducing organism have very little variations over generations. The change resulting from geological isolation would not be passed to the next generation.
Asexually reproducing organism have very little variations over generations. The change resulting from geological isolation would not be passed to the next generation.
PAGE No: 156
1. Give an example of characteristics being used to determine how close two species are in evolutionary terms ?
Structure of fore limb of animals such as frog, lizard, bird and humans are homologous . That is they all have same structure in order to do different functions. From this we can assume that they all have a common ancestor2. Can the wing of a butterfly and the wing of a bat be considered a homologous organs? Why or why not?
No.
The wing of a butterfly and the wing of a bat are used for the same function , that is flying.
But the structures of there wings are very different.
Hence they are not considered as homologous organs but as analogous organs
The wing of a butterfly and the wing of a bat are used for the same function , that is flying.
But the structures of there wings are very different.
Hence they are not considered as homologous organs but as analogous organs
3. What are fossils ? What do they tell us about the process of evolution?
PAGE No: 158
1. Why are human beings who look so different from each other in terms of size , colour and looks said to belong to the same species?
2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a better body design ? Why or why not?
PAGE No: 159
EXERCISES
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
2. An example of homologous organs is
3. In evalutionary terms , we have more in common with
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?
5. How are the areas of study - evolution and classification- interlinked?
6. Explain the terms analogous and homologous organs with examples
7. Outline a project which aims to find the dominant coat colour in dogs.
8. Explain the impotence of fossils in deciding evolutionary relationships
9. What evidence do we have for the origin of life from inanimate matter?
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?
11. How is the equal genetic contribution of male and female parents ensured in the progeny?
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?
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?
11. How is the equal genetic contribution of male and female parents ensured in the progeny?
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?
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