Lesson: Heredity and Evolution
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Trait B is likely to have arisen earlier because it is present in a higher percentage of the population.
How does the creation of variations in a species promote survival?
Variations in a species take place in response to the changes in the environment. This enables a species to cope with new changes. Depending on the nature of variations, different individuals would have different kinds of advantages. For example, bacterial variants that can withstand heat have better chances to survive a heat wave than the non-variant bacteria. Thus, variations in a population of a species help in survival of a species.
How do Mendel’s experiments show that traits may be dominant or recessive?
During monohybrid cross by conducted by Mendel, one trait did not appear in the F1 generation. However, it appeared in the F2 generation obtained by self-fertilization of the F1 generation.
From his experiment, he concluded:
a) The trait which appeared in all the members of F1 generation and in 75% members of the F2 generation was a dominant trait.
b) The trait which did not appear in F1 generation but reappeared in 25% of F2 generation was a recessive trait.
How do Mendel’s experiments show that traits are inherited independently?
During dihybrid cross, Mendel crossed the pure-bred tall plants having round seeds with pure bred short plants having wrinkled seeds. It was observed that all the F1 generation plants were tall with round seeds. This indicated that the traits of tallness and round seeds were dominant.
Later, the self-breeding of F1 generation seeds yielded F2 generation. The F2 generation plants had characteristics of tall with round seeds (9 plants), tall with wrinkled seeds (3 plants), short with round seeds (3 plants) and short with wrinkled seeds (1 plant). The tall wrinkled seeded and short round seeds were the new combinations. This could develop only when the traits were inherited independently. Thus, Mendel was able to propose the law of independent assortment which explains independent inheritance of traits.
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits blood group A or O is dominant? Why or why not?
No. This information is not sufficient to determine which of the traits is dominant or recessive. We need data of at least three generations whereas the given data is about two generations.
How is the sex of the child determined in human beings?
The sex of a new-born in human is genetically determined i.e., genes inherited from parents decide whether the new born will be a boy or a girl. If a sperm with X chromosome fertilizes the egg, it results in the development of a girl child. Whereas, if a sperm with Y chromosome fertilizes the egg, it results in the development of a male child.
What are the different ways in which individuals with a particular trait may increase in a population?
Individuals with a particular trait may increase in a population:
· When a trait is acquired during the individual's lifetime
· When some genes governing the trait become common in a population
· When the trait offers some survival advantage
Why are the traits acquired during an individual’s lifetime, not inherited?
Acquired traits do not bring any change in the genotype of an individual. Therefore, these traits are not inherited.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Variations are essential to the survival of a species. The small number of surviving tigers does not allow many variations to occur. A deadly disease or any calamity may cause death of all the tigers. Hence, a small number of surviving tigers is a cause of worry.
What factors could lead to the rise of a new species?
Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
In self-pollinating plant species, pollens are transferred from the anther of one flower to the stigma of the same flower or another flower of the same plant.
So, geographical segregation cannot be a major factor in speciation. However, there are chances of some environmental changes that can lead to some variations.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
No. Asexually reproducing organisms pass on the parent DNA to offspring that leaves no chance of speciation. Hence, geographical isolation does not affect much in asexually reproducing organisms. However, geographical isolation may work as a major factor in cross-pollinated species.
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
A few ancient reptiles such as dinosaurs had feathers. However, they could not fly with those feathers. The feathers were used only to provide insulation in cold weather. Later, birds adapted the feathers for flight. This means that birds are very closely related to reptiles, as dinosaurs were reptile.
Can wings of a butterfly and wings of a bat be considered homologous organs? Why or why not?
Wings of bats are skin folds stretched mainly between elongated fingers. The wings of birds are a feathery covering all along the arm. Wing of a butterfly and the wings of a bat are similar in function. They help them in flying. Since they perform similar function and have different origins, they are analogous organs.
What are fossils? What do they tell us about the process of evolution?
The remains of organisms that once existed on earth are called fossils. They tell us about the development of simple structured organisms to complex structured organisms. They also give insights into how evolution could have taken place in an organism to sustain themselves in a competitive environment.
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?
A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. In spite of wide differences in size, colour and looks, human beings can interbreed. Hence, all of them are considered as one species.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Evolution cannot always be equated with progress or better body designs. It does not mean that simple body designs are inefficient. When we take complexity as a criterion, the chimpanzee is better than other given organisms. On the other hand, if we take the ability of survival in almost all kinds of habitat as a criterion, bacteria, having a simple body design, are still the most cosmopolitan organisms found on earth.
Therefore, bacteria, spiders, fish and chimpanzees are all different branches of evolution.