HEREDITY AND EVOLUTION
One Marks Questions
Answer: The transmission of characteristics from one generation to another is knows as heredity.
Answer: Cellular DNA is the information source for making proteins in the cells.
Answer:
i) Genetics is the study of mechanism by which variations are created and inherited.
ii) Evolution is used for studying the development of new type of organisms from the existing ones.
Answer: No two individuals are absolutely alike in a population because variations arises due to DNA copying.
Answer: Comparing the DNA of different species gives a direct estimate of how much the DNA has changed during the information of these species .Thus it helps us to a great extent in tracing the evolutionary pathways.
Answer: Genes carry information for producing proteins, which in turn control the various body characteristics.
Answer: Black
Two Marks Questions
Answer:
Characteristics are details of appearance of behavior, in other words , a particular form or a particular function. Presence of four limbs in humans is an example of characteristics.
Answer:
Genes are located on chromosomes in linear sequence and at fixed positions.
Chemically genes are made up of nucleic acids which constitute DNA.
Answer:
The genes controlling a particular trait separate from each other during gamete formation . Hence gamete is always pure is far as contrasting characters are considered and will possess only one gene set.
Answer: In asexually reproducing organisms . there is no mixing of genes of two different individual since only one partner is involved. There are very minor variations generated in such organisms due to small inaccuracies in DNA copying.
Answer:
Male individual have 46 chromosomes but because the gametes are always are always haploid i.e they have half the number of chromosomes sperms will be haploid (23 chromosomes) Female individual also contains only 23 chromosomes in egg . it is the fusion of the sperm and egg which leads to an offsprings with 46 chromosomes.
| F1 generations | F2 generations |
|---|---|
| F1 generations refers to the offspring resulting immediately from a cross between the first set of parents. | F2 generations on the other hand , refers to the offspring resulting from among the members of F1 generation. |
| The nucleus first divides automatically into two, followed by the division of the cytoplasm | The nucleus of the cell divides repeatedly producing many nuclei. |
Answer:
In crossing if two or more traits are involved , their genes assort independently, irrespective of the combinations present in the parents.
So, new combinations of genes appear in the offsprings leading to new traits .
Answer: The experiences of an individual may only affect the somatic cells, but will not changes the DNA the germ cells.
Three Marks Questions
Answer:
(i) When a cross was made between a tall pea plant with round seeds and a short pea plant with wrinkled seeds, the F1 progeny plants are all tall with round seeds. This indicates that tallness and round seeds are the dominant traits.
(ii) When the F1 plants are self pollinated, the F2 progeny consisted of some tall plants with round seeds and some short plants with wrinkled seeds which are the parental traits.
(iii) There were also some new combinations like tall plants with wrinkled seeds and short plants with round seeds.
(iv) Thus it may be concluded that tall and short traits and round and wrinkled seed traits have been inherited independently.
Answer:
i)The structure of DNA molecule resembles a spirally twisted ladder.
(ii) Each strand of ladder is made up to pentose sugar and phosphate arranged alternatively.
(iii) There are two types of nitrogenous bases namely purines and pyrimidines.
Answer:
(i)Genetics is the branch of biology that deals with the study of heredity and variations.
(ii)Gregor Johann Mendel/ garden pea.
(iii) Garden pea plants were easily available / they grow in one season/ fertilization was easy.
Answer:
Such traits are called acquired traits. Acquired traits are experienced by an individual during his lifetime. These traits involve changes in non reproductive cells (somatic cells) which are not transferred to germ cells. So, these traits cannot be passed on to the next generation. For example: Learning skills like swimming, dancing, cooking, body building, etc are acquired traits and cannot be passed on to the next generation.
Answer:
Mendel conducted breeding experiments with garden peas:
(i) He studied (pure) plants of a tall/short varieties.
(ii) He crossed them and obtained F1 progeny.
(ili) He found that F1 progeny was all tali plants.
(iv) Heselfed the (hybrid) plants of F1 progeny.
(v) He found that in F2progeny there were tall as well as short plants.
(vi) The three quarter plants were tall and one quarter was short.
Four Marks Questions
| Dominant Trait | Recessive trait |
|---|---|
| The trait which appears in the F1 progeny is dominant | The trait which remains hidden or which does not appear in the F1 progeny in the recessive trait |
| It appears in more numbers. | It appears in less numbers. |
Answer:
. (a) Reasons
(i) Pea plant is small and easy to grow.
(ii) A large number of true breeding varieties of pea plant are available.
(iii) Short life cycle.
(iv) Both self and cross pollination can be made possible. (Any two reasons)
(b) Contrasting characters:
Round/Wrinkled seeds
Tall/Short plants
White/purple flowers
Green/yellow seeds
(c) When Mendel crossed two pea plants with a pair of contrasting characters only one character appeared in all the members of F1 progeny, the others remain hidden.
On selfing F1, the hidden characters reappeared in just 259% of the offsprings and the other 75% shared the characters expressed in F1.
Mendel concluded that the character which expresses itself in F1 and in 75% of the individuals of F2, is dominating while the other is recessive.
Answer:
(i) Mendel conducted experiment on garden peaplant selecting seven visible contrasting characters.He selected and crossed homozygous tall pea planthaving the genotype TT with a homozygous dwarfpea plant having the genotype tt. F generationconsists only of tall plants having genotype Tt.
The expressed allele T for tallness is dominantover the unexpressed allele t for dwarfness. Hencethe trait of tallness is dominant while dwarfnessor shortness is the recessive characteristics. Thus,Mendel's experiment showed that traits may bedominant or recessive.
(ii) Mendel performed an experiment in which hetook two different traits like tall and dwarf plantand round and wrinkled seeds. In F2 (second)generation, some plants were tall with round seedsand some were dwarf with wrinkled seeds. Therewould also be dwarf plants having round seeds. Thus, the tal/short traits and round/wrinkled seedtraits are independently inherited.
Answer:
(i) Traits: A characteristic feature is called trait.
(ii) Inherited Traits are the traits which are transferredfrom parents to young ones.
Acquired Traits are the traits which an organism acquires in life time.
(iii) Formation of new species from the existing ones iscalled speciation.
Factors which could lead to the rise of new speciesare geographical isolation, genetic drift, tt natural selection.
Answer:
(i) This is to show that each trait is influenced byboth paternal and maternal DNA.
(ii) No.
This is because all the F progeny plants showthe genetic makeup Pp, which results in purple flowers.
(iii) Dominant trait is a genetic trait that is expressed ina person who has only one copy of that gene. Recessive trait is a genetic trait that is expressedonly when two copies of the gene are present
(ii) Variations in individuals during sexual reproductiongives survival advantages to them, and help them toadapt even in extreme environments.
