CBSE Class 10 Science Heredity and Evolution Worksheet

Question. What is the functional unit of heredity?
Answer : Gene

Question. When a black guinea pig is crossed with a white guinea pig, what coloured guinea pigs are obtained in F1 generation if black colour is dominant over white?
Answer : Guinea pigs of black colour will be obtained in F1 generation.

Question. Give any two examples where sex determination is regulated by environmental factors ?
Answer : In turtles and lizards sex determination is regulated by environmental factor temperature. In turtle high incubation temperature leads to development of female offsprings. In lizards high incubation temperature leads to development of male offsprings.

Question. In a cross between round yellow seeds (RRYY) and wrinkled green seeds (rryy) of pea plant, what is the ratio of plants obtained in F2 generation?
Answer : The ratio of plants obtained in F2 generation is 9: 3: 3: 1.

Question. In turtle, high incubation temperature leads to the development of female offspring. On the other hand in lizards, high incubation temperature leads to the development of male offspring. What determines the sex of the offspring in these examples?
Answer : In the examples given in the question sex of the offspring is determined by environmental factors.

Question. If Y bearing sperm fuses with the egg what will be the sex of the child? Also state the chromosomal constitution.
Answer : If Y bearing sperm fuses with the egg then a male child results with chromosomal constitution of 44 autosomes and one X and one Y chromosome.

Question. How many X chromosomes can be found in the cells of the body of (i) a boy, and (ii) a girl.
Answer : Females have two X chromosomes, while males have one X and one Y chromosome.

Question. If a X bearing sperm fuses with an egg, what will be the sex of the individual developing from the zygote?
Answer : When X bearing sperm fuses with the egg, a female child results with 44 autosomes, and two X chromosomes.

Question. How do the variations in a species promote survival?
Answer : Variations increases the adaptability of an individual to its changing environment thus promotes survival of the species.

Question. A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plant bearing white flowers. What will be the result in F1 progeny?
Answer : All the progeny of F1 generation will have violet flowers because violet colour is dominant over the recessive white colour.

Question. What is speciation? How does it occur?
Answer : Formation of new species from the existing ones over the period of time is called speciation.
Speciation takes place due to gene flow, genetic drift, reproductive isolation and finally natural selection.

Question. Define Genetics. What did Mendel’s contribution to genetics?
Answer : The science of heredity and variation is called Genetics.
Mendel conducted breeding experiments in a plant called garden pea (pisum sativum) with contrasting pair of characters, found that only one character of the pairs appeared in the first generation but both the characters appeared in the subsequent generation.
On the basis of these results of his experiments he put forth the various principals of inheritance. He also suggested that each character is controlled by a pair of factors which are now called as genes.

Question. Define variation in relation to a species: Why is variation beneficial is the species.
Answer : Variations are differences that occur between the organisms of the same species in spite of the same basic features.
Variation in species promotes survival of an organism in changing environment by increasing the adaptability.

Question. Describe briefly four ways in which individual with a particular trait may increase in population. 
Answer : Four ways in which individual with a particular trait may increase in population are:
(a) Variations that occur in species helps in the survival of individuals.
(b) Organisms when show genetic drift which cope them to survive in the given environment.
(c) Adaptation and natural selection.
(d) Sexual reproduction results in variation.

Question. What are fossils? What do they tell about the process of evolution? 
Answer : Fossils are preserved traces or remains of living organism of geological past. Fossils help to trace the racial history of organisms. Fossils found closer to the surface are more recent than fossils found in the deepest layers.

Question. Clones of sheep are carbon copy of each other except physical health. What kind of variation is it? 
Answer : Phenotypic variation

Question. What will be the sex of a baby if sperm carrying X chromosome fertilizes egg in human beings. Why? 
Answer : It will be a baby girl because fusion of gametes having X chromosomes leads to homozygous condition producing zygote with XX composition.

Question. Feather imprints were preserved along the dinosaur’s bones but dinosaurs could not fly. What was the significance of feathers in reptiles and later on for other species?
Answer : It is believed that feathers in dinosaurs might have provided insulation in cold weather but later on became useful for flights in birds.

Question. Wild cabbage was converted into number of variants like cauliflower, broccoli and cabbage by man. What is this process known as? Does it play an important role in organic evolution? 3 Marks
Answer : This process is known as artificial selection. It plays an important role in organic evolution because it is parallel to natural selection. It helps to produce new species having useful traits in less time.

Question. How are variant genotypes produced? 
Answer : Variant genotypes can be produced by:-
1. Mutation in genes and chromosomes.
2. Recombination of genes.
3. Hybridization of genes.

Question. Can geographical isolation lead to speciation? How? 
Answer : Yes, geographical isolation can lead to speciation. Due to geographical isolation, the members of two sub groups may not be able to interbreed as a result of genetic drift. Natural selection also operates differently in these subgroups. This leads to speciation.

Question. What will be the blood groups of offspring’s produced by the parents having following genotype?
Male - I^AI^B
Female -I^OI^A
Answer :

Blood groups will be:
(i) A
(ii) A
(iii) B
(iv) AB

Question. A woman with blonde curly hair married a man with black soft hair. All of their children in first generation had black soft hair but in next generation children had different combinations in the ratio of 9:3:3:1. State the law that governs this expression.
Answer : Law of independent assortment which states that the factors of different pairs of contrasting characters do not influence each other. They are independent of one another in their assortment.