Solutions of Heredity and Evolution Lakhmir Singh Manjit Kaur HOTS, VSAQ, and SAQ Pg No. 195 Class 10 Biology
66. In humans, if gene B gives brown eyes and gene b gives blue eyes. What will be the color of eyes of the persons having the following combination of genes?
(a) Bb (b) bb (c) BB
Answer
→ (a)Bb-Brown eyes.(B is dominant which gives brown eyes)
(b)bb-Blue eyes.(b is recessive which gives blue eyes and none dominant gene present)
(c)BB-Brown eyes.(B is dominant which gives brown eyes)
67. Pure-bred pea plants A are crossed with pure-bred pea plants B. It is found that the plants which look like A do not appear in F1 generation but re-emerge in F2 generation. Which of the plants A and B are : (i) tall, and (ii) dwarf? Give reason for your answer.
Answer
→ (i) tall- B plant
(ii) dwarf- A plant.
This is because only tall plants appear in the F1 generation and dwarf plants appear in the F2 generation along with tall plants.
68. Pure-bred tall pea plants are first crossed with pure-bred dwarf pea plants. The pea plants obtained in F1 generation are then cross-bred to produce F2 generation of pea plants.
(a) What do the plants of F1 generation look like ?
(b) What is the ratio of tall plants to dwarf plants in F2 generation?
(c) Which type of plants were missing in F1 generation but reappeared in F2 generation?
Answer
→ (a) Tall plants
(b) 3:1
(c) Dwarf plants.
69. A plant has two varieties, one with red petals and the other with white petals. When these two varieties are cross-pollinated, all the offspring have red petals?
(a) Which gene is dominant?
(b) Choose suitable letters to represent the two genes.
Answer
→ (a) Red color (Dominancy means ruling over the other)
(b) R and r (R for Dominant and r for recessive)
70. A red-haired woman marries a brown-haired man, and all the children are brown haired. Explain this genetically.
Answer
→ Brown hair color genes are dominant and the red hair color genes are recessive ; The genotype of brown hair is BB (dominant always represented by capital letter) and that of red hair bb (Recessive represented by small letter)
71. A black mouse mates with a brown mouse, and all the offspring are black
(a) Why are no brown off springs produced?
(b) If two of the black offspring mate with each other what kind of offspring would you expect and in what proportions? Give reason for your answer.
Answer
→ (a) No brown offspring are produced because brown color is recessive here and black being dominant rules.
(b)Three black mice and one brown mouse will be obtained in F2 generation; It is a monohybrid cross(Punett Square)
72. (a) E is the gene for brown eye color and e is the gene for blue eye color. Which gene is
(i) Recessive, and
(ii) Dominant
(b) Both father and mother have the genes Ee in their cells. What color are their eyes?
(c) Which combination of genes in the zygote will produce children with blue eyes?
(d) Which combinations of genes in the zygote will produce children with brown eyes?
Answer
→ (a) (i) e blue color gene is recessive; recessive is always represented by small letters.
(ii) E brown color gene is dominant; dominant is always represented by capital letters.
(b) They have brown eye color because dominant gene for brown eye color is present which suppresses the recessive gene for blue eye color and hence brown eye color is expressed
(c) Combination of ee will produce children with blue eyes because for blue eye color to be expressed there should not be gene for brown eye color that is E because if E gene will be present it will dominate the eye color and then brown eye color will be expressed and if there will be no dominant gene i.e. ee then the eye color expressed will be blue.
(d) The combinations EE and Ee will produce children with brown eyes because for brown eyes to be expressed there must be at-least one dominant gene for brown eye color i.e. E be present.
73. What are the possible blood groups likely to be inherited by children born to a group A mother and a group B father? Explain your reasoning.
Answer
→ The possible genotype that will be inherited by the children when the mother is group A and the father is group B are IA IB, IA IO, IB IO and IOIO. The possible blood group likely to be inherited will be either AB,A,B and O.
74. A couple with a newborn baby is troubled that the child does not resemble either of them. Suspecting that a mix-up occurred at the hospital, they check the blood type of the infant. It is type 0. Because the father is type A and the mother type B, they conclude that a mix-up has definitely occurred. Are they correct? Give reason for your answer.
Answer
→ No, the parents are not correct. The father is type A and the Mother is type B; the possible genotypes that are inherited by the baby are IA IB, IA IO, IB IO and IOIO. This means that any of the blood type AB, A, B, and O can be inherited by the child. If the child inherits any of the one blood type, which is occurring here in this case that the child is inheriting type O blood group, no error has occurred.
75. A man with blood group A marries a woman with blood group 0 and their daughter has blood group 0. Is this information enough to tell you which of the traits - blood group A or 0 -is dominant? Why or why not?
Answer
→ Case 1: Man with blood group A married a woman with blood group B. Blood group for man can be expressed by dominant genotype IAIA orIAIO and blood group O for woman is expressed by recessive genotype IOIO. The daughter will have O blood group type as a result of this IOIO inheritance of recessive traits from mother and father.
Case 2: Blood group A in father if has recessive genotype IAIA and mother has dominant genotype IAIO or IOIO. The daughter will have O blood type as a result of inheritance of dominant allele IO from mother and recessive allele IA from father.
Blood group A is expressed in both homozygous and heterozygous condition but Blood group O is expressed in recessive condition.
76. A Mendelian experiment consisted of breeding tall TT pea plants bearing violet flowers with short t pea plants bearing white w flowers. The progeny all bore violet W flowers, but almost half of them were short. This suggested that the genetic make-up (or genotype) of the tall parent can be depicted as:
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Give reason for your choice
Answer
→ The genetic makeup of the tall parent can be depicted as (C) TtWW. As the question says, Tall Pea plants bearing violet flowers; Tallness is a dominant trait and is always represented by capital letters so ‘T’ and short/dwarfness is represented by small letters so ‘t’ – hence Tt. Violet Flowers is a dominant trait and is represented by capital letters so ‘W’. The progeny had short plants but no white flowers which means that Violet flowers are being passed on. Therefore, the genotype of the tall parent can be depicted as TtWW. There is a dominant gene for tallness which suppresses the recessive gene for height and for all violet flowers were present in tall pea plant.
77. A person first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only A-B type of seeds were produced in the F1generation. When F1 generation pea plants having A-B type of seeds were cross-bred by self-pollination, then in addition to the original round-yellow and wrinkled-green seeds, two new varieties A-D and C-B type of seeds were also obtained.
(a) What are A-B type of seeds?
(b) State whether A and B are dominant traits or recessive traits.
(c) What are A-D type of seeds?
(d) What are C-B type of seeds?
(e) Out of A-B and A-D types of seeds, which one will be produced in
(i) minimum numbers, and
(ii) maximum numbers, in the F2 generation ?
Answer
→ (a)Round Yellow.
Round yellow- RRYY, wrinkled green-rryy. On crossing these two pea plants we get RrYy combination which has dominant gene R for Round shape and Dominant gene Y for yellow color. Hence A-B types of seed produced as a result of the first cross are Round yellow.
(b) A and B are dominant traits since they are Round (R) and yellow (Y)
(c) Round-green
When RrYy obtained in the first generation is self-pollinated, the new varieties obtained are RY, Ry, rY, ry; where RY- Round yellow, Ry-Round green, rY-Wrinkled yellow, and ry- wrinkled green. Since A-B type of seed is Round and yellow, therefore A-D type of seed is Round and Green.
(d) Wrinkled-yellow
When RrYy obtained in the first generation is self-pollinated, the new varieties obtained are RY, Ry, rY, ry; where RY- Round yellow, Ry-Round green, rY-Wrinkled yellow, and ry- wrinkled green. Since A-B type of seed is Round and yellow, therefore C-B type of seed is wrinkled and yellow.
(e)(i) A-D (Round and green ‘Ry’ will be produced in minimum number)
(ii) A-B (Round and yellow ‘RY’ will be produced in maximum number in F2 generation)
78. The person A has only B chromosomes in all its gametes. On the other hand, another person C has chromosome D in half of gametes and chromosome E in the other half of gametes. When chromosomes B and D combine during fertilization, a female zygote results. On the other hand, combination of B and E chromosomes produces a male zygote.
(a) What are chromosomes?
(i) B
(ii) D, and
(iii) E ?
(b) Out of B, D and E, which two chromosomes are of the same type?
(c) Which chromosome is smaller in size?
(d) What is the general name of chromosomes such as B and E?
(e) Out of the two persons A and C, which one is
(i) male, and
(ii) female ?
Answer
→ (a) (i) The chromosome B are X chromosomes because if person A is entirely madeup of B chromosomes it means the person is a female an has all X chromosomes.
(ii) The chromosome D is X chromosome again because when B and D combine a female offspring is produced. A female zygote can only be produced when both of the chromosomes in the gamete are ‘X’. Chromosome B is X as already said above; now chromosome D is also X. Thus only then when B and D chromosome i.e. X and X chromosome combine, a female zygote is produced.
(iii) The chromosome E is a Y chromosome because when B and E combine a male zygote is produced. B is a X chromosome as discussed above and when E i.e. Y chromosome combine , a male zygote is produced(XY)
(b) Chromosome B and D are of the same type, i.e. X chromosome.
(c) Chromosome E is smaller in size since it is a Y chromosome.
(d) Chromosome B (X) and chromosome E (Y) are known as Sex Chromosomes
(e) (i) C is male since it has half genes from D and half genes from E.
D is a X chromosome and E is a Y chromosome so when they combine a male zygote is formed.
(ii) A is female since it has all B chromosomes in it i.e. X chromosome which is only possible in female.
79. Mendel first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only round-yellow seeds were produced in the F1 generation. When F1 generation pea plants having round-yellow seeds were cross-bred by self-pollination, then peas having round � yellow seeds, round green seeds, wrinkled-yellow seeds and wrinkled-green seeds were produced. Mendel collected a total of 2160 seeds.
(a)What will be the number of?
(i) Round green seeds
(ii) Wrinkled green seeds
(iii) Round yellow seeds, and
(iv) Wrinkled-yellow seeds
(b) Which 'ratio' as established by Mendel have you made use of in answering the part (a) above?
Answer
→ (a) The F2 generation obtained had Round yellow: Round green: Wrinkled yellow: Wrinkled green in the ratio 9:3:3:1
(i) Round Green seeds- (3/16)*2160= 405
(ii) Wrinkled Green seeds- (1/16)*2160= 135
(iii) Round yellow seeds- (9/16)*2160= 1215
(iv) Wrinkled yellow seeds- (3/16)*2160= 405
(b) Dihybrid ratio has been used in answering this question because here are two different varieties, that differ in two observed traits i.e. Shape : round and wrinkled; Color: yellow and green.
80. Pure-bred round-yellow pea seeds have genotype RRYY and the pure-bred wrinkled-green pea seeds have genotype rryy. Keeping this in mind, write the phenotypes of the following genotypes of hybrid pea seeds:
(a) Rryy
(b) rrYy
(c) rrYY
(d) RrYy
(e) RRyy
Answer
→ (a) Round-green (RR-round; dominant, yy-green; recessive)
(b) Wrinkled-yellow (rr-wrinkled; recessive, Yy- since one dominant gene Y Is present- yellow)
(c) Wrinkled-yellow (rr-wrinkled; recessive, YY-yellow, dominant)
(d) Round-yellow (Rr-one gene dominant R is present-round; Yy- since one dominant gene Y is present- yellow)
(e) Round-green(RR-round; dominant, yy-green; recessive)
Very Short Answer Type Questions-Pg-208
1. What name is given to the sequence of gradual changes over millions of years in which new species are produced?
Answer
→ Evolution is the process of gradual changes in heritable characteristics over long time which leads to the formation of new species. These new species develop from their earlier forms during time.
2. Name the scientist who gave the theory of evolution.
Answer
→ Charles Robert Darwin gave the theory of evolution in his book ‘Origin of Species’ by means of Natural Selection.
3. State whether the following statement is true or false: Human beings have evolved from chimpanzees.
Answer
→ The given statement is False. Human beings are more closely related to modern apes but did not evolve from them too. Human beings just share a common ancestor with modern African apes like gorillas and chimps but did not evolve from them.
4. State one characteristic which shows that birds are very closely related to dinosaurs.
Answer
→ A feature that is common to both birds and dinosaurs is presence of feathers on their body which shows that birds and dinosaurs are closely related. Dinosaurs had feathers but they could not fly and birds used feathers to provide insulation to their bodies in harsh weather but later on the feathers became useful for flying.
5. Name an animal having rudimentary eyes.
Answer
→ Flatworm – Planaria has rudimentary eyes as eye spots.
6. Name the ancestor of the following: Broccoli, Kohlrabi, Kale.
Answer
→ All the three, Broccoli, Kohlrabi and Kale have a common ancestor that is wild cabbage.
Plant parts of Wild cabbage or Brassica oleracea are modified by artificial selection to produce these varieties of cabbage
Flower buds and stem are modified-Broccoli
Stem is modified- Kohlrabi
Leaves are modified- Kale
7. Where did life originate on the earth?
Answer
→ It is believed that life originated in sea water, near deep sea hydrothermal vents.
8. Write the names of at least three inorganic molecules which helped in the origin of life on the earth.
Answer
→ Methane, Ammonia and Hydrogen Sulphide are the three inorganic molecules that helped in origin of life on earth. Stanley Miller and Harold Urey performed experiments that showed that organic compounds could b synthesized by stimulating conditions of the early earth atmosphere.
9. Name the famous book written by Charles Robert Darwin.
Answer
→ Charles Robert Darwin wrote the book “Origin of Species” in which he gave theories of Evolution.
10. The forelimbs of a frog, a bird and a man show the same basic design (or basic structure) of bones. What name is given to such organs?
Answer
→ Organs that are similar in structures are known as homologous organs because they have basic design of bones but they have different functions. Forelimbs of frog are used to prop up the front ends of the body when at rest, forelimbs of bird are used for flying, and forelimbs of man are used for grasping.
11. Name two organisms which are now extinct and studied from their fossils.
Answer
→ Two organisms that are now extinct and studied from their fossils are Dinosaurs and Archaeopteryx lithographica.
Dinosaurs are believed to be ancestors of birds. Archaeopteryx is link between reptiles and birds.
12. Out of the wing of a bird, wing of an insect and the wing of a bat:
(a) Which two are homologous organs?
(b) Which two are analogous organs?
Answer
→ (a) Wing of a bird and wing of a bat are homologous organs. They are homologous with their forelimbs which they inherit from common ancestor.
(b) Wing of an insect and wing of a bird are analogous organs. They perform the same function of uplifting the body in air but their basic structure is totally different.
13. Why are human beings who look so different from each other in terms of size, color and looks said to belong to the same species
Answer
→ This is because human beings reproduce. There are no geographical barriers so they interbreed easily and produce viable offspring. It is the result of variations that human beings look different from each other in terms of size, color and looks.
14. Name five varieties of vegetables which have been produced from 'wild cabbage' by the process of artificial selection.
Answer
→ Brassica oleracea (wild cabbage) is modified by artificial selection to produce many varieties of vegetables. 5 of such varieties are- Broccoli, Kohlrabi, Kale, Cabbage and Cauliflower.
15. Choose the one term from the following which includes the other three: broccoli, wildcabbage, cauliflower, cabbage.
Answer
→ Various plant parts of Wild Cabbage (Brassica oleracea) are modified by artificial selection to give broccoli, cauliflower and cabbage. Thus, Wild cabbage includes the other three.
16. Fill in the following blanks with suitable words:
(a) The human forelimb and bat's forelimb are examples of..................... organs whereas an insect's wing and a bat's wing are an example of ..................... organs.
(b) The evolution of eye is an example of evolution by .....................
(c) The scientific name of all human beings is....................
(d) Broccoli has evolved from ..................... by the process of artificial selection.
(e) The theory of natural selection for evolution was proposed by……………..
Answer
→(a) Homologous organs; Analogous organs.
(Homologous organs are those which have a similar structure; whereas analogous organs are those which have a similar function).
(b) Stages.
(c) Homo Sapiens
(Modern specie of humans is Homo Sapiens). Homo sapiens evolved between 250,000 and 100,000 years ago in Africa.
(d) Wild cabbage (Brassica oleracea)
(Flower buds and stem are modified traits to produce Kohlrabi)
(e) Charles Robert Darwin.
(Darwin proposed the theory of evolution in his book “Origin Of species”, by means of Natural Selection.
Short Answer Type Questions-Pg-209
17Match the terms given in column I with those given in column II :
Column I Column II (i) Fossil (a) A famous evolutionist (ii) A theory of evolution (b) Survival of the fittest (iii) Probable ancestor of bird (c) Petrified remains of prehistoric life (iv) Charles Darwin (d) Father of genetics (v) Gregor Mendel (e) Archaeopteryx
Answer
→ (i) c – petrified remains of prehistoric life
(Dead remains of animals and plants that petrified under environmental conditions over millions of years)
(ii) b – Survival of the fittest
(Evolution occurs over years by the process of natural selection which is based on survival of the fittest)
(iii) e - Archaeopteryx
(Archaeopteryx is a fossil that had been found and studies revealed that it is a fossil of bird since it had avian features)
(iv) a- a famous evolutionist
Charles Darwin wrote the book “Origin of species”
(v) d- father of genetics
Gregor Mendel is the father of genetics.
18. What is meant by acquired and inherited traits? Explain with one example each.
Answer
→ Acquired traits are not inherited by the organism genetically but by environmental conditions present around the organism or the environmental conditions in which the organism lives. For example, Beetles will reduce in weight if not given enough food.
Whereas,
Inherited traits are those characteristics that an organism inherits from his/her parents i.e., passed on genetically through DNA. (Change in DNA). For example –Change of beetles in color from red to green.
19. Why are the traits acquired during the life time of an individual not inherited?
Answer
→ A trait can be only inherited when it brings a change in genes present in the gametes of an organism. Changes in non-reproductive tissues cannot be passed on to DNA of germ cells. Therefore traits acquired during lifetime of an individual are not inherited by the offspring because they are changes in somatic cells and not in germ cells.
20. Can the wing of a butterfly and the wing of a bat .be considered homologous organs? Why or why not?
Answer
→ No, the wings of a butterfly and the wings of a bat cannot be considered homologous organs because they don’t have similar basic structure, even if they perform similar functions i.e. flying. The wings of bat are supported by bones whereas the wing of a butterfly has no bones but is supported by membranous folds which are attached with muscles and not bones. Wings of a butterfly and wings of a bat are analogous organs which have similar functions but different origins.
21. Name two animals having homologous organs and two having analogous organs. Name these organs.
Answer
→ Homologous organs are found in humans and lizards. The forelimbs of humans and lizards have different functions completely but the basic structure of bones is similar, i.e. they have same origin. Another example is forelimbs of frog and forelimbs of humans.
Analogous organs are found in bat and butterfly. The wings of a bat and wings of a butterfly have similar function i.e. flying but they have completely different origin.
Another example is wing of an insect and wing of a bird.
22. What are fossils? Giving one example, explain how fossils provide evidence for evolution.
Answer
→ Fossils are the dead remains of plants and animals which undergo several physical and chemical processes after they are dead.
Example- Archaeopteryx lithographica is a fossil that resembles a bird(has feathers and wings) but has several features of reptiles(tail and teeth) . So Archaeopteryx is supposed to be the connecting link between aves and reptiles thus suggesting that birds have evolved from reptiles.
23. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer
→ If different organisms have common ancestors then it is possible that they have similar characteristics due to inheritance. These similarities are used to determine their close relations in evolutionary terms. For example – forelimbs of bird and forelimb of humans have similar basic structure of bones which suggests that they have a common ancestor i.e. they are closely related in evolutionary terms. Over time these structures have developed to function as per the requirement. Thus homologous organs help in determining closeness in evolution.
24. In what way is homologous organs evidence for evolution?
Answer
→ Homologous organs are the organs that have different functions but they are believed to have originated from a common ancestor because of their basic structure of bones. Thus if homologous organs are present in different organisms, it can be inferred that they have same ancestors which provide evidences for evolution.
Example- forelimbs of humans and forelimbs of frog; they have different functions but they have same basic design which tells that they have a common ancestor.
25. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer
→ Small numbers of surviving tigers are a cause of worry from the point of view of genetics because if all the tigers in the world die and become extinct, their genes will be lost forever, they will not come into sight ever again if they become extinct.
26. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually?
Give reason for your answer.
Answer
→ No; Asexual reproduction is a reproduction wherein an organism does not require another organism to reproduce i.e. there is no fusion of gametes. There is very little variation over generations. Thus, geographical isolation cannot be a major factor in the speciation of an organism that reproduces asexually since variations in DNA are not enough to raise a new species.
27. Name the various tools of tracing evolutionary relationships which have been used for studying human evolution.
Answer
→ •Carbon dating is determination of age by studying relative proportion of carbon isotopes.
•Excavating,-Digging the earth.
•Determining DNA sequences and fossil studies
These are some of the techniques that are being used to study evolution.
28. Out of bacteria, spider, fish and chimpanzee, which organism has a better body design in evolutionary terms? Give reason for your answer.
Answer
→ Bacteria has a better body design in evolutionary terms because they can survive hot springs, deep sea and even freezing environment which most of the other organisms cannot.
29. With the help of an example, explain how variation leads to evolution.
Answer
→ Large Variations occur when organisms reproduce sexually. Variations refer to changes in the genetic material of a population. Those which are useful for the population and help in survival are selected by process of natural selection. The accumulation of these variations over time leads to the development of new species. Asexual reproduction brings about very less variation and hence it causes no evolution.
For example- animals that reproduce sexually like birds. If birds with long beaks and few birds with short beaks inhabit a new area which has food that can be eaten only with short beaks. Birds with short beaks will have greater survival chances in such an area and hence they will reproduce more, thus increasing their number and evolving.
30A. What is meant by a species ? Give two examples of plant species and two of animals.
Answer
→ (A) A species refers to a group of organisms consisting of similar individuals capable of exchanging genes (interbreeding)
Example
•Plant species- Wheat, Daisies, Conifers, etc.
•Animal species- Cow, Dog, Elephant, etc.
30B. State the various factors which could lead to the formation of new species.
Answer
→ (B) Various factors that could lead to formation of new species are Geographical barrier, natural selection and genetic drift.
•Geographical barrier- if sexually reproducing organisms are isolated by geographical barriers then the gene flow through gametes stops and the isolated members interbreed thus leading to the formation of new species.
•Natural Selection- Nature selects individuals that are better adapted to the environment. The organisms that are better adapted survive and reproduce more, whereas the organisms that are not adapted well to the environmental conditions are slowly erased from the environment.
•Genetic drift- genetic drift is changes in the relative frequency of particular genes which leads to disappearance of those genes as individuals either die or they do not reproduce.
31. What evidence do we have for the origin of life from inanimate matter (lifeless matter)?
Answer
→ The evidence for the origin of life from lifeless matter was given by Stanley Miller and Harold Urey in 1953. They recreated the probable conditions of primitive atmosphere of early earth and demonstrated that simple organic compound like amino acids, hydroxyl acids, sugars and urea can by synthesized in the laboratory from a mixture of methane, hydrogen, water vapour and ammonia. They supplied energy by heating the chamber containing the above mixture to 800 degree C and discharges by electric sparks. After about one week, the liquid was found to contain a number of amino acids such as glycine, alanine and aspartic acid.
32. Does geographical isolation of individuals of a species lead to the formation of a new species? Provide a suitable explanation for your answer.
Answer
→ Geographical isolation of a species will lead to the formation of a new species if the species reproduces sexually because isolation will stop the gene flow between the isolated populations since they will not be able to reproduce. As a result, the members of isolated populations will interbreed, leading to the formation of new species.
On the other hand if species that reproduce asexually are geographically isolated, there will be no formation of a new species because such species do not need fusion of gametes to reproduce, they reproduce on their own. Hence there will be no formation of a new species.
33. Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Explain your answer.
Answer
→ Since bacteria have a simpler body plan when compared with human being it does not mean that human beings are more evolved. Bacteria do have a simpler body plan but they have ability to survive harsh environmental conditions/ unfavorable habitats such as high temperature, deep sea hydrothermal vents and freezing temperatures as well. Human beings are also well adapted to the environment they live in. Both, bacteria and human beings have evolved differently.