Solutions of Heredity and Evolution Lakhmir Singh Manjit Kaur VSAQ, and SAQ Pg No. 191 Class 10 Biology
1. Which of the processes, sexual reproduction or asexual reproduction, brings about maximum variations in the offspring?
Answer
→ Sexual Reproduction brings about maximum variations in the offspring because it involves fusion of gametes thus causing variations whereas asexual reproduction does not involves fusion of gametes so the offspring inherits genes from one parent only and thus variation is rare.
2. Name one variation in humans connected with ears.
Answer
→ Some humans have attached earlobes while some have few earlobes which is due to variation in genes.
5. Mendel said that the characteristics or traits of organisms are carried from one generation to the next by internal factors which occur in pairs. What is the modem name for these factors?
Answer
→ These internal factors are known as genes. Genes are found in pairs on chromosomes and they carry traits from parents to the offspring.
6. Some plants occur in one of the two sizes: tall or dwarf. This characteristic is controlled by one pair of genes. Tallness is dominant to dwarfness. Choose suitable letters for this gene pair.
Answer
→ Gene pair can be represented as Tt. T-Tallness-T and Dwarfness-t.(Dominant is always represented with a capital letter and recessive with a small letter).
7. What are the chromosomes XY and XX known as?
Answer
→ These are known as the sex chromosomes. Females have XX as the set of sex chromosome whereas males have XY as the set of sex chromosome
8. Which of the two, sperm or ovum, decides the sex of the child?
Answer
→ Sperm decides the sex of the child. During fertilization if X of the sperm fertilizes with egg (having one X chromosome) a girl child is born; if Y of the sperm fertilizes with egg a boy child is born.
9. State whether the following statement is true or false:
Answer
→ The sex of an infant is not a case of inheritance of characteristics.
False, sex of an infant is case of inheritance of characteristics. Inheritance of characters determines the sex of an infant.
10. A new born child has an XY pair of chromosomes. Will it be a baby boy or a baby girl?
Answer
→ The new born child will be a baby boy. The unfertilized egg has one X chromosome; the sperm either carries a X chromosome or a Y chromosome. If X of the sperm fertilizes with the egg the child born will be female (XX), and if Y of the sperm fertilizes with the egg the child born will be male (XY). Thus the new born child with an XY pair of chromosome will be a baby boy.
11. Which of the following combinations of sex chromosomes produce a male child: XX or XY?
Answer
→ The Combination XY produces a male child. The unfertilized egg has one X chromosome. The sperm either has a X chromosome or a Y chromosome. Male child will be produced if sperm carrying Y chromosome fertilizes with the egg. Female child will be produced if sperm carrying X chromosome fertilized with the egg. Therefore, combination XY will produce a male child.
12. Name the first scientist who studied the inheritance of traits from one generation to the next.
Answer
→ Gregor Johann Mendel studied the inheritance of traits from one generation to the next. He discovered basic principles of heredity through his experiments on pea plant.
13. What type of plants were used by Mendel for conducting his experiments on inheritance?
Answer
→ Mendel used pea plant for conducting experiments on inheritance. Reasons for selecting pea plant were
a) they are easy to raise
b) give many offspring per mating
c) self-fertilization
d) have varieties in genotype and phenotype.
14. The gene for red hair is recessive to the gene for black hair. What will be the hair color of a person if he inherits a gene for red hair from his mother and a gene for black hair from his father ?
Answer
→ Black hair color; it is because gene for black hair color is dominant so it will be expressed and since gene for red hair is repressive so it will be suppressed under the influence of black hair gene.
15. What are the four blood groups in humans?
Answer
→ The four blood groups in humans are blood group A, B, AB and O. The ABO blood group system was given by Karl Landsteiner in 1900. He identified the blood types O, A and B.
16. Name one reptile in each case where higher incubation temperature leads to the development of:
(a) Male progeny,
(b) Female progeny.
Answer
→ (a) Incubation of eggs Lizard (Agama agama) at high temperature produces male progeny.
(b)Incubation of eggs of Turtle (Chrysema Picta) at high temperature produces female progeny.
17. Fill in the following blanks with suitable words :
(a) Genes always work in ......................
(b) In pea plants, the gene for dwarfness is………………………..whereas that for tallness is………………
(c) Most people have .................earlobes but some have ..............earlobes.
(d) A human gamete contains................... chromosomes whereas a normal body cell has ................... chromosomes in it.
(e) All races of man have.............blood groups.
(f) The.................chromosomes for a ...............are XX whereas that for a ......................are XY.
Answer
→ (a) Pair
(b) Recessive; Dominant.
(c) Free; Attached.
(d) 23; 46
(e) Same
(f) Sex; Female; Male.
Short Answer Type Questions-Pg-192
18. Which of the following represent tall plants and which represent short plants (or dwarf plants)?
(a) Tt (b) tt (c) TT
Give reason for your choice (The symbols have their usual meaning).
Answer
→ Tt- represents tall plant. This is because T is dominant so it is expressed and since t is recessive, it gets suppressed. (Where T=tall plant; t= dwarf plant)
tt- represents dwarf plant. This is because both the genes for determining the height of the plant are recessive and none of the dominating genes are present.
TT- represents tall plant. This is because T is dominant gene for height and both the dominant genes are present.
19. A man having blood group 0 marries a woman having blood group B and they have a daughter. What will be the blood group of the daughter?
Answer
→ There are equal possibilities of the daughter having blood group O and B.
Blood group O will have O and O genes whereas blood group B will have B gene as dominant and O as recessive so the gene pairs that could be formed will be either O and B or O and O ; either B and O or O and O. Hence the equal possibility i.e. 50-50.
20A. Name the scientist who gave the laws of inheritance.
Answer
→ (A) Gregor Johann Mendel gave the laws of inheritance. He studied heredity on pea plants and gave three laws of inheritance. 1. Law of Dominance. 2. Law of segregation. 3. Law of independent assortment.
20B. Name an animal in which individuals can change sex. What does this indicate?
Answer
→ (B) Snail can change sex amongst its individuals. It is usually done among the endangered snail species in order to keep themselves Alive. This indicates that genes do not play a role in determining the sex of the individual.
21. Explain with an example, how genes control the characteristics (or traits).
Answer
→ Genes are the units of heredity i.e. they transfer characteristics from parents to offspring and determine the characteristics of the offspring. Example- Transfer of hair color from parents to the offspring. Let’s say that the mother has dominant genes for black hair, (BB gene constitution) and the father has recessive gene for blonde hair (bb gene constitution). When fertilization will occur the mother will transfer one B gene for black hair to the zygote and the father will transfer one b gene for blonde hair to the zygote. The resulting offspring will have Bb gene for hair where B is a dominant gene and b is a recessive gene. Since B is dominant it will be expressed and b will be suppressed, the child will have black hair.
22A. State one advantage of variation to a species.
Answer
→ (A) Variations are heritable differences within individuals of a species. Advantage- Nature always selects the fittest organism so if no variation occurred in genes there would not have been so many species of the organism. In a changing environment, variation always increases the chances of survival of a species.
22B. What are sex chromosomes? How many sex chromosomes are there? Name them.
Answer
→ (B) Sex chromosomes are a pair of chromosome that decide/determine the sex of an individual. The 23rd pair of chromosome is Allosome (or sex chromosome).
There are 2 sex chromosomes (one pair). X and Y chromosome. Y chromosome is found only in males. X chromosome is found in both male and female.
23. Explain how, sex is determined in human babies.
Answer
→ The unfertilized egg has one X chromosome. The sperm either has a X chromosome or a Y chromosome. If sperm carrying Y chromosome fertilizes with the egg, male baby will be born with the genetic constitution XY. But if sperm carrying X chromosome fertilized with the egg, female baby will be born with the genetic constitution XX.
24. What do the following symbols used in the topic on heredity represent?
(a) TT (b) tt
(c) XX (d) XY
Answer
→ (a) TT – Tall plant (T is a dominant gene).
(b)tt- dwarf plant (t is a recessive gene and there is no dominant gene to rule over it so dwarf height).
(c)XX- Female. (Female have both the sex chromosome as X X).
(d)XY- Male. (Male have One X chromosome and the other is Y chromosome as their sex chromosome).
25A. What will you get in the F1 and F2 generations in the following cross ? Pure tall pea plant x pure dwarf pea plant?
Answer
→ (A) In the F1 generation we will get all tall plants with Tt gene combination and in the F2 generation we will get 3 tall plants (TT/Tt) and one dwarf plant (tt).
25B. Is it an example of monohybrid cross or dihybrid cross?
Answer
→ (B) This is an example of a monohybrid cross because there is just one trait i.e. height whose inheritance pattern is being studied.
26. In the F2 generation of a cross, progeny having different traits are produced in the ratio 3 : 1. State whether it is a monohybrid cross or a dihybrid cross? Give one example of such a cross.
Answer
→ It is a monohybrid cross. A monohybrid cross is a cross between two individuals with two different alleles on one gene. It produces a phenotypic monohybrid ratio of 3:1 in the F2 generation. Whereas a Dihybrid cross produces a phenotypic Dihybrid ratio of 9:3:3:1 in the F2 generation.
For example- When pure tall plant (TT) are crossed with pure dwarf plants (tt), the offspring of the F1 generation is all tall plants (Tt). When these Tall plants cross bred with each other, they produce ‘TT’ ‘Tt’ ‘Tt’ ‘tt’ offspring i.e. tall : short = 3:1. The phenotypic monohybrid ratio in the F2 generation is 3:1.
27A. What is the genotype of dwarf plants which always produced dwarf offspring ?
Answer
→ (A) Dwarf-ness is denoted by letter ‘t’ . For plants that have always produced dwarf offspring, the genotype will be ‘tt’ as dwarf-ness will only be expressed when both the genes are recessive i.e. ‘tt’
27B. What is the genotype of tall plants which always produced tall offspring?
Answer
→ (B) Tallness is denoted by letter ‘T’. For plants that have always produced tall offspring, the genotype will be TT. It can also be Tt because since dominant gene T is present it will not let the recessive trait i.e. dwarf-ness express itself.
27C. What is the genotype of (i) dwarf plants, and (ii) tall plants, whose parental cross always produces tall offspring?
Answer
→ (C) (i)Genotype of dwarf plants will be ‘tt’ because dwarf-ness is a recessive trait that is expressed only when both the genes are recessive.
(ii)Genotype of tall plant will be ‘TT’ because the parental cross is producing tall offspring always.
28A. If a normal human cell has 46 chromosomes, how many chromosomes will be there in a human (i) sperm cell, and (ii) zygote?
Answer
→ (A) (i) sperm cell will have 23 chromosomes as gametes consist of half the number of chromosome of somatic cells.
(ii) Zygote will have 46 chromosomes as 23 chromosomes from the gamete of mother (egg) and 23 chromosome from the gamete of the father (sperm) will fuse to a total of 46 chromosomes.
28B. (b) What sizes of plants are produced if both parents have genes Tt?
Answer
→ (b) When both parents have same genes Tt and Tt and they are made to cross bred, we get a phenotypic ratio of 3:1 of tall: dwarf. (TT, Tt, Tt, tt)
29. In a human, how many chromosomes are present in:
(a) a brain cell ?
(b) a sperm in the testes ?
(c) an egg which has just been produced by the ovary?
(d) a skin cell ?
(e) a fertilized egg ?
Answer
→ (a) 46 (23 pairs of chromosome)
(b) 23 chromosomes (haploid)
(c) 23 chromosomes (haploid)
(d) 46 chromosomes (23 pairs of chromosome)
(e) 46 chromosomes (since it is fertilized by the sperm)
30. Gregor Mendel's first law of genetics states "Of a pair of contrasted characters, only one can be represented in a gamete by its internal 'factor'.
(a) Give the modem name for this 'factor'.
(b) State where these factors are found in gametes.
Answer
→ (a) This factor is known as Genes. They are unit of heredity transferred from parents to offspring. Each parent has a gene pair in each cell for each trait studied. One member of the gene pair segregates into a gamete, thus each gamete only carries one member of the gene pair and hence only one out of a pair of contrasted characters is represented in a gamete by its gene.
(b) These internal factors known as genes are found on chromosomes which are made of DNA and protein and found in the nucleus of the cell.
31. Does genetic combination of mother play a significant role in determining the sex of a new born baby?
Answer
→ No, the genetic constitution of mother does not play a significant role in determining the sex of baby. This is because mother has 2 X sex-chromosomes (i.e. XX) so the baby will inherit an X chromosome from the mother. It is the father whose genetic constitution plays important role. Father has XY sex chromosomes so the baby will either inherit X chromosome or Y chromosome through sperm. If the sperm carries X chromosome the baby born will be a girl (XX) and if the sperm carries Y chromosome the baby born will be a boy (XY).
32. Give the contrasting traits of the following characters in pea plant and mention which is dominant and which is recessive:
(a) Yellow seed (b) Round seed
Answer
→ (a) Green seed is the contrasting trait of yellow seed where Green is recessive and yellow is dominant.
(b) Wrinkled seed is the contrasting of round seed where Wrinkled is recessive and round is dominant.