SSLC Biology: Chapter 06 Unravelling Genetic Mysteries - Questions and Answers


Study Notes for Class 10 Biology (English Medium) ഇഴപിരിയുന്ന ജനിതക രഹസ്യങ്ങൾ | Text Books Solution Biology (English Medium) Chapter 06 Unravelling Genetic Mysteries

SCERT Solutions for Std X Biology Chapterwise

Class 10 Biology Questions and Answers
Chapter 06 Unravelling Genetic Mysteries
* Study Notes
The genes of all organisms are present in the DNA in the nucleus. Genes are controlling the characters. Offsprings have similarities (heredity) and diversity (variation) from parents. The study of heredity and variation is called genetics. Gregor Johann Mendel is the father of genetics. He conducted hybridization experiments in garden pea (Pisum sativum) plants. 

• Genetics -Heredity and Variations.
• Experiments and inferences of Gregor Johann Mendel.
• Genes and Alleles.
• DNA, Nucleotides, RNA.
• Gene action (protein synthesis).
• Chromosomes, Sex determination.
• Variations – Fertilization, Crossing over & Mutation

1. What is genetics (Hereditary science)?
Answer: Genetics is the branch of science that deals with heredity and variations.
• Heredity is the transmission of characters from parents to their offspring.
• Variations are the features seen in offspring that are different from their parents.

2. Who is known as 'the Father of Genetics'? Why is he known as so?
Answer: Gregor Johann Mendel.
The inferences from his hybridization experiments in pea plants led to the foundation of genetics.

3. What were the traits which Gregor Mendel considered for his hybridization experiments in garden pea plants?
Answer:
• Height of the plant 
• Position of the flowers 
• Shape of the seeds 
• Colour of seeds 
• Colour of the flowers 
• Shape of the pods 
• Colour of the fruits 

4. Illustration of Mendel's experiment on garden pea considering one pair of contrasting traits of a character height. (tallness-dwarfness)
5. What, according to Mendel, the terms dominant character and recessive character are referred to?
Answer: 
The expressed character, out of the two factors of a particular trait, is known as a dominant character and the other factor which remains hidden is known as recessive character.
For example, if 'Tt' are the two factors of the trait 'height', the ''T' is dominant and 't' is recessive.

6. When Gregor Mendel conducted experiments considering one pair of contrasting characters, the plants obtained in the second generation were always in -------- ratio.
Answer: 3:1

7.  The main inferences of Gregor Mendel that paved the way for the emergence of Genetics?
Answer:
• A trait is controlled by the combination of two factors.
• One character is expressed (dominant character) and the other remains hidden (recessive character) in the first generation.
• The trait which remains hidden in the first generation appears in the second generation.
• The ratio of the dominant and recessive traits in the second generation is 3:1.

8. Illustration of Mendel's experiment considering a pair of contrasting traits of two characters. (tallness-dwarfness and round seed- wrinkled seed)
9. The hereditary factors, first described by Gregor Mendel, are now known as ------?
Answer: Genes.

10.  Define the term 'genes'.
Answer: Genes are parts of DNA that control metabolic activities and are responsible for specific characteristic features.

11. Define the term 'allele'?
Answer: Alleles are the different forms of a gene that controls a trait.
Eg:- Suppose 'Tt' is the factor responsible for the trait, 'height', the allele 'T' determines tallness and the allele 't' determines dwarfness. 

12. Offsprings of the same parents may show differences among themselves. Why?
Answer: Fertilization causes change in the allele combination in the chromosomes and it causes variations in the offspring.

13. How many chromosomes are seen in each cell of a human being?
Answer: 46 chromosomes (23 pairs)
Out of which, 44 (22 pairs) are somatic chromosomes and 2 (one pair) are sex chromosomes.
44+XX is female and 44+XY is male

14. The two types of sex chromosomes?
Answer: X and Y chromosomes.  [XY in males and XX in females]

15. The 'Y' chromosome of male gamete: Male child ;     
 X chromosome of male gamete:  -----------?
Answer: Female child

16. Who proposed the double-helical model of DNA?
Answer: James Watson and Francis Crick (in1953)

17. Explain the Watson-Crick model of DNA.
Answer: Chromosome contains DNA and it is made up of several nucleotides. DNA is a double helical structured molecule. The two long strands of DNA contain deoxyribose sugar and phosphate groups, and its steps are made of pairs of nitrogen bases. The nitrogen base, adenine pairs with thymine and the nitrogen base, cytosine pairs with guanine. In other words, the DNA molecule is made up of four kinds of nucleotides, namely adenine nucleotide, thymine nucleotide, cytosine nucleotide and guanine nucleotide.

18. Define a nucleotide.
Answer: Nucleotides are the basic units of nucleic acids, (DNA, RNA). 
A nucleotide is made up of a nitrogen base, a sugar molecule and a phosphate group.

19. Molecules seen in the nucleic acids that contain nitrogen and are alkaline in nature?
Answer: Nitrogen bases.

20. Adenine: Thymine;
Guanine: ----------?
Answer: Cytosine.

21. Comparison between the two nucleic acids, DNA and RNA.
22. How do genes act?
Answer: Genes, which are the specific parts of DNA, act through synthesizing proteins.
Different types of RNA are involved in this process. Proteins are formed in the ribosomes.

23. Name different types of RNA.
Answer: mRNA (messenger RNA),  tRNA (transfer RNA),  rRNA (ribosomal RNA).

24. DNA unwinds and ---------- is synthesized which carries the information from DNA to the ribosomes.
Answer: mRNA. 

25. The stages of protein synthesis of DNA (The action of genes)?
Answer: 
• mRNA, which carries information, forms from DNA.
• mRNA reaches outside the nucleus.
• mRNA reaches ribosome.
• Based on the information, amino acids are transferred to ribosomes by the tRNA.
• Ribosomes bind amino acids to form protein molecules.

26. The cell organelles where protein synthesis occur?
Answer: Ribosomes.

27. What are the reasons for variations in organisms?
Answer: Fertilization, Crossing over and mutation.

28. How does fertilization causes variations in offspring?
Answer: During fertilization, a combination of alleles changes, which causes variations.

29. Define the term 'crossing over. How does crossing over cause variations?
Answer: The process of pairing chromosomes and exchanging their parts, during the initial phase of meiosis, is called crossing over.  As a result of this, part of one DNA becomes the part of another DNA, causing a difference in the normal distribution of genes. This may lead to the expression of new characters (variations) in the offspring. 

30. Define mutation.
Answer: Mutation is a sudden inheritable change in the genetic constitution of an organism. It may occur due to defects in the duplication of DNA, certain chemicals, radiations etc. Mutations lead to variations in characters. Certain mutations are harmful while certain others are helpful for the survival of the organism.

31. The protein which gives colour to our skin?
Answer: Melanin.

32. What may be the reason for the colour difference of skin in people living in various parts of the world?
Answer: Melanin, a pigment protein, imparts colour to the skin. The difference in gene function is the reason for the colour differences of skin. The differences in skin colour are mere an adaptation to live under the sun.

Let Us Assess

1. The nitrogen base is absent in RNA.
a. Adenine
b. Thymine
c. Uracil
d. Cytosine
Answer: RNA (Ribonucleic acid) do not contain a thymine nitrogenous base because it contains uracil in place of it. Four nitrogenous bases present in RNA are Adenine, Guanine, Cytosine and Uracil.
Thymine is absent in it and therefore, the correct option is (b) Thymine.

2. Arrange the stages of protein synthesis in the form of a flow chart.
• protein synthesized by adding amino acids.
• mRNA reaches ribosomes.
• mRNA is formed.
• amino acids are carried to the ribosomes.
Answer:
The following picture also depict the flow in which proteins are synthesised:
3. Observe the hybridization experiment given below.
a. Illustrate this hybridization experiment using symbols.
b. Illustrate the second generation formed by the self-pollination of the first-generation plants.
Answer:
a. In pea plants yellow colour is the dominant trait for the colour of the seeds and green colour is recessive.
We use the ‘YY’ symbol for the yellow coloured seeds and ‘yy’ for green seeds.
Following is the hybridisation experiment using symbols:
Here in the case of yellow seeds, we had taken heterozygous combination because in the given question recessive trait is appearing in First-generation and it only happens when we have heterozygous dominant as our parental generation. If we had chosen homozygous dominant as our parental generation we can’t have the recessive traits in the first generation. So, in order to satisfy the question’s condition, we had done so.

b. Since in the question we have green seeds in our First generation, we will use green seeds as our parents and self-pollinate them. The symbol for the green seeds is ‘yy’. This will be homozygous as the recessive trait is always expressed in homozygous conditions.
Extended Activities

1. Prepare an edition including information on scientists who have made contributions in the progress of genetics.
Answer: Genetics is a broad subject and it involves the contribution of many scientists.
This branch of science had started many years ago. The information for these scientists can be collected from the famous books on genetics and the internet with the role each scientist played.
There are some scientists whose discoveries and contributions had to make great changes in the field of genetics, information about those can also be collected from classical books of genetics.

2. Prepare models of DNA and RNA using locally available materials and present them in a science exhibition.
Answer: It is quite easy to make models of DNA and RNA using some very easy to get materials.
Things you need to require for these models are as follows:
1. Wires: Since they are flexible you can easily mould them and this wire will act as the strands.
2. Beads: Beads of different colours can be used as representing different nitrogenous bases.
3. Coloured sticks or ribbons: They can be used to represent the hydrogen bands between the nitrogenous bases.
4. Wooden block or piece of Thermocol: This can act as the base of the model.




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