Kerala Syllabus 10th Standard Biology Guide Chapter 6 Unravelling Genetic Mysteries
Sslc Biology Chapter 6 Question 1.
Observe the picture.
What are the features that the children show different from their parents?
Answer:
- The hair of deer and cat differ from their parents.
- The daughters have a different hair pattern from the mother.
- The forehead and ear of the son are different from his mother.
Question 2.
Explain the terms heredity, variations and genetics.
Answer:
The transmission of features of parents to offsprings is termed as heredity. The features seen in offsprings that are different from their parents are called variations. The branch of science that deals with heredity and variations is called Genetics.
Question 3.
Why is Mendel considered as the Father of Genetics?
Answer:
Certain laws of inheritance, formulated by Gregor Johann Mendel, on the basis of hybridization experiments in pea plants, have led to the foundation of genetics. This is why Mendel is considered as the Father of Genetics.
Question 4.
What are the traits that were experimented by Mendel?
Answer:
Gregor Johann Mendel studied the inheritance of 7 pairs of contrasting traits in pea plants, scientifically known as Pisum sativum. He formulated the laws of inheritance by analysing the inheritance of characters like height of plants, position of flower, shape of seed, colour of seed coat, colour of cotyledon, colour of fruit and shape of fruit.
Question 5.
What are the contributions of Gregor Johann Mendel?
Answer:
Through Gregor Johann Mendel’s studies on inheritance, he explained that each character is controlled by a pair of factors, which he illustrated using symbols.
The illustration of the hybridization experiment conducted on the basis of two contrasting traits of the character height in pea plant. Here the factors are illustrated using symbols.
Question 6.
Which character of pea plants is considered in this experiment?
Answer:
Height of plants
Question 7.
What are the contrasting traits of the character height?
Answer:
Tall and dwarf.
Class 10 Biology Kerala Syllabus Question 8.
What are the traits those were apparent and not apparent in the first generation?
Answer:
Expressed trait – tall Hidden trait – Dwarf
Question 9.
Difference in the factors of tall parent plant and the first generation plant.
Answer:
Tallness in parent plant is controlled by the factor T. But in the first generation tallness is controlled by the factors T, t.
When plants that differ in a pair of contrasting traits are hybridized, only one trait is expressed while the other remains hidden in the offsprings of the first generation. The expressed trait is called dominant trait and the hidden trait is called recessive trait.
Question 10.
What are alleles?
Answer:
The gene present in the chromosome of the nucleus determines the character. A gene that controls a .trait has different forms. The different forms of a gene are called alleles. Generally, a gene has two alleles.
Question 11.
Which are the alleles of a tall plant?
Answer:
The alleles of a tall plant are ‘TT’.
Question 12.
Which are the alleles of a dwarf planet?
Answer:
The alleles of a dwarf plant are ‘tt’.
Biology Class 10 Kerala Syllabus Question 13.
How are alleles represented?
Answer:
The different forms of a gene are called alleles. Generally a gene has two alleles. The different alleles of the gene that control the trait, height in the illustration of hybridization, given above are T and t. The allele T determines the trait tallness and the allele t determines the trait dwarfness. When we illustrate hybridization experiment, the allele that controls the dominant character that is expressed in the first generation is generally indicated by a capital letter and the allelle that controls recessive character is indicated by a small letter.
Question 14.
Explain dominant trait and recessive trait.
Answer:
When plants that differ in a pair of contrasting traits are hybridized, only one trait is expressed while the other remains hidden in the offsprings of the first generation. The expressed trait is called dominant trait and the hidden trait is called recessive trait.
Question 15.
What are the characters of plants in the second generation and their factors?
Answer:
In second generation three plants were tall and one plant was dwarf.
Question 16.
Explain the characters of plants and their alleles in the second generation.
Ans:
Tall – 1 (TT), Tall – 2 (Tt), Dwarf – 1 (tt).
Question 17.
Recessive trait in the first generation and the second generation?
Answer:
The recessive trait in the first generation is expressed in the second generation.
Question 18.
Why does the recessive trait in the first generation appear in the second generation?
Answer:
Mendel came up with the assumption that during gamete formation, the factors that determine a particular character segregate without getting mixed; ie., half of the gametes formed from first generation plant Tt, contains T and the other half contains t.
Class 10 Biology Chapter 6 Kerala Syllabus Question 19.
What are the inferences formulated by Mendel from hybridization experiments?
Answer:
A character is controlled by the combination of two factors.
One trait is expressed (dominant trait) and the other trait remains hidden (recessive trait) in the offsprings of the first generation.
The traits that remain hidden in the first generation appear in the second generation.
The ratio of the dominant and the recessive traits in the second generation is 3 : 1.
Hybridization experiment conducted on two characters
Question 20.
What are the factors present in the gametes produced by first-generation?
Answer:
The factors present in the gametes produced by first-generation are, TR, Tr, tR, tr.
Question 21.
What are the characters in the plants of second-generation?
Answer:
Tall plant with round seed, Tall plant with wrinkled seed, Dwarf plant with round seed, Dwarf plant with wrinkled seed.
Question 22.
What are the characters different front parents that appeared in the second generation?
Answer:
The characters different from parents that appeared in the second generation are tall plant with wrinkled seed and dwarf plant with round seed.
Question 23.
What is the reason for the appearance of new combination of characters in offsprings that were not expressed in parents?
Answer:
Mendel explained that the appearance of variations in offsprings (characters not present in previous generation) is due to the independent assortment of each character.
Question 24.
Explain the double-helical model of DNA.
Answer:
Two scientists, James Watson and Francis Crick presented the double-helical model of DNA in 1953. This model got wide acceptance in the scientific world. As per the double-helical model, DNA contains two strands. A model of two long strands with sugar and phosphate and steps with nitrogen bases were suggested.
Question 25.
What are nitrogen bases? Which are the nitrogen bases seen in DNA?
Answer:
Nitrogen bases are molecules that contain nitrogen and are alkaline in nature. DNA contains four kinds of nitrogen bases. They are adenine, thymine, guanine and cytosine.
Question 26.
What is the speciality seen in the pairing of nitrogen bases?
Answer:
Nitrogen bases which are the basic units of DNA are molecules with special features. In DNA, the base adenine pairs with thymine and guanine pairs with cytosine.
Question 27.
What are the components of nucleotides?
Answer:
DNA molecule is the repetitive unit of a deoxyribose sugar molecule, a phosphate molecule and a nitrogen base. This unit is called nucleotide. Since DNA has four kinds of nitrogen bases, DNA has four kinds of nucleotides too.
Question 28.
Illustrate the arrangement of nucleotides in a DNA molecule.
Answer:
Question 29.
Write the differences between DNA and RNA.
Answer:
| DNA | RNA | |
| 1.Number of strands | Double | Single |
| 2. Type of sugar | Deoxyribose sugar | Ribose sugar |
| 3. Nitrogen bases | Adenine, Adenine, Thymine, Uracil, | Guanine, Guanine, Cytosine Cytosine |
Kerala Syllabus 10th Standard Biology Notes Pdf Question 30.
Prepare a short note on genes.
Answer:
The activity of particular proteins (enzymes) controls metabolic activities and is responsible for specific characteristics. Genes contain information for protein synthesis. Genes are particular segments of DNA.
Question 31.
How do genes act? Explain.
Answer:
Genes which are the specific units of DNA control metabolic activities and they are responsible for specific characters. DNA does not participate directly in protein synthesis. RNA (Ribo Nucleic Acid) is the molecule that carries information from DNA to ribosomes and controls protein synthesis. Since this RNA is the messenger of DNA, it is called messenger RNA or mRNA. mRNA reaches ribosomes outside the nucleus. Different kinds of amino acids reach ribosomes.
Question 32.
Write the difference between mRNA, tRNA, rRNA.
Answer:
- mRNA – Since this RNA is the messenger of DNA, it is called messenger RNA or mRNA.
- tRNA – tRNA (Transfer RNA) carries amino acids to the ribosome.
- rRNA – rRNA (Ribosomal RNA) are seen associated with ribosomes.
Protein molecule is synthesized by adding amino acids as a result of all these activities.
10th Standard Biology Notes Question 33.
Write note on human chromosomes.
Answer:
46 chromosomes are seen in humans. Among these, 44 chromosomes are autosomes (somatic chromosomes) and two chromosomes are sex chromosomes. An autosomal pair constitutes two identical chromosomes. Hence 22 pairs of autosomes are found in humans.
Question 34.
What are the sex chromosomes in humans?
Answer:
Sex chromosomes are of two types. They are called X chromosome and Y chromosome. Two X chromosomes are seen in female but an X chromosome and a Y chromosome are seen in male. That is, the genetic constitution of female is 44 + XX and that of male is 44 + XY.
Question 35.
What is crossing over of chromosomes?
Answer:
During the initial phase of meiosis, chromosomes pair and exchange their parts. This process is called crossing over of chromosomes.
Question 36.
How does crossing over cause variation?
Answer:
As a result of crossing over, part of a DNA crosses over to become the part of another DNA. This causes a difference in the distribution of genes. When these chromosomes are transferred to the next generation, it causes the expression of new characters in offsprings.
Question 37.
How the combination of allele during fertilization causes variations in the next generation?
Answer:
The chromosomes of parents reach the offsprings through gametes. When gametes undergo fusion, the combination of allele changes. This causes the expression of characteristics in offsprings that are different from parents. Thus, fertilization causes variations in the next generation.
Kerala Syllabus 10th Standard Biology Question 38.
What is mutation?
Answer:
A sudden heritable change in the genetic constitution of art organism is called mutation.
Question 39.
What are the reasons for mutation?
Answer:
Mutation may occur due to the defects in the duplication of DNA, certain chemicals, radiations, etc.
Question 40.
What is the importance of mutation?
Answer:
Certain mutations are harmful and some are helpful for survival. Mutations lead to variations in characters. The effects of certain mutations are visible immediately while some are expressed after many generations. Mutation has great relevance in evolution.
Question 41.
Is there any difference in the number of chromosomes in male and female?
Answer:
46 chromosomes are seen in humans. Among these, 44 chromosomes are autosomes (somatic chromosomes) and two chromosomes are sex chromosomes. An autosomal pair constitutes two identical chromosomes. Hence 22 pairs of autosomes are found in humans. Sex chromosomes are of two types.
They are called X chromosome and Y chromosome. Two X chromosomes are seen in female but a X chromosome and a Y chromosome are seen in male. That is, the genetic constitution of female is 44 + XX and that of male is 44 + XY.
Question 42.
What is the possibility for the birth of a male or a female child?
Answer:
The XY chromosomes of the father determine whether the child is male or female. Child with XX sex chromosomes is female and one with XY sex chromosomes is male.
Question 43.
What may be the reason for the difference in the colour of skin in people living in various parts of the world?
Answer:
Melanin, a pigment protein imparts colour to the skin. It can be assumed that the difference in gene function is the reason for the colour difference of skin.
Let Us Assess
Question 1.
The nitrogen base absent in RNA
a. Adenine
b. Thymine
c. Uracil
d. Cytosine
Answer:
b. Thymine
Question 2.
Arrange the stages of protein synthesis in the form of a flow chart.
- combines amino acids
- mRNA reaches ribosomes
- mRNA is formed
- amino acids are carried to the ribosomes
Answer:
mRNA is formed → mRNA reaches ribosomes → amino acids are carried to the ribosomes → combines amino acids.
Question 3.
Observe the hybridisation experiment given below.
a. Prepare an illustration of this hybridization experiment using symbols.
b. Prepare an illustration for the second generation.
Answer:
a.
b. Self-pollination in first-generation
Biology Class 10 Kerala Syllabus Notes Question 4.
Three processes that cause variations in new generations are given. Prepare a short note on each of the processes.
- Crossing over of chromosome
- Fertilization
- Mutation
Answer:
Crossing over of chromosome – During the initial phase of meiosis, chromosomes pair and exchange their parts. This process is called crossing over of chromosomes. As a result of this, part of a DNA crosses over to become the part of another DNA. This causes a difference in the distribution of genes. When these chromosomes are transferred to the next generation, it causes the expression of new characters in offsprings.
Fertilization – The chromosomes of parents reach the offsprings through gametes. When gametes undergo fusion, the combination of allele changes. This causes the expression of characteristics in offsprings that are different from parents. Thus, fertilization causes variations in the next generation
Mutation – A sudden heritable change in the genetic constitution of an organism is called mutation. This may occur due to defects in the duplication of DNA, certain chemicals, radiations, etc. Mutations bring about changes in genes which can be transmitted over generations and thus leading to variations in characters. Mutations have great relevance in evolution.
Kerala Syllabus 10th Standard Biology Guide