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Genetics Book Back Questions 10th Science Lesson 18

10th Science Lesson 18

18] Genetics

Book Back Questions with Answer and Do You Know Box Content

Do You Know?

Punnett square is a checker board form devised by a British geneticist. R.C. Punnett for study of genetics. It is a graphical representation to calculate the probability of all possible genotypes of offsprings in a genetic cross.

T.H Morgan was awarded Nobel Prize in 1993 for determining the role of chromosomes in heredity.

Telomeres act as aging clock in every cell. Telomeres are protective sequences of nucleotides found in chromosomes. As a cell divides every time, they become shorter. Telomeres get too short to do their job, causing our cells to age.

Chargaff rule of DNA base pairing: Erwin Chargaff states that in DNA, the proportion of adenine is always equal to that of thymine and the proportion of guanine always equal to that of cytosine.

Sickle cell anaemia is caused by the mutation of a single gene. Alternation in the gene brings a change in the structure of the protein part of haemoglobin molecule. Due to the change in the protein molecule, the red blood cell (RBC) that carries the haemoglobin is sickle shaped.

Choose the best answers:

1. According to Mendel alleles have the following character

(a) Pair of genes

(b) Responsible for character

(c) Production of gametes

(d) Recessive factors

2. 9 : 3 : 3 : 1 ratio is due to

(a) Segregation

(b) Aneuploidy

(c) Euploidy

(d) Polyploidy

3. The region of the chromosome where the spindle fibres get attached during cell division

(a) Chromomere

(b) Centrosome

(c) Centromere

(d) Chromonema

4. The centromere is found at the centre of the _______________ chromosome.

(a) Telocentric

(b) Metacentric

(c) Sub-metacentric

(d) Acrocentric

5. The ________________ units forms the backbone of the DNA.

(a) 5 carbon sugar

(b) Phosphate

(c) Nitrogenous bases

(d) Sugar phosphate

6. Okasaki fragments are joined together by ____________________

(a) Helicase

(b) DNA polymerase

(c) RNA primer

(d) DNA ligase

7. The number of chromosomes found in human beings are _____________

(a) 22 pairs of autosomes and 1 pair of allosomes

(b) 22 autosomes and 1 allosome

(c) 46 autosomes

(d) 46 pairs autosomes and 1 pair of allosomes

8. The loss of one more chromosome in a ploidy is called ______________

(a) Tetraploidy

(b) Aneuploidy

(c) Euploidy

(d) Polyploidy

Fill in the blanks:

1. The pairs of contrasting character (traits) of Mendel are called _______________

  1. Genes
  2. Alleles
  3. Allotropes
  4. None of the above

2. Physical expression of a gene is called ___________

  1. Phenotype
  2. Genotype
  3. Allotrope
  4. None of the above

3. The thin thread like structures found in the nucleus of each cell are called _________

  1. Gene
  2. Centromere
  3. Chromosomes
  4. None of the above

4. DNA consists of two ___________ chains.

  1. Nucleotide
  2. Di nucleotide
  3. Tri Nucleotide
  4. Poly nucleotide

5. An inheritable change in the amount or the structure of a gene or a chromosome is called _______________

  1. Mutation
  2. Hybridization
  3. Gene alteration
  4. Gene Modification

State true or false. If false, correct the statement:

1. A typical mendelian dihybrid ration of F generation is 3:1.

2. A recessive factor is altered by the presence of a dominant factor.

3. Each gamete has only one allele of a gene.

4. Hybrid is an offspring from a cross between genetically differenctparent.

5. Some of the chromosomes have an elongated knob-like appendages known as telomere.

6. New nucleotides are added and new complementary strand of DNA is formed with the help of enzyme DNA polymerase.

7. Down’s syndrome is the genetic condition with 45 chromosomes.

Match the following:

1. Autosomes – Trisomy 21

2. Diploid condition – 9:3:3:1

3. Allosome – 22 pair chromosome

4. Down’s syndrome – 2n

5. Dihybrid ratio – 23rd pair of chromosome.


Choose the correct answers:

1.Pair of genes 2. Independent assortment 3. Centromere 4. Metacentric 5.

  1. Nitrogenous bases 6. DNA Ligase

7. 22 pairs of autosomes and 1 pair of allosomes 8.

  1. Aneuploidy

Fill in the blanks:

1.Alleles 2. Phenotypes 3. Chromosomes 4. Polynucleotide 5. Mutation

True or false:

  1. False – A typical Mendelian dihybrid ratio of F2 generation is 9: 3 : 3 : 1.
  2. True
  3. True
  4. True
  5. False – Some of the chromosomes have an elongated knob – like appendage known as the satellite.
  6. True
  7. False – Down’s syndrome is the genetic condition with 21 chromosomes.

Match the following:

1. 22 pair chromosome 2. 2n 3. 23rd pair of chromosome. 4. Trisomy 21 5. 9:3:3:1

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