Short & Long Answer Questions: Heredity - Science Class 10

Ques 1: What is heredity?
Ans: The continuity of features from one generation to another is known as heredity. It is also defined as the transmission of traits from parents to offsprings. The transmission of characters or traits from parents to their offspring (children) is termed as heredity.

Ques 2: Name the plant on which Mendel performed his experiments.
Ans: Mendel performed his experiments on the plant, Pisum sativum – the garden pea plant. Through the selective cross-breeding of common pea plants (Pisum sativum) over many generations, Mendel discovered that certain traits show up in offspring without any blending of parent characteristics. For instance, the pea flowers are either purple or white, intermediate colours do not appear in the offspring of cross-pollinated pea plants.  

Ques 3: Define variation.
Ans: Variation can be defined as any difference between the individuals in a species or groups of organisms of any species. The differences can be caused by environmental factors (phenotypic variation), called environmental variation. The variation passed on from parents to offspring, via genes, during reproduction is called inherited variation.

Ques 4: Define a gene.
Ans: A gene is a small portion of the DNA, with codes for a particular polypeptide or a protein. In other words, it is the functional unit of the DNA. It is also responsible for the transmission of hereditary characteristics from the parents to the offspring.

Ques 5: Write the expanded form of DNA.
Ans: The expansion for DNA is Deoxyribonucleic Acid.

Ques 6: What are the components of the chromosome?
Ans: Chromosome is the compact and organized structure made up of DNA and proteins. So, the major components of chromosomes are DNA. and proteins.

Ques 7: What is a retrovirus?
Ans: Retrovirus is any of a group of RNA viruses that insert a DNA copy of their genome into the host cell in order to replicate, e.g. HIV.
A virus that is composed not of DNA but of RNA. Retroviruses have an enzyme, called reverse transcriptase, that gives them the unique property of transcribing their RNA into DNA after entering a cell.

Ques 8: What is a sex chromosome?
Ans: Chromosomes that are responsible for the determination of sex in an individual are known as sex chromosomes. There are two types sex chromosomes – the X chromosome and the Y chromosome. Males possess one X and one Y chromosome and females possess two X chromosomes.

Ques 9: How is sex determined in human beings?
Ans: The male sex gametes have X and Y chromosomes, whereas the female sex gametes have two X chromosomes. When a sperm containing a Y chromosome fuses with the ovum containing X chromosome, the zygote develops into a male. When a sperm containing the X chromosome fuses with an ovum containing X chromosome, the zygote develops into a female. Thus the sex of an individual is determined by the sex chromosomes X and Y, which is present in the male chromosomes.

Ques 10: Define homologous organs.
Ans: Homologous organs are defined as the organs of different animals that are having a similar structure but differ in their functions. The structure of the two different animals resemble but the functions of their organs vary. 
Example

• Example of homologous organs are the forelimbs of frog, man, and the flippers of the whale.
• The structure of these animals are the same but they function in a different manner. The flippers are used for swimming, the forelimbs of frogs are used for jumping and propping, and the forelimbs of man are used for writing, eating, holding things, etc.

Ques 11: Explain Darwin’s theory of evolution.
Ans: Darwin’s theory of evolution is also known as the Theory of Natural Selection or Darwinism. Darwin explained that despite having enormous potential of fertility, the population size of any kind of organism remains within a limit. It is due to the struggle between members of the same species and different species for food, space, and mate. This struggle eliminates the unfit individuals. In other words, the fit organisms possess some variations, which are favorable and can leave the progeny to continue the variations. This is called Natural Selection.

Evolution
Ques 12: Define Genetics. What is the contribution of Mendel in the field of genetics?
Ans: The branch of biology that deals with the study of heredity and variations is known as Genetics. Gregor Johann Mendel  is considered the Father of Genetics. He was the first person to carry out experiments regarding the heredity of certain characters from one generation to another in a scientific manner.

• Mendel conducted breeding experiments in a plant called garden pea (Pisum sativum) with contrasting pair of characters, found that only one character of the pairs appeared in the first generation but both the characters appeared in the subsequent generation. 
• On the basis of these results of his experiments, he put forth the various principles of inheritance. He also suggested that each character is controlled by a pair of factors which are now called as genes. 

 Ques 13: Where are the genes located? What is the chemical nature of genes?
Ans: Genes are segments of the DNA, which are bound compactly into chromosomes. A gene is composed of a specific sequence of nucleotides. A nucleotide is made up of a nitrogenous base, a sugar molecule, and a phosphate group.

Ques 14: During which stage can the chromosomes be seen clearly? Write the features of the eukaryotic and prokaryotic chromosomes.
Ans: Chromosomes are distinctly visible during the Metaphase stage of mitosis of a cell.
The features of eukaryotic and prokaryotic chromosomes are as follows:
Eukaryotic chromosomes:
1. They are present in large numbers.
2. In higher organisms it occurs in paired condition.
3. They are visible distinctly only during the metaphase stage of mitosis.
4. Each chromosome consists of two chromatics attached together by a centromere.
Prokaryotic chromosomes:
1. They are simple in composition when compared to the eukaryotic chromosomes.
2. They are generally circular in shape.
3. There is only one chromosome in a cell.

Ques 15: Who provided the evidence of DNA as the genetic material? Write the names of the components of the DNA molecule.
Ans: Frederick Griffith, Avery, Mc Leod, and Mc Carty established that DNA was the carrier of genetic information.
The DNA molecule is a polynucleotide. A nucleotide is made up of a nitrogenous base, a sugar molecule, and a phosphate group.

Ques 16: What do you understand by the double helical structure of DNA? Who proposed this structure?
Ans: James Watson and Francis Crick proposed the double helical structure of the DNA. According to this structure,
• DNA molecule consists of two polynucleotide strands forming a double helix. Each helical turn has a length of 3.4nm in which ten nucleotides are present.
• Each polynucleotide strand has a backbone of sugar and phosphate. The nitrogenous base is attached to the sugar.
• The nitrogenous bases of the two strands of a double helix form a pair with the help of hydrogen bonds. Adenine pairs with thymine by two hydrogen bonds, whereas guanine pairs with cytosine by three hydrogen bonds.
• The hydrogen bonds hold the two strands of the helix together.

Double Helical Structure of DNA
Ques 17: Describe the different types of chromosomes.
Ans: The different types of chromosomes are:
Metacentric:
It is a chromosome with the centromere near the middle and the two chromatics are of equal lengths.
Sub-metacentric:
Here the centromere is situated slightly closer to one end than the other. Thus one chromatic is slightly longer than the other.
Acrocentric:
Here the chromosome is situated near one end of the chromosome. Thus one chromatic is very long while the other is very small.
Telocentric:
Here the centromere is situated at the tip of the chromosome.

Ques 18: How do embryological studies provide evidence for evolution?
Ans: The embryology of different vertebrates provide very strong evidence favoring organic evolution. The early embryos of different vertebrates show striking similarities. This indicates the common origin and ancestry of different vertebrates. Thus embryological studies provide direct evidence for evolution.

Ques 19: Define evolution. Describe the contribution of Lamarck.
Ans: Evolution is referred to as the changes acquired by a species or a certain population of a species gradually over a long period of time. These changes should be heritable.
Contribution of Lamarck:
According to the Theory of inheritance of acquired characters or Lamarckism, put forward by Lamarck, the use and disuse of an organ lead to acquiring change in the features of that organ. These changes are also inherited by the offspring. The favorable variations caused due to use and disuse after a considerably long period of time, results in evolution of a new species.

Ques 20: How do homologous organs provide evidence in support of evolution?
Ans: The presence of homologous organs indicates that all vertebrates have a common ancestry. Similarly, all organs and systems of the vertebrates show fundamental similarities, which point toward common ancestry.