Maharashtra Board Class 9 Science Solution Chapter 16 – Heredity and Variation
Balbharati Maharashtra Board Class 9 Science Solution Chapter 16: Heredity and Variation. Marathi or English Medium Students of Class 9 get here Heredity and Variation full Exercise Solution.
Std |
Maharashtra Class 9 |
Subject |
Science Solution |
Chapter |
Heredity and Variation |
1.) Complete the following sentences by choosing the appropriate words from the bracket.
(Inheritance, sexual reproduction, asexual reproduction, chromosomes, DNA, RNA, gene)
Ans:
a) Hereditary characters are transferred from parents to offspring’s by gene hence they are said to be structural and functional units of heredity.
b) Organisms produced by asexual reproduction show minor variations.
c) The component which is in the nuclei of cells and carries hereditary characteristics is called chromosomes.
d) Chromosomes are mainly made up of DNA.
e) Organisms produced through sexual reproduction show major variations.
2.) Explain the following.
- a) Explain Mendel’s monohybrid progeny with the help of any one cross.
Ans:
Monohybrid cross is the cross between two parents which are having one of the contrasting character.
For example:
- When we cross pea plant with yellow seed coat with the pea plant with green seed coating then there will be all yellow seeds are produced in F1 generation.
- The cross between tall and dwarf plants as shown in figure.
b) Explain Mendel’s dihybrid ratio with any one of the cross.
Ans:
Dihybrid cross is the cross between two parents which are having two contrasting character.
For example:
- When we cross between round and yellow seeds of pea plant with the wrinkled and green seeds of pea plant then in F1 generation round and yellow seeds of pea plant produced.
- The following figure shows the dihybrid cross between seeds of pea plant having contrasting characters.
c) Distinguish between monohybrid and dihybrid cross.
Ans:
Monohybrid cross:
- Monohybrid cross is the cross between the two parents which are having only one contrasting character.
- Monohybrid cross is helpful in calculating the dominance in genes.
For example:
- The cross between tall and dwarf plant is the monohybrid cross.
- The cross between pea plant with yellow seed coating and the pea plant with green seed coating is also the example of monohybrid cross.
- When we cross pea plant with yellow seed coat with the pea plant with green seed coating then there will be all yellow seeds are produced in F1 generation.
Dihybrid cross:
- Dihybrid cross is the cross between two parents which are having two contrasting character.
- Dihybrid cross is helpful in studying the assortment of the offsprings.
For example:
- The cross between the tall plant with red flower and the dwarf plant with white flower is the dihybrid cross.
- Also the cross between round and yellow seed of pea plant with the wrinkled and green seeds of pea plant is also the dihybrid cross.
- When we cross between round and yellow seeds of pea plant with the wrinkled and green seeds of pea plant then in F1 generation round and yellow seeds of pea plant produced.
- The following figure shows the dihybrid cross between seeds of pea plant having contrasting characters.
d) Is it right to avoid living with the person suffering from genetic disorder.
Ans:
- It’s not right to avoid living with the person suffering from genetic disorders. Because genetic disorders are not the communicable disease which may spread when we come in contact with that person.
- But genetic disorders may transmitted from one generation to another generation under certain circumstances which are caused due to the changes in the DNA sequences.
- Hence we can’t avoid to live with people suffering from genetic disorders, we have to live normal life with them so that they can also be feel better.
3.) Answer the following questions in your own words.
a) What is mean by chromosome? Explain its types.
Ans:
- The structure in the nucleus of cells which carries hereditary characteristics is called as chromosome which is mainly made up of nucleic acids and proteins.
- It is made up of DNA appearing dumbbell shaped midway during the cell division.
- There are four types of chromosomes which are classified on the basis of position of their centromeres.
The following are the types of chromosomes.
1) metacentric chromosome:
- In metacentric chromosome the centromere is situated at the middle so that two equal arms will be formed and hence the chromosome looks like English letter V as shown in figure below.
2) sub – metacentric chromosome:
- In sub-metacentric chromosome the centromere is situated slightly apart from the exact middle position so that two arms will be formed out of which one is longer than the other and hence it looks like the English letter L as shown in figure below.
3) Acrocentric chromosome:
- In Acrocentric chromosome the centromere is situated at the one end of the chromosome due to which one arm formed will be very longer and the other arm will be very shorter and hence it looks like a English letter j as shown in figure below.
4) Telocentric chromosome:
In Telocentric chromosome the centromere is located at the one of the terminal end so that the chromosome has only one arm and hence looks like English letter i as shown in figure below.
b) Describe the structure of DNA molecule.
Ans:
- Molecules of DNA are present in all organisms from viruses and bacteria to human beings which controls the functioning, growth and reproduction of the cell and hence they are called as the master molecules.
- The DNA structure is same in all organisms. In which two parallel threads of nucleotides are coiled around each other which is called as double helix which is compared with the coiled and flexible ladder.
- There are four types of nitrogenous bases namely adenine, guanine, cytosine and thymine.
- Adenine and guanine are collectively called as purines while cytosine and thymine are collectively called as pyrimidines.
- Nucleotide structure are formed by a molecule of nitrogenous base and phosphoric acid which are joined to each sugar molecule.
- Nucleotides in DNA are arranged like a chain. The two threads of the DNA molecule are comparable with the two rails of a ladder and out of which each rail is made up of alternated sugar and phosphoric acid molecule.
- Each rail of the ladder is the pair of nitrogenous bases which are joined by hydrogen bonding
- And here adenine always pair with thymine while cytosine always pairs with guanine.
c) Explain your opinion about the DNA fingerprinting.
Ans:
- DNA fingerprinting is the sequence of genes in the DNA of a person i.e. genome of the person is This technology is useful to identify the lineage and identify the criminals because it is unique to every person.
- DNA fingerprinting method is used only for comparing the DNA sequences of any two individuals as discussed earlier.
- In all the individuals 99.9% sequences of DNA are same or equal only 0.1% of the sequence are different which make each individual as unique and hence we can use DNA fingerprinting technology in identifying the criminals also.
- There are huge application of DNA fingerprinting technology in now a days which are discussed as below.
- DNA fingerprinting technology is mainly used in forensic and it is also used in studying the evolution and genetic diversity in population.
- All these are the uses of DNA fingerprinting technology which has huge importance.
d) Explain the structure, function and types of RNA.
Ans:
- RNA is the second most important nucleic acid present in the cell which is made up of ribose sugar, phosphate molecules and four types of nitrogenous bases adenine, guanine, cytosine and uracil.
- Nucleotide is the smallest unit of the chain of the RNA which is formed by the combination of a ribose sugar, phosphate molecule and any one of the nitrogenous base.
- When large number of nucleotides are bonded together then there will be macromolecule of RNA will be formed.
- According to function of RNA there are three types of RNA molecule which are discussed below.
- Ribosomal RNA (rRNA):rRNA is the component of ribosome organelle which performs the function of protein synthesis.
- Messenger RNA (mRNA): Messenger RNA carries the information from genes that means from DNA chain in the nucleus to ribosome in the cytoplasm which produces the proteins.
- Transfer RNA (tRNA):according to message of mRNA carries the amino acid up to the ribosomes is called as tRNA.
e) Why it is necessary for people to have their blood examined before their marriage?
Ans:
- It is necessary for people to have their blood examined before their marriage because genetic disorders are mainly transmitted through the reproduction.
- If both the person’s getting married are carrier or sufferer from genetic disorders then there will be 100% chances of getting genetic disorders to their offspring’s also. To avoid this transmission of genetic disorder people have to examine their blood before their marriage.
4.) Write a brief note on each.
a) Down syndrome
Ans:
- It is the disorder arises due to chromosomal abnormality. Down syndrome is the first discovered and described chromosomal disorder in the human beings which is mainly characterised by the presence of 47 chromosomes.
- That means it is described as the trisomy of 21st The infant’s suffering from this disorder has the one extra chromosome with 21st pair in every cell of their body and hence they possesses 47 chromosomes instead of 46.
- The children’s suffering from down syndrome are mentally retarded and are having short lifespan.
- The symptoms also included are short height, short wide neck, flat nose, short fingers, scanty hair, single horizontal crease on palm and having life span of about 16-20 years only.
b) Monogenic disorders
Ans:
- The disorders occuring due to mutation in any single gene into a defective one are called as monogenic disorders. Approximately 400 different disorders of this monogenic type are known today.
- Due to this disorder there will be abnormal metabolism which may leads to death at a tender age.
- The genetic disorders caused due to mutation in single gene are the Monogenic disorders and it will be present on one or both of the chromosomes.
- For example: Hutchinson’s disease, Tay-Sachs disease, galactosemia, phenylketonuria, sickle cell anemia, cystic fibrosis, Albinism, haemophilia, night blindness etc.
c) Sickle cell anaemia: symptoms and treatment
Ans:
- In normal haemoglobin has glutamic acid as the 6thamino acid in its molecular structure, when it is replaced by valine then there will be change in shape or structure of the haemoglobin molecule takes place.
- Due to which RBCs which are biconcave already becomes sickle shaped and the condition is called as sickle cell anaemia.
- In such individuals the oxygen carrying capacity of haemoglobin is very low due to which there will be clumping and destruction of erythrocytes occured mostly.
- Hence blood vessels get obstructed and the circulatory system, brain, lungs, kidney may get damaged. As sickle cell anaemia is the hereditary disorder hence it occurs due to changes in DNA genes during conception.
The symptoms of sickle cell anaemia are as follows:
- Swelling of hands and legs, pain in joints, severe general body aches, frequent colds and coughs, constant low grade fever, exhaustion, pale face and low haemoglobin contents.
Treatment of sickle cell anaemia:
- Under the national health scheme, the solubility test for the treatment of sickle cell anaemia is available at all district level hospitals.
- The confirmatory test which is electrophoresis is done at rural and sub district hospitals level.
5.) How are the items in group A, B and C interrelated.
Ans:
1) Leber hereditary optic neuropathy: Mitochondrial disorder: This disorder aries during development of zygote.
2) Diabetes: Polygenic disorder: Effect on blood glucose level.
3) Albinism: Monogenic disorder: Pale skin, white hairs.
4) Turner syndrome: (45+X): Women are sterile.
5) Klinefelter syndrome: (44+XXY) : Men are sterile.
6.) Fill in the blanks based on the given relationship.
Ans:
a) 44+X: Turner’s syndrome; 44+XXY: Klinefelter Syndrome
b) 3:1: Monohybrid; 9:3:3:1: Dihybrid cross
c) Women: Turner’s syndrome; Men: Klinefelter syndrome
7.) Complete the tree diagram below based on types of hereditary disorders.
Ans: