Heredity in Organisms & evolution
Biology
Q/A
1. What is RNA?
Ans: RNA stands for ribonucleic acid. Most RNA has contained a single polypeptide strand. It is composed of 5 carbon ribose sugar, inorganic phosphate and nitrogen bases (adenine, guanine, cytosine and uracil).
Q.2. Why is chromosome called the physical basis of heredity?
Q.3. What is gene?
Q.4. What is chromosome?
5. What is an autosome?
Ans: In human and other mammals sex is determined in the same way. In the cells of the human body, the number of chromosomes is 46, i.e. 23 pairs. Among them 22 pairs are autosomes and the remaining pair is the sex chromosome. Autosomes play roles in physiological and embryonic development and the formation of the body of organisms which have no part in determining sex.
6. What does Thalassemia mean?
Ans: Thalassemia is a disease of abnormal state of red blood cells. Because of this disease, red blood cells disintegrate. the patient suffers from anemia. This disease genetically passes from generation to generation. It is an autosomal recessive disorder. i.e., when both father and mother are the carrier or both are the patient of thalassemia, only then does it dominates in the offspring. When the marriage is held between maternal and paternal cousins or between close ( blood related) relatives there is a higher probability of giving birth to a child with thalassemia.
7. Describe with diagrams, how DNA replicates itself.
Ans: Through the process, a new DNA molecule is synthesized from an existing molecule of DNA. DNA replicates in a half-conservative way. Through this process, the double stranded DNA becomes single stranded by breaking hydrogen bonds. Then the floating nucleotide in a cell creates new complimentary strands by combining "A" (adenine) with 'T' (Thymine), 'T' with A, 'C' with 'G' and 'G' with 'C'. Thus one of the old strands remains and combines with a new strand to make a complete DNA. At the end, a new strand, combining with another old strand, forms the structure of a molecule of DNA. As the new DNA emerges, it has a new and an old strand. This principle is knows as the semiconservative method. In 1956 Watson and Crick first successfully proposed the replication process of DNA.
8. What is allele?
Ans: Each gene can have different forms and these alternative forms of the same gene are called alleles. For example, the gene for height of pea plants has two alleles: short and tall. On the other hand, the gene for pea flower colour has two alleles: purple and white. Mendel's "factor" are the alleles in modern terminology.
Multiple Choice Questions
1. Where is uracil found?
a. DNA
b. RNA
c. Gene
d. Locus
2. Which one does RNA contain?
i. ribose sugar
ii. inorganic phosphate
iii. nitrogenous bases
Which one of the following is correct?
a. i
b. i & ii
c. ii & iii
d. i , ii & iii
Answer the questions 3 & 4 using the figure given below -
3. In the state of X what is the number of chromosomes?
a. 46
b. 44
c. 23
d. 22
4. What type of chromosomes are there in A and B?
a. X, XY
b. X, XX
c. Y, XX
d. Y, XY
CREATIVE QUESTIONS:
1. Sifat is a farmer. He has two daughters. The older daughter looks like her father. While the younger daughter's hair and complexion are like her father, she looks like her mother. As the mother has given birth to a female child recently. Sifat became aggrieved with his wife. One day he learned from the health workers of his village that he is responsible in determining the sex of his offspring.
a. What is heredity?
Ans: The process of transferring characteristics of parents to offsprings generation often generation is called heredity.
b. What is replication?
Ans: Replication is a process by which a new DNA molecule is synthesized from a molecule of DNA. Through this process the double stranded DNA becomes single stranded by breaking Hydrogen bonds in between them and each strand causes the emergence of a new strand. At the end, a new strand, combining with another old strand forms the structure of molecule of DNA.
c. What are the causes of physical development differences found in the offspring of Sifat?
Ans: As Sifat's elder daughter is like his father. So, the dominant gene comes from her father face and the gene of her mother's face is located in her body as recessive gene.
In other way the younger girl's hair colour and colour of her body is like her father but the face is like her mother. So the dominant gene for hair or body colour in her body come from his father and dominant gene for her face comes from her mother.
d. It is irrational that Sifat got aggrieved with his wife. Explain why.
Ans: Sifat got anguished with his wife because they have only two daughter, no son. So, Sifat thinks that his wife is responsible for having only daughter but from health worker he can know that he is responsible for having only daughter. Because if he wants a baby boy then a Y chromosome from him have to make the XY chromosome pair to have a son. His wife is not responsible because female has only XX chromosome pair. They do not have Y chromosome.
So, it is irrational that Sifat got anguished with his wife.
2. Ronzon has seen on television that an exhibition of pet cats is going on in a town of Brazil. He saw that in spite of their belonging to the same species, they look different in size, colour. Some days later, he watched film about growing up of wild cats. His father explained to him the concept of evolution and adaptation when he became interested to know more about it.
a. What is locus?
Ans: The location of a gene throughout a chromosome is called locus.
b. What do you understand by the term adaptation?
Ans: In this world the different creatures are living in the different atmosphere of the world. With the change in environment the organisms are struggling to survive and to protect themselves different types of changes occur. This process of surviving in different atmosphere of the world is called adaptation.
c. Explain the causes of difference with the animals seen by Ronzon.
Ans: Ronzon has watched on television channel that pet cats are being killed in a town of Brazil. In spite of their belonging to the same species, they look different in size and colour. These happens because of adaption.
With the change in the environment living creatures face different changes in them to survive in this world. This is the cause of difference with the animal seen by Ronzon.
d. What will happen if the organisms in the stem first group are left in the environment where the animals of the second group were found?
Ans: The organisms found in the stem are pet cats and wild cats. If the pet cats are left in the environment where the animals of second group found. Then the first group will try to adapt themselves in the environment. There will be changes in them to cope with the environment. Little animals have to fight or escape from big animals may be some of them will die and others will struggle to survive.
DNA:
The main component of a chromosome is deoxyribonucleic acid (DNA). It is usually a double stranded spiral structure of polynucleotides. One strand is complementary to the other. In it there are five carbon sugars, nitrogen bases (adenine, guanine, cytosine, thymine) and inorganic phosphate. These three components collectively are called a nucleotide. DNA is a stable substance in a chromosome. In 1953 American scientist Watson and British scientist Crick first described the double helical structure of DNA and for this contribution both of them won the Nobel Prize. Nitrogen bases are of two types,
a purine and
a pyrimidine.
Adenine, guanine are purines and cytosine and thymine are pyrimidines.
The Adenine of one strand bonds with the thymine of another strand by two hydrogen bonds, and guanine of a helix connects with a cytosine of another helix by three hydrogen bonds. This bond is always developed between a purine and pyrimidine. So, a strand of DNA is complementary to another strand but not identical to it. A complete twist in a helix is 34 A long and in a complete twist, there are ten nucleotides. So, the length between the two adjacent nucleotides is 3.4 A. The two strands of polynucleotides in DNA are positioned antiparallelly. It looks like rungs in a twisted ladder. The bases are connected flatly and horizontally in position from the main axis. The external two strands or two axes of DNA are composed of consecutive arrangements of sugar and phosphate and internal nitrogen bases are plainly aligned.
Differences between DNA and RNA :
DNA:
The main component of a chromosome is deoxyribonucleic acid (DNA).
It is usually a double-stranded spiral structure of polynucleotides.
DNA is a stable substance in a chromosome.
In a DNA molecule, there are four: adenine, thymine, guanine and cytosine.
RNA:
RNA stands for ribonucleic acid. Most RNA has contained single polypeptide strand.It is composed of 5 carbon ribose sugar, inorganic phosphate and nitrogen bases (adenine, guanine, cytosine and uracil).
DNA Test:
A scientific and practical method of DNA test is called DNA fingerprinting. The name DNA typing or DNA testing is also used. To perform the DNA test, the first requirement is an organic specimen. Bone of a person, teeth, hair, blood, saliva, semen can serve as valuable organic specimens. The profile from the place of occurrence of crime or the profile from the specimens of the victim of a crime is compared with the profile obtained from the blood or organic specimen of a suspect.In this method DNA is isolated from the sample by a chemical process and then DNA are cut into pieces by one or more restricted enzymes. Then, through a special method the pieces of DNA are sorted according to the length of different bands.Active isotope DNA pro is hybridized, keeping it on a special nitro cellulose paper and then putting it on an x-ray film to determine different visible bands by autoradiography method. After that, the sample is compared with DNA band of the victim or suspected person. This method is termed as finger print method. Currently by using polymerase chain reaction (PCR) method DNA test is done with even a small sample for identification without any error.
Difference Between Chromosome and Gene:
Gene:
Chromosome:
How Genotype affects Phenotype?
Ans:
Phenotype:
The expressed trait in an individual, e.g. outward appearances such as height and eye colour.
Therefore, the characteristics of an organism which can be seen, such as tallness and dwarfness in pea plants, are phenotypes.
This is the genetic make-up of an organism, i.e. the genes and their respective alleles. So, dwarf pea plants have the genotype tt while a tall plant may have the genotype either TT or Tt.
Therefore, a dominant allele expresses itself and gives the same phenotype in both the homozygous (TT) and heterozygous condition. It expresses itself only in the homozygous condition (tt).
The phenotypes depends on the alleles of a gene present in the cells of an organism. Every cell contains two alleles of each gene - one from each parent. The phenotype they produce depends on whether the alleles are dominant or recessive.
Genotypes:
Genotypes affects phenotype:
A person with the genotype HbAHbA has two copies of the gene in each cell coding for the production of the normal beta - globin polypeptide. All of the person's haemoglobin will be normal.
A person with the genotype Hbs Hbs has two copies of the gene in each cell coding for the production of the sickle cell Beta-globin polypeptide. All of this person's haemoglobin will be sickle cell haemoglobin, which is inefficient at transporting oxygen. The person will have sickle cell anaemia. This is a very dangerous disease, in which great care has to be taken not to allow the blood to become short of oxygen, or death may occur. A person with the genotype HbAHbs has one allele of the Beta-globin gene in each cell coding for the production of the normal B-globin, and one coding for the production of the sickle cell Beta-globin, Half of the person's haemoglobin will be normal,and half will be sickle cell haemoglobin. Such people have sickle cell trait, and are sometimes referred to as 'carrier'. They will probably be completely unaware that they have sickle cell trait, because they have enough normal haemoglobin to carry enough oxygen, and so will have no problems at all. They will appear to be perfectly healthy. Difficulties arise only very occasionally - for example, if a person with sickle cell trait does strenuous exercise at high altitudes, when oxygen concentrations in the blood might become very low.
Genotypes of eggs
Chapter-5: The mitotic cell cycle
AQA-2018:
Q. 6.8. Some people disagree with the use of stem cells because of the risk of cancer.
Ans: Some people disagree with the use of stem cells to create new organs for transplants because idea of ethical concerns about use of embryos such as loss of human life.
Q.3. Describe the significance of stem cell.
A stem cell is a cell that can divide an unlimited number of times (by mitosis). When it divides, each new cell has the potential to remain a stem cell or to develop (differentiate) into a specialised cell such as a blood cell or muscle cell. So, let me show you what I mean by that.
The extent of the power of a stem cell to produce diferrent cell types is variable and is referred to as its potency. Stem cells that can produce any type of cell are described as totipotent. The zygote formed by the fusion of a sperm with an egg at fertilization is totipotent, as are the cells up to the 16- cell stage of development in humans.
After that, some cells become specialised to form the placenta, while others lose this ability but can form all the cells that will lead to the development of the embryo and later the adult. These embryonic stem cells are described as pluripotent. As tissues, organs, and systems develop, cells become more and more specialized. There are more than 200 different cell types in an adult human body.
The more 'committed' cells become to particular roles, the more they lose the ability to divide until, in the adult, most cells do not divide.
However, for growth and repair it's essential that small populations of stem cells remain which can produce new cells. Adult stem cells have already lost some of the potency associated with embryonic stem cells and are no longer pluripotent. They are only able to produce a few types of cell and may be described as multipotent. For example, the stem cells found in bone marrow are of this type. They can replicate any number of times but can produce only blood cells such as red blood cells, such as red blood cells, monocytes neutrophils, and lymphocytes. Mature blood cells have a relatively short lifespan, so the existence of these stem cells is essential. For example, around 250 thousand million red blood cells and 20 billion white blood cells are lost and must be replaced each day.
In the adult, stem cells are found throughout the body- for example in the bone marrow, skin, gut, heart and brain. Research into stem cells has opened up some exciting medical applications. Stem cell therapy is the introduction of new adult stem cells into damaged tissue to treat disease or injury. Bone marrow transplantation is the only form of this therapy that has progressed beyond the experimental stage into routine medical practice, but in the future, it's hoped to be able to treat conditions like diabetes muscle and nerve damage, and brain disorders such as Parkinson's and Huntington's diseases.
Differences Between Continuous & Discontinuous Variation
Q. 1. What is variation?
Q.2. What are the differences between continuous and discontinuous variation?
Continuous variation:
Discontinuous variation:
