why do we fall ill? notes class 9th

 Question 1.

State any two conditions essential for good health.
Solution:

• Better sanitation or clean surroundings
• Good economic conditions.

Question 2.
State any two conditions essential for being free of disease.
Solution:

• Living in hygienic environment.
• Getting vaccinated against common infectious diseases.

Question 3.
Are the answers to the above questions (2 and 3) necessarily the same or different? Why?
Solution:
Answers to above questions are interconnected but different. It is so because being disease free does not mean one is healthy.

Question 4.
List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor ? Why or why not?
Solution:
The three reasons of feeling sick and to go to see a doctor are as follows :

• having body temperature,
• having diarrhoea (loose motions), and
• having cough/cold.

If only one symptom persists, then also one should go to a doctor. The doctor will diagnose on the basis of the symptoms. Doctor will also get laboratory tests done to pin point the disease further.

Question 5.
In which of the following case do you think the long-term effects on your health are likely to be most unpleasant ?
(a) If you get jaundice,
(b) If you get lice,
(c) If you get acne. Why?
Solution:
In case of attack of jaundice, there would be long-term effects on my body. It is so because jaundice is a disease in which liver is affected. It takes more time to recover from this disease. On the other hand, lice can be removed easily with short treatment and so is the acne. Both these do not produce long¬term effects on the body.

Question 6.
Why are we normally advised to take bland and nourishing food when we are sick?
Solution:
Bland food is soft and can be easily digested and assimilated in body. Nourishing food increases resistance for disease and is essential for repair and growth of body tissue.

Question 7.
What are the different means by which infectious diseases are spread ?
Solution:
Infectious diseases are generally spread through air, water, sexual contact, vectors, physical contact with affected person and through articles of use of affected person.

Question 8.
What precautions can you take in your school to reduce the incidence of infectious diseases?
Solution:
Following precautions can be taken in the school to reduce the incidence of infectious diseases :

• Providing clean drinking water,
• Educating students about causes of infectious diseases, .
• Vacccination of students against common infectious diseases from time to time,
• Proper sanitation or clean environment in school and its surroundings to eradicate vectors of infectious diseases, and
• By not allowing the affected students to attend the classes till they recover from infectious diseases.

Question 9.
What is immunisation ?
Solution:
Immunisation is a technique in which people are given particular vaccine so that they develop temporary/permanent immunity against a particular infectious disease. In other words, immunisation is a specific way of preventing infectious diseases.

Question 10.
What are the immunisation programmes available at the nearest health centre in your locality ? Which of these diseases are the major health problems in your area ?
Solution:
Immunisation programmes are as follows :

• BCG vaccination against tuberculosis
• Polio drops against polio disease
• Vaccination against chicken pox
• Vaccination against hepatitis
• DPT vaccination against diphtheria, pertussis (Whooping cough) and tetanus.
• Immunisation against measles.

Major health problems are :

• Hepatitis
• Chicken-pox
• Tuberculosis
• Polio.

NCERT Exercises

Question 1.
How many times did you fall ill in the last one year? What were the illnesses?
(a) Think of one change you could make in your habits in order to avoid any of/most of the above illnesses.
(b) Think of one change you would wish for in your surroundings in order to avoid any of/ most of the above illnesses.
Solution:
I suffered last year from cough and cold (twice) and malaria (once).
(a) Change in habits : Wear suitable clothes in order to give protection to the body during changing season and against mosquito bite.
(b) Change in surroundings :

• Improve the sanitary conditions in the surroundings,
• Do not allow water to collect near the houses, because it provides the breeding ground for mosquitoes.

Question 2.
A doctor/nurse/health-worker is exposed to more sick people than others in the community. Find out how she/he avoids getting sick herself/ himself.
Solution:
A doctor/nurse/health worker is exposed to more sick people in the community. He/she avoids getting sick by:

• keeping place of work sterilised by using phenyl etc.
• keeping equipments, that are regularly in use, sterilised.
• washing hands with soap thoroughly after serious examination of patients.
• getting themselves vaccinated against various diseases.

Question 3.
Conduct a survey in your neighbourhood to find out what the three most common diseases are. Suggest three steps that could be taken by your local authorities to bring down the incidence of these diseases.
Solution:
After conducting a survey in my neighbourhood, I found out that the three most common diseases in my area are diarrhoea, malaria and typhoid. Three steps that could be taken by local authorities to bring down the incidences of these diseases are :

• proper disposal of garbage and regular cleaning of roads and streets
• regular cleaning of drains and spraying of insecticides
• provision of clean drinking water.

Question 4.
A baby is not able to tell her/his caretakers that she/he is sick. What would help us to find out
(a) that the baby is sick?
(b) what is the sickness?
Solution:
(a) Symptoms that help us to find that baby is sick, are :

• Continuous crying and restlessness of the child
• Improper intake of food and body temperature.

(b) Kind of sickness can be known by certain organ-specific and tissue-specific symptoms for e.g., yellowness of skin and eyes indicate the jaundice and hepatitis.

Question 5.
Under which o’, the following conditions is a person most likely to fall sick ?
(a) When she is recovering from malaria.
(b) When she has recovered from malaria and is caking care of someone suffering from chicken-pox.
(c) When she is on a four-day fast after recovering from malaria and is taking care of someone suffering from chicken-pox. Why?
Solution:
A person is most likely to fall sick in (c) condition because malaria attack has caused large scale destruction of her blood cells so she is weak and anaemic. Then she is on a four- day fast and not getting proper and sufficient food which further decreases the functioning of her immune system and lastly chickenpox is a communicable and contagious disease.

Question 6.
Under which of the following conditions are you most likely to fall sick ?
(a) When you are taking examinations.
(b) When you have travelled by bus and train for two days.
(c) When your friend is suffering from measles. Why?
Solution:
I will be most likely to fall sick when my friend is suffering from measles and I come in contact with him because measles is contagious disease and also spreads by droplet infection.

short answer questions 

Question 1.
What are the constituents of a balanced diet?
Answer:
Constituents of a balanced diet are as follows:

• Carbohydrate: It provides 50-70% of total energy intake.
• Fat: For an adult, fat should provide 20% of total energy intake. Children require more fat so as to suffice 50% of the total energy intake.
• Proteins: Protein intake should be about 15-20% of the total daily energy intake.
• Vitamins and minerals
• Water
• Roughage

Question 2.
Write four common symptoms of malaria.
Answer:

• Sudden appearance of fever with pain and sensation of cold shivering.
• Body temperature rises up to 106°F and patient becomes burning hot. He or she experiences intense headache, faster breathing rate and heart beat.
• Fever later comes down with profuse sweating. This occurs either daily at a particular time or is repeated every third or fourth day depending upon the species of the parasite.
• Enlargement of spleen and anaemia occurs.

Question 3.
Write the distinct species of malarial parasite in man.
Answer:
Malaria in man is caused by four distinct species of malarial parasites:

• Plasmodium vivax: incubation period in human is 8-17 days.
• P. falciparum: incubation period in human is 9-14 days.
• P. malariae: incubation period in human is 18-40 days.
• P. ovale: incubation period in human is 16-18 days.

Question 4.
What is the difference between being ‘healthy’ and ‘disease-free’?
Answer:
A person is said to be healthy when:

• All the organs and systems of the body are intact and working well.
• One is mentally balanced, free from anxieties and tensions.
• One is socially well-adjusted in the family, friends and society.

Whereas being ‘disease-free’ means absence of any body discomfort. Thus, being healthy is not just freedom from disease.

Question 5.
What are the immediate and contributory causes of diseases? Explain it with the example of a child suffering from diarrhoea.
Answer:
Immediate cause of a disease is the primary factor causing a disease. Contributory causes are factors, which do not cause the disease themselves but provide conditions for the disease to occur. Virus causing diarrhoea is the immediate cause. Contaminated drinking water and lack of resistance due to under-nourishment are the contributory causes.

Question 6.
Write the symptoms when following organs are targeted by microbes.
(a) Lungs
(b) Liver
(c) Brain
Answer:
(a) Lungs — cough, breathlessness
(b) Liver —jaundice
(c) Brain — headache, vomiting, fits.

Question 7.
Enlist the cause of diseases.
Answer:
Disease may be caused due to any of the following reasons:

• infection
• Lack of nutritive and sufficient food
• Poor health
• Lack of public services
• Hereditary reasons.

Question 8.
Describe health care.
Answer:
Health care is provided to vast majority of poor, rural and urban people through effective health care centres. Health care services provide different types of care at primary health care centre and ‘ secondary health care centers.
Primary health care is provided by the primary health centres established in small towns and villages, through the agency of health workers, village health guide and trained dhayas.
Secondary health care deals with more complex problems. It is generally provided in district hospitals and community health centers.

Question 9.

What determines the severity of disease manifestation?
Answer:
The number of disease-causing microbes in the body decide the severity of disease manifestation. If the number of microbes is very small, the disease manifestations may be minor and even go unnoticed. But if the number of microbes is large, the disease can be severe. In fact if the number of microbes is very large, the disease can even be fatal. Our immune system is a major factor that determines the number of microbes surviving in the body.

Question 10.
Differentiate between communicable and non-communicable diseases.
Answer:

Communicable Diseases	Non-communicable Diseases

1. These diseases can be transmitted from an infected person to a healthy person.

1. These diseases cannot be transmitted.

2. These are spread by microorganisms called pathogens.	2. These are caused by deficiency of nutrients or hormone, tumour formation, etc.
3. e.g., Cholera, influenza, AIDS, malaria, etc.	3. e.g., Diabetes, marasmus, goitre, cancer, etc.

Question 11.
Name the infectious disease that leads to immunodeficiency. Give the scientific name of the pathogen causing the disease and mention the body organs it primarily affects.
Answer:
AIDS is an infectious disease that leads to immune deficiency and wasting of body parts. It is caused by Human Immunodeficiency Virus (HIV). HIV attacks helper T-lymphocytes, thus causing cell-mediated immunodeficiency, which makes the body more prone to various infections.

Question 12.
Name fat-soluble vitamins and diseases caused by them.
Answer:
Fat-soluble vitamins include vitamin A, D, E and K.

Vitamin	Deficiency Diseases
A	Xerophthalmia, night-blindness, keratomalacia
D	Rickets in children, osteomalacia in adults
E	Anaemia
K	Bleeding disease

Question 13.
What are the causes and symptoms of goitre?
Answer:
Goitre is caused due to deficiency of iodine in the diet.
Symptoms of goitre are as follows:

• Abnormal growth of thyroid gland situated in the front part of the neck.

• Increase in body weight due to accumulation of fat and retention of water in the body.
• Increased rate of spontaneous abortion and still birth.
• Disorder in nervous system. Iodine deficiency in childhood causes reduced functioning of the thyroid gland resulting in retarded growth.

Question 14.

What are the sources of iodine? What are the prevention and control methods of goitre.
Answer:
Sources of iodine: T he best sources of iodine are sea foods and cod liver oil. A smaller amount of iodine occurs in milk, leafy vegetables, cereals and meat, etc. Iodised salt contains sufficient amount of iodine.

Prevention and control of goitre: It can be prevented by providing iodine in the diet in the form of iodised salts, such as potassium iodate and potassium iodide. These can be added in drinking water or in common salt used daily. Intra-muscular injection of iodised oil or sodium iodide tablets developed by Indian Council of Medical Research is quite effective in curing goitre.

Question 15.
What are the indirect modes of transmission of infectious diseases?
Answer:
Indirect transmission occurs through flies, food and fluid, etc. Infectious agents are transmitted through water and food including vegetable, fruits, milk, milk products, ice, blood serum, plasma, etc. Their transmission is vehicle-borne. Some examples are as follows:

2. Diarrhoea, typhoid fever, polio, cholera	Transmitted by water and food
3. Hepatitis B, malaria, syphilis, chagas disease	Transmitted by vectors

Question 16.
What are the common preventive measures against communicable diseases?
Answer:
The common preventive measures against communicable diseases include:

• Eradication of vectors and carriers.
• Immunisation (vaccination).
• Proper and safe water supply.
• Personal and community hygiene.
• Sterilisation of articles used by the patients.
• Isolation of patients from the healthy persons.
• Health education.

Question 17.
Name the diseases caused by the following—

• Protozoa,
• Virus,
• Bacteria,
• Fungi. How is malaria transmitted?

Answer:
The diseases caused by various microorganisms are as follows:

• Protozoa: Malaria, amoebiosis, dysentery, giardiasis, kala-azar, etc.
• Virus: AIDS, polio, dengue, rabies, chicken pox, influenza, etc.
• Bacteria: Pneumonia, diphtheria, tuberculosis, meningitis, leprosy, typhoid, tetanus, syphilis, etc.
• Fungi: Fungi mainly causes skin diseases and food poisoning.

Malaria is caused by a parasite found in female Anopheles mosquitoes. When the mosquitoes carrying the malarial parasite bite a person, the parasite enters the blood stream and the person suffers from malaria.

Question 18.
What are the three limitations which one has to face while dealing with an infectious disease?
Answer:
The three limitations which one has to face while dealing with an infectious disease are:

• The body functions are damaged drastically and may never recover completely if not cared.
• The treatment will take time, which means that someone suffering from a disease is likely to be bed-ridden for sometime.
• The person suffering from an infectious disease can serve as a source from where the infection may further spread to other people.

Question 19.
What is immunity? Explain natural and acquired immunity.
Answer:
Immunity means the resistance of the body to a disease. It is due to the presence of antibodies in our body against the disease-causing microorganisms known as antigens. When these antigens enter our body, antibodies are formed which prevent the disease.

Natural immunity means that a person has these antibodies since birth, e.g., whenever antigens, say of cholera enter the body, the person will not suffer from the disease.

Acquired immunity means when a person suffers from a disease once, antibodies for these particular disease-causing antigens will be formed in the body and he will not get the same disease again.

Question 20.
Give an example where tissue specificity of the infection leads to very general seeming effects.
Answer:
We can see the tissue specificity of the infection leading to very general seeming effects in case of HIV infection. The HIV attacks the immune system via the lymph nodes. From here it spreads all over the body and damages its functions. Because of this, the body becomes prone to various diseases as it cannot fight off even the minor infections which otherwise would not have lasted longer.

For example, even a small cold can become pneumonia and a minor gut infection may lead to a severe case of diarrhoea with blood loss.
In the same way, other infections kill people that are suffering from, e.g., HIV-AIDS.
The tissue specificity of the infection (HIV-AIDS) is lymph nodes. General seeming effects are loss of immunity even to minor diseases or infections that ultimately lead to the death of the patient.

Question 21.
What precautions will you take to justify “prevention is better than cure”? [NCERT Exemplar]
Answer:
Following precautions should be taken for prevention of diseases:

• Maintaining hygienic conditions.
• Awareness about the disease and its causal organism.
• Intake of a balanced diet.
• Regular medical check-up.

Question 22.
Give any four factors necessary for a healthy person.
Answer:
For a healthy person it is necessary that

• the surrounding environment should be clean. Air and water-borne diseases should not spread.
• personal hygiene is maintained to prevent infectious diseases.
• proper, sufficient nourishment and food is available for good immune system of our body.
• body is immunised against severe diseases.

Internal Assessment Activity for class X A, C &G

 For October ,You have to prepare mind map using different tools for following topics 

R.NO. 1-10 Heredity

11-20     How do organisms reproduce

21-40     Life process 

41-50    Our environment

This has to be uploaded in the classroom by Wednesday i.e. 21 October 2020 

Marks will be allotted for it 

Internal assessment activity for October class 9th

 Class 9th ------Group wise have to prepare presentation on different topics of Why do We fall ill .Topics would be allocated in the class .stay attentive on 20 October is assessment for 9th A &C  and 22nd October 9th H

Latest CBSE Sample paper and Marking Scheme @Class X

 All the class tenth students have been sent 2020-2021 latest CBSE sample paper and marking scheme ,

You all  must go through it thoroughly as the same pattern  would be used hence forth.

notes on Heredity

 Heredity 

Heredity refers to the transmission of characters from parents to offsprings. An inherited trait is a particular genetically determined feature that distinguishes a person from the others for example; attached or free ear lobes in human beings.

Mendel selected garden pea Pisum sativum plant for his experiments because of the following characteristics:

(i) The flowers of this plant are bisexual. 

(ii) They are self-pollinating, and thus, self and cross pollination can easily be performed. 

(iii) The different physical characteristics were easy to recognise and study. 

(iv) They have a shorter life span and are the plants are easier to maintain.

Rules for the inheritance of traits:
Mendel’s contribution: The rules for inheritance of traits in human beings are related to the fact that both mother and father contribute an equal amount of genetic material i.e. DNA to their offspring. So an offspring will get two versions of that trait from the two parents. Mendel worked out rules for inheritance of these traits. Gregor Johann Mendel regarded as the ‘Father of Genetics’ performed his experiments with garden peas (Pisum sativum) in the garden behind his monastery. He observed a number of contrasting characters in garden peas and observed their inheritance.

Some important terms
1. Chromosomes are long thread-like structures present in the nucleus of a cell which contain hereditary information of the cell in the form of genes.

2. DNA is a chemical in the chromosome which carries the traits in a coded form.

3. Gene is the part of a chromosome which controls a specific biological function.

4. Contrasting characters: A pair of visible charactes such as tall and dwarf, white and violet flowers, round and wrinkled seeds, green and yellow seeds etc.

5. Dominant trait: The character which expresses itself in a (Ft) generation is dominant trait. Example : Tallness is a dominant character in pea plant.

6. Recessive trait: The character which does not express itself but is present in a generation is recessive trait. Ex. dwarfism in the pea plant.

7. Homozygous: A condition in which both the genes of same type are present for example; an organism has both the genes for tallness it is expressed as TT and genes for dwarfness are written as tt.

8. Heterozygous: A condition in which both the genes are of different types for example; an organism has genes Tt it means it has a gene for tallness and the other for dwarfness only tall character is expressed.

9. Genotype: It is genetic make up of an individual for example; A pure tall plant is expressed as TT and hybrid tall as Tt.

10. Phenotype: It is external appearance of the organism for example; a plant having Tt composition will appear tall although it has gene for dwarfness.

11. Homologous pair of characters are those in which one member is contributed by the father and the other member by the mother and both have genes for the same character at the same position.

Mendel’s Experiment: Mendel started his experiment on the pea plants. He conducted first monohybrid and then dihybrid crosses.

he took pure tall (genotype TT) and pure dwarf (genotype tt) pea plants and cross pollinated them to obtain first generation or first filial generation. In this figuration (F1 generation) he obtained only tall plants. This meant that only one of the parental traits was seen, not the mixture of the two. The plants of F generation or progeny are then self pollinated to obtain F2 generation or progeny. Now all plants were not tall. He obtained 75% tall plants and 25% dwarf plants i.e. the phenotypic ratio was 3:1. This indicates that in the F, generation both tall and dwarf traits were inherited but tallness expressed it self. Tallness is a dominant trait and dwarfness is a recessive trait. F2 generation has a genotypic ratio of 1 : 2 : 1 of three types of plants represented by TT, Tt and tt as shown in the cross.

Conclusion: Phenotypic ratio—Tall : Dwarf 3 : 1
Genotype ratio—Pure Tall : Hybrid Tall : Pure Dwarf 1 : 2 : 1

Law of Dominance: When parents having pure contrasting characters are crossed then only one character expresses itself in the Ft generation. This character is the dominant character and the character/factor which cannot express itself is called the recessive character.

Dihybrid Cross: Mendel also carried out experiments to observe inheritance of two pairs of contrasting characters, which is called dihybrid cross. He cross breed pea plants bearing round green seed with plants bearing wrinkled and yellow seeds. In the Fx generation he obtained all round and yellow seeds it means round and yellow traits of seeds are dominant features while wrinkled and green are recessive. He self-pollinated the plants of F: generation to obtain F2 generation, he obtained four different types of seeds round yellow, round green, wrinkled yellow and wrinkled green in the ratio of 9 : 3 : 3 : 1. He concluded that traits are independently inherited

Conclusion

• Round and yellow seeds-9.
• Round and green seeds-3.
• Wrinkled and yellow seeds-3.
• Wrinkled and green seeds-1.
• How do traits get expressed?
  Cellular DNA is the information source for making proteins in the cell.
  A part of DNA that provides information for one particular protein is called a gene for that protein for example; the height of a plant depends upon the growth hormone which is in turn controlled by the gene. If the gene is efficient and more growth hormone is secreted the plant will grow tall. If the gene for that particular protein gets altered and less of it is secreted when the plant will remain short. Both the parents contribute equally to the DNA of next generation during sexual reproduction. They actually contribute a copy of the same gene for example; when tall plant is crossed with short plant the gametes will have single gene either for tallness or for shortness. F1 generation will get one gene for tallness and other for shortness also.
  

How do germ cells i.e. gametes get single set of genes from parents who have two copies in them ?
Each gene set is present, not as a single long thread of DNA, but as separate independent pieces each called a chromosome. Each cell gets two copies of the chromosome, one from each parent. Each germ cell or gamete has one copy of it because there is reductional division in the sex organs at the time of formation of gametes. When fertilization takes place normal number of chromosomes is restored in the progeny ensuring the stability of DNA of the species.

How is the sex of a newborn individual determined?
It is the process by which sex of a newborn can be determined.

Different species use different strategies for this :

• In some animals the temperature at which fertilized eggs are kept determines whether the developing animals will be males or females.
• Some animals like snails can change sex indicating that sex is not genetically determined.
• In human beings sex of the individual is determined genetically; means genes inherited from the parents decide the sex of the offspring.




Sex determination in human beings: In human beings, all chromosomes are not paired. 22 chromosomes are paired but one pair called sex chromosome is odd in not having a perfect pair in males. Females have a perfect pair both represented by XX. On the other hand males have a normal sized X but the other is short called Y so it is shown as XY. All gametes or ova formed by the homogenetic female are similar i.e. have X chromosome. Males heterogenetic form two types of sperms i.e. half with X chromosome and the other half with Y chromosome. Sex of the baby will depend on fertilization. There are two possibilities :


Autosomes: Those chromosomes which do not play any role in sex determination.

Sex chromosomes: Those chromosomes which play a role in determining sex of the newborn.

• If the sperm having X chromosome fertilizes with ovum with X chromosome then the baby will have XX chromosome and it will be female.
• If the sperm having Y chromosome fertilizes with ovum with X chromosome then the baby will have XY chromosomes and it will be male.

• Remember!
  Variations are produced both in sexual and asexual reproduction but amount of variations produced in asexual reproduction are subtle (so little) that they are hardly noticeable as compared to variations caused due to sexual reproduction.

  4. Genotype : The genetic constitution of an organism e.g., Genotype of human male is 44 + XY and
  genotype of human female is 44 + XX

  5. Phenotype : The appearance of the organism, i.e., the way in which genotype is expressed. Phenotype is the result of interaction of genes with the environment.
  e.g., Red colour may be controlled by a pair of genes RR. Now if genotype is RR phenotype will be red only but if genotype is Rr then also phenotype will be red since R is a dominant gene.

  6. Gene : It is the basic unit of inheritance by which characters are transferred from parents to their offspring. Gene consists of a specific length of DNA on a chromosome. A specific Segment of DNA that provides the information for one protein is called gene for that protein.
  According to Mendel, both parents must contribute equally to the DNA of the progeny during sexual reproduction. As both parents determine the trait in the progeny, so both parents must be contributing a copy of the same gene.

  7. Chromosomes : These are the long threads present in the nucleus of every cell. Chromosomes are made- up of DNA and protein. Each chromosome contains very long molecule of DNA.
  Remember!
  Each gene set is present as separate independent pieces each called a chromosome. Each cell have two copies of each chromosome, one each from male and female parents. Every germ cell will take one chromosome from each pair and these may be of either maternal or paternal origin. When two germ cells combine, they will restore the normal number of chromosomes in the progeny, ensuring the stability of the DNA of the species. Such mechanism of inheritance is used by all sexually and asexually reproducing organisms.

  8. Allele: It is an alternative form of a gene occupying the same position on a chromosome and affecting the same characters but in two alternative ways, e.g., the free and attached ear lobe are the alleles of ear lobe character.
  Expressing allele of a gene :

  • Homozygous dominant in capital letters, e.g., tallness(TT)
  • Homozygous recessive in smalMetters, e.g., shortness or dwarfness (tt)
  • Heterozygous (Tt)-lt will be called hybrid tall.

  9. Dominant allele: An allele that affects the phenotype of an organism both in heterozygous and homozygous condition. It is denoted by a capital letter, e.g., tallness in pea plant is denoted by ‘T.

  10. Recessive allele: An allele that affects the phenotype of the organism in absence of a dominant allele, i.e., in homozygous recessive individuals. It is denoted by a small alphabet, e.g., dwarfness in pea plant is denoted by’t’.

  11. Homozygous: When both alleles of a particular gene are the same, e.g., TT

  12. Heterozygous : When both alleles of a particular gene are different, e.g., Tt

  13. Diploid : Cells or organism containing two sets of genes, e.g., human body cells. Diploid cells have genetic constitution of 2n.

  14. Haploid : Cells or organism containing one set of genes, e.g., human reproductive cells (sperms and ova). Haploid cells have genetic constitution of n.

  15. Monohybrid cross : A cross between two parents taking the alternative traits of one single character, e.g., A cross between tall and dwarf pea plants.
  Monohybrid Ratio :

  • In F1 generation : 100% hybrid
  • In F2 generation : phenotypic ratio is 3 : 1 and genotypic ratio is 1 : 2 : 1

  16. Dihybrid cross: A cross between two parents taking into consideration alternative traits of two different characters, e.g., A cross between two pea plants one having round, green seeds and the other having wrinkled, yellow seeds.
  Dihybrid Ratio :

  • F1 ratio is 100% Hybrid type.
  • F2 ratio : Phenotypic is 9 : 3 : 3 : 1 and Genotypic . ratio is very complex.

  17. Human Blood Groups: There are four types of blood groups A, B, AB or O. These are controlled by a gene which is denoted by symbols IA, IB and IO (sometimes also denoted as i). The genes IA and IB show no dominance over each other (they are codominant, i.e., both expresses themselves independently). But these both genes are dominant over the gene IO. Therefore, blood group of a person depends on the type of genes present, e.g., (i) Blood group A has the following gene types :
  

  18. Determining sex of a newborn individual genetically:

  • In human beings the sex of the individual is ” determined genetically.
  • There are 23 pairs of chromosomes of which 22 are similar in male and female and are known as autosomes.
  • The remaining one is sex chromosome which is XY in males and XX in females.
  • Males produce two types of sperms X and Y, while female produces one type of egg X.
  • If a X type of sperm fertilizers the egg then the sex of baby will be female (XX).
  • If Y type of sperm fertilizers the egg then the sex of the baby will be male (XY).
    

  19. Mendel’s experiment to show that traits may be dominant or recessive:

  • Mendel conducted breeding experiments in garden pea.
  • selected pure plant of a tall/short plant.
  • produced first generation plants by crossing them.
  • found that all plants were tall.
  • produced the second generation by self-fertilization of hybrids.
  • found that three-quarter of the plants was tall and one quarter was short.