Genetics – Some Basic Fundamentals Class 10 ICSE Notes
ICSE Class 10 Biology Chapter 3 Genetics – Some Basic Fundamentals Notes, Summary, Definition, Diagram. Genetics – Some Basic Fundamentals Notes.
3.1 What is genetics?
It is the study of how genes transfer from parent to offspring. There are two parts in study of genetics one-part deals with the transfer of characters which is referred to as heredity. And the second part deals with variations.
Gregor Mendel: FATHER OF GENETICS
- He was a monk by profession.
- He gave the basic laws of genetics now popularly known as the Mendel’s laws of inheritance.
- The law is based on the inheritance pattern of garden peas.
Modern applications of genetics:
- Genetic engineering is a technique of creating genetically modified organisms which can be then used for large scale production of molecules like insulin.
- Genetic counselling for determining the possibility of getting diseases like thalassemia, hemophilia etc.
- Heredity: it is the transfer of characters to children from parent organisms in form of genetic materials. Due to this organism produces organisms similar to itself.
3.2 Variations in a population:
- All organisms belonging to a species are not identical. There are small differences in a population which are called as variations.
- Any feature of an organism is called a character. Any alternate form of a character is called a trait.
3.3 Chromosomes: carriers of heredity
- Karyotyping: the chromosomesare of differentsizesand shapes. The comparative study of different sizes and arrangement of chromosomes is called karyotyping.
- For any given organism the number of chromosomes is constant.
- The chromosomes are found in pairs. An organism receives one copy of a chromosome from each parent.
- Homologous chromosomes are similar chromosomes from each parent which have similarstructureand function.
- For example, is humans have 23 chromosomes which have come from each parent have 46 copies of chromosomes of all together.
3.4 Autosomes and sex chromosomes:
- There are 2 types of chromosomes autosomes and sex chromosomes.
- In humans the female parent provides withX chromosomes. Female have 2 copies of the X chromosome.
- In case of males, they have one copy of X chromosome and another copy of Y chromosome.
- The Y chromosome is smaller in size as compared to Y chromosomes.
- Autosomes are responsible for general or somatic characters like height, color etc.
- Sex chromosomes are responsible for determining the sex of the baby.
3.5 SEX DETERMINATION
- There are two possible genders males and females. Which are determined depending on the type of sex chromosomes they receive from parents
- The egg of female has only a single type of gamete which is the X chromosome.
- The sperms on the contrary are composed of 2 different types of chromosomes. Half of the sperms have X chromosomes and the other half have Y chromosome.
- If the fusion between the egg containg X chromosome with a sperm containg y chromosome is carried out then male offspring or sons are produced
- If the fusion between the egg containg X chromosome with a sperm containg X chromosome is carried out then female offspring or sons are produced.
- The sex of the baby is dependent on which sperm fertilizes the egg.
3.6Chromosomes: carriers of Genes.
- Genes are the structural and functional unit of life. They are specific segments of DNA
- They are carriers of information from one generation to the next.
- The genome is composed of genes and intergenic regions.
- Current studies suggest that human have about 19000 genes. Of which maximum are present in on chromosome no.1 and the least no are present on Y chromosome.
3.7 Genes and alleles
- Alternative form of a gene is referred to as alleles. It is present on the same locus/position in homologues chromosomes.
- Alleles code for variations in characters encoded by genes.
- These variations are responsible for a character in an organism
- Due to such variations in characters an allele can be classified as either dominant allele or recessive allele.
- Dominant allele: The character which is expressed in the F1 Generation irrespective of presence or absence of another allele is called dominant characters.
- Recessive allele: the form of gene whose expression is masked by dominant gene is termed as recessive.
3.8 Genotype and Phenotype
- Genotype: it is kind of genes an organism possesses.
- Phenotype: the expressed genes provide the organisms with a unique form.
- Heterozygous dominant: they have two different types of alleles e.g., Rr
- Homozygous dominant: they have same type of Allele e.g., RR
- Recessive alleles are expressed only in homozygous form
3.9 how to read a pedigree
- Males are denoted by
- Females are denoted by
- Solid or filled circle indicate affected organism
- If offspring has recessive trait, then at least one parent should also have same recessive allele
- recessive traitis expressed in homozygous condition only so one copy of each recessive allele should be received from both the parents.
- In case of heterozygous offspring one dominant allele and one recessive allele is obtained from either parent.
3.10 Sex linked inheritance
- It is the genetic disease caused due to presence of gene only on sex chromosomes
- Examples include hemophilia and color blindness
- Its cause is inheriting a recessive allele on the X Chromosome
- Hemophilia is one such disease.in it the blood is prevented from clotting in case of wound or injury
- Sex linked diseases are passed in crisscross manner that is from father to daughter (may be carrier/affected) to grandson who is affected
- CASE 1: when Normal mother and color-blind father have children all the daughter will be carrier (XX°) as they receive X° from affected father and sons are normal
- CASE 2: when carrier mother and normal father have children, they might have normal daughter, normal son, carrier daughter (XX°) and color-blind son (X°Y) as they receive X° from affected mother.
3.11 Mendel’s experiment on an experiment
- Mendel performed his inheritance experiment on garden peas
- He selected the plant for the following reason;
- multiple characters can be studied at the same time.
- Pure lines can be established with ease
- Self-pollination and cross pollination can be easily performed.
- Less lifespan enables to obtain many generations in less time.
- Mendel studied the pea plant considering one character at a time (monohybrid cross). after that he also described the dihybrid cross.
The following characters were studied by Mendel: flower color, seed color, seed shape, pod color, pod shape, flower position, plant height.
Monohybrid cross:
- 2 contrasting characters are crossed.
- For example, consider a tall plant (TT) crossed with (tt).
- The resulting offspring will have genotype Tt and phenotype will be tall.
- If this heterozygous plant is selfed the resulting phenotype and genotype will be follows;
· | · T | · t |
· T | · TT (tall) | · Tt (tall) |
· t | · Tt (tall) | · tt (dwarf) |
3.12 Mendel’s laws of inheritance:
1.) Concept of dominance:
- This law states that if there are 2 different alleles then only one of the alleles will be expressed. This is the dominant character whereas the other contrasting character is recessive.
2.) Law of segregation or law of purity of gametes:
- During the process of gamete formation,the factors separate independently. They do not get mixed. Hence this law is called law of purity of gametes.
3.) Law of independent assortment:
- When 2 gametes are formed the alleles are separated independently of each other.
Application of Mendel’s Laws:
- It gives account of how the characters are expressed in hybrid plants and their pattern of inheritance.
- It is helpful in plant and animal breeding
- Hybridization can be used to make plants and crops with better quality.
3.13 Mutations:
- Mutations can cause change in structure of gene or sequence of DNA
- These changes result in alteration in gene function.
- One example of disease caused due to mutation is sickle cellanemia.in this disease a single nucleotide change causes the shape of RBCs to become sickle shaded or deformed.
- Another source of mutation in DNA is radioactive radiations. These radiations alter the gene structure and their effect can be seen up to various generations.
- One such example of effect of radiation is seen in Japan after the nuclear attack during World War II.
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