Heredity and Evolution Class 10 Notes PDF

CLASS 10 NOTES SCIENCE Heredity and Evolution PRASHANT KIRAD  PRASHANT KIRAD Heredity Heredity involves the transmission of characteristics from one generation to the next, as traits are passed down fro...

CLASS 10 NOTES SCIENCE Heredity and Evolution PRASHANT KIRAD  PRASHANT KIRAD Heredity Heredity involves the transmission of characteristics from one generation to the next, as traits are passed down from parents. Heredity is the result of genes being inherited. Study of Heredity and Inheritance is term as Genetics. A trait that is Genetically passed down from one generation to another is termed as Inherited trait. Variations: Variations in traits among individuals in a species arise from genetic D mutations and environmental factors, such as diet, chemicals, and pollution. RA Inherited Traits: Inherited traits are characteristics passed from parents to offspring through generations, controlled by genes. Examples include height and KI skin colour. T AN Gregor Johann Mendel is a central figure in the field of genetics, often referred to as the H "Father of Genetics." AS Mendel conducted experiments between 1856 and 1863 using pea plants (Pisum sativum). He chose PR pea plants because they had easily observable traits, such as flower color and seed shape. Mendel carefully cross-pollinated pea plants with different traits and observed how these traits Gregor Johann Mendel were passed on to the next generation. It is easy to cultivate. It has a short life span so easy to study various generations. Why pea plant?  PRASHANT KIRAD Important Terms EMA Gene: The basic unit of heredity, made of DNA, that codes for a specific trait. Allele: Different forms of a gene that can exist at a particular locus. Genotype: The genetic makeup of an organism, representing the combination of alleles. Phenotype: The observable characteristics or traits of an organism, resulting from the interaction of its genotype with the environment. Dominant Allele: An allele that expresses its trait even when only one copy is present (e.g., "A" in Aa). Recessive Allele: An allele that only expresses its trait when two copies are present (e.g., "a" in aa). Homozygous: An organism with two identical alleles for a trait (e.g., AA or aa). D Heterozygous: An organism with two different alleles for a trait (e.g., Aa) RA Chromosomes: Chromosomes are thread-like structures in the cell nucleus that carry genetic information (DNA). KI Monohybrid Cross: A cross that focuses on one pair of contrasting traits is referred to as a monohybrid cross, resulting in a 3:1 ratio known as the T monohybrid ratio. AN Dihybrid Cross: A cross that involves two pairs of contrasting traits is termed a dihybrid cross, and it yields a 9:3:3:1 ratio, which is known as the dihybrid ratio. H Dominant Trait: The trait that can be visibly expressed in the first generation. AS Recessive Trait: The trait that is not able to express itself in F1 generation but reappears in f2 generation. PR Dominant Gene: The gene that can be expressed in both homozygous and heterozygous conditions. Recessive Gene: A gene that can only express itself in the homozygous condition. Inherited traits from previous generations provide a shared body plan and introduce subtle modifications for the next generation. Depending on the nature of variations, various individuals may possess diverse advantages.  PRASHANT KIRAD Mendel’s Experiment: Mendel discovered that traits can be either dominant or recessive. When he crossed a tall pea plant with a short one, all the offspring in the first generation were tall. To investigate the disappearance of the short trait, he allowed the first-generation plants to self- pollinate. In the second generation, he observed both tall and short plants in a 3:1 ratio. This led Mendel to conclude that the short trait was hidden in the first generation, unable to express itself because it was recessive. D RA KI T AN H AS PR  PRASHANT KIRAD Mendel crossed pea plants with round yellow seeds and green wrinkled seeds. In the first generation, all offspring had round yellow seeds. To investigate the missing traits of wrinkled and green seeds, he self-pollinated these plants. In the second generation, he found new combinations of traits along with the original ones, revealing that seed shape and color are inherited independently of each other. D RA KI T AN H AS PR Sabse zyada pucha jata hai - Mendel’s Experiment - Prashant Bhaiya  PRASHANT KIRAD Chromosomes: Chromosome pairs refer to the two sets of chromosomes present in most human cells. Each set consists of 23 individual chromosomes, with one set inherited from the mother and the other from the father. These pairs include sex chromosomes (X and Y in humans) and autosomes, which carry genetic information and are essential for genetic inheritance. Sex Determination EMA Environmental Factors: In certain reptiles, such as turtles and crocodiles, the D temperature at which eggs are incubated determines the sex of the offspring. RA Higher incubation temperatures result in females, while lower temperatures result in males. KI T Genetic Factors: The sex of the baby is determined by the type of male gamete AN that fuses with the female gamete. If the fertilizing sperm contains X chromosome, then the baby produced will be a girl and if the fertilizing sperm contains Y chromosome, then the baby produced will be a boy. H AS In humans, there are 23 pairs of chromosomes, making a total of 46 chromosomes. Among these, 22 PR pairs are autosomes, and one pair is sex chromosomes. In males, the sex chromosomes are XY, and in females, they are XX. The sex of a child is determined during fertilization. If an X-carrying sperm fertilizes the egg, the child will be female (XX), and if a Y-carrying sperm fertilizes the egg, the child will be male (XY). Therefore, the sperm's genetic contribution determines the child's sex. Most repeated topic! - Prashant Bhaiya  PRASHANT KIRAD # TOP 7 IMPORTANT QUESTIONS 1. It is a matter of chance whether a couple will have a male or a female child.” Justify this statement by drawing a flow chart. Solution: Women produce only one type of ovum (carrying X chromosome) and males produce two types of sperms (carrying either X or Y chromosome) in equal proportions. So the sex of a child is a matter of chance depending upon the type of sperm fertilizing the ovum. D RA 2. Why traits such as intelligence and knowledge cannot be passes on to the next generation? KI Solution: T AN Traits such as intelligence and knowledge are not heritable traits, which do not bring upon any changes in the DNA of the germ cells and, therefore, cannot be passed on H to the progeny. AS 3. Distinguish between inherited traits and acquired traits in a tabular form, giving PR one example of each. Solution: Inherited Trait Acquired Trait Experiences of an individual during Genetically Inherited its lifetime. They can be passed on from one It cannot be passed on from one generation to the next. generation to the next. Example: power to lift weights and Example: Eye colour or height reading French.  PRASHANT KIRAD 4.What is a dominant trait with respect to height in pea plants? Give any two examples. Solution: Characters/Traits like ‘T’ are called dominant trait (because it express itself) ‘t’ are recessive trait (because it remains suppressed) 5. What are chromosomes? Explain how sexually reproducing organisms the number of chromosomes in the progeny is maintained. D RA Solution: Chromosomes - Thread-like structures made up of DNA found in the nucleus. The KI original number of chromosomes becomes half during gamete formation. Hence, when the gametes combine, the original number of chromosomes gets restored in the T progeny. AN 6.Rekha has a dark complexion and seeks beauty products to lighten her skin. Her friend Lila tells her that skin color is determined by birth and advises against H excessive use of such products. (All India 2013) AS a. What might have caused Rekha’s color to be dark? b. Is it possible that all the family members of Rekha’s family were dark? PR c. What value do you learn? Solution: a. Her dark colour may be due to genetic inheritance. b. All may not be dark, depending upon the genes inherited and the environmental conditions that each one of them living in. c. Awareness, logical thinking, and scientific temperament. 7. How do Mendel’s experiment show that traits are inherited independently? Solution: Mendel performed dihybrid crosses by mating pea plants with different traits in two characteristics. like yellow round seeds With green wrinkled seeds. In the F2 generation, he observed both parental (yellow round and green wrinkled) and recombinant (yellow wrinkled and green round) phenotypes. This showed that these traits separated from their original combinations and were inherited independently.