Important Equations and Definitions: Heredity | Science Class 10 PDF Download

Definitions

• Genetics is the branch of biology that studies how traits and characteristics are passed down and how they differ among individuals in a population.
• Heredity is the process of passing traits from one generation to the next, while variation refers to the differences in these traits among individuals.
• Somatic Variation: Changes in body cells that are not inherited and do not get passed to offspring; these are also known as acquired traits and can result from environmental influences.
• Gametic Variation: Changes in reproductive cells (gametes) that are inherited, contributing to the diversity of traits in offspring.
• Determination of sex: The method by which the gender of an offspring is decided, influenced by genetic and environmental factors. A child's sex is determined by whether the paternal chromosome is X (for girls) or Y (for boys).
• Factors responsible for Sex Determination: Environmental factors like temperature in some species or genetic factors such as sex chromosomes (XX for females and XY for males) influence sex determination.
• Acquired Traits: Characteristics developed in an individual due to specific conditions or experiences that are not passed on to offspring, unlike inherited traits.
• Inherited Traits: Traits passed down through genetics from one generation to the next, which can affect the evolution of species.
• Gene Flow: The movement of genes between partially separated populations, allowing for the exchange of genetic material.
• Genetic Drift: Random changes in the frequency of genes in a population over generations, often due to chance events.
• Natural Selection: A process where nature favours organisms with beneficial variations, enhancing their chances of survival.
• Geographical Isolation: Occurs when physical barriers, like mountains or rivers, divide populations, leading to reproductive isolation and potential new species.
• Variation: Differences among individuals of the same species, resulting from either heredity or environmental influences.
• Heredity: The passing of traits from parents to offspring through genetic information.
• Reproduction: The biological process of creating new individuals of the same species.
• Asexual Reproduction: Involves one parent and produces offspring that are genetically identical to that parent.
• Sexual Reproduction: Involves combining genetic material from two parents, resulting in offspring with a unique mix of traits.
• Trait: A specific characteristic or feature of an organism, like height, colour, or shape.
• Dominant Trait: A trait that appears in an individual's phenotype even if only one copy of the gene is present.
• Recessive Trait: A trait that shows in the phenotype only when two copies of the gene are present.
• Genes: DNA segments with instructions for making proteins and determining specific traits.
• Chromosomes: Thread-like structures made of DNA and proteins in the cell nucleus that carry genetic information.
• Sex Chromosomes: Chromosomes that determine an individual's sex; in humans, these are the X and Y chromosomes.
• Genetic Linkage: The tendency of genes on the same chromosome to be inherited together.

Principles Of Inheritance And Variation

1. Gamete Calculation
   The types of gametes produced can be calculated using a formula:
   Number of gametes: 2ⁿ, where 'n' is the number of heterozygous alleles, which refer to different alleles at a locus.
2. Recombination Frequency
   A numerical value that describes the proportion of recombinant offspring produced in a genetic cross is referred to as recombinant frequency. It is calculated as:
   Recombinant Frequency: (Number of Recombinant Offspring / Total Number of Offspring) × 100.
3. Genetic Linkage
   Learn about the formula to determine the possibility of genetic linkage concerning the position of genes on a chromosome through an interesting GIF. Each gene set exists not as a single long thread of DNA but as separate independent pieces called chromosomes. Thus:
   • Each cell has two copies of each chromosome, one from each parent.
   • When two germ cells combine, they restore the normal number of chromosomes in the progeny, ensuring the stability of the DNA of the species.

Equations:

• Number of Gametes: 2ⁿ, where 'n' is the number of heterozygous alleles.
• Recombinant Frequency: The proportion of recombinant offspring in a genetic cross, calculated as (Number of Recombinant Offspring / Total Number of Offspring) × 100.