Genetics (NCERT Biology Part-II, Class-XII )##

• 1. Mendelian Genetics:(Ch-5)_

• Laws of Inheritance (Mendel’s Laws)

  • Law of Segregation: During gamete formation, the two alleles for each gene segregate (separate) and randomly unite with gametes from the other parent.
  • Law of Independent Assortment: The alleles of different genes assort independently of one another during gamete formation.

• Dominance, Recessiveness, and Gene Interactions

  • Dominant Allele: An allele that expresses its phenotype even in the presence of a recessive allele.
  • Recessive Allele: An allele that expresses its phenotype only in the absence of the dominant allele.
  • Incomplete Dominance: When heterozygous individuals show an intermediate phenotype between the phenotypes of the homozygous dominant and recessive individuals.
  • Co-dominance: When both alleles of a gene are fully expressed in heterozygous individuals, resulting in two distinct phenotypes.

• Inheritance Patterns

  • Monohybrid Cross: A cross between individuals that differ in one gene pair.
  • Dihybrid Cross: A cross between individuals that differ in two gene pairs.

• Linked Genes and Genetic Mapping

  • Genetic Linkage: The tendency of two or more genes to be inherited together more often than expected by chance due to their close physical proximity on the same chromosome.
  • Genetic Mapping: Determining the relative positions of genes on a chromosome by measuring the frequency of recombination between them.

• 2. Molecular Basis of Inheritance:_ (Ch-6:Ch-7 Class XII)_

• Structure and Replication of DNA

  • DNA Structure: Double helix composed of deoxyribonucleotides (adenine, thymine, guanine, and cytosine) linked by phosphodiester bonds.
  • Replication: Semi-conservative process by which DNA makes an identical copy of itself.

• Transcription and Translation

  • Transcription: Synthesis of RNA from a DNA template.
  • Translation: Synthesis of proteins from mRNA template using transfer RNA (tRNA) and ribosomes.

• Gene Expression and Regulation

  • Gene Expression: The process by which the information encoded in a gene is used to direct the synthesis of a functional product, such as a protein.
  • Gene Regulation: The control of gene expression to ensure that the right genes are expressed at the right time and in the right amount.

• 3. Chromosomes and Cell Division:_ (Ch-5, 10 Class-XII)_

• Structure of Chromosomes

  • Chromosomes: Thread-like structures in the nucleus that carry genetic information.
  • Centromere: The region of the chromosome where sister chromatids are attached.
  • Telomere: The repeating nucleotide sequences at the ends of chromosomes that protect them from degradation.

• Mitosis and Meiosis

  • Mitosis: Cell division that results in two genetically identical daughter cells.
  • Meiosis: Cell division that produces haploid gametes (eggs and sperm) with half the number of chromosomes as the parent cell.

• 4. Genetic Variations:_ (Ch-8,10,11 Class XII)_

• Mutations

  • Types of Mutations: Point mutations, deletions, insertions, inversions, and translocations.
  • Causes of Mutations: Errors in DNA replication, environmental factors (radiation, chemicals), and transposable elements.

-Genetic Recombination

• Crossover: The exchange of genetic material between homologous chromosomes during meiosis.
• Independent Assortment: The random assortment of chromosomes during meiosis, leading to genetic diversity.

-Gene Flow, Genetic Drift, and Hardy-Weinberg Equilibrium - Gene Flow: The movement of alleles between populations. - Genetic Drift: The random change in allele frequencies in a population over time. -Hardy-Weinberg Equilibrium: The state in which the allele and genotype frequencies in a population remain constant from generation to generation.

• 5. Evolution:(Ch-7 to Ch-11, Class-XII)

• Darwin’s Theory of Evolution by Natural Selection

  • Variation: Differences in traits among individuals in a population. -Natural Selection: The process by which individuals that are better adapted to their environment are more likely to survive and reproduce. -Evolution: The change in the genetic composition of a population over time due to natural selection.

• Mechanisms of Evolution (Variation, Selection, Inheritance)

  • Variation: Mutations, genetic recombination, and sexual reproduction.
  • Selection: Natural selection, sexual selection, and artificial selection.
  • Inheritance: The passing on of traits from parents to offspring through genes.

• Evidence for Evolution

  • Morphological Evidence: Similarities and differences in the physical characteristics of organisms.
  • Molecular Evidence: Comparison of DNA and protein sequences.
  • Paleontological Evidence: The study of fossils.
  • Biogeographical Evidence: The distribution of organisms around the world.

• 6. Speciation and Patterns of Evolution:_ (Ch-10,11 Class-XII)_

• Isolating Mechanisms and Speciation

  • Geographic Isolation: Physical barriers, such as mountains or rivers, that prevent gene flow between populations.
  • Reproductive Isolation: Differences in reproductive behaviors or structures that prevent interbreeding between populations.

• Patterns of Evolution

  • Divergent Evolution: Two or more species evolve from a common ancestor and become increasingly different over time.
  • Convergent Evolution: Unrelated species evolve similar traits independently due to similar environmental pressures.
  • Coevolution: The evolution of two or more species in response to each other.

• Phylogeny and the Tree of Life

  • Phylogeny: The evolutionary history of a group of organisms.
  • Tree of Life: A diagram that represents the evolutionary relationships among different groups of organisms.

• 7. Human Genetics:(Ch-8 Class-XII)

• Pedigree Analysis

  • A method of tracking the inheritance of traits within a family over several generations.

• Inheritance of Human Traits

  • Single-Gene Inheritance: Traits controlled by a single gene.
  • Polygenic Inheritance: Traits controlled by multiple genes.

• Genetic Disorders

  • Autosomal Dominant Disorders: Disorders caused by a dominant allele located on an autosome (non-sex chromosome).
  • Autosomal Recessive Disorders: Disorders caused by two recessive alleles located on an autosome.
  • X-Linked Disorders: Disorders caused by a recessive allele located on the X chromosome.