Interesting way to Learn Biology with Syeda: Chapter 15

Interesting way to Learn Biology with Syeda: Chapter 15

Chapter15: Inheritance


Understanding the fundamental principles of genetics is crucial for students delving into the fascinating world of biology. This comprehensive guide explores essential genetic concepts, starting with the intricate structure of chromatin, the foundation of genetic material within cells. We then delve into Mendel’s pioneering laws of segregation and independent assortment, which laid the groundwork for modern genetics. By examining how variations lead to evolution, we gain insight into the dynamic nature of life on Earth. Additionally, the phenomena of incomplete dominance and co-dominance are explained with clear examples, illustrating the complexity of genetic inheritance. Finally, basic genetic terminology and the differences between natural and artificial selection are elucidated, providing a solid foundation for further study in the field of genetics.

Gregor Mendel, the Moravian Augustinian friar who founded the modern science of genetics


  1. Describe the structure of chromatin. Chromatin is a complex of DNA and protein found in the nucleus of eukaryotic cells. It is composed of DNA wrapped around histone proteins, forming nucleosomes. These nucleosomes coil and fold to form a more compact structure, ultimately condensing into chromosomes during cell division. Chromatin can exist in two forms: euchromatin, which is less condensed and transcriptionally active, and heterochromatin, which is highly condensed and transcriptionally inactive.
  2. Describe Mendel’s law of segregation. Mendel’s law of segregation states that during the formation of gametes (egg and sperm cells), the two alleles responsible for a trait separate from each other. This means each gamete carries only one allele for each trait. When fertilization occurs, the offspring inherits one allele from each parent, restoring the pair of alleles.
  3. Explain how Mendel proved the law of independent assortment. Mendel proved the law of independent assortment through dihybrid crosses, where he studied the inheritance of two different traits simultaneously. He crossed pea plants with two different traits (e.g., seed shape and seed color) and observed that the inheritance of one trait did not affect the inheritance of the other. This demonstrated that alleles of different genes assort independently during gamete formation.
  4. How would you prove that variations lead to evolution? Variations within a population can be observed through changes in allele frequencies over time. By studying populations over many generations, scientists can track how certain traits become more common due to natural selection, genetic drift, mutations, and gene flow. Fossil records, comparative anatomy, and molecular biology provide evidence that accumulated variations can lead to the emergence of new species, demonstrating evolution.
  5. Explain the phenomenon of incomplete dominance with the help of example. Incomplete dominance occurs when neither allele is completely dominant over the other, resulting in a phenotype that is a blend of the two parent phenotypes. For example, in snapdragon flowers, crossing a red flower (RR) with a white flower (WW) results in offspring with pink flowers (RW). The pink color is an intermediate phenotype, showcasing incomplete dominance.
  6. What do you mean by co-dominance? Give an example. Co-dominance occurs when both alleles in a heterozygous organism are fully expressed, resulting in a phenotype that clearly shows both traits simultaneously. An example of co-dominance is seen in ABO blood types. Individuals with the genotype IAIB have both A and B antigens on their red blood cells, showing both traits equally.

Short Questions

  1. Define genotype and phenotype.
    • Genotype: The genetic makeup of an organism, consisting of all the alleles inherited from the parents.
    • Phenotype: The observable physical and physiological traits of an organism, determined by its genotype and environmental influences.
  2. What do you mean by dominant and recessive alleles?
    • Dominant Alleles: Alleles that express their effect even when present in just one copy (heterozygous condition). Represented by a capital letter (e.g., A).
    • Recessive Alleles: Alleles that only express their effect when present in two copies (homozygous condition). Represented by a lowercase letter (e.g., a).
  3. What are homozygous and heterozygous genotypes?
    • Homozygous Genotypes: Genotypes with two identical alleles for a particular gene (e.g., AA or aa).
    • Heterozygous Genotypes: Genotypes with two different alleles for a particular gene (e.g., Aa).
  4. Differentiate between natural and artificial selection.
    • Natural Selection: The process where organisms with favorable traits are more likely to survive and reproduce, passing those traits to the next generation.
    • Artificial Selection: The process where humans selectively breed organisms for specific traits, enhancing desired characteristics over successive generations.


This guide covers key genetic concepts, including chromatin structure, Mendel’s laws of segregation and independent assortment, the impact of variations on evolution, and the phenomena of incomplete dominance and co-dominance. Additionally, it explains basic genetic terms and differentiates between natural and artificial selection.


  1.  William BatesonMendel’s Principles of Heredity – A Defence, with a Translation of Mendel’s Original Papers on Hybridisation Cambridge University Press 2009, ISBN 978-1-108-00613-2
  2.  Grafen, Alan; Ridley, Mark (2006). Richard Dawkins: How A Scientist Changed the Way We Think. New York, New York: Oxford University Press. p. 69ISBN 978-0-19-929116-8.
  3.  Jump up to:a b c Fairbanks, Daniel J.; Rytting, Bryce (May 2001). “Mendelian controversies: a botanical and historical review”American Journal of Botany88 (5): 737–752. doi:10.2307/2657027ISSN 0002-9122JSTOR 2657027PMID 11353700.
  4.  Jump up to:a b c Henig, Robin Marantz (2000). The monk in the garden : the lost and found genius of Gregor Mendel, the father of genetics. Internet Archive. Boston : Houghton Mifflin. ISBN 978-0-395-97765-1.
  5.  Mendel, Gregor; Mendel, Gregor (1866). Versuche über Pflanzen-Hybriden. Brünn: Im Verlage des Vereines.

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