Heredity is the passing of characters or traits from its parent or ancestors to their offspring.
The study of heredity in biology is called genetics. It explains that organisms resemble each other because they arise from common ancestor. The offspring of cats are cats, fish are fish and humans are humans only.
- Trait – A genetically determined characteristic or condition e.g. eye colour, height, blood type,hair color, tooth shape, beak shape, bone size, or muscle structure. etc.
- Inheritance – The genetic characters transmitted from parents to offsprings, taken collectively.
- Inherited traits – A trait or character that is genetically inherited or passed down from generation to generation e.g. – dimples, Hitchhiker’s thumb versus regular thumb, tongue rolling, longer second toe than big toe (or vice versa), left-thumbed or right-thumbed when interlocking fingers, earlobes as either attached or unattached. They bear all basic features with great deal of variation.
- Acquired traits – Things develop during your life (not born with it) which cannot pass to offsprings. e.g. riding a cycle, writing, reading etc.
Gregor Johann Mendel (July 20, 1822 – Jan 6, 1884) was a priest and geneticist. He is known as the ‘Father of Genetics’. His work is the foundation of modern genetics. He conducted experiments to study the pattern of inheritance. He experimented and formulated laws for inheritance of traits on garden peas (Pisum sativum).
Mendel’s Contributions on Inheritance of Traits –
Both mother and father contribute practically equal amounts of genetic material to the child i.e. each trait can be influenced by both paternal and maternal DNA.
As the contribution by each parent is equal, then what trait will be seen in the child?
Mendel worked on such questions and formulated the main laws for such inheritance.
- Mendel stated that physical traits are inherited as ‘particles or factors (now called genes)’.
- Mendel did not know the ‘particles’ were actually chromosomes and DNA.
- Mendel’s Laws are as follows:
- The Law of Dominance
- The Law of Segregation
- The Law of Independent Assortment
Mendel chose pea – plants with different characteristics for his experiments.
Why peas, Pisum sativum?
This is because they –
(a) can be grown in small areas.
(b) produce lots of offspring.
(c) produce pure plants when allowed to self-pollinate several generations.
Mendel used a number of contrasting visible characters (traits) of garden peas. They are –
(a) Seed shape – Round (R) or Wrinkled (r)
(b) Seed colour – Yellow (Y) or Green (y)
(c) Pod shape – Smooth / Inflated (S) or Wrinkled / Constricted (s)
(d) Pod colour – Green (G) or Yellow (g)
(e) Seed coat colour – Gray (G) or White (g)
(f) Flower position – Axial (A) or Terminal (a)
(g) Plant / Stem height – Tall (T) or Dwarf (t)
(h) Flower colour – Purple / Violet (P) or White (p)
Mendel took pea plants with different characteristics such as a tall plant and a short plant, produced progeny (offspring) by crossing them, and calculated the percentages of tall or short progeny.
Types of Genetic Crosses