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3. Inheritance and Variation

-CREATED BY-

PROF. DESHMUKH A. B.

ASST. TEACHER

AGASTI ARTS, COMMERCE & DADASAHEB RUPWATE SCIENCE JUNIOR COLLEGE, AKOLE, TAL. – AKOLE, DIST. - AHMEDNAGAR

3.6 Chromosomal Theory of Inheritance

Deshmukh A. B.

A B’s Biology

https://www.onlinesciencestudy.com

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3.6 Chromosomal Theory of Inheritance :

  • Gregor Johann Mendel published his work in 1866.
  • But it remained unnoticed or unrecognised till 1900, as
    • communication was not easy in those days.
  • His work was not widely recognized.
    • His approach of using mathematics and statistics to explain biological phenomenon was totally new and unacceptable to the then biologists.
    • As continuous variations were observed in nature, Mendel’s concept of factors (genes) as stable and discrete unit which controlled the expression of characters, and that a pair of alleles did not β€œblend” with each other, was not accepted by his contemporaries.
    • He also did not know the physical location of the β€˜factors’ (genes) in the gametic cell.

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  • In 1900, three scientists, independently rediscovered Mendel’s work on the inheritance of traits.

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Hugo de Vries

Carl Correns

Erich von Tschermak

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  • Due to advancements in microcopy, scientists were able to observe cell division and the structure of chromosomes under microscope.

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  • Walter Sutton along with Theodor Boveri (1903) studied the parallel behaviour of Mendel’s factors (genes) and behaviour of chromosomes, at the time of meiosis.

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Walter Sutton

Theodor Boveri

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  • Based on these observations, chromosomal theory of inheritance was put forth by Sutton and Boveri.
  • This theory identifies chromosomes as the carriers of genetic material.

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  • This theory states that –
    • The chromosomes are present in pairs in somatic cells.

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Synapsis

DNA Replication

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    • During gamete formation homologous chromosome pair, segregate and assort independently during meiosis.
      • Thus, each gamete contains only one chromosome from a pair.

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Mother Cell (2n)

Gametes (n)

MEIOSIS

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    • Nucleus of gametes contains chromosomes, which carry all hereditary traits.

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Eye Colour

Hair Colour

Skin Colour

Eye Shape

Hair Texture

Ear Size

Gamete Cell

Chromosome

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    • Male and female gametes (sperms and eggs) carry all the hereditary traits.

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    • They are the link between parents and offsprings.

Male Gamete (n)

Female Gamete (n)

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    • The fusion of haploid male gamete and haploid female gamete, restores the diploid number of chromosomes of the species.

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Male Gamete (n)

Female Gamete (n)

Zygote (2n)

8 Chromosomes

8 Chromosomes

16 Chromosomes

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