The Bio Brief

(Mendel’s Contributions)

 Who was Mendel?

Gregor Mendel is called the Father of Genetics.

He discovered how traits are passed from parents to offspring by experimenting on pea plants.

 Equal Contribution from Parents

• Mother gives 50% genes
• Father gives 50% genes

So:

 Every child gets two versions of each trait

(one from mother + one from father)

These versions are called alleles.

 Mendel’s First Experiment (One Trait – Plant Height)

Parents (P Generation):

Tall plant (TT)  ×  Short plant (tt)

First Generation (F1):

All plants are Tall (Tt)

 No medium-height plants appeared.

Meaning:

Only tallness appeared → tall is dominant

 Dominant & Recessive Traits

• Dominant trait → shows even if only ONE copy is present
• Recessive trait → shows only when BOTH copies are recessive

Example:

TT → Tall 

Tt → Tall 

tt → Short

So:

 Tall (T) = Dominant

 Short (t) = Recessive

Second Generation (F2) – Self Pollination of F1

Tt × Tt

Result:

TT   Tt   Tt   tt

Ratio:

3 Tall : 1 Short

Simple Diagram (Monohybrid Cross)

     T     t

  ————

T |  TT   Tt

t |  Tt   tt

 Conclusion from First Experiment

• Traits occur in pairs
• One may dominate the other
• Recessive trait is hidden in F1 but reappears in F2

 Second Experiment (Two Traits Together)

Traits studied:

• Height → Tall / Short
• Seed shape → Round / Wrinkled

Parents:

Tall Round × Short Wrinkled

F1 Generation:

All Tall + Round

So:

 Tall = Dominant

 Round = Dominant

F2 Generation (Selfing F1)

Different combinations appear:

• Tall + Round
• Tall + Wrinkled
• Short + Round
• Short + Wrinkled

Important Observation

New combinations appeared:

 Tall with wrinkled seeds

 Short with round seeds

This proves:

 Traits are inherited independently.

This is called:

 Law of Independent Assortment

Simple Flow Chart

Parents

   ↓

F1 (Only dominant traits visible)

   ↓

F2 (Dominant + recessive + new combinations)

 Mendel’s Main Conclusions

1. Traits are controlled by genes.
2. Each trait has two alleles.
3. One allele may dominate (Dominant).
4. The hidden one is Recessive.
5. Traits separate during reproduction (Law of Segregation).
6. Different traits inherit independently (Law of Independent Assortment).

 One-Line Summary

Mendel proved that traits are inherited in pairs, dominant traits appear first, recessive traits reappear later, and different traits assort independently.