Mendel’s Contribution

Mendel’s Contribution

Genetics is the term which includes heredity and variations. Many scientist gave the meaningful terms in genetics but the major contribution in genetics played by the scientist Gregor Johann Mendel 20th July 1822 -6th January 1884. The scientist performed a pea plant experiment in 1856-1863.

Mendel selected pea plant for his experiment. The scientific name of pea plant is Pisum sativum.

Mendel selected the pea plant because of its characteristics:

Why pea plant?

1) It has short life span.

2) Pea plant is easy to grow and handle.

3) Fertilization can be self or cross.

4) It requires less space.

5) From the experiment pure line can be obtained.

Characteristics used by Mendel:

Mendel used seven characteristics of pea plant and these characteristics are called as Mendelian characteristics.

1) Characters: The characters considered by Mendel are mainly height, color and shape etc.

2) Trait: Trait can be dominant or recessive such as:

Sr. No. Characters Dominant Recessive
1 Height Tall Dwarf
2 Color Yellow, white Green, purple
3 Shape Wrinkled Round

3) Gene: Functional unit of heredity. It is also called as factor.

4) Alleles: Factor has 2 alternate forms of genes.

5) Locus: The alternative form of a gene called as allele and to decide the position of allele called as locus.

6) Genotype: The genetic makeup of living organism or internal characteristics called as genotype.

7) Phenotype: The external characters of living organisms called phenotype.

Therefore the characters can be summarized in two types by Mendel:

A) Vegetative characteristics: It includes height of the plant such as tall or dwarf.

B) Sexual characteristics: It includes flower, fruit and seeds.

  1. Flower: It contains flower color and flower position. The dominant color of flower is purple and white is recessive. Flower dominant position is axial whereas the recessive is terminal.
  2. Fruit: The pea plant fruit shape is either inflated or constricted. And the color of the fruit is either green or yellow.
  3. Seed: The shape of the seed can be round or wrinkled and color of the seed is yellow or green.

Monohybrid cross:

A monohybrid cross can be defined as a cross between two organisms which having variation in trait and both the organisms having homozygous condition called as monohybrid cross. For example: The two pea plants were crossed one was tall and other was dwarf. Therefore the 1st generation was hybrid.

Genotypic ratio: TT : Tt : tt  = 1 : 2 : 1

Phenotypic ratio : Tall : Dwarf = 3 : 1

Dihybrid cross:

It can be defined as the cross which involves two contrasting pairs in both the parents. For example: The pea plant with yellow round seed appearance was crossed with green wrinkled pea plant. Yellow (Y) color of seed is dominant over (y) green color and round (R) shape of seed is dominant over wrinkled (r)seed.

Phenotypic ratio = 9:3:3:1

Genotypic ratio = 1:2:2:1:4:1:2:2:1

Question and answers:

1) On which plant Mendel did his experiment?

Answer: Mendel selected pea plant for his experiment. The scientific name of pea plant is Pisum sativum.Mendel selected the pea plant because of its characteristics

2) Why does Mendel choose pea plant?

Answer:

1) It has short life span.

2) Pea plant is easy to grow and handle.

3) Fertilization can be self or cross.

4) It requires less space.

5) From the experiment pure line can be obtained.

3) What are the characteristics of pea plant?

Answer:Mendel used seven characteristics of pea plant and these characteristics are called as Mendelian characteristics.

1) Characters: The characters considered by Mendel are mainly height, color and shape etc.

2) Trait: Trait can be dominant or recessive such as:

 

Sr. No. Characters Dominant Recessive
1 Height Tall Dwarf
2 Color Yellow, white Green, purple
3 Shape Wrinkled Round

3) Gene: Functional unit of heredity. It is also called as factor.

4) Alleles: Factor has 2 alternate forms of genes.

5) Locus: The alternative form of a gene called as allele and to decide the position of allele called as locus.

6) Genotype: The genetic makeup of living organism or internal characteristics called as genotype.

7) Phenotype: The external characters of living organisms called phenotype.

4) What are the vegetative and sexual characteristics of pea plant?

Answer:

A) Vegetative characteristics: It includes height of the plant such as tall or dwarf.

B) Sexual characteristics: It includes flower, fruit and seeds.

  1. Flower: It contains flower color and flower position. The dominant color of flower is purple and white is recessive. Flower dominant position is axial whereas the recessive is terminal.
  2. Fruit: The pea plant fruit shape is either inflated or constricted. And the color of the fruit is either green or yellow.
  3. Seed: The shape of the seed can be round or wrinkled and color of the seed is yellow or green.

5) What is monohybrid cross?

Answer:A monohybrid cross can be defined as a cross between two organisms which having variation in trait and both the organisms having homozygous condition called as monohybrid cross. For example: The two pea plants were crossed one was tall and other was dwarf. Therefore the 1st generation was hybrid.

6) What is dihybrid cross?

Answer:It can be defined as the cross which involves two contrasting pairs in both the parents. For example: The pea plant with yellow round seed appearance was crossed with green wrinkled pea plant. Yellow (Y) color of seed is dominant over (y) green color and round (R) shape of seed is dominant over wrinkled (r)seed.

7) What is genotypic and phenotypic ratio of monohybrid cross?

Answer:Genotypic ratio: TT : Tt : tt  = 1 : 2 : 1

Phenotypic ratio : Tall : Dwarf = 3 : 1

8) What is genotypic and phenotypic ratio of dihybrid cross?

Answer:Phenotypic ratio = 9:3:3:1

Genotypic ratio = 1:2:2:1:4:1:2:2:1

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