2. - Gregor Johann
Mendel is ‘the father
of genetics’
- His contribution to
the genetics is called
as mendelism.
3. The basic principles of genetics were
first discovered by Gregor Johann
Mendel. He conducted or performed a
series of breeding experiments on
several types of garden pea (Pisum
sativum) plants.
Through his experiments, he studied
the different characters among the pea
plants and found out the number
contrasting characters contained in a
pea plant.
4. Out of the many contrasting characters
that Mendel observed, he selected only
seven characters for his experiment.
Each of the seven characters had two
varieties or alternatives forms.
7. Mendel’s experiment were
successful because:
1. Flowers of pea plant are normally
self-pollinated.
2. Pea plant show clear cut contrasting
characters.
3. Many pure breeding varieties of pea
plant were available.
4. It has short growth period and life
cycle.
5. He studied the inheritance of only
one character as a time.
6. He maintained a proper statistical
record.
8. A genetic cross is defined as the conscious
breeding of two different individuals
resulting in offspring that carries a portion
of the genetic material of both parents.
The different genetic crosses occurring
between breeding individuals are
monohybrid cross and dihybrid cross.
9. The crossing of plants differing in only one character is
called monohybrid cross.
The resulting hybrid is called as monohybrids.
Mendel in his first experiment crossed two parents
different in one character only.
For instance, Mendel crossed the plant having tall stem
with another plant with dwarf stem.
Tall stem character was dominant (TT) over dwarf stem
(tt).
10.
11.
12.
13. All the plants in first filial (F1 generation) were tall.
The selfing of F1 generation results in F2 generation which
were found to be two types, both tall and dwarf but with
different %.
75% offspring were tall and 25% were dwarf.
Tall and dwarf ratio was 3:1 (phenotypic ratio) (3 tall plants
and one dwarf)
Genotypic ration was 1:2:1 (1 TT, homozygous dominant)
2 Tt (Heterozygous dominant) 1 tt (homozygous recessive)
14. A dihybrid cross is a breeding experiment between
two organisms which are identical hybrids for two
traits. In other words, a dihybrid cross is a cross
between two organisms, with both being
heterozygous for two different traits. The
individuals in this type of trait are homozygous for
a specific trait. These traits are determined by DNA
segments called genes.
In a dihybrid cross, the parents carry different pair
of alleles for each trait. One parent carries
homozygous dominant allele, while the other one
carries homozygous recessive allele.
The offsprings produced after the crosses in the F1
generation are all heterozygous for specific traits.
15.
16. 1. Law of dominance: states that when two contrasting
alleles are present together, only one is able to
express itself while the other remains suppressed.
2. Law of segregation: states that during the gamete
formation, the two alleles responsible for traits
separates or segregate from each other.
3. Law of independent assortment: states that when
there are two pairs of contrasting characters, the
distribution of the members of one pair into the
gametes is independent of the distribution of the other
pair.
17. Find the genotypic ratio and phenotypic ratio
of the F2 generation offsprings of pea plant
when a pure parent with axial flowers is
crossed with a pure parent having terminal
flowers. Note that axial flower position is
dominant over terminal.
18. In guinea pigs, rough coat is dominant to
smooth coat; and short hair is dominant over
long hair. Cross a guinea pig homozygous for
a rough coat and short hair with a guinea pig
with a smooth coat and long hair. Predict the
phenotype and genotype of the F1 offspring.
Also calculate the phonotypic ratio of the F2
offsprings if two offsprings of the F1
generation are crossed with each other. Use
Punnet square for the calculations.
