BAL BHARATI PUBLIC SCHOOL, NAVI MUMBAI
Subject: Biology
Class: X
Topic: Dihybrid cross
Observations:
Round Yellow= 9/16
Wrinkled yellow= 3/16
Round green= 3/16
Wrinkled green= 1/16
Parental combination-
Round Yellow & Wrinkled
green
New combination-
Round green & Wrinkled
yellow
Conclusion:
Occurrence of new phenotype
combinations show that
factors for Round and Yellow
seeds are inherited
independently of each other.
Parents
Gametes
F1 Generation
Conclusion:
New combinations of traits are formed in F2
offspring when factors controlling for seed
shape and seed colour recombine to form
zygote leading to form F2 offspring
Phenotypic Ratio
Round, yellow : 9/16
Round, green : 3/16
Wrinkled, yellow : 3/16
Wrinkled, green : 1/16
Observations
(i) When RRyy was crossed with rrYY in F1 generation all were Rr Yy round and yellow
seeds.
(ii) Self pollination of F1 plants gave parental phenotype and two mixtures (recombinants
round yellow and wrinkled green) seeds plants in the ratio of 9 : 3 : 3 : 1.
Conclusions
1. Round and yellow seeds are Dominant characters.
2. Occurrence of new phenotype combinations show that genes for round and yellow
seeds are inherited independently of each other.
Dihybrid Cross
A Cross between pure Smooth and
yellow seeded Pea plant with pure
Wrinkled and green seeded Pea
plant
Parents: SSYY X ssyy
(smooth & yellow) (wrinkled &green)
Gametes: SY sy
F1 SsYy
All plants with Smooth and Yellow seeds
A Cross between pure
Green pod and yellow
seeded Pea plant with
pure yellow pod and
green seeded Pea plant
Parents: GGYY X ggyy
(Green pod & yellow seed) (yellow pod &green seed)
Gametes: GY gy
F1 GgYy
All plants with Green pod and Yellow seeds
How do traits get expressed?
Cellular DNA (Information source)
For synthesis of
Proteins (Enzyme)
Works efficiently
More Hormone
Triggers growth
Tallness of plant
Therefore, genes control characteristics/traits.
Let us Recapitulate....
• Traits in one individual may be inherited separately, giving rise to new combinations of traits in
the offspring of sexual reproduction.
• New combinations of traits are formed in F2 offspring when factors controlling for different traits
recombine to form zygote leading to form F2 offspring
• Cellular DNA is the information source for making proteins in the cell
• Both parents contribute equally to the DNA of the progeny during sexual reproduction, that help
determine the trait in the progeny.
• Each cell will have two copies of each chromosome, one each from the male and female parents.
• Every germ cell will take one chromosome from each pair and these may be of either maternal or
paternal origin.
• When two germ cells combine, they will restore the normal number of chromosomes in the
progeny, ensuring the stability of the DNA of the species.
Assignment-3
1. A cross was made between pure breeding pea plants one with round and
green seeds and the Other with wrinkled and yellow seeds.
a) Write the phenotype of F1 progeny. Give reason for your answer.
b) Write the different types of F2 progeny obtained along with their ratio when
F1 progeny was selfed
2. One pure bred plant with dominant tall height bearing purple flowers crossed
with another pure bred plant with recessive dwarf and white flowers.
a) What do the plants of F1 generation look like ?
b) What type of cross is it ?
c) What is the phenotypic ratio in F2 generation and name the type of plants
obtained according to phenotypic ratio.
Assignment-3 (Contd.)
3. a) What do the progeny of a pure bred tall plant with round seeds and a
short plant with wrinkled-seeds look like?
b) What happens when these F1 progeny are used to generate F2 progeny
by self-pollination?
c) Illustrate this cross on a Punnet Square.
4. A cross was made between pea plants one with purple flower and short
height (Pptt) and the Other with white flower and tall height(ppTt).
a) Write the different types of progeny obtained along with their ratio
b) Illustrate this cross on a Punnet square.
Links
• DihybridCross (Tall & round seeds X dwarf & wrinkled Seeds)
https://www.youtube.com/watch?v=NEo0uuUC_TI
• DihybridCross (round & yellow seeds X wrinkled & green Seeds)
https://www.youtube.com/watch?v=1QU2phs-hws
• How Mendel's pea plants helped us understand genetics
https://www.youtube.com/watch?v=Mehz7tCxjSE
