 Homozygous/ Purebred - TT, BB
 Heterozygous/ Hybrid – Tt, Bb
Punnett Square
• Punnett square is a chart which shows/predicts
all possible gene combinations. It shows all of
the possible combinations of male and female
gametes
Punnett Square
• the dominant gene for black fur "F,' and the
recessive gene for yellow fur "f.“
• "Heterozygous" means it has two different alleles
(Ff).
• "Homozygous dominant" means it has two copies
of the dominant allele (FF).
• "Homozygous recessive" means two copies of the
recessive allele (ff). Any parent that shows the
recessive trait (has yellow fur) belongs to this
category.
• the female bear is heterozygous for fur color (Ff).
We can conclude that:
• we have two boxes with Ff (heterozygous). 25% + 25% = 50%, so
each child has a 50% chance of inheriting Ff genes.
• The other two boxes are each ff (homozygous recessive). Each
child has a 50% chance of inheriting ff genes.
• there are two squares with at least one F, so each child has a 50%
chance to have black fur. There are two squares with ff, so each
child has a 50% chance to have yellow fur.
Draw the punnett square:
• Mother (heterozygous) Bb
• Father (heterozygous) Bb
• Dominant gene for brown eyes (B), recessive gene for
blue eyes
Example: Brown and blue eyes
• What can you conclude from the possibilities.
Draw the Punnett Square:
Curly hair = C
Straight hair = c
Female Cc
Male Cc
Punnett Square
Curly hair = C
Straight hair = c
Female Cc
Male Cc
C
c
CC
C
Cc
c
Cc
cc
Example:
Example:
• TT = 5 times
• Tt = 13 times
• tt = 2 times
90% offspring are tall and 10% offspring short
5 x5 : 13 x 5: 2 x 5
• TT : Tt : tt = 25% : 65% : 10%
Probability and Punnett square
Monohybrid
• Genetics is the study of heredity and variation
in organisms.
• A hybrid is the offspring produced when two
genetically different parents are crossed. This
usually results in a heterozygous individual.
• Monohybrid cross: In a monohybrid cross,
organisms differing in only one trait are
crossed.
Dihybrid cross
• A dihybrid cross involves a study of inheritance
patterns for organisms differing in two traits.
• A dihybrid cross is a cross between two
individuals that are both heterozygous for two
different genes. RrYy x RrYy
Dihybrid cross
•
Heterozygous parent
• RrYy x RrYy
• RY, Ry, rY, ry (parent 1) and RY, Ry, rY, ry (parent 2)
4x4 Punnet square
Dihybrid cross
• Heterozygous parent
• RrTt x RrTt
Dihybrid cross
Dihybrid cross
• Heterozygous parent
• SsYy x SsYy
Dihybrid cross
• __________ parent
• _____ x _____