Transcript Dihybrid Crosses - ScienceGeek.net

Dihybrid
Crosses
The Law of Independent
Assortment
Independent Assortment
• The inheritance pattern of one trait will
not affect the inheritance pattern of
another
• Independent assortment occurs during
meiosis
• For a single human gamete, the possible
ways chromosomes may assort is
astounding:
223 = 8,388,608 possible combinations
Dihybrid Cross
In snapdragons, tallness (T) is dominant to dwarfness(t),
while red color is due to gene (R) and white to its
corresponding allele (r). The heterozygous condition
results in pink (Rr) flower color. A dwarf pink snapdragon
is crossed with a plant homozygous for tallness and red
flowers. Give the possible genotypes and corresponding
phenotypes for all of the possible F1 generation.
Step #1: Determine Genotypes
of Parents
“A dwarf pink snapdragon is crossed with
a plant homozygous for tallness and red
flowers. “
Dwarf pink = ttRr
Homozygous tall, red = TTRR
Step #2: Determine Genotypes
of Gametes
“A dwarf pink snapdragon is crossed with
a plant homozygous for tallness and red
flowers. “
Dwarf pink = ttRr
tR
tr
tR
tr
Homozygous tall, red = TTRR
TR TR
TR TR
Step #3: Punnett Square
The Punnett square
determines the
genotypes of the
offspring
Gametes from
dwarf pink parent
Gametes from
TALL red parent
TR
TR
TR
tR
TtRR
TtRR
TtRR
TtRR
tr
TtRr
TtRr
TtRr
TtRr
tR
TtRR
TtRR
TtRR
TtRR
tr
TtRr
TtRr
TtRr
TtRr
TR
Step #4: Identify Phenotype
Ratios in Offspring
TtRR
TtRR
TtRR
TtRR
Tall, red = 8/16
Tall, pink = 8/16
TtRr
TtRr
TtRr
TtRr
TtRR
TtRR
TtRR
TtRR
TtRr
TtRr
TtRr
TtRr
Tall, white = 0/16
Short, red = 0/16
Short, pink = 0/16
Short, white = 0/16