Monohybrid Crosses

1
Monohybrid Crosses

• Studying the inheritance of a single trait while
  ignoring all other traits
• Start with 2 pure parents
• P Generation
• GG (only green)
• gg (only yellow)
• F1 generation
• All green heterozygous

2
Determining Genotype (1 Trait)
PARENT
green
yellow
F1
4
All green
Cannot see the yellow in this generation
Self- fertilized
F2
Self fertilization of this generation produces a
different pattern for homozygous vs. heterozygous
Yellow returns
3
Using a Punnett Square

• Grid for Organizing Genetic Information
• Shows Probability that a combination will occur

g g
Alleles From Parent 2
Gg
G G
Gg
1) Determine Parent alleles 2) Place alleles on
edge of square 3) Combine alleles inside the
boxes 4) Determine genotypes and phenotypes
Gg
Gg
Possible offspring genotypes for F1
Alleles from Parent 1
4
Heterozygous cross

• Phenotypes vs. Genotypes
• The recessive trait will show ONLY in the absence
  of the dominant (G) trait.

G g
GENOTYPE
G g
GG Gg or gG gg 1 2 1
GG
Gg
PHENOTYPE
Green Yellow 3 1
gg
gG