Monohybrid Crosses
Haploid Organism
Spore Colour Gene
Light spore allele
Dark spore allele
Parents
light
dark
• A parent with light spores is crossed
with a parent with dark spores.
• Gametes are produced by mitosis.
mitosis
Gametes
fusion
• Gametes fuse to give a diploid cell.
Diploid Cell
replication
• The chromosomes are replicated.
meiosis 1
• The diploid cell undergoes meiosis,
producing four spores.
meiosis 2
• The spores grow into new organisms.
Two will have light spores and two
will have dark spores.
light
light
dark
Offspring
Genetics Handout 12.1
dark
Diploid Organism
Flower Colour Gene
Purple flower allele (dominant)
White flower allele (recessive)
Parents
purple
white
• A pure breeding purple
flowered parent is crossed
with a pure breeding white
flowered parent.
meiosis 1
• Gametes are produced by
meiosis.
meiosis 2
fusion
Gametes
Gametes
• Gametes fuse to give a
diploid zygote.
Zygote
replication
purple
Offspring
Genetics Handout 12.2
• The chromosomes are
replicated.
• The zygote grows into a
new organism with purple
flowers.
Diploid Organism
Flower Colour Gene
Purple flower allele (dominant)
White flower allele (recessive)
Parents
purple
purple
• Two heterozygous parents
are crossed.
meiosis 1
• Gametes are produced by
meiosis.
meiosis 2
fusion
Gametes
Gametes
Zygotes
• Gametes fuse to give a
diploid zygote.
replication
• The chromosomes are
replicated.
purple
purple
purple
white
Offspring
Offspring
Offspring
Offspring
Genetics Handout 12.3
• The zygotes grow into new
organisms with a 3:1 ratio
of purple:white flowers.