Transcript Alleles segregate during gamete formation, but do they do

Alleles segregate during
gamete formation, but do
they do it independently?
Two-factor Cross, F1
RRYY
x
Round/yellow peas
rryy
wrinkled/green
What will offspring look like?
Gives hybrid plants needed for next cross
Two-Factor Cross, F2
RrYy x RrYy
Independent Assortment
• Genes for different traits can
segregate independently during
the formation of gametes.
• Leads to genetic variation in
plants, animals, and other
organisms.
Not all genes show simple
patterns of dominant and
recessive
• Incomplete dominance
• Codominance
• Multiple alleles
• Polygenic traits
• Sex-linked
Incomplete Dominance
• One allele NOT dominant over
another
• Four o’clock plants
RR x
RW
WW
Codominance
• Both alleles contribute to the
phenotype
• Chicken: black feathers codom with
white
• Heterozygous = erminette (speckled)
• Humans: protein controlling cholesterol
levels
• Blood type
Multiple Alleles
• Many genes have more
than 2 alleles
• Coat color in rabbits
• Human gene for blood type
Polygenic Traits
• Traits controlled by two or more genes
• At least three genes involved in reddishbrown pigment in eyes of fruit flies
• Different combinations of alleles produce
different eye colors
• Polygenic traits often show a wide range
of phenotypes
• Skin color in humans partly because more
than four different genes probably control
this trait
Sex-linked Genes