Chapter 9
Dominance relation and
multiple alleles in diploid
organisms
Genetics Third edition
Monroe W.strickberg
, • The basic contribution of Mendel was his disc
of the unit nature of inheritance-that it consis
particulate factors, or genes, whose presence
Introduction be traced from one generation to another wit
change or dilution.
• F2 mendelian ratios of 3:1 in monohybrid cros
and 9:3:3:1 in dihybrid crosses among diploids
found as expected.
• These ratios has been found as expected ratio
derive from segregation of two different allele
each gene pair, one dominant and one recessi
• Experiments have revealed appearance of
phenotypes in novel proportions that can't be
explained on basis of simple dominance or
presence of only two kind of alleles.
,Incomplete
dominance
, • In simple or complete dominance, the
heterozygote, although genetically differe
has same phenotype as one of the
Incomplete homozygotes (i.e.,Aa=AA) and the presen
recessive gene is functionally hidden
Dominance • In Mendel's example the chosen gene
differences all showed simple dominance
except for one-character, flowering time,
which his experiments were unfortunatel
incomplete.
• Rasmusson, found that influenced by diff
factors among a pair of alleles called A an
• There was a 5-day difference in flowering
between homozygous AA and aa.
Dominance relation and
multiple alleles in diploid
organisms
Genetics Third edition
Monroe W.strickberg
, • The basic contribution of Mendel was his disc
of the unit nature of inheritance-that it consis
particulate factors, or genes, whose presence
Introduction be traced from one generation to another wit
change or dilution.
• F2 mendelian ratios of 3:1 in monohybrid cros
and 9:3:3:1 in dihybrid crosses among diploids
found as expected.
• These ratios has been found as expected ratio
derive from segregation of two different allele
each gene pair, one dominant and one recessi
• Experiments have revealed appearance of
phenotypes in novel proportions that can't be
explained on basis of simple dominance or
presence of only two kind of alleles.
,Incomplete
dominance
, • In simple or complete dominance, the
heterozygote, although genetically differe
has same phenotype as one of the
Incomplete homozygotes (i.e.,Aa=AA) and the presen
recessive gene is functionally hidden
Dominance • In Mendel's example the chosen gene
differences all showed simple dominance
except for one-character, flowering time,
which his experiments were unfortunatel
incomplete.
• Rasmusson, found that influenced by diff
factors among a pair of alleles called A an
• There was a 5-day difference in flowering
between homozygous AA and aa.
