notes: types of inheritance
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Notes: Types of Inheritance
Test Cross
• Used to determine the genotype of an individual that displays a dominant trait. – Don’t know whether the
genotype is PP or Pp
Test Cross
• Used to determine the genotype of an individual that displays a dominant trait. – Either PP or Pp
• Cross with homozygous recessive (pp)
• If in the offspring, there are pp, then the parent had to be Pp
Types of Inheritance
• Complete Dominance• Incomplete Dominance• Codominance• Sex-linked• Polygenic• Epistasis
You will be responsible to complete punnett squares for the types in red
Complete Dominance
• One allele is completely dominant over the other • Only two phenotypes exist • One phenotype is masked• The heterozygous phenotype shows dominant
trait– Ex: Purple flowers are dominant to white– PP= purple– Pp= purple– pp= white
Complete Dominance
Autosomal Genetic Disorders.Carrier: A heterozygote for a recessive disorder (ex/ Cc). • Carrier does not show symptoms but can pass
recessive allele to offspring• Affected person must inherit two recessive alleles• Example Cystic Fibrosis, Tay-sachs, sickle-cell
anemia• CC &Cc = unaffected• cc = affected
Practice Problem
A male and female are both carriers for sickle-cell anemia. What percent chance do they have of having a child with sickle-cell anemia?
Incomplete Dominance
• Neither allele is completely dominant over the other
Incomplete Dominance
• Neither allele is completely dominant over the other
• Three phenotypes exist • The heterozygous phenotype
shows blended trait
Incomplete Dominance• Neither allele is completely dominant over the
other • Three phenotypes exist • The heterozygous phenotype shows blended
trait• Ex: Flowers can be pink, red, or white. – RR=red– rr= white– Rr =pink
Incomplete Dominance
• Cross two pink flowers• What percent of their offspring will have white
flowers?
• Fish can be green (GG), blue (BB), or teal (GB)
Green (GG) Teal (Gg) Blue (gg)
Codominance
• Both alleles are dominant
Codominance
• Both alleles are dominant• Three phenotypes exist • Neither phenotype is masked• The heterozygous phenotype shows both
traits at once
Codominance
• Both alleles are dominant• Three phenotypes exist • Neither phenotype is masked• The heterozygous phenotype shows both
traits at once.
X =
red (RR) white (WW)
Codominance
• Both alleles are dominant• Three phenotypes exist • Neither phenotype is masked• The heterozygous phenotype shows both
traits at once.
X =
red (RR) white (WW) red & white(WR)
Codominance
EX: In Smileys, eye shape can be starred, circular, or a circle with a star.
Write ALL the phenotypes and genotypes that exist.
Codominance
EX: In Smileys, eye shape can be starred, circular, or a circle with a star.
Write ALL the phenotypes and genotypes that exist.
• CC = circle SS = star SC = circle-star
Codominance
• Example: Blood Types• Trait controlled by three
alleles, with two that are codominant and one recessive
IA : produces A antigens on surface of cell
IB : produces B antigens i: does not produce
antigens
Genotypes PhenotypesAA or AO Type A BB or BO Type BAB Type ABOO Type O
Practice Problem
• What possible blood types could the children of a homozygous A female and a male with AB blood have?
• Parents Genotype_______X ________
Sex Linked• Disorder/trait found on the “X” chromosome• Which gender has more instances of having an
x-linked disorder?
Sex Linked• Disorder/trait found on the “X” chromosome• Which gender has more instances of having an
x-linked disorder?• Men-Males have no second copies of X-linked genes
(XY).• Females have two X chromosomes (XX) so if one has a
defect they can use the other normal X chromosome.
Sex-Linked
• EX: color blindness• Punnett square determines sex and trait• First, Use X and Y to show gender• Second, use a letter on the X chromosome to
show which allele they inherited.
Sex-Linked• EX: color blindness• Punnett square determines sex and trait• First, Use X and Y to show gender• Second, as a letter on the X chromosome to show which allele
they inherited.
Possible genotypes and phenotypes:XR XR = Female, normal visionXR Xr = Female, normal visionXr Xr = Female, color blindXR Y = Male, normal visionXr Y = Male, color blind
Sex Linked
What percentage of offspring would be color blind if a female carrier and a male who has normal vision had children?
Sex Linked
What percentage of offspring would be color blind if a female carrier and a male who has normal vision had children?
Step 1: Determine genotype of parents ____________ x ____________
Sex Linked
Step 2: set up and complete punnett square.What percent of their children would be
colorblind?
Polygenic
• Many genes may interact to produce one trait
• Ex: Skin color result of four genes that interact to produce range of colors
Epistasis
• One gene controls many traits• EX: Albinism• Albinos are unable to synthesize melanin, the
pigment molecule responsible for most human coloring
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