Download Chapter 4 Lesson 2 (pg182-190) Modeling Inheritance • Punnett

Chapter 4 Lesson 2 (pg182-190)
Modeling Inheritance
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Punnett square
o “a model used to predict possible genotypes and phenotypes of offspring”
o Need genotypes of the parents to predict the genotypes and phenotypes of the
offspring
o Genotypes-coding of the genes that determine traits or characteristics
o Phenotypes—what you actually see—observable traits/characteristics
One trait model
o Breed a true-breeding yellow pea plant with a true-breeding green pea plant
 Dominant (Y) = yellow peas
 Recessive (y) = green peas
Y
y
y
Yy
Yy
Yy
Yy
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Y
All offspring yellow = 100% of the offspring will be yellow
100% of the offspring are heterozygous (Yy)
A true breeding with a true breeding will give hybrid heterozygous offspring
that show the dominant trait
Hybrid Cross Model
Y
y
Y
YY
Yy
Y
YY
Yy
Genotypes:
o 25% homozygous dominant
o 25% homozygous recessive
o 50% heterozygous
Phenotype:
o 75% will be yellow (show dominance)
o 25% will be green (show recessive)
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Pedigree
o ‘family tree’ that shows inherited traits
o Only phenotypes---only traits that show
o Using phenotypes and knowledge of genetics, sometimes genotypes can be determined
o Key—
 squares = men, circles = woman
 Connecting lines show relationship of individuals in pedigrees
o Pedigrees useful tracking complex patterns of genetics & inherited traits/diseases
Types of Dominance
o Dominant-Recessive
 Dominant will show in phenotype
 Double recessive show in the phenotype
o Incomplete Dominance
 Ex) camellia flowers
 Red flower and white flower that crossed make only pink flowers
o Co-Dominance
 Ex) blood types:
 Parent with blood type A (dominant) and a parent with blood type B
(dominant), make a offspring with blood typed AB (codominant)
o Multiple Alleles
 Ex) blood types
 Three alleles (instead two alleles)
 You only get two alleles (one from each parent), but because there are
three allele options, there are actually four blood types that can be
created
Phenotype
Possible
Genotypes
Blood Type A
AA or Ai
Blood Type B
BB or Bi
Blood Type AB
AB
Blood Type O
ii
Sex-Linked Inheritance
o 23 pairs of homologous chromosomes
o All chromosomes are the same size and carry the same genes (with different
information), except the X and Y chromosome pair (#23)
o All male cells have X and Y chromosome
o All female cells have X and X chromosome
o X chromosome is longer than the Y chromosome, which means the X chromosome has
more genes than the Y chromosome
o
So…if the male gets a the X chromosome with a recessive trait there is no gene on the Y
chromosome to dominate, so males will show a recessive trait
 These are called X-linked recessive conditions
 Color blindness
 Muscular dystrophy
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