4-2 Notes – Understanding Inheritance
Punnett Squares
• A Punnett square is a model used to predict possible _______________ and _______________ of offspring.
• If the genotypes of the _________ are known, the genotypes and phenotypes of the ________________ can be
predicted.
One-Trait Model
• A cross between two homozygous pea plants - one with ________ seeds (YY) and one
with _________ seeds (yy) .
• All offspring have the ___________________________ genotype (_____).
• All offspring have the ________________ phenotype because Y is dominant to y.
•
We call these offspring ___________ because they have one of each type of allele.
Two-Trait Model
• A cross between two ______________________ genotypes (Yy and Yy)
• The offspring would have ___________ different genotypes and ______ phenotypes.
• Cross a freckled Dad (Ff) with a freckled Mom (Ff). (F = freckles) (f = no freckles)
Genotypes
Phenotypes
_____% are FF
_____% have freckles
_____% are Ff
_____% have no freckles
_____% are ff
Pedigrees
• All the ________________ related members of a family are part of a family tree.
• A _______________ shows genetic _______ that were inherited by members of a family tree.
• Pedigrees are important tools for tracking complex patterns of ___________________ and genetic ____________
in families.
• This pedigree chart shows three generations of a family:
p. 153
Incomplete Dominance
• This is a _________ of the parents’ phenotypes.
Codominance
• This is when _______ alleles can be observed in the phenotype because both are _________________.
• The human blood type _______ is an example of codominance.
Multiple Alleles
• Some genes have more than ___ alleles, or _________________ alleles.
• The human ______ blood group is determined by multiple alleles as well as ___________________ .
• There are ______ different alleles for blood types: ____ , ____ , and ____ .
Phenotype
Possible Genotypes
type A
type B
type O
type AB
Sex-Linked Inheritance
• Chromosomes __ and __ are the sex chromosomes - they contain the genes that determine sex (male or female).
• Except for sperm and eggs, each cell in a male has an ___ and a ___ chromosome, and each cell in a female has
two ___ chromosomes.
• A ________________ phenotype is observed in a male when a one-allele gene on his X chromosome has a
•
recessive allele . There is no allele on his Y chromosome to “_________” the recessive allele.
Example: red-green __________________________.
Polygenic Inheritance
• This is when more than one _________ determines the phenotype of a trait.
• Many ____________________ are possible when possible when polygenic inheritance determines a trait.
• Examples: ______________ color, height , __________ color
Human Genetic Disorders
• If a change occurs in a ________ , the organism with the mutation may not be able to function as it should.
•
An inherited mutation can result in a phenotype called a _______________ disorder .
Genetic Disorder
Type of Disorder
Health Problems
dominant
breakdown of brain tissue; shortened lifespan
codominant
red blood cell destruction; clogged blood vessels
abnormally thick mucus; affects many organ
recessive
systems
X-linked recessive excessive bleeding due to blood clotting problems
Trisomy – extra
mental retardation; heart defects
chromosome #21
Genes and the Environment
• An organism’s ______________________ can affect its phenotype.
– Genes affect ____________ _____________ , but so do _______ and ___________________ .
– Genes affect _________ __________, but so does exposure to ________________ .
Review
____ 1. Punnett squares model the ____ of offspring.
A. genotypes
B. phenotypes
C. genotypes and phenotypes
D. genes
____ 2. What is the term for when alleles produce a phenotype that is a blend of the parents’ phenotypes?
A. incomplete dominance
C. multiple alleles
B. codominance
D. polygenic inheritance
____ 3. How many Y chromosomes do females have?
A. 0
B. 1
C. 2
D. 4
____ 4. What is a good example of a trait that is determined by multiple alleles?
A. color of camellia flowers
B. human AB blood type
C. color blindness
D. human ABO blood group
____ 5. Why are male humans more likely to be color-blind than females?
A. maternal inheritance
B. sex-linked inheritance
C. polygenic inheritance
D. incomplete dominance
____ 6. If two plants with genotypes Mm are crossed, what percent of the offspring will have phenotype M?
A. 0%
B. 25%
C. 75%
D. 100%
____ 7. What is the term for when more than one gene determine a trait?
A. incomplete dominance
B. multiple alleles
C. polygenic inheritance
D. sex-linked inheritance
____ 8. What type of genetic disorder is hemophilia?
A. dominant
B. X-linked recessive
C. codominant
D. recessive
4-2 Notes – Understanding Inheritance
Punnett Squares
• A Punnett square is a model used to predict possible genotypes and phenotypes of offspring.
• If the genotypes of the parents are known, the genotypes and phenotypes of the offspring can be predicted.
One-Trait Model
• A cross between two homozygous pea plants - one with yellow seeds (YY) and one
with green seeds (yy).
• All offspring have the heterozygous genotype (Yy).
• All offspring have the yellow phenotype because Y is dominant to y.
• We call these offspring hybrid because they have one of each type of allele.
Two-Trait Model
• A cross between two heterozygous genotypes (Yy and Yy)
•
•
The offspring would have three different genotypes and two phenotypes.
Cross a freckled Dad (Ff) with a freckled Mom (Ff). (F = freckles) (f = no freckles)
Genotypes
Phenotypes
25% are FF
75% have freckles
50% are Ff
25% have no freckles
25% are ff
Pedigrees
• All the genetically related members of a family are part of a family tree.
•
•
•
A pedigree shows genetic traits that were inherited by members of a family tree.
Pedigrees are important tools for tracking complex patterns of inheritance and genetic disorders in families.
This pedigree chart shows three generations of a family:
Incomplete Dominance
• This is a blend of the parents’ phenotypes.
Codominance
• This is when both alleles can be observed in the phenotype because both are dominant.
• The human blood type AB is an example of codominance.
Multiple Alleles
• Some genes have more than two alleles, or multiple alleles.
• The human ABO blood group is determined by multiple alleles as well as codominance.
• There are three different alleles for blood types: IA, IB, and i.
Sex-Linked Inheritance
• Chromosomes X and Y are the sex chromosomes - they contain the genes that determine sex (male or female).
• Except for sperm and eggs, each cell in a male has an X and a Y chromosome, and each cell in a female has two
X chromosomes.
• A recessive phenotype is observed in a male when a one-allele gene on his X chromosome has a recessive allele.
•
•
There is no allele on his Y chromosome to “mask” the recessive allele.
In this family, the grandmother’s genome included the color blindness allele.
Example: red-green colorblindness
Polygenic Inheritance
• This is when more than one gene determines the phenotype of a trait.
• Many phenotypes are possible when possible when polygenic inheritance determines a trait.
•
Examples: hair color, height, skin color
Human Genetic Disorders
•
•
If a change occurs in a gene, the organism with the mutation may not be able to function as it should.
An inherited mutation can result in a phenotype called a genetic disorder.
Genes and the Environment
• An organism’s environment can affect its phenotype.
– Genes affect heart disease, but so do diet and exercise.
– Genes affect skin color, but so does exposure to sunlight.
Review (Answers: 1-C, 2-A, 3-A, 4-D, 5-B, 6-C, 7-C, 8-B)
____ 1. Punnett squares model the ____ of offspring.
A. genotypes
B. phenotypes
C. genotypes and phenotypes
D. genes
____ 2. What is the term for when alleles produce a phenotype that is a blend of the parents’ phenotypes?
A. incomplete dominance
C. multiple alleles
B. codominance
D. polygenic inheritance
____ 3. How many Y chromosomes do females have?
A. 0
B. 1
C. 2
D. 4
____ 4. What is a good example of a trait that is determined by multiple alleles?
A. color of camellia flowers
B. human AB blood type
C. color blindness
D. human ABO blood group
____ 5. Why are male humans more likely to be color-blind than females?
A. maternal inheritance
B. sex-linked inheritance
C. polygenic inheritance
D. incomplete dominance
____ 6. If two plants with genotypes Mm are crossed, what percent of the offspring will have phenotype M?
A. 0%
B. 25%
C. 75%
D. 100%
____ 7. What is the term for when more than one gene determine a trait?
A. incomplete dominance
B. multiple alleles
C. polygenic inheritance
D. sex-linked inheritance
____ 8. What type of genetic disorder is hemophilia?
A. dominant
B. X-linked recessive
C. codominant
D. recessive