4-2 Notes – Understanding Inheritance Chapter 4, Lesson 2.
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Transcript of 4-2 Notes – Understanding Inheritance Chapter 4, Lesson 2.
4-2 Notes – Understanding Inheritance
Chapter 4, Lesson 2
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.
Punnett SquaresB = black furb = brown fur
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B B
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B B
b
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B B
b
b
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B B
b
b
B b
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B B
b
b
B b B b
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B B
b
b
B b B b
bB
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B B
b
b
B b B b
bB B b
Punnett SquaresB = black furb = brown fur
Female = BB
Male = bb
B B
b
b
B b B b
bB B b
black black
black black
Punnett Squares (5:00)
One-Trait Model
• A cross between two homozygous pea plants: one with yellow seeds (YY) and one with green seeds (yy).
One-Trait Model
• 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
Two-Trait Model
• A cross between two heterozygous genotypes (Yy and Yy)
Two-Trait Model
• The offspring would have three different genotypes and two phenotypes.
Two-Trait Model
FF Ff
Ff ff
F = frecklesf = no freckles
freckles freckles
freckles no freckles
• Cross a freckled Dad (Ff) with a freckled Mom (Ff).
Two-Trait Model
Genotypes:
___% are FF
___% are Ff
___% are ffFF Ff
Ff ff
F = frecklesf = no freckles
freckles freckles
freckles no freckles
25
50
25
Two-Trait Model
Phenotypes:
___% have freckles
___% have no freckles
F = frecklesf = no freckles
FF Ff
Ff ff
freckles freckles
freckles no freckles
75
25
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.
Pedigrees
• This pedigree chart shows three generations of a family.
Pedigrees Fill in the key!
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.
Codominance
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.
Multiple Alleles
Sex-Linked Inheritance• Chromosomes X and Y are the sex
chromosomes - they contain the genes that determine sex (male or female).
Sex-Linked Inheritance• 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.
Sex-Linked Inheritance• 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.
Sex-Linked Inheritance
Sex-Linked InheritanceIn this family, the grandmother’s genome included the color blindness allele.
Sex-Linked Inheritance• Example: red-green
colorblindness
A carrier has one recessive allele and one dominant allele for a trait. They don’t have the trait but can pass it on to offspring.
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.
Chris Sutter
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.
Genes and the Environment
Siamese cats have a gene that codes for darker pigments - this gene is more active at low temperatures. Parts of the body that are colder (ears, feet, tail) will develop the darker pigmentation of the Siamese cats.
Punnett squares model the ____ of offspring.
A genotypes
B phenotypes
C genotypes and phenotypes
D genes
4.2 Understanding Inheritance
What is the term for when alleles produce a phenotype that is a blend of the parents’ phenotypes?
A incomplete dominance
B codominance
C multiple alleles
D polygenic inheritance
4.2 Understanding Inheritance
How many Y chromosomes do females have?
A 0
B 1
C 2
D 4
4.2 Understanding Inheritance
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
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
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%
SCI 2.d
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
SCI 2.c, 2.d
What type of genetic disorder is hemophilia?
A dominant
B X-linked recessive
C codominant
D recessive
SCI 2.d
4-2 Vocab – Understanding Inheritancetext p. 182-190
1. Punnett square
2. pedigree
3. incomplete dominance
4. codominance
5. multiple alleles
6. sex chromosome
7. polygenic inheritance
8. genetic disorder
1. Cross a tall plant (Tt) with a tall plant (Tt).
T = tall, t = short
_____ % tall
_____ % short
Under each genotype, write the correct phenotype.
2. Tall plant (TT) with short plant (tt).
_____ % tall
_____ % short
3. Short plant (tt) with tall plant (Tt).
_____ % tall
_____ % short
4. Tall plant (TT) with tall plant (Tt).
_____ % tall
_____ % short
1. Cross a tall plant (Tt) with a tall plant (Tt).
T = tall, t = short
_75__ % tall
_25__ % short
T t
T
t
TTtall
Tttall
Tttall
ttshort
2. Tall plant (TT) with short plant (tt).
_100__ % tall
_0__ % short
T T
t
t
Tttall
Tttall
Tttall
Tttall
3. Short plant (tt) with tall plant (Tt).
_50__ % tall
_50__ % short
t t
T
t
Tttall
Tttall
ttshort
ttshort
4. Tall plant (TT) with tall plant (Tt).
_100__ % tall
_0__ % short
T T
T
t
TTtall
TTtall
Tttall
Tttall