2. 4.2 Understanding Inheritance
Punnett square
pedigree
incomplete dominance
codominance
multiple alleles
sex chromosomes
polygenic inheritance
genetic disorder

3. 4.2 Understanding Inheritance
Modeling Inheritance
Two tools can be used to identify and predict traits among genetically related individuals.
Punnett square
pedigree
Heredity

4. 4.2 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.

5. 4.2 Understanding Inheritance
One-Trait Model
The Punnett square shows the possible offspring of a cross between two true-breeding pea plants—one with yellow seeds and one with green.

6. One-Trait Model (cont.)
4.2 Understanding Inheritance
One-Trait Model (cont.)
The only possible genotype for hybrid offspring is heterozygous—Yy.
The phenotype will be yellow seeds because Y is dominant to y.

7. One-Trait Model (cont.)
4.2 Understanding Inheritance
One-Trait Model (cont.)

8. 4.2 Understanding Inheritance
Two-Trait Model
The possible offspring of two heterozygous genotypes—Yy and Yy—would have three different genotypes and two phenotypes.

9. 4.2 Understanding Inheritance
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 pattern of inheritance and genetic disorders in families.

10. 4.2 Understanding Inheritance
Pedigrees (cont.)
A pedigree chart that shows three generations of a family.

11. Pedigrees
Let’s read about pedigrees from our textbook page 184.

12. Types of Dominance *Incomplete Dominance
4.2 Understanding Inheritance
Types of Dominance *Incomplete Dominance
Alleles show incomplete dominance when they produce a phenotype that is a blend of the parents’ phenotypes.
Let’s read about this on page 185 of our textbook.

13. Incomplete Dominance Video

14. Types of Dominance *Codominance
When both alleles can be observed in the phenotype, the interaction is called codominance.
The human blood type AB is an example of codominance.

15. 4.2 Understanding Inheritance
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 the ABO blood type—IA, IB, and i.
Let’s read about codominance on page 185 of our textbook.

16. Multiple Alleles (cont.)
4.2 Understanding Inheritance
Multiple Alleles (cont.)

17. Multiple Alleles & Codominance Video

19. Sex-Linked Inheritance
4.2 Understanding Inheritance
Sex-Linked Inheritance
Chromosomes X and Y are the sex chromosomes—they contain the genes that determine gender or sex.
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.

20. Sex-Linked Inheritance (cont.)
4.2 Understanding Inheritance
Sex-Linked Inheritance (cont.)
In this family, the grandmother’s genome included the color blindness allele.
Let’s read about this on page 186 of our textbook.

21. Sex-Linked Inheritance Video

22. Polygenic Inheritance
4.2 Understanding Inheritance
Polygenic Inheritance
Polygenic inheritance is when multiple genes determine the phenotype of a trait.
Many phenotypes are possible when possible when polygenic inheritance determines a trait.
Let’s read about Polygenic Inheritance on page 187.

23. 4.2 Understanding Inheritance
Maternal Inheritance
Humans inherit mitochondrial genes only from their mothers.
Inheritance of traits related to the mitochondria can be traced from grandmother to grandchildren.
Let’s read about Maternal Inheritance on page 187.
How are the traits of parents inherited and expressed in offspring?

24. Human Genetic Disorders
4.2 Understanding Inheritance
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.

25. Genetic Diseases

26. Human Genetic Disorders (cont.)
4.2 Understanding Inheritance
Human Genetic Disorders (cont.)

27. Hemophylia – Human Genetic Disorder

28. Genes and the Environment
4.2 Understanding Inheritance
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.

29. Genes and the Environment Heart Disease

30. Human Genetic Disorders Genes and the Environment
Read page 188 in your textbook.

31. Punnett squares model the ____ of offspring. A genotypes B phenotypes
4.2 Understanding Inheritance A B C D
Punnett squares model the ____ of offspring.
A genotypes
B phenotypes
C genotypes and phenotypes
D genes
Lesson 2 Review

32. A incomplete dominance B codominance C multiple alleles
4.2 Understanding Inheritance A B C D
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
Lesson 2 Review

33. How many Y chromosomes do females have? A 0 B 1 C 2 D 4
4.2 Understanding Inheritance A B C D
How many Y chromosomes do females have?
A 0
B 1
C 2
D 4
Lesson 2 Review

34. End of Lesson 2