2. Chapter Menu Lesson 1: Foundations of Genetics
Lesson 2: Understanding Inheritance
Click on a hyperlink to view the corresponding lesson.

3. 4.1 Foundations of Genetics
heredity
genetics
dominant
recessive
gene
law of segregation
law of independent assortment
allele
phenotype
genotype
homozygous
heterozygous

4. Early Ideas About Heredity
4.1 Foundations of Genetics
Early Ideas About Heredity
Combined genetic material from a sperm and an egg determines the traits or features of an offspring.
Heredity is the passing of traits from parents to offspring.

5. Early Ideas About Heredity (cont.)
4.1 Foundations of Genetics
Early Ideas About Heredity (cont.)
The idea of blending inheritance is offspring are a blend of genetic material from both parents.
The genetic material mixed or blended like colors of paint.
Over many generations, populations would eventually look alike.
Blending inheritance cannot explain why some traits skip a generation.

6. Gregor Mendel and His Experiments
4.1 Foundations of Genetics
Gregor Mendel and His Experiments
Gregor Mendel was the first to record evidence that traits are determined by factors passed from parents to offspring.
Mendel established the basic laws of heredity.
Genetics is the study of how traits of organisms are passed from parents to offspring.

7. Mendel’s Experimental Methods
4.1 Foundations of Genetics
Mendel’s Experimental Methods
Mendel conducted breeding experiments by studying seven traits of pea plants and each traits had only two variations.

8. Controlled Experiments
4.1 Foundations of Genetics
Controlled Experiments
Mendel controlled fertilization in the pea plants, allowing him to see how traits pass from one generation to another.
Mendel allowed some flowers to self-fertilize.
He also performed cross-fertilization by transferring pollen from one pea flower to another.

9. Mendel’s Unique Methods
4.1 Foundations of Genetics
Mendel’s Unique Methods
Used true-breeding plants for each trait—plants that always produce offspring with that trait when they self-pollinate
Recorded the inheritance of traits for several generations
Used a mathematical approach

10. Mendel’s Experimental Results
4.1 Foundations of Genetics
Mendel’s Experimental Results
Mendel concluded that two factors control each inherited trait.
When organisms reproduce, each gamete— sperm or egg—contributes one factor for each trait.

11. 4.1 Foundations of Genetics
Dominant Factors
A genetic factor that blocks another genetic factor is called dominant.
A dominant trait is observed when offspring have one or two dominant factors.

12. 4.1 Foundations of Genetics
Recessive Factors
A genetic factor that is hidden by the presence of a dominant factor is recessive.
A recessive trait can be observed only when two recessive genetic factors are present in offspring.

13. Mendel’s Laws of Heredity
4.1 Foundations of Genetics
Mendel’s Laws of Heredity
Law of segregation: the two factors for each trait segregate—separate from each other—during meiosis when gametes form
Law of independent assortment: the factors for one trait separate independently of how factors for other traits separate

14. Modern Definitions of Mendel’s Ideas
4.1 Foundations of Genetics
Modern Definitions of Mendel’s Ideas
Mendel did not know about DNA or how cells reproduce, but his ideas about inheritance are still true today.

15. 4.1 Foundations of Genetics
Genes and Alleles
A gene is a section of DNA that has information about a trait in an organism.
Each form of a gene with different information is called an allele.

16. Genes and Alleles (cont.)
4.1 Foundations of Genetics
Genes and Alleles (cont.)

17. Phenotype and Genotype
4.1 Foundations of Genetics
Phenotype and Genotype
The observable traits and all characteristics of an organism make up the organism’s phenotype.
The alleles that make up an organism is the organism’s genotype.
The alleles of a particular gene is that gene’s genotype.

18. Homozygous and Heterozygous Genotypes
4.1 Foundations of Genetics
Homozygous and Heterozygous Genotypes
Because eukaryotes have pairs of chromosomes, a genotype for a gene has two alleles.
If the two alleles have the same information, the genotype is homozygous.
If the two alleles have different information, the genotype is heterozygous.

19. Homozygous and Heterozygous Genotypes (cont.)
4.1 Foundations of Genetics
Homozygous and Heterozygous Genotypes (cont.)

20. Law of Segregation Explained
4.1 Foundations of Genetics
Law of Segregation Explained
The movement of chromosomes during meiosis explains Mendel’s law of segregation.
Each set of chromatids separates into different gametes during meiosis II.
Each gamete receives only one allele.

21. Law of Segregation Explained (cont.)
4.1 Foundations of Genetics
Law of Segregation Explained (cont.)

22. Law of Independent Assortment Explained
4.1 Foundations of Genetics
Law of Independent Assortment Explained
The daughter cells produced by meiosis receive only one chromosome from each pair of homologous chromosomes.
A daughter cell might receive the A or a chromosome from pair 1 and the B or b chromosome from pair 2.
This results in four possible allele combinations for two homologous pairs of chromosomes.

23. Law of Independent Assortment Explained (cont.)
4.1 Foundations of Genetics
Law of Independent Assortment Explained (cont.)

24. Importance of Mendel’s Genetic Studies
4.1 Foundations of Genetics
Importance of Mendel’s Genetic Studies
In the 1860s, no one knew about chromosomes or meiosis so it was hard to understand Mendel’s discoveries.
All the research of modern genetics is based on Mendel’s conclusions from his work with pea plants.

25. What is the passing of traits from parents to offspring called?
4.1 Foundations of Genetics
What is the passing of traits from parents to offspring called?
A inheritance
B genetics
C heredity
D allele
Lesson 1 Review

26. What are the alleles that make up an organism called? A genes
4.1 Foundations of Genetics
What are the alleles that make up an organism called?
A genes
B genotype
C phenotype
D factors
Lesson 1 Review

27. 4.1 Foundations of Genetics
If two alleles for a gene have the same information, what kind of genotype does that gene have?
A homologous
B recessive
C heterozygous
D homozygous
Lesson 1 Review

28. End of Lesson 1

29. 4.2 Understanding Inheritance
Punnett square
pedigree
incomplete dominance
codominance
multiple alleles
sex chromosomes
polygenic inheritance
genetic disorder

30. 4.2 Understanding Inheritance
Modeling Inheritance
Two tools can be used to identify and predict traits among genetically related individuals.
Punnett square
pedigree
Heredity

31. 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.

32. 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.

33. 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.

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

35. 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.

36. 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.

37. 4.2 Understanding Inheritance
Pedigrees (cont.)
A pedigree chart that shows three generations of a family.

38. 4.2 Understanding Inheritance
Types of Dominance
Alleles show incomplete dominance when they produce a phenotype that is a blend of the parents’ phenotypes.
When both alleles can be observed in the phenotype, the interaction is called codominance.
The human blood type AB is an example of codominance.

39. 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.

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

41. 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.

42. Sex-Linked Inheritance (cont.)
4.2 Understanding Inheritance
Sex-Linked Inheritance (cont.)
In this family, the grandmother’s genome included the color blindness allele.

43. 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.

44. 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.
How are the traits of parents inherited and expressed in offspring?

45. 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.

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

47. 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.

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

49. A incomplete dominance B codominance C multiple alleles
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
Lesson 2 Review

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

51. End of Lesson 2

52. Chapter Resources Menu
Chapter Assessment
California Standards Practice
Concepts in Motion
Image Bank
Science Online
Click on a hyperlink to view the corresponding feature.

53. A polygenic inheritance B sex-linked inheritance
What is the term for the idea that offspring are a blend of genetic material from both parents?
A polygenic inheritance
B sex-linked inheritance
C maternal inheritance
D blending inheritance
Chapter Assessment 1

54. What type of alleles can only be observed in the phenotype when they are present as a homozygous genotype?
A dominant
B recessive
C inherited
D heterozygous
Chapter Assessment 2

55. A law of independent assortment B law of heredity C law of segregation
What is the term for the idea that inheritance of one trait is not influenced by inheritance of another trait?
A law of independent assortment
B law of heredity
C law of segregation
D maternal inheritance
Chapter Assessment 3

56. A color of camellia flowers B human AB blood type C color blindness
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
Chapter Assessment 4

57. 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
Chapter Assessment 5

58. Which pea trait did Mendel not study? A seed color B pod color
SCI 2.c
Which pea trait did Mendel not study?
A seed color
B pod color
C flower position
D flower shape
CA Standards Practice 1

59. SCI 2.d
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%
CA Standards Practice 2

60. What is the term for when more than one gene determine a trait?
SCI 2.c, 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
CA Standards Practice 3

61. Which does NOT describe Mendel’s experiments?
SCI 2.d
Which does NOT describe Mendel’s experiments?
A Mendel observed several generations of plants.
B Mendel chose pea plants because they reproduce quickly.
C Mendel counted small numbers of offspring.
D Mendel used true-breeding plants.
CA Standards Practice 4

62. What type of genetic disorder is hemophilia? A dominant
SCI 2.d
What type of genetic disorder is hemophilia?
A dominant
B X-linked recessive
C codominant
D recessive
CA Standards Practice 5

63. Concepts in Motion 1

64. Concepts in Motion 2

65. Image Bank

66. End of Resources