1. Chapter 12: Patterns of Heredity & Human Genetics
Section 1: Mendelian Inheritance of Human Traits

2. Making a Pedigree
When genetic inheritance is represented by a picture, this is called a pedigree.
Pedigrees are used by geneticists to map inheritance from generation to generation.

3. It is a diagram made of symbols that identify three things:
1. Male or female
2. Individuals affected by the trait being studied
3. Family relationships

4. Symbols of a pedigree: ***need to know***
Carrier –
heterozygous individual

5. Constructing and Reading a pedigree
****a horizontal line between a male and female with a strike means the persons are divorced.**** (Need to know)
***an inverted “v” means the married couple had twins*** (know)

6. Constructing and Reading a pedigree1 2
II. 1 2 3 4 5
III. 1 2 3 4 5 6
***Roman Numerals (I, II, III) refers to the generations.***
*Arabic numbers refers to individuals. (1, 2, 3, 4, 5, …)

7. How many generations are there? How many children did II-1 have? II-7?
Reading the pedigree… I. 1 2
II. 1 2 3 4 5 6 7
III. 1 2 3 4 5
How many generations are there?
How many children did II-1 have? II-7?
How are III-5 and III-2 related?
Who is III-2 in reference to I-2?

8. Types of Pedigrees
Pedigrees can be: a.) autosomal *There is a 50/50 ratio between men and women of affected individuals. b.) X- linked *Most of the males in the pedigree are affected.

9. Colorblindness Pedigree
Facts about X-linked Disorders *carried on the X-chromosome
*X-linked are carried by females, but not expressed in females.
*X-linked are expressed most often in MALES.
*In males, to express an X-linked disorder, he only needs to have one gene. (XY - heterozygous)
*In females, to express an X-linked disorder, she needs TWO alleles to show the disorder. (XX – homozygous recessive)
Ex: Colorblindness, hemophilia, baldness
Colorblindness Pedigree

10. Test Name: Ishihara Test
Colorblindness Tests
Normal color:
yellow square &
faint brown circle
Colorblind sees:
yellow square
Colorblind sees:
the number 17
Normal Color sees:
the number 15
Test Name: Ishihara Test

11. Simple Recessive Heredity
Most genetic disorders are caused by recessive alleles. This means the disorder is inherited when both parents have a recessive allele.

12. Common Recessive Disorders
Cystic Fibrosis (CF):
A defective protein in the plasma membrane of cells causes thick mucus to build up in the lungs and digestive system.
Mostly found among white Americans.

13. Pedigree for Cystic Fibrosis

14. Tay-Sachs Disease:
The absence of an enzyme causes lipids to accumulate in the tissues and nerve cells of the brain.
blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in and other neurological symptoms
Death usually by age 4

15. Pedigree for Tay-Sachs

16. Simple Dominant Heredity
Dominant disorders are inherited as Mendel’s rule of dominance predicted: Only one dominant allele has to be inherited from either parent.

17. Common Dominant Traits & Disorders
Simple Dominant Traits
1. cleft chin
2. unattached earlobes
3. almond shaped eyes

18. Disorders: Huntington’s Disease
A lethal genetic disorder that causes certain areas of the brain to break down.
Does not occur until years of age so this is why it can be passed along.
There is a genetic test that can test the presence of the allele…would you want to know?

19. Is it Dominant or Recessive…1 2 3 4
II. 6 4 5 1 2 3
III. 1 2 3
Dominant, only one parent has the disorder.

20. Is it Dominant or Recessive…1 2 3 4
II. 6 4 5 1 2 3
III. 1 2 3
Recessive, neither parent has the disorder. Both are heterozygous.

21. Section 2: When Heredity Rules are Different
Chapter 12
Section 2: When Heredity Rules are Different

22. Complex Patterns of Heredity
Most traits are not simply dominant or recessive
Incomplete dominance: when the phenotype of the heterozygous individual is in between those of the two homozygotes (homozygous dominant & homozygous recessive)

23. Red flower color (RR) is dominant
White flower color (rr) is recessive
Pink colored flowers (Rr)

24. Codominace: when the alleles of both homozygotes (BB or WW) are expressed equally in the heterozygous individual
If a black chicken (BB) is crossed with a white chicken (WW), all offspring will be checkered
Example: sickle-cell anemia

25. X-linked disorders: generally passed on from mother to son
Sex-linked traits: when traits are controlled by genes located on sex chromosomes
X-linked disorders: generally passed on from mother to son
The genetic abnormality is found on the X chromosome
Females are XX, males are XY

26. If a female has a normal X, it would be dominant over the defective X
In males, it will not be masked by a corresponding dominant allele because they have a “Y” chromosome
Ex: hemophilia & Lesch-Nyhan syndrome

27. Y-linked disorders: only passed on from father to son
Examples: excessive hair growth of the ears & male infertility

28. Polygenic inheritance: when a trait is controlled by many genes
Examples: height, eye color, skin color, & blood type

29. Changes in Chromosomal Numbers
Humans have 23 pairs of chromosomes (46 total); more or less = disorder
Autosomes: a non-sex chromosome
Known as chromosomes 1-22

30. Sex chromosomes: 23rd pair in humans that determine a person’s sex
Example: Down’s Syndrome (trisomy 21)

32. 8 Environmental Factors That Can Also Influence Gene Expresssion
1. temperature
2. light
3. nutrition
4. chemicals
5. infectious agents
6. hormones
7. structural differences
8. age
*** know examples***