1. Analyzing Human Inheritance

2. How Can We Study Human Inheritance?
Pedigrees are graphic representations of an individual’s family tree
Used to predict the chances of an offspring receiving a trait
Used to determine the inheritance pattern of a particular trait

3. Pedigrees

4. Pedigree Symbols
Normal Male Normal Female Affected Male Affected Female Mating Siblings Known Carriers

5. Inherited Genetic Disorders
Cystic Fibrosis (CF)
Caused by a recessive allele
A missing membrane protein causes mucous build up in places like the lungs
Most common among Caucasions

6. Inherited Genetic Disorders
Sickle-cell Anemia
Caused by a codominant allele
An altered hemoglobin protein changes the shape of the red blood cells
Most common among African-Americans

7. Inherited Genetic Disorders
Tay-Sachs
Caused by a recessive allele
A missing enzyme causes lipid build up in the brain (death by age 4)
Most common among eastern European Jews

8. Inherited Genetic Disorders
Huntington’s
Caused by a dominant allele
Late-onset of symptoms (age 40) result in the deterioration of the nervous system

9. Inherited Genetic Disorders
Phenylketonuria (PKU)
Caused by a recessive allele
A missing enzyme prevents the break down of phenylalanine (the build up can cause brain damage)
If caught early, an altered diet can prevent damage

10. Analyzing Chromosomes

11. Analyzing Chromosomes
A karyotype is an ordered display of an individual’s chromosomes
Scientists take a picture of the chromosomes during metaphase

12. Analyzing Chromosomes
Each chromosome is paired with its homologue
The display is used to detect chromosomal abnormalities

13. How Do Chromosomal Abnormalities Occur?
During (meiosis) cell division, sometimes chromosomes fail to separate correctly
Nondisjunction
This produces gametes with incorrect numbers of chromosomes

14. Meiotic Nondisjunction

15. Results of Nondisjunction
Two types of zygotes can result from nondisjunction:
Trisomy
Zygote has 3 copies of a chromosome
Monosomy
Zygote only has 1 copy of a chromosome

16. Chromosomal Abnormalities
Down Syndrome
Caused by a trisomy 21
Most common serious birth defect in the U.S.

17. Chromosomal Abnormalities
Klinefelter Syndrome
Caused by an extra X chromosome in males (ex. XXY)

18. Chromosomal Abnormalities
Jacobs or Extra Y
Caused by an extra Y chromosome in males (ex. XYY)

19. Chromosomal Abnormalities
Metafemale or Triple X
Caused by an extra X chromosome in females (ex. XXX)
Turner Syndrome
Caused when females only get one X chromosome (XO)
This is the only viable human
monosomy

20. Prenatal Genetic Testing