2. What is a mutation?
Mutation = any change in DNA (the order of nucleotide bases/letters)
Can occur in any cell in the body. Remember from the cells unit that mutations can lead to cancer (uncontrolled cell growth)
Caused by:
Mistakes made during DNA replication, mitosis, meiosis, or protein synthesis
Mutagens = chemicals that can cause DNA mutations Ex. radiation, UV light, cigarette smoke
Viruses

3. There are 2 main types of mutations:
Gene mutations—happen during DNA replication = A change to the original DNA sequence
Ex. Cystic Fibrosis, Dwarfism, and Sickle Cell Anemia
Chromosome mutations—happen during meiosis = Changes the number or location of genes
Ex. Down Syndrome, Klinefelter’s Syndrome, Turner’s Syndrome

4. Gene Mutations Point mutations: substitute one nucleotide for another
ATTACC AATACC
Frameshift mutations: the insertion or deletion of a nucleotide
ATTACC  ATACC (deletion)
ATTACC  ACTTACC (insertion)
These will affect all the codons that come after the insertion or deletion

5. Chromosome Mutations
Duplication: changes the size of chromosomes and results in multiple copies of a single gene
Translocation: pieces of non-homologous chromosomes exchange segments (during crossing over)
Nondisjunction: Chromosomes do not separate correctly during anaphase, resulting in 1 or 3 chromosomes rather than 2 per cell.
Nondisjunction

6. Down Syndrome
An example of nondisjunction  3 copies of chromosome 21

7. Types of Human Genetic Disorders
Autosomal Recessive Disorders
Autosomal Dominant Disorders
Sex-Linked Disorders
Autosomal Chromosome Disorders
Sex Chromosome Disorders

8. Autosomal Recessive Disorders
Caused by the presence of 2 recessive alleles on autosomes
Carrier – does NOT show disease, but can pass the disease-causing allele to offspring.
Examples:
Cystic fibrosis – affects the sweat glands & mucus glands.
PKU - lacks enzyme that is needed to break down phenylalanine, an amino acid in milk and many other foods.
Ex. 2 carriers have a 25% chance of having a child with the disease.

9. Autosomal Dominant Disorders
At least one parent must have the disease in order to pass it on
Caused by the presence of at least 1 dominant allele on autosomes
Dominant genetic disorders are less common than recessive disorders.
Why do you think that is?
Examples:
Achondroplasia (Dwarfism)
Huntington’s disease – damages the nervous system and usually appears during adulthood.
Still possible to have unaffected children if one parent is hetero and the other is homo. recessive

10. Sex-Linked Disorders
Caused by the presence of an allele on the X-chromosome
Examples:
Colorblindness - found in 1 in 10 males and 1 in 100 females.
Hemophilia - does not allow normal blood clotting to occur
Muscular dystrophy - results in the progressive weakening and loss of skeletal muscle
If mom is carrier and Dad is normal, boys get the disease instead of girls

11. Autosomal Chromosome Disorders
Often caused by nondisjunction of autosomes = the failure to separate homologous chromosomes during meiosis.
Causes an abnormal number of chromosomes due to a mistake in meiosis
Example:
Down syndrome - most common form of trisomy involving three copies of chromosomes 21.

12. Sex Chromosome Disorders
Often caused by nondisjunction of sex chromosomes
Causes an abnormal number of sex chromosomes due to a mistake in meiosis
Examples:
Turner’s syndrome - inherit only one X chromosome.
Klinefelter’s syndrome - occurs in males when an extra X chromosome. Males can have XXY, XXXY or XXXXY sex chromosomes.

13. Pedigree
Pedigree – chart used to trace the phenotypes and genotypes in a family to determine whether people carry diseases or traits
Similar to a family tree, but it traces a trait or disease through the family line
Can be used by potential parents or genetic counselors to determine the probability of passing on the disease to children.
Studying pedigrees can help scientists determine the inheritance pattern for a trait (dominant or recessive, sex-linked or autosomal)

14. Pedigree Notation Male Female I Married Kids II III Has it
Doesn’t have it

15. Autosomal Recessive
Most common inheritance pattern for genetic diseases
Disease is rare in the family (only a few affected family members)
Males and females are equally likely to inherit this disease
Disease often skips generations (a child may inherit the disease even though neither of the parents have the disease.)
Examples: Cystic Fibrosis, Sickle Cell Anemia, Phenylketonuria (PKU), Tay-Sachs Disease.

16. Autosomal Recessive Example

17. Autosomal Dominant
Disease is common in the family (many affected family members)
Males and females are equally likely to inherit this disease.
Disease will never skip a generation – a child cannot inherit the disease if both parents are healthy!
Examples: Achondroplasia (dwarfism), Huntington’s Disease, Neurofibromatosis

18. Autosomal Dominant Example

19. Sex-Linked Recessive
Disease is rare in the family (only a few affected family members)
Disease often skips generations
Males are more often affected than females
Affected fathers DO NOT pass on to their sons! (Why??)
Examples: Hemophilia, Duchene Muscular Dystrophy, Colorblindness

20. Sex-Linked Recessive Example

21. How to determine the pattern of inheritance in a pedigree:
If there are way more males than females affected (shaded in,) than the pedigree is tracing a Sex-Linked trait.
If not, look for two parents that are the same shade that have a child who is different from them. Label that child homozygous recessive (Ex. rr) and the parents heterozygous (Ex. Rr)
If the child was shaded, the pedigree is tracing an Autosomal Recessive trait.
If the parents were shaded, the pedigree is tracing an Autosomal Dominant trait.

22. Determine the inheritance pattern and label the genotypes.
Example #1
Determine the inheritance pattern and label the genotypes.
Autosomal Recessive R? rr Rr Rr Rr Rr Rr rr rr R? R? rr Rr

23. Determine the inheritance pattern and label the genotypes.
Example #2
Determine the inheritance pattern and label the genotypes.
Sex-Linked Recessive
XrY
XRXr
XRXr
XrY
XRXr
XRXr
XRY
Could a male ever be a carrier? Why or why not?
Could the oldest son have inherited colorblindness from his father? Why or why not?
XrXr
XRY
XRXr
XrY
XRY