1. Human Genetics
Genetic Mutations

2. Mutations – changes in DNA
Types of changes
permanent changes to nucleotide base sequence
Extra genetic material
Missing genetic material
Results of changes
increase the amount of variation among offspring.
Harmful – cancer
Helpful – antibiotic resistant bacteria (bad for us good for them)
Neutral – many occur on introns so they are not expressed by proteins

3. Two main categories
Germ Cell Mutations
Occur during meiosis
Take place in sex cells
Affects offspring
Typically doesn’t affect parent
Ex. Aneuploidy – irregular number of chromosomes; too many or not enough.
Somatic Mutations
Take place in body cells
Is not passed to offspring
Typically localized to a single or small group of cells
Ex. Skin cancer from UV radiation exposure

4. Gene Mutation - Changes in the sequence of Nucleotides
Point Mutations (2 types)
Base –pair substitutes:
may have no effect,
change amino acid;
or change to stop codon
sickle-cell disease is caused by a
single point mutation (a missense mutation)

5. Frameshift Mutations
Base-pair insertion
or deletion
Result is a nonfunctional protein
Alters the reading frame of mRNA triplets
Specific diseases caused by point mutations
Cystic fibrosis
Cancer
Neurofibromatosis

6. III. Chromosome Mutations – changes in chromosome structure
Deletion: removal of a chromosomal segment
Duplication: repeats a chromosomal segment
Inversion: segment reversal in a chromosome
Translocation: movement of a chromosomal segment to another non-homologous chromosome

8. Causes of Mutations
Chance
errors in DNA replication
Errors during meiosis
Mutagen - environmental factor that damages DNA
Ex. UV light (sun; skin cancer), cigarette tar, asbestos, virus, radiation

9. V. Karyotypes
Shows chromosomes paired by size, shape, and appearance in metaphase.
Cells are treated, photographed, sorted and arranged by homologous pairs.
Chorionic villi sampling, and amniocentesis can be used to diagnose chromosomal abnormalities.

10. VI. Sex Determination Thomas Hunt Morgan
Experiments with Drosophila (fruit fly)
Sex Chromosomes Determine Gender
Autosomes are non-sex chromosomes
Sex chromosomes differ between males and females.
Normal Human female is XX
Normal Human male is XY.

11. VII. Irregular Chromosome Number (Aneuploidy)
Nondisjunction =
Failure of chromosomes to separate during Prophase I of meiosis
Result is extra, or missing chromosomes

12. B. Nondisjunction Syndromes
Monosomy (1 missing)
A single chromosome is missing (45 instead of 46)
Nearly all monosomies are fatal.
XO females (Turner syndrome)- short, webbed neck, no puberty.
Cri du chat (partial deletion of Chromosome 5) – infant’s cry sounds like kitten meowing, excessive drooling, speech and behavioral problems, small head and jaw.

13. Turner syndrome affects approximately 1 out of every 2,500 female live births worldwide. It embraces a broad spectrum of features, from major heart defects to minor cosmetic issues. Some individuals with Turner syndrome may have only a few features, while others may have many. Almost all people with Turner syndrome have short stature and loss of ovarian function, but the severity of these problems varies considerably amongst individuals.

14. One extra single chromosome is present (47 instead of 46)
Trisomy
One extra single chromosome is present (47 instead of 46)
Many are fatal
Examples
Klinefelter Syndrome = XXY; male, some retardation, low fertility (rare cases (48,XXXY) or (49,XXXXY)
Jacob syndrome (XYY males) - tall, acne, not overly aggressive like people once thought.

15. Triple X syndrome (XXX) – usually no physical abnormalities
Triple X syndrome (XXX) – usually no physical abnormalities. Rare complications include mental retardation, increased width between eyes, ovarian failure.
Fragile X Syndrome – X chromosome broken; males; hyperactive or autistic, delayed speech
Down Syndrome = extra 21st chromosome; mental retardation, fold of skin above eyes, weak muscles, and other neurological, sense and physical abnormalities.

16. OUT: Compare and contrast gene mutations and chromosome mutations using a Venn Diagram: