1. Human Genetics-Mutations
Genetics-Unit 3-Part B

2. Mutations Mutation – any change in the genetic make-up of an organism
Mutations may lead to organisms making different proteins, expressing or not expressing a trait or traits, or even death
Mutations have been called the driving force of evolution because they change organisms and may lead to the formation of new species
Although slightly more than 99% of mutations are deleterious (death causing), some actually increase the survivability of the organism
If the mutation occurs in a somatic body cell, it is not passed on, if it occurs in a gamete, then that change will be passed on

3. continuing Two types of mutations:
1.) spontaneous – caused by errors during replication
2.) induced – caused by outside agents (mutagens)
Mutagens cause mutations. Examples of mutagens include:
x-rays
ultraviolet light
chemicals (Carbon Tetrachloride) (DDT)
other genes
viruses
sunlight (etc.)

4. in-depth analysis
a.) Deletion – mutation involving the loss of a segment of chromosome
ex.
Cri-du-chat (“Cry of the Cat”) syndrome is caused by a deletion of chromosome #5
deletion has occurred

5. continuing
b.) Duplication – mutation that results in the doubling of a segment of chromosome. The duplication may occur more than once, producing many copies of the same segment
Duplications caused multiple copies of hemoglobin gene to evolve, molecule is now made up of multiple chains
normal
duplications

6. still going
c.) Inversion – a mutation that involves a chromosome segment “flipping” so that it is in reverse order
This type of mutation can affect crossing over, as well as gene expression A B D C E A B C D E
inversion of
region C +D

7. more
d.) Translocation – mutation in which there is a change in position of chromosome segments. The change may be within the same chromosome or between different chromosomes A B C D E F A E C D B F

8. Finishing this example
Translocations are a known cause of an assortment of human tumors
ex. Chronic myelogenous leukemia patients show a translocation between chromosomes , known as the Philadelphia chromosome

9. more
e.) Position effect – other mutations such as inversions or translocations put gene sequences in different spots, this change in position may cause a change in expression
f.) Fragile sites – narrowings or gaps found in chromosomes, the most famous is fragile X-Syndrome, a break in the X-chromosome, may cause retardation
g.) Change in number – normal organisms are said to be euploid, organisms that have different #’s of chromosomes are said to be aneuploid
examples of aneuploidy:
1.) nullisomy – one pair of chromosomes is missing (2n-2)
2.) monosomy – loss of a single chromosome (2n-1)
3.) trisomy – getting a single extra chromosome (2n+1)
4.) tetrasomy – getting an extra chromosome pair (2n+2)

10. genetic diseases
Examples of genetic diseases involving chromosome number changes:
A.) Autosomal
1.) trisomy 21 (Down Syndrome)
2.) trisomy 13 (Patau Syndrome)
3.) trisomy 18 (Edwards Syndrome)
B.) Sex chromosomes:
1.) monosomic X – Turner Syndrome
2.) XYY Trisomy – normal male (acne)
3.) XXY Trisomy – Klinefelter Syndrome
XXYY also has Klinefelter-like symptoms

11. Gene mutations
2.) Gene mutation – the process by which a DNA base pair change is produced and not repaired. Most times gene mutations are repaired.
these types of mutations can also be spontaneous or induced
Types of gene mutations:
a.) point mutation (base-pair substitution) – one base pair is replaced by another
b.) transition mutation – specific base pair substitution of one purine/pyrimidine to another
four types: (AT to GC) (GC to AT) (TA to CG) (CG to TA)

12. more mutations
c.) Transverse mutation – another specific base-pair substitution. Includes AT to TA, GC to CG
d.) Missense mutation – a base pair change causes a change in mRNA, so a different amino acid is placed in a protein (ex. sickle cell anemia)
e.) Nonsense mutation – change in a base pair that will produce a stop codon where it shouldn’t be
f.) Frameshift mutation – addition or deletion of one or more base pairs in a gene, causing different amino acids to be produced

13. last slide Examples of genetic diseases caused by gene mutations
I. Inborn errors of metabolism – caused by point mutations which lead to lack of/or overproduction of certain enzymes: most are inherited recessively
examples:
maple syrup urine disease
alkaptonuria
albinism
PKU
II.) Diseases related to defective DNA repair – caused when mutated DNA is not repaired
Xeroderma pigmentosum
Bloom’s Syndrome