1. Human Genetics 3

2. Chromosome Review
Remember that a chromosome is a piece of tightly coiled DNA.
Chromosomes occur in pairs.
Example: The chromosome 1 that you inherited from mom has the same types of genes as chromosome 1 you inherited from dad. Both chromosome 1s pair together.
Genes are in the DNA on a chromosome.
When genes occur together on a chromosome they are linked.

3. Chromosome Mutations Mutation: any change in one’s DNA
An alteration of a chromosome may change the DNA sequence contained within.
Lethal Mutation: a deadly mutation
Germ Cell Mutation: mutation in a gamete that does not affect parent but will affect offspring
Ex: an egg with too many chromosomes
Somatic Cell Mutation: mutation in an parent’s body cells that is not passed onto an offspring
Ex: Cancer

4. Detecting Chromosome Mutations
Karyotype
A photograph of an organism’s chromosomes
Used to diagnose disorders related to physically noticeable chromosomal mutations

5. Types of Chromosome Mutation
Deletion (
A section of a chromosome breaks and is lost
Consequence: genetic information is lost
Loss of information in a germ cell will likely affect the offspring; loss could be lethal

6. Survey of Genetic Disorders
Cri du Chat Syndrome
Caused by a deletion of a section of chromosome #5
Phenotype:
Cat-like (mewing) cry
Broad face
Small head
Severe retardation & behavioral disorders

7. Types of Chromosome Mutation
Inversion
Piece of a chromosome breaks off and reattaches in reverse order
Consequence: reordering of genes
Often harmless, but certain genes when reordered will not produce surviving offspring

8. Types of Chromosome Mutation
Translocation (
Piece of a chromosome breaks off and reattaches elsewhere
Consequence: reordering of genes
Most often a lethal chromosome mutation

9. Types of Chromosome Mutation
Nondisjunction
During meiosis, chromosomes fail to separate properly into gametes
Consequence: too many or too few chromosomes in a gamete

10. Monosomy vs. Trisomy Monosomy Trisomy
Trisomy

11. Monosomy vs. Trisomy Monosomy & Trisomy result from nondisjunction
Monosomy: baby after fertilization has only 1 chromosome instead of the normal pair
Trisomy: baby after fertilization has 3 of the same chromosome

12. Survey of Genetic Disorders
Turner’s Syndrome
Cause: missing X chromosome in egg (monosomy)
Phenotype:
Occurs in females
Will not mature sexually (sterile)
Short body with webbed neck
May have kidney and heart defects

13. Survey of Genetic Disorders
Down Syndrome
A.k.a. Trisomy 21
Caused by inheriting 3 of chromosome 21
1/660 births
Phenotype:
Small head, flattened nose, protruding tongue, eyes slant up
Mental disability
Stunted growth

14. Survey of Genetic Disorders
Klinefelter’s Syndrome
Present in males with XXY genotype
1/850 men affected
Phenotype:
Often not noticed
Show fewer secondary sex characteristics
Infertility
Mental disability

15. Survey of Genetic Disorders
XYY or “Supermale”
~1/1000 men
Phenotype:
Wiry build, elbows turned out, increased acne, not usually athletic
Higher than average testosterone
Evil stereotypes claim XYY’s more likely to be violent or have behavioral problems

16. Survey of Genetic Disorders
XXX or “Superfemale”
~1/1000 women
Phenotype
Pretty normal
May have lower IQ
XXXX
Mild mental disability
XXXXX
Severely disabled
May or may not survive…

17. Detecting Genetic Disorders
There are several methods used to diagnose genetic disorders before a baby is born.
Sometimes prevention is possible through:
Genetic Counseling
Proper pre-natal care
Good parental health before and during conception
After birth, there is no cure for a genetic disease, only medical and psychological therapies to help children and their families cope with a disorder.