1. Human Genetics Chapter 12

2. Difficulties in Studying Human Heredity
Controlled experiments are not possible
Small numbers of offspring per generation
Long periods between generations

3. Sex Determination Autosomes – body chromosomes – first 22 pair
Same in both male and female
Sex Chromosomes – 1 pair, last pair
XX – Female
XY - Male

4. Sex Linked Traits
Traits controlled by recessive genes located on sex chromosomes (normally associated with the X chromosome)
SRY Gene on the Y chromosome “sex determining region Y” ( codes for a protein that causes the gonads of an embryo to develop as testes). This protein is involved in male sexual development.
The x chromosome is much larger than the y chromosome so there are more x-linked than y-linked traits.

5. Hereditary Disorders
Karyotyping – an enlarged photo of the chromosome pairs (map) to identify any abnormalities in the chromosomes

6. Mutations
Chromosome mutations involve changes in the structure of a chromosome or the loss or gain of a chromosome.
There are three types of chromosome mutations:
1. deletion: the loss of a piece of a chromosome due to breakage.
2. inversion: a chromosomal segment breaks off, flips around backward and then re-attaches.
3. translocation: a piece of one chromosome breaks off and re attaches to a non-homologous chromosome.

8. Pedigree Charts
Chart which shows how a trait and the genes that control it are inherited within a family
Identifies the presence or absence of particular trait in members of each generation
Basic patterns of inheritance
autosomal, recessive
autosomal, dominant
X-linked, recessive
X-linked, dominant (very rare)

9. Pedigree Charts Males = Females = Generations = Roman Numerals
Individuals = Numbered sequentially
Trait Expressed = Filled in
Non Carriers = Empty
Carrier (not ill) = Half filled
Individual who carries a recessive allele that is not expressed