Human GeneticsChapter 12

Difficulties in Studying Human Heredity

• Controlled experiments are not possible

• Small numbers of offspring per generation

• Long periods between generations

Sex Determination

• Autosomes – body chromosomes – first 22 pair

– Same in both male and female

• Sex Chromosomes – 1 pair, last pair

– XX – Female

– XY - Male

Sex Linked Traits• Traits controlled by recessive genes located on sex

chromosomes (normally associated with the X chromosome)

• SRY Gene on the Y chromosome ( codes for a protein that causes the gonads of an embryo to develop as testes)

• The x chromosome is much larger than the y chromosome so there are more x-linked than y-linked traits.

Hereditary Disorders

• Karyotyping – an enlarged photo of the chromosome pairs (map) to identify any abnormalities in the chromosomes

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.

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 inheritanceautosomal, recessiveautosomal, dominantX-linked, recessiveX-linked, dominant (very rare)

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