Human Genetics Chapter 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 “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.

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 inheritance autosomal, recessive autosomal, dominant X-linked, recessive X-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