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