Inheritance Patterns
Human Genetics
Chromosomes
• Two Types
– Autosomes: body cells
– Sex chromosome: gametes (genders)
• SRY (males)
• Gene Location
– Sex-linked traits
• Allele is on sex chromosome
• Affected individuals are usually male
Sex-linked Genes & Traits
• Most alleles on the X chromosome have no
Y chromosome homologue
• X chromosome is much larger than Y
chromosome, and so, has more genes
• Linked genes are close to each other on same
chromosome
• Crossing-over rearranges allele combinations
– Increases in frequency the further apart genes are
Gene Map of Fruit Fly
Mutations
• Two Major Types
– Germ-cell mutations
• Affects offspring only
– Somatic-cell mutations
• Affects individual only
• Chromosomal Mutations
• Genetic Mutations
– Changes in a single nucleotide
Chromosomal Mutations
• Deletion
• Insertion
• Inversion
– Segment breaks off, flips around, & reattaches
• Translocation
– Segment breaks off, reattaches to nonhomologue
• Nondisjunction
– Homologues fail to separate in meiosis
Gene Mutations
• Point
– Single nucleotide
• Substitution
– One nucleotide replaces another
– May change codon/ amino acid (or not)
• Insertion / Deletion
– One or more nucleotides gained or lost
• Frameshift
– Incorrect grouping of all subsequent codons
Human Heredity
• Trace traits through generations
– Autosomal vs. sex-linked (gender-specific)
– Most sex-linked traits are recessive
• Pedigree is visual representation of traits
– Circle = female; Square = male
– Open = unaffected; Shaded = affected
– Half-shaded = carrier (heterozygote)
• Patterns of inheritance observed
– Autosomal recessive traits are “carried”
Genetic Traits & Disorders I
• Genetic basis for disease/ condition
• Most characteristics are polygenic
– Show many degrees of variation
– Eye color, skin color, hair color, height, weight
• Many conditions are complex characters
– Affected by both genes & environment
– Height, weight, health issues/ diseases/ cancer
• Multiple alleles for many genes
– Blood types & codominance (IA, IB, i  A, B, AB, O)
Genetic Traits & Disorders II
• Incomplete dominance
– Intermediate expression between parents
• X-linked Traits
– Determined by X-linked genes (colorblindness)
• Sex-influenced Traits
– Influenced by gender & other complex characters
• Single-allele Traits
– Governed by single dominant allele
– Huntington’s Disease is one of ~ 200 human traits
Detecting Genetic Diseases
• Amniocentesis
– Test amniotic fluid from amnion sac (14-16 wks)
• Chorionic Villi Sampling
– Test cells between uterus & placenta (8-10 wks)
• Fetal Karyotypes
– From tests above
• Blood Tests for marker proteins
• Direct DNA testing
Genetic Counseling/ Treatment
• Counseling
– Inform individual(s) about their genetic makeup
– Predict possible genetic problems of offspring
• Treatment
– Treat symptoms
– Prevent symptoms from developing
• Gene Therapy
– Somatic cell vs. Germ cell