chapter 10

• Gene - segment of DNA that contains instructions for synthesizing a protein
• locus - location on a chromosome
• When two haploid sex cells fuse during fertilization, a diploid zygote with two full sets of chromosomes is formed
• Humans have 22 homologous pairs of autosomes and 1 pair of sex chromosomes
• alleles - different versions of genes
• Gregor Mendel - used pea plants to study heredity and genetics
• True-breeding - plants that produce offspring identical to themselves
• Hybrid - outwardly resemble true-breeders but produce mixed offspring
• Dominant - exert effects whenever present
• Recessive - masked if dominant allele is present
• phenotype - physical appearance of a gene
• Homozygous dominant - individuals have two dominant alleles for a gene
• Heterozygous - individuals have one dominant and one recessive allele
• Homozygous recessive - individuals have two recessive alleles
• Punnett square - uses the genotypes of the parents to reveal which alleles the offspring may inherit
• monohybrid cross - a cross between two individuals for a single trait
• Cystic Fibrosis is an autosomal recessive disorder
• Dihybrid cross - track the inheritence of two genes
• law of independent assortment - alleles are randomly segregated during meiosis
• Genes close together on the same chromosome are linked. The linked genes are not inherited independently of each other.
• Incomplete dominance - the heterozygote has an intermediate phenotype
• Codominance - both phenotypes are present
• pleiotrophy - one gene has multiple effects on the phenotype
• epistasis - when one gene’s product affects the expression of another gene
• X-linked recessive disorders affect more males than females
• X-inactivation prevents double dosing of gene products
• pedigree - depicts family relationships and phenotypes
• Epigenetics - a field of research that explores how cells adjust gene expression without altering underlying DNA sequence
• Skin color is a polygenic trait; it is affected by more than one gene
• X-linked Recessive Disorders

  • Duchenne muscular distrophy: rapid muscle degeneration early in life, affects more boys
  • Fragile X syndrome: most common form of inherited intellectual disability
  • Hemophilia A: uncontrolled bleeding, easy bruising
  • Red-green color blindness: reduced ability to distinguish between red and green, affects more boys
  • Rett Syndrome: severe developmental problems, mostly female; male babies rarely survive
• Autosomal Dominant Inheritance

  • Achondroplasia: dwarfism
  • Familial hypercholesterolemia: high cholesterol, heart disease
  • Huntington disease: progessive uncontrollable movements and personality changes, beginning in middle age
  • Marfan Syndrome: long limbs, sunken chest, spindly fingers
• Autosomal Recessive Inheritance

  • Albinism: Lack of pigmentation in skin, hair, and eyes
  • Cystic Fibrosis: Lung congestion, poor weight gain, salty sweat
  • Phenylketonuria (PKU): intellectual disablilty caused by buildup of metabolic byproducts
  • Tay-Sachs disease: nervous system degeneration caused by buildup of byproducts