Lo11

• P generation


  Parental generation
• F1 generation


  1. Identical and resembled one of the parents

  2. Mated to produce F2 generation
• Heredity


  The transmission of genetic information from parent to offspring
• Gregor Mendel


  • Applied quantitative methods to breeding pea plants
  • Studied phenotypic traits by true breeding populations
• True breeding


  When all individuals are phenotypically the same
• Phenotype


  Physical characteristics
• Genotype


  Genetic makeup of an organism
• Mendel mated plants from different the breeding populations
• Alleles


  Versions of the same gene that differ in DNA sequence
• Locus


  Physical location of alleles on their respective homologs
• Dominant allele


  Expressed, recessive allele is hidden (heterozygous)
• Principle of segregation


  Alleles separate as homologs separate during anaphase I of meiosis
• Short phenotype from P generation had not been lost or irreversibly blended, just hidden (no blending inheritance)
• Independent assortment


  Alleles on non-homologs are distributed randomly into gametes during anaphase I, independently
• Due to random orientation of homologs along the equator during metaphase I, the orientation of one homologous chromosome pair does not influence the orientation of any other pairs
• Product rule


  Predicts the combined probabilities of independent events
• Independent events


  Outcome of one event does not impact the outcome of another event
• Sum rule


  Predicts the probability of mutually exclusive events
• Mutually exclusive events


  Events that cannot both occur
• The probability is equal to the sum of the individual probabilities
• Thomas hunt Morgan showed independent assortment does not apply to genes close together on the same chromosome
• Linkage


  The tendency for alleles close together to be inherited together
• Sex determining genes


  • In mammals, birds and many insects, they are on sex chromosomes
  • In mammals, phenotypic females are XX and males are XY
• X chromosome


  Critical for survival and contains many genes unrelated to sex determination
• 1. linked genes


  Genes on the X chromosome
• Females receive one X from each parent, but males receive their X only from their mother
• Males are homozygous for x-linked genes because they have one allele per gene, so every X allele is expressed in males
• Dosage compensation


  Equalizes expression of X linked genes
• In female mammal somatic cells, only one X chromosome is active in gene expression, the other X chromosome is inactive (Barr body)
• If a female is heterozygous for any x-linked trait, one allele is expressed in half of her body, while the other allele for that trait is expressed in the other half
• Incomplete dominance


  The heterozygote has a phenotype that is intermediate between the two homozygous phenotypes because no allele is completely dominant
• ABO blood group


  Determined by three alleles in the human population
• Alleles from different loci

  Can interact
• Epistasis


  Occurs when an allele from one locus masks the expression of alleles at a different locus
• Epistatic gene


  Determines whether or not the pigment gene is expressed
• Polygenic inheritance


  Multiple, independent genes have similar and additive effects on a single trait
• For some traits, genes set the limit for the phenotype but the environment may shape the phenotype within those limits
• Human height is polygenic
• Hydrangeas of the same genotype can have different colored flowers depending on soil pH