Mendelian Genetics

  1. Gregor Johann Mendel
    • discovered the fundamental properties of heredity
    • replaced blending theory with the particulate theory
    • experimented with garden peas
  2. blending theory assumptions:
    • the offspring's traits are typically intermediate between the two parents' traits
    • the traits could no longer be separated out to appear again in later generations
    • individuals of a population should reach a uniform appearance after many generations
  3. blending theory inconsistencies:
    • offspring do not necessarily show intermediate characteristics
    • some traits appeared to skip one generation
    • individuals in a population do not reach a uniform appearance
  4. particulate theory of heredity
    refers to an idea that the parents transmit to their offspring discrete inheritable factors that remain as discrete inheritable factors from one generation to the next
  5. alleles
    contrasting forms of a gene
  6. gene
    • a segment of DNA that encodes for the specific amino acid sequence of a protein (enzyme)
    • located at a specific location (gene locus) on a chromosome
  7. true-breeding
    • the peas normally always produced offspring that had the same traits as the parents (diceous)
    • because the plants self-fertilized
  8. generations:
    • P gen : parental gen
    • F1 : first filial gen
    • F2 : second filial gen
  9. the law of dominance
    • each inherited characteristic is determined by two heredity factors which are inherited from the parents; one is recessive, one is dominant
    • different alleles are responsible for variations
    • an organism inherits two alleles; each genetic locus is represented twice (in diploid organisms)
    • if two alleles differ, one is fully expressed in the phenotype (dominant); the other is completely masked in the phenotype (recessive)
  10. the law of parental equivalence
    • sex of the parent was irrelevent
    • either trait (dom or rec) can be inherited from either parent
  11. the two allelethe law of segregation
    • the two alleles for each trait are packaged into separate gametes
    • allele pairs presumably segregate from each other during gamete production
    • 50% change a gamete will receive the dominant allele, 50% chance that it will recieve the recessive allele
    • "lost trait" theory was rejected; strong evidence against blending
  12. specific predictions concluded from the law of segregation:
    • the 3:1 ratio observation in the F2 gen of a monohybrid cross
    • the F1 hybrids produce two types of gametes when the alleles segregate in gamete formation
    • during self-pollination, these two types of gametes will unite randomly; 4 equally likely combinations of sperm and ova, as shown by the punnett square
  13. approximate ratios of a monohybrid cross
    • 3:1 phenotypic ratio
    • 1:2:1 genotypic ratio
  14. the law of independent assortment
    • each pair of alleles segregates into gametes independently
    • results support the modern hypothesis that the alleles of one gene segregate independently of the alleles of another gene locus during gamete formation
  15. law of independent assortment holds only if one or both of the following conditions are met:
    • the genes are on separate chromosomes
    • the genes are widely separated on the same chromosome
  16. dihybrid cross
    • between two parental varieties that differ in two distinct characters
    • 9:3:3:1 phenotypic ratio
    • four possible gamete types
  17. The relationship betwee genotype and phenotype is rarely simple because...
    ... there are many variations in respect to dominance.
  18. chi-square statistical analysis of monohybrid crosses
    • x2 = SUM[(O-E)2/E]
    • x2cal > x2crit --> reject HO
    • d.f. = # of categories - 1
  19. pedigree analysis
    • we can determine the mode of inheritance for a given gene, whether it is autosomal or sex-linked, and whether it is dominant or recessive
    • indicates the parentage, marriages (matings), sex, and birth order of the people in a family tree
Card Set
Mendelian Genetics
Unit 16