Gregor Mendel laid the foundations for genetics
used the garden pea
Question 1: How are traits inherited?
Experiment 1: true-breeding plants with purple flowers X true-breeding plants with white flowers (P)
result: all plants had purple flowers (F1)
Experiment 2: let F1 self-fertilize
result: 3/4 purple and 1/4 white (F2)
Traits are controlled by discrete units (called genes).
There can be multiple versions of a gene (purple or white, here) (called alleles).
Each individual has 2 alleles for each gene.
Each parent gives 1 allele through the sex cells.
Some alleles (dominant alleles) can mask other alleles (recessive alleles).
The allele pairs are randomly separated during meiosis.
other genetic terms to know:
Punnett square method can be used to predict the outcome of a cross [see text for examples]
Question 2: How are multiple traits inherited?
Experiment: make a cross and follow 2 traits
followed the traits of flower color and plant height
Cross 1: purple, tall X white, dwarf (P)
result: all purple, tall (F1)
Cross 2: F1 were self-fertilized
result: purple, tall and purple, dwarf and white, tall and white, dwarf
Conclusion: traits are not inherited as sets, there is independent assortment of alleles
one trait is not totally dominant over the other
heterozygous phenotype is a mix [Figure 10.10]
e.g. snapdragon flower color
one gene may have more than 2 alleles
more than 1 allele is expressed at the same time [Figure 10.11]
e.g. blood type
one gene affecting multiple traits
e.g. sickle-cell anemia [Figure 10.12]
e.g. SRY gene for male development
multiple genes affecting the same trait
e.g. fur color [Figure 10.13]
e.g. continuous variation [Figures 10.16 & 10.17]
e.g. Himalayan rabbit and Hydrangea [Figure 10.18 & 10.19]
© Carol L. Wymer, 2003