GENETICS QUIZ STUDY GUIDE
Historical Contributions to the study of Genetics:
1800’s - Gregor Mendel discovered that traits are passed down from parents to offspring when he studied pea plants.
He also discovered dominant and recessive traits.
1950’s - Rosalind Franklin took an x-ray of DNA and discovered the structure of DNA.
1950’s - Watson and Crick used Rosalind Franklins discoveries to develop the first model of DNA.
DNA Structure:
DNA is shaped like a double helix, spiral staircase or twisted ladder.
DNA is made up of nucleotides. Each nucleotide contains a sugar, phosphate, and a base. The sugars and phosphates
make up the backbone of DNA and the bases make up the “rungs” of the DNA ladder.
A and T bond together and C and G bond together.
Genes are the pieces of DNA that code for our traits.
We inherit 2 genes from our parents, one from our mom and one from our dad. Alleles are alternate forms of our
genes. For example, the gene for eye color has multiple alleles – brown, blue, green, etc.
(BB)
(Brown Fur)
Patterns of Inheritance – Genotypes and Phenotypes:
Dominant Alleles are shown by using large letters or uppercase D.
Recessive alleles are shown by using small letters or lowercase
d.
Genotype: type of genes you inherit, for example: DD, Dd or dd
Phenotype: is what the trait you inherit physically looks like, for example; brown, blue, or green eyes.
Homozygous or Purebred - Genotypes that have two of the same alleles - either dominant (DD) or
recessive (dd).
Heterozygous or Hybrid– Genotypes that include 2 different alleles, (Dd).
Genotype Examples:
*Genotypes can be homozygous (purepred) or heterozygous (hybrid).
Ex: homozygous = BB & bb heterozygous = Bb
*If someone has brown eyes, they may or may not be carrying a gene for blue eyes. Their genotype could be
BB (homozygous dominant) or Bb (heterozygous)
*If someone has blue eyes, their genotype would have to be bb (homozygous recessive).