Unit 4 - Genetics: The Science of Heredity
Mendel’s Work
Gregor Mendel was a priest in the 19th century who loved to garden.
While tending his garden he wondered why some plants had traits similar to
their parents, and some plants had different traits then those of their parents.
_____________: Each different form of a characteristic that an organism can
pass on to it’s offspring.
Mendel decided to study _____________. His research would eventually earn
him the nick name “the father of ______________”.
_____________: the passing of physical characteristics from parent to offspring.
_____________: the scientific study of heredity.
Mendel started his experiments with ________________ plants.
_____________: an organism that is the offspring of many generations that
have the same trait. (purebred short pea plants come from short parents and
short grandparents, and short great grandparents)
Once Mendel had purebred plants, he crossbred plants with different traits
with one another.
In Mendel’s experiments, he called plants in the first cross the parental
generation or ________________________.
The offspring of the P genertation he called the _________________________.
The offspring of the F1 generation he called the ________________________.
Mendel’s Results
In all of Mendel’s crosses only one form of the trait appeared in the F1
generation, however, in the F2 generation the lost form of the trait always
reappeared in about__________ of the plants.
Dominant and Recessive Alleles
_________________: A section of the DNA that codes for a specific trait. (hair
color gene)
_________________: the different forms of a particular gene. (brown or
blonde)
An organisms traits are controlled by the alleles it inherits from it’s parents.
Some alleles are dominant while other alleles are recessive.
A _________________ allele is one whose trait always shows up in the
organism when the allele is present.(written as a _______________ letter)
A _________________ allele is one whose trait is hidden when the dominant
allele is present. (written as a__________________ letter)
Inheriting Alleles
For every _____________ you have, your DNA is carrying 2 __________. One
came from your _____________and one came from your _____________.
If both are the _________________ version, you show the ______________
trait.
If both are the ________________ version, you show the ______________
trait.
If one is the ___________________ version and one is the _______________
version, you show the ___________________ trait.
Genotypes and Phenotypes
An organism that has two identical alleles for a trait is said to be
_____________________.
RR= homozygous _________________
rr= homozygous _________________
An organism that has two different alleles for a trait is said to be
_____________________.
Rr = heterozygous
An organism’s__________________ is its physical appearance or visible traits.
(tall, blonde, round seeds, brown eyes)
An organism’s __________________ is its genetic makeup or allele
combinations.
(Tt, bb, RR, Bb)