NAME_________________________________ CLASS:______

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
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 ______________
If both are the ________________ version, you show the ______________
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
(Tt, bb, RR, Bb)
The Cell and Inheritance
According to _____________________________________, genes are carried
from their parents to their offspring on _____________________.
Remember, humans have 46 chromosomes.
Those chromosomes are in pairs. 23 come from the father’s ____________,
and 23 come from the mother’s ______________.
When the sperm and egg come together, the resulting ______________ has all
46 chromosomes.
How do sperm and eggs end up with only half the number of chromosomes?
Instead of dividing by _________________, the parent cells of sperm and eggs
divide by a process called _______________.
During meiosis the chromosomes pairs separate and are distributed to two
different cells. The resulting cells have only ____________ as many
chromosomes as the other cells in the organism.
When the chromosomes pairs separate and go into two different sex cells, so
do the alleles carried on each chromosome. One allele from each pair goes to
each sex cell.
Probability and Heredity
_________________is a number that describes how likely it is that an event
will occur.
Probability can be expressed as a ____________, or as a _______________.
If you flip a coin, there is a one in two chance it will land on heads…. ½, or 50%
If you roll a dice, there is a one in six chance you will roll a 5… 1/6, or about
Independence of Events
When you toss a coin more than once, the results of one toss do not affect the
results of the next toss.
Flipping a heads the first time, does not make you more likely to flip a tails the
next time.
Punnett Squares
A _______________
_____________ is a chart that shows all possible
combinations of alleles that can result from a genetic cross.
Incomplete Dominance
In __________________
_______________, neither allele is dominant or
recessive to the other allele. As a result, the alleles ____________ and show a
third possible phenotype in the offspring.
In ________________, neither alleles is dominant to the other, so
heterozygous organisms show __________ of the possible phenotypes at the
same time.
Sex Linked Traits
The genes of some traits are carried on the sex chromosomes. These traits are
called ________________
Because males only have one X chromosome, often even recessive alleles
carried on the X chromosome will appear in the male phenotype.
Many more males are colorblind than females.
A pedigree is a chart that shows a family tree.
Geneticists use pedigrees to track which members of a family have a particular
trait and which people are “_______________”.