Name__________________________________________ Date ________________ Class ___________________
Genetics Notes
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I.
II.
III.
IV.
V.
________________________________ is the father of modern genetics. He performed experiments on
_____________________________ and determined how traits are passed from one generation to the next.
How are offspring influenced by genetic combinations?
a. Parents pass on units of information called __________________________.
b. These genes produce _________________________, which are characteristics that make up an
organism. Examples: _____________________________________________________
c. For each trait, an individual has two _________________ (different forms of a gene). Alleles are
represented as ___________________________ (ex: TT can stand for the trait of tallness).
Mendel’s principle of dominance
a. Mendel’s ________________________________________ states that some alleles are
____________________________ and others are _____________________________________.
b. Dominant alleles are written with _____________________ letters (ex: TT, Tt)
c. Recessive alleles are always written in ___________________________ letters (ex: tt)
d. The recessive allele is exhibited only when the dominant allele is ___________________________.
e. *How do I know if it’s dominant? _________________________________________________________
f. *Why is Tt dominant if it has a small letter? _________________________________________________
g. *How do I know if it’s recessive? __________________________________________________________
Homozygous vs. Heterozygous
a. When both alleles (letters) are the same, the individual is ________________________ for that trait.
This is also called ___________________________________.
b. When the alleles are different, the individual is ____________________________ for the trait. This is
also called _________________________.
c. *What if the letters are both big, like SS or TT? _______________________________________________
d. *What if the letters are both little, like ss or tt?_______________________________________________
e. *What if one letter is big and one letter is little, like Ss or Tt?____________________________________
Genotype vs. Phenotype
a. The ___________________ makeup of an organism is called its ____________________. Write this as
______________________________, like TT.
b. The organism's physical traits are its _____________________________________. Write this as a
_____________________ like tall, red..
c. *Is Aa a genotype or phenotype?__________________________________________________________
d. *Are purple, tall, short, white, and round genotypes or phenotypes?_____________________________
e. *What is an organism’s genotype if it receives two recessive alleles for height (T=tall, t=short)?________
____________________________________________________________________________________
Monohybrid Crosses
a. When doing a genetic cross, the parent organisms are the P, or _________________________________.
b. The offspring are called the F1, or ___________________________________________.
c. A ____________________________ is a cross in which there are two contrasting alleles for a single trait.
d. A ________________________________________ is a diagram that helps predict combinations in
genetic crosses.
e. Do the practice on the back of this sheet.
VI.
Dihybrid Crosses
a. A dihybrid cross is a cross that shows the possible offspring for ___________________ traits.
b. Example 1: A heterozygous black/heterozygous rough individual with another heterozygous
black/heterozygous rough individual. Their genotypes will be: ___________________.
How many of the offspring would have a black, rough coat? ________________________________
How many of the offspring would have a black, smooth coat?_______________________________
How many of the offspring would have a white, rough coat?________________________________
How many of the offspring would have a white, smooth coat?______________________________
c. Example 2: In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are
dominant over wrinkled peas (r). Cross a plant that is heterozygous for both traits with a plant that is
homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and
determine the genotypic and phenotypic ratios. Do this on the back-Label as Example 2.
VII.
Incomplete Dominance
a. Neither allele is dominant, so the traits ___________________________.
b. Example 3: red snapdragon + white snapdragon = _________________ snapdragons for offspring.
i. You can use two different letters now! RR (red) X WW (white) Do the punnett square.
c. Example 4: Cross of two purple flowers (what 2 colors make purple?) _________ x ___________
i. What are the genotype ratios? _______________________________________
ii. What are the phenotype ratios? ______________________________________
iii. Can you have a heterozygous red or hybrid blue flower? _________
VIII.
Codominance
a. Expression of both alleles __________________________.
b. _______________________________ of both traits are seen in heterozygous individuals.
c. Example black rooster and white chicken produce offspring with _________________________ feathers
d. Example 5: Expressed as two separate traits in a Punnett Square Cross - BB (black) X WW (white). Do the
punnett square.