Name________________________________ Class _________
Genetics: The Science of Heredity
Science Explorer: Cells and Heredity, Chapter 3
Section 1: Mendel’s Work
A. Introduction
a. Who? Gregor ___________, a monk
b. When? 1850s
c. Where? In the garden of a ___________ (home for monks) in Central Europe
d. What? ___________ plants with different characteristics
e. Traits = ___________ characteristics (examples: for humans, eye color; for
pea plants, height of plant)
f. Mendel observed that sometimes pea plants had similar traits to their
___________ and sometimes they had different traits than the parents.
g. Heredity = the passing of ___________ from parents to offspring
h. ___________ = the scientific study of heredity (testing, experimenting)
B. Mendel’s Peas
a. Why use pea plants?
i. Many traits exist in just ___________ (how many?) forms.
ii. Produce many ___________ (babies) in one generation (large sample).
iii. Pea plants are usually self-___________ (one parent), but Mendel
figured out how to cross pea plants (2 parents).
C. Mendel’s Experiments
a. Purebred = always produces ___________ with the same form of a trait as the
parent
b. First cross was Pure ___________ x Pure ___________ = all Tall F1
generation!
DRAW A PICTURE:
c. Second cross was F1 x F1 = 3/4 Tall plants and 1/4 Short plants in the F2
generation (___________had skipped a generation)
DRAW A PICTURE:
D. Experiments With Other Traits
a. Only one form of the trait ___________ in F1 generation. That “lost” trait
then reappeared in the F2 generation.
E. Dominant and ___________ Alleles
a. Genes = factors that control ___________
b. Alleles = different forms of a ___________ (short or tall)
c. Rules:
i. Each offspring inherits a combination of two ___________ for a trait
(one from each ___________).
ii. Individual alleles control the inheritance of traits. Some alleles are
___________, while other alleles are recessive.
d. ___________ allele = an allele whose trait always shows up in the organism
when the allele is present
e. Recessive allele = an allele that is covered up whenever the ___________
allele is present (this trait only shows up when the organism has two recessive
alleles)
F. Alleles in Mendel’s Crosses
a. Hybrids = have two ___________ alleles for a trait
G. Symbols for Alleles
a. Alleles are represented with ___________.
b. Dominant = _________ letter; recessive = __________ letter
c. Example: Length of plant stems is represented by the letter ____. ( ___ for
tall plant stems and ____ for short plant stems)
H. Significance of Mendel’s Contribution
a. Mendel wasn’t recognized for his important work for many years.
b. The principles of ___________ that he discovered are still used today.
Section 2: Probability and Genetics
Punnett Squares = used to show all of the possible ___________ of a genetic
cross and determine the probability of a particular outcome.
a.
b.
BB x bb
Bb x Bb
% BB =_____; % Bb = _____; % bb =_____
% Homozygous = _____;
% Heterozygous = _____
% Blue = _____; % Brown = _____
% BB =_____; % Bb = _____; % bb =_____
% Homozygous = _____;
% Heterozygous = _____
% Blue = _____; % Brown = _____
c.
Bb x bb
d.
Bb x BB
e.
BB x BB
% BB =_____; % Bb = _____; % bb =_____
% Homozygous = _____;
% Heterozygous = _____
% Blue = _____; % Brown = _____
% BB =_____; % Bb = _____; % bb =_____
% Homozygous = _____;
% Heterozygous = _____
% Blue = _____; % Brown = _____
% BB =_____; % Bb = _____; % bb =_____
% Homozygous = _____;
% Heterozygous = _____
% Blue = _____; % Brown = _____
f.
bb x bb
% BB =_____; % Bb = _____; % bb =_____
% Homozygous = _____;
% Heterozygous = _____
% Blue = _____; % Brown = _____
Definitions
1) ___________ = an organism’s physical appearance or visible traits (what the
eye color looks like; blue eyes or brown eyes)
2) ___________ = an organism’s genetic makeup or allele combinations (what
the genes are for eye color; BB or Bb or bb)
3) ___________ = two identical alleles for that trait (BB or bb)
4) ___________ = two different alleles for that trait (Bb); a.k.a. hybrid
5) ___________ = the alleles are neither dominant or recessive (both alleles are
expressed)