CHAPTER 4
NOTE PACKET
Genetics: the science of heredity
NAME _______________________________________ Period ________
Chapter 4 SECTION 1: MENdEl’S WOrk
Gregor Mendel

_________________________________________________________________________________________________________________

__________________________________ named Gregor Mendel

Worked in a garden at a ____________________________________________

Heredity: ____________________________________________________________________________________________________
Why do pea plants have different characteristics?

Traits: __________________________________________________________________________
o Examples: ____________________ (tall or short), ________________________ (green or yellow)

Pea plant TRAITS were often ________________________________ to those of their parents and sometimes
they were _______________________________________.

His studies laid the foundation for __________________________________– the scientific study of heredity
Mendel’s Experiments

The flower’s petals surround the _______________________ and the ______________________________.

Pistil: _________________________________________________________________________________________________________

_____________________________________: produce pollen, which contains male sex cells, or sperm

Fertilization: _________________________________________________________________________________________________
Self-Pollinating


Pea plants are usually ____________________________________________________
Pollen from a flower lands on a pistil of the same flower
Cross-Pollinating


“___________________________”
Mendel removed _____________________________ from a flower on one plant, then
______________________________________ onto a flower on a second plant.
Crossing Pea Plants
How are you going to study the inheritance of traits in pea plants?

Mendel decided to “cross” plants with ____________________________________________________________________
o Example: ______________________________________________________________________

He started with purebred plants

Purebred: ____________________________________________________________________________________________________
The F1 and F2 Offspring
1. Mendel crossed ____________________________________ tall plants with purebred _________________ plants
a. This is called parental generation, or the ___________________________________________
2. _____________________________________________ are all tall
a. The offspring from this cross are the first filial generation, or the
__________________________________________
3. He then allowed for the F1 offspring to _________________________________________________
4. F2 offspring are tall and short
a. The offspring from this cross are the second filial generation, or the
________________________________________________
 What other traits did Mendel study? ______________________________________________________________________
________________________________________________________________________________________________________________

What were the two forms of the seed shape? _____________________________________________________________
_________________________________________________________________________________________________________________
Genes and Alleles

____________________________: factors that control a trait

Alleles: _______________________________________________________________________________

An organism’s traits are controlled by alleles it inherits from its parents. Some alleles are dominant,
while others are recessive
Dominant Alleles vs. Recessive Alleles

__________________________________________: an allele whose trait always shows up in the organism when
the allele is present

Recessive Allele: _____________________________________________________________________________________________
Let’s do some math….Examples for Stem Height

One recessive allele + one dominant allele = ______________________________________________________________

One recessive allele + one recessive allele = _______________________________________________________________
Alleles in Mendel’s Crosses
Combination of Alleles:

Hybrid tall: ___________________________________________________________________________________________________

__________________________________: two alleles for tall stems

__________________________________: two alleles for short stems
Symbols for Alleles

Geneticists use letters to represent alleles

Dominant allele is represented by a ________________________________________
o Example: tall stems = _____________

Recessive allele is represented by a _______________________________________
o Example: short stems = _________________
PRACTICE PROBLEMS:
2 dominant alleles for tall stems =
2 recessive alleles for short stems =
1 recessive allele for short stems and 1 dominant allele for tall stems =
Significance of Mendel’s Contribution

The importance of Mendel’s discovery was _________________ recognized during his lifetime

Mendel is often called the ______________________________________________________
Chapter 4 Section 2: Probability and Heredity
Principles of Probability

Probability: _________________________________________________________________________________________________

Coin toss: ____________________________________________________________________________________________________
o 1 in 2 chance, ½, 50%

The Laws of Probability predict what is ______________________________ to occur
Independence of Events

When you toss a coin more than once, _____________________________________________________________________
_________________________________________________________________________________________________________________
Principles of Probability with Genetics

_________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________

He could say that the probability of producing…
o A tall plant was _______________________
o A short plant was _______________________
Punnett Squares

Punnett square: _________________________________________________________________________________________
_____________________________________________________________________________________________________________

They show all the possible outcomes of a genetic cross and determine the
______________________________ of that outcome
Example

Hybrid: _____________________________________________________________________________________
o R: _____________________________________________________
o r: _____________________________________________________
Using a Punnett Square

Use a Punnett square to calculate the _______________________________________________

In a genetic cross, ____________________________________________________________________________________________
Punnett Square and Probability Problems
What is the probability that the offspring will be RR?
What is the probability that the offspring will be rr?
What is the probability that the offspring will be Rr?
What is the probability that the offspring will be a round seed?
What is the probability that the offspring will be a wrinkled seed?
Predicting Probabilities

Dominant: ______________________________

Recessive: ______________________________
What are the possible allele combinations?
What is the probability the guinea pig has black fur?
Phenotypes and Genotypes

Phenotype: ___________________________________________________________________________________________________

Genotype: ____________________________________________________________________________________________________
Homozygous and Heterozygous
Purebred = _____________________________________________ = ______________________________________________

SS or ss
Hybrid = ________________________________________________ = ______________________________________________

Ss
Codominance
Codominance: _______________________________________________________________________________________________________
Chapter 4 Section 3: The Cell and Inheritance
What structures in cells contained genes?

“The Clue in the Grasshopper’s Cells”

Walter Sutton, an American _____________________________________ who studied the cells of grasshoppers

Wanted to know how _______________________________ form (sperm and egg)

___________________________________________ are they key to understanding how offspring have traits similar
to those of their parents
Chromosomes in a Grasshopper…

_______________________________________ of grasshoppers have __________ chromosomes

Sutton found that the grasshopper’s _______________________________________________________________________

Grasshopper’s sex cells ______________________________________________________________________________________
_________________________________________________________________________________________________________________
Chromosome Pairs

When a sperm cell and an egg cell __________________________________________________________________________

_________________________________________________________________________________________________________________

The grasshopper offspring had ________________________ number of chromosomes in its cells as did
each of its _______________________________________
Genes on Chromosomes

Alleles: ________________________________________________________________________________________________________

Ex: __________________________________________

One allele in a pair comes from ______________________, one allele comes from ____________________________
Chromosome Theory of Inheritance

_________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________
How do sex cells end up with half the number of chromosomes as
body cells?
 __________________________
o The process by which the number of chromosomes is reduced by ______________ to form sex
cells– sperm and eggs
What happens during meiosis?
Refer to pg. 128-129
Before Meiosis

_________________________________________________________________________________________________________________
Meiosis I

A: _____________________________________________________________________________________________________________

B: The pairs ______________________________ and __________________________________to opposite ends of the cell

C: __________________________________ form, each with _______________________the number of chromosomes
Meiosis II

A: _____________________________________________________________________________________________________________

B: The ___________________________________________________ and move to opposite ends of the cell
End of Meiosis

__________________ sex cells form with half the number of chromosomes as the parental cells
Meiosis and Punnett Squares

_______________________________________ is actually a way to
show the events that occur in _________________

____________________ allele from each pair goes to each
_____________________________ (sperm and egg)
A Lineup of Genes

The body cells in humans contain ___________________________________________________
(or _________chromosomes)

Chromosomes ________________________________________________________________________________________________
_________________________________________________________________________________________________________________

Although you have only 23 pairs of chromosomes, _______________________________________________________
_________________________________________________________________________________________________________________

Each gene controls a trait.
Genes on Chromosomes
(Refer to pg. 130)

Genes are located _______________ chromosomes

For which genes is this organism homozygous?

For which genes is it heterozygous?
Chapter 4 Section 4: The DNA Connection
The Genetic Code

The main function of a gene is _________________________________________________________________________________
____________________________________________________________________________________________________________________

Proteins help determine the _________________________________________________________________ of an organism.
Genes and DNA

Chromosomes are composed mostly of __________________________

Review: DNA is made up of _____________________different nitrogen bases…
o ____________________________________________________________________________________________________________

A gene ____________________________________________________________________________________________________________
____________________________________________________________________________________________________________________

A gene is made up of a series of ____________________ in a row

The bases on a _________________________ are arranged in a __________________________________________________
Order of the Bases

The order of the nitrogen bases along a gene _____________________________________________________________
_________________________________________________________________________________________________________________

Proteins: long-chain molecules made of ___________________________________________________________________

A group of ___________________ DNA bases codes for one specific _____________________________________
How Cells Make Proteins

Protein synthesis: ____________________________________________________________________________________

During protein synthesis, the cell uses information from a ___________________________on a
chromosome to produce a specific ______________________________.

Where? ______________________________________________________________________________________________________
The Role of RNA

_________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________

The genetic “messenger” is called _________________________________________________________, or RNA

RNA and DNA differ in some important ways…
o RNA only has ____________________ strand
o ________________________________________________________ molecule
o RNA contains _________________________ instead of thymine
Types of RNA

Messenger RNA (mRNA): copies the coded message from the _______________ in the nucleus, and
_______________________ the message from the ribosome in the cytoplasm.

Transfer RNA (tRNA): carries ______________________ ______________________ to the ribosomes and adds
them to the ____________________________ _____________________________
Mutations

Mutations: ____________________________________________________________________________________________________

Can cause a cell to produce an incorrect __________________________________ during protein synthesis

The _________________________________, or phenotype may be different from what it normally would have
been
o Body cell – the mutation will _______________ passed to offspring
o Sex cell –the mutation _________________ ______________ passed to an offspring and affect the
offspring phenotype
Type of Mutations

Substitution: ____________________________________________________________________________

Deletion: ________________________________________________________________________________

Addition: ________________________________________________________________________________
Effects of Mutations

Can be a source of _________________________________________________________________

Some mutations are ____________________________________, other mutations are
____________________________________

A mutation is harmful if it ___________________________________________________________________________________
_________________________________________________________________________________________________________________

White lemurs living in the wild? ___________________________________

Antibiotic resistance in bacteria? ___________________________________

A mutation that is harmful or helpful depends partly on its ___________________________________________.