Reading Check 12.1
Complete this outline while you read section 12.1 of your textbook. You do not
need to answer in complete sentences.
Chapter 12, Section 1: Origins of Hereditary Science
Mendel’s breeding experiments
_____________________________ is the science of heredity and the mechanism by which traits are passed
from parents to offspring.
Modern genetics is based on Mendel’s explanations for the patterns of
_____________________________ in garden _____________________________.
To cross two plants, as Mendel did, means to ____________________________________________.
When Mendel crossed a pea plant with purples flowers with a type that had white flowers, all
the offspring had _____________________________ flowers. But when two of these offspring were
crossed, some of their offspring had _____________________________ flowers and some had purple
flowers.
Features of pea plants
List three reasons why pea plants are good subjects for heredity studies:
_____________________________________________________________________________________________
Physics features that are inherited are called _____________________________. A
_____________________________ is one of several possible forms of a character. For example,
purple is one of two possible _____________________________ for the flower color
_____________________________ in pea plants.
Since pea plant flowers contain both male and female reproductive parts, they can
_____________________________, or fertilize themselves. Pea plants can also reproduce by
_____________________________, when pollen from one flowers is carried to another flower.
Mendel’s first experiments
Mendel’s first experiments had three steps. First, he produced a true-breeding _____ or
_____________________________ generation. Second, he crossed two P generation plants with
different traits and called the offspring the _____ or _____________________________ generation.
Third, he allowed the F1 generation to self-pollinate and produce new plants. This created
the _____ or _____________________________ generation.
Mendel’s results
For each character that Mendel studied, he found a _____________________________ ratio of contrasting
traits in the F2 generation.
Reading Check 12.2
Complete this outline while you read section 12.2 of your textbook. You do
not need to answer in complete sentences.
Chapter 12, Section 2: Mendel’s theory
Explaining Mendel’s results
Mendel’s hypotheses about inheritance were basically correct but
have been _____________________________ with newer terms and more complete knowledge.
Before Mendel’s experiments, many people though that traits of offspring were always a
_____________________________ of the traits from parents. Mendelian theory explains patterns
of inheritance, where different traits result from different versions of genes. Today, each
version of a gene is called an _____________________________. Each individual has two alleles
for a given _____________________________. A single _____________________________ carries only
one of the two alleles.
Mendel noticed that some traits always seemed to “win” over the others. The expressed
allele is called _____________________________, while the allele that is not expressed when the
dominant allele is present is called _____________________________.
The law of _____________________________ holds that when an organisms produces
_____________________________, each pair of alleles is separated and each gamete has an equal chance of
receiving either allele.
Mendel’s findings in modern terms
The set of alleles an individual has for a character is called the _____________________________,
while the trait that results from a set of alleles is the _____________________________.
Mendel’s second experiments
A _____________________________ cross examines two characters at the same time.
If an individual has two of the same alleles of a certain gene, the individual is
_____________________________ for the character. On the other hand, if an individual has two
different alleles for a certain gene, the individual is _____________________________.
The law of _____________________________ _____________________________ holds that when gametes are
formed, the alleles of each gene separate independently.
Reading Check 12.3
Complete this outline while you read section 12.3 of your textbook. You do not
need to answer in complete sentences.
Chapter 12, Section 3: Modeling Mendel’s laws
Using Punnett squares
A Punnett square shows all of the _____________________________ that could result from a given cross.
Fill in the offspring genotypes in the following crosses:
In the left Punnett square, both parents are _____________________________ for seed color.
About one-____________________ of the offspring will be YY. About two-____________________ (or
one-half) will be Yy. And about one-_______________________ will be yy.
In the right Punnet square, both parents are _____________________________ for seed color, but
one parent is yellow and the other is green. Here, _____________________________ is the
dominant trait. All the offspring in this cross will be _____________________________ (Yy) and
will express the dominant trait of _____________________________ seed color.
Using probability
_____________________________ is the likelihood that a specific event will occur.
Using a pedigree
A _____________________________ is a family history that shows how a trait is inherited over
several generations. A genetic _____________________________ is a disease that can be
inherited. _____________________________ have alleles for a disorder but do not show
symptoms. They can pass the allele for the disorder to their _____________________________. A
_____________________________ trait is located on either an X or Y chromosome.
Reading Check 12.4
Complete this outline while you read section 12.4 of your textbook. You do not
need to answer in complete sentences.
Chapter 12, Section 4: Beyond Mendelian heredity
Many genes, many alleles
Not all genes have only two _____________________________. Not all characters are controlled
by only one _____________________________.
When several genes affect a character, it is called a _____________________________ character.
An example is _____________________________ in humans.
An inheritance pattern in which the offspring has a phenotype that is intermediate (or in
between) the traits of its parents is called _____________________________ dominance. An
example is when a red snapdragon is crossed with a white snapdragon, and their offspring
all have _____________________________ flowers.
Genes that have three or more possible alleles are said to have _____________________________ alleles.
For some characters, two traits can appear at the same time. _____________________________ is
a condition in which both alleles for the same gene are fully expressed. An example is
human _____________________________ groups.
Genes affected by the environment
_____________________________ can be affected by conditions in the environment, such as
_____________________________ and _____________________________. An example is the arctic fox,
whose fur is __________________________ during the summer and __________________________
during the winter.