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Chapter 4 Study Guide
Name: ____________________________
Date: ________________Per. _________
Lesson 1: FOUNDATIONS OF GENETICS. Gregor Mendel discovered the basic principles of genetics.
A. Early Ideas About Heredity.
1. The passing of traits from parents to offspring is called ________________________.
2. Blending inheritance is the (incorrect) idea that offspring are a ____________ of genetic material from both parents.
a. Supporters of this idea proclaim over many generations populations would look alike…this does ______ happen. It
. also does not explain why some traits appear to ________ _______________________.
B. Gregor Mendel – The first person known to record evidence that _______ of organisms are determined by factors passed from
. parents to offspring.
1. Mendel is known as the _______________ of ______________. Genetics is the study of how traits of organisms are
passed from parents to ____________________.
a. Mendel studied _______ different traits of pea plants. Each ________ had only _____ _________________.
b. Mendel controlled ________________ in the experimental pea plants. He also performed _________-fertilization
by transferring pollen from the ___________ of one flower to the ____________ of another flower. This allowed him
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to record the parents of the offspring and observe how traits pass from one ______________________ to the next.
c. Mendel’s methods were unique. First, he used only (purebred, which he called) ________-____________ plants.
Second, he recorded inheritance for several ________________. Lastly, he used a __________________________
approach and collected and recorded large amounts of data.
2. Mendel concluded that two ____________ control each trait. He also proposed that when organisms reproduce each
. . gamete--_____________ or ____________ ---contributes one factor for each ___________________.
a. Mendel often crossed true-breeding plants to create ___________, which inherit a different form of a specific trait .
from each __________________.
b. A genetic factor that blocks another factor is called_______________________.
c. A genetic factor that is blocked by the presence of a dominant factor is called ________________. A ____________
. trait can only be observed when ________________ recessive genetic factors are present in offspring.
C. Mendel’s Laws of Heredity
1. According to the law of _____________________, the two factors for each trait separate during _____________ when
sperm and ________ form.
2. The law of _____________________________________ states that factors for one trait separate independently of how
factors for other traits separate.
D. Modern Definitions of Mendel’s Ideas
1. Chromosomes are made up of _________ and proteins. A section of _______ that has information about a specific trait
of an organism is called a _________________.
2. Each form of a gene with different information is called a(n) _______________. Mendel called these ____________.
3. The observable traits and all characteristics of an organism make up the organism’s ___________________________.
a. An organism’s phenotype results from the _________________ among its _____________ and _____________.
4. The alleles of all the genes on an organism’s chromosomes make up the organism’s _____________________.
5. A genotype is called _____________________ if the two alleles have the same information (ex: _____ , _____)
6. If the two alleles for a gene have different information their genotype is called __________________. (ex: _____, _____)
Lesson 2: UNDERSTANDING INHERITANCE. The interactions among alleles, genes, and the environment determine an
organism’s traits.
A. Modeling Inheritance
1. If the genotypes of the parents are known, a __________ __________ , a model that can
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predict the genotypes and phenotypes of offspring can be used.
a. One-Trait Model for two true-breeding (purebred) pea plants is shown
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by this ______________ square. (complete square at right, see figure 12)
b. Y represents the ______________ allele for yellow seeds, and y represents
the _________________ allele for green seeds.
___
c. Here the only possible genotype for the hybrid offspring is ________________, (Yy).
d. The true-breeding pea plant for yellow seeds can only contribute a _____. The true-breeding
pea plant for green seeds can only contribute a ___. So, 100% of the offspring will have the Yy ________________.
e. The phenotype (what it looks like) of the genotype Yy is ______________ seeds because Y is ________________ to y.
f. Hybrid-Cross Model show in the Punnett square at the right the results of a
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hybrid cross of the offspring with ____________________ genotypes of Yy
g. The possible offspring from this cross are ______ different genotypes which are
____, ____, ____. These result in only two different phenotypes which are either yellow ___
seeds or ______________seeds.
h. We see that three-fourths, ____%, of the offspring will have ________ seeds and
one-fourth, _____%, will have green seeds. This can also be stated as a ___:___ ratio.
___
2. A pedigree shows genetic _______ that were inherited by members of a family tree and
usually only indicates __________________ as genotypes might not be known but can often be determined.
B. Complex Patterns of Inheritance
1. Types of Dominance
a. Sometimes traits appear to be blends of the parents’ phenotypes, when this occurs alleles show _______________
______________. An example of this is ______________________________________________________________.
b. When two (both) alleles can be observed in the phenotype, this type of interaction is called ______________. Human
. blood type _____ is an example of this. The phenotypes of human blood types are ____,____, ____, _______.
2. Some genes that have only two alleles, however there are genes that have more than two alleles or _____________
__________. The three alleles for the ABO blood type are ____, ____, and ____. Even though there are multiple alleles,
. in the human population, a person can only inherit two alleles, one from each parent.
3. Chromosomes X and Y are the ______ ______________ because they hold the genes that determine a person’s gender.
4. When multiple genes determine the phenotype of a trait it is called _____________ ____________. Height, weight and
. ________ ______________ are traits determined by this type of inheritance.
5. Remember from Chapter 1 that mitochondria have their own DNA, also remember that mitochondria are scattered
. throughout each cell, but are only in the _______ of the sperm cell. Because the sperm’s tail does not enter the egg
during fertilization, humans inherit ______________ genes , the genes involved in making ATP during cellular respiration
only from their ________________. This is called ___________________ inheritance.
C. Human Genetic Disorders
1. An inherited mutation can result in a phenotype called a _________ __________. This can result in minor or _________
. health problems and sometimes shorten a person’s ___________.
D. Genes and the Environment
1. As you read earlier, genotype determines the _________________. Scientists have determined that genes are not the
only ___________ that affect the phenotype. An organisms _________________________ can also affect phenotype.
a. Many genes affect a person’s chance of having heart disease, however, what a person ________ and the amount of
____________________ he or she gets can influence whether heart disease will develop.
Extra Practice:
1. A capitalized letter representing an allele (S) means the allele is _________________. A lower case letter representing an allele
(s) means the allele is _____________________.
2. Using the following information show the results: T=allele for tall plant, t=allele for short plant.
a. Genotype for homozygous dominant plant ___________. Will this plant be tall or short? _____________. What kind of alleles
can this plant give to its offspring? _____________. Its offspring will be ___________________________________________.
b. Genotype for heterozygous tall plant ___________. Will this plant be short or tall? __________________. What kind of alleles
can this plant give to its offspring? ____________. Its offspring will be ___________________________________________.
3. Show a Punnett square for the following and answer the questions. Show a cross between a
heterozygous plant and a homozygous recessive plant (use letters from question 2 in the Punnett square).
____
____
a. How many plants will be tall? _______________ . What percent is that? _____________
b. How many plants will be short? ______________. What percent is that? ______________
c. We can say the ratio of tall to short plants is ____ :____.
___
4. A genotype for homozygous dominant is __________ (use any letters).
5. A genotype for heterozygous ____________ (use any letters).
6. A genotype for homozygous recessive _______ (use any letters).
7. In order for a recessive trait to show in the phenotype, ________ ________ must be recessive.
___
8. A hybrid genotype is _________ , a pure-bred (true breeding) genotype is __________ (use any letters).
9. What kind of cells have DNA in them? _______________________________________________________________.
12. The control center of the cell is the __________________.