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Chapter 4 (Sections 1 &2) Study Guide: Genetics
Pages 172-190
Vocabulary: You may re-write vocabulary definitions below, prepare flashcards, or printout eflashcards and attach to your study guide.
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heredity the passing of traits from parents to offspring
genetics the study of how traits of organisms are passed from parents to offspring
dominant a genetic factor that blocks another genetic factor
recessive a genetic factor that is hidden by the presence of a dominant factor
gene a section of DNA that has information about a specific trait of an organism
law of segregation the two factors for each trait segregate or separate from each other during
meiosis when gametes form
law of independent assortment the factors for one trait separate independently of how factors for
other traits separate
allele each form of a gene with different information
phenotype observable traits and all characteristics of an organism
genotype alleles that make up an organism
homozygous two alleles for a gene having the same information
heterozygous two alleles for a gene having different information
Punnett square a model used to predict possible genotypes and phenotypes of offspring
pedigree a model that shows the genetic traits that were inherited by members of a family tree
incomplete dominance alleles that produce a phenotype that is a blended form of the parents’
phenotypes
codominance the interaction of two alleles in which both alleles can be observed in the
phenotype
multiple alleles genes that have more than two alleles
sex chromosome chromosomes that contain genes that determine an organism’s gender
polygenic inheritance when multiple genes determine the phenotype of a trait
genetic disorder a genetic or chromosomal mutation that is inherited
Main Ideas: Answer each question in complete sentences.
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Who was Gregor Mendel and why is he important? The first person known to record evidence
that traits of organisms are determined by factors passed from parents to offspring. All the
research of modern genetics is based on Mendel’s conclusions from his work with pea plants.
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What plant did Mendel use for his experiments and what were the seven traits he studied? Pea
plants: flower color, flower position, seed color, seed shape, pod shape, pod color, stem length
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Why were these plants a good choice for conducting genetic experiments? Easy to grow, they
flower and reproduce quickly, they come in many varieties, each trait has only two variations.
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Analyze the relationships among genes, alleles, chromosomes, and DNA. (notebook p. 38) A
chromosome is made up of DNA. A section of DNA that has information about a specific trait is
called a gene. A gene contains two alleles.
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Make a Punnett square to cross a homozygous yellow pea plant with a green pea plant. Predict
the percentage of offspring to have a genotype of YY, Yy, yy and phenotype of green seeds and
yellow seeds. YY = 0%, Yy = 100%, yy = 0% Yellow = 100 %, Green = 0%
Y
y
y
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Y
Yy
Yy
Yy
Yy
Make a Punnett square to cross two heterozygous free earlobe parents. What is the probability an
offspring will have free earlobes? What is the probability an offspring will have attached
earlobes? Free earlobes = 75%, attached earlobes = 25%
F
F
f
f
FF
Ff
Ff
ff
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What is an example of a trait that is determined by multiple alleles? Human ABO blood groups
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Make a chart of the phenotypes and possible genotypes for human blood types. What allele(s) are
dominant and what allele(s) is recessive? A and B are codominant and dominant over O. O is
recessive.
Phenotype
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Possible Genotypes
Type A
IAIA or IAi
Type B
IBIB or IBi
Type O
ii
Type AB
IAIB
Why are males more likely than females to have X-linked recessive conditions? They only have
one X chromosome so they only need to inherit one recessive allele to get the condition.
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Make a Punnett square to cross a male with a female that is a carrier for color blindness. What is
the probablility that the males will be color-blind? What is the probability that the females will
be color-blind? Color-blind males = 25%, Color-blind females = 0%
X
Xc X Xc
X
Xc
XX
Y
XcY
Y
XY
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How are genes and the environment related? A person could have genes that affect his or her
chances of getting a disease but what the person eats and the amount of exercise he or she gets can
influence whether or not the disease will develop.
Diagram: Practice Punnett Square Problems
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Cross two heterozygous black guinea pigs.
75%
What is the probability that an offspring will have black fur? _______
What is the probability that an offspring will have white fur? _______
25%
B
b
B
BB
Bb
b
Bb
bb
Cross a homozygous round seed pea plant with a homozygous wrinkled seed pea plant.
What is the probability that an offspring will have round seeds? _______
100%
0%
What is the probability that an offspring will have wrinkled seeds? _______
r
r
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R
R
Rr
Rr
Rr
Rr
Cross a white rabbit with a heterozygous black rabbit.
50%
What is the probability that an offspring will have black fur? _______
50%
What is the probability that an offspring will have white fur? _______
B
b
b
Bb
bb
b
Bb
bb
Online Review: Use these online sources to help you review for your chapter test. Place a
check mark in the box when you have completed the review.
 Standards Assessment Chapter 4
Score _____
http://glencoe.mcgraw-hill.com/sites/007874184x/student_view0/unit2/chapter4/standard_assessment-english.html
 Vocabulary eFlashcards Chapter 4
http://www.glencoe.com/qe/efcwin.php?qi=10226
 Interactive Tutor Chapter 4
Score _____
http://www.glencoe.com/olc_games/game_engine/content/gln_sci/fops_06_ca/grade07/chapter04/text_id/