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Chapter 13 Study Guide
Patterns of Inheritance
Objectives:
 Understand the historical background for Mendel’s pea experiments.
 Know the key details in Mendel’s experiments that enabled him to postulate his laws of inheritance
where others had failed.
 State Mendel’s model of heredity and Sutton’s theory of chromosomal inheritance.
 Understand how gene segregation and independent assortment are different but yet related.
 Calculate expected phenotypic and genotypic ratios from various crosses using the Punnett square
method.
 Explain the experimental rationale behind the classical testcross.
 Explain how Mendelian inheritance changes with respect to continuous variation, pleiotropic genes,
lack of complete dominance, environmental modifications of genes, and epistasis.
 Understand the importance of crossing over in terms of gene assortment and construction of genetic
maps.
 Describe the many genetic disorders discussed in the text, their symptoms, relative frequency in
specialized populations, and their genetic basis.
 Understand the consequences of nondisjunction at various stages of gametogenesis and its affect on the
sex chromosomes.
 Understand the value and purpose of genetic counseling and describe two techniques of prenatal
genetic screening.
Key Terms (Understand meanings in context, and give examples if applicable
codominant
hybridizations
ABO blood groups
character
Rh blood group
segregating
pedigree
self-fertilization
hemophilia
cross-fertilization
sickle cell anemia
pure-breeding
gene transfer therapy
first filial generation
chromosomal theory of inheritance
dominant
mutant
recessive
X chromosome
second filial generation (F2)
Y chromosome
Mendelian ratio
sex-linked
alleles
crossing over
homozygous
genetic recombination
heterozygous
genetic map
genes
centimorgan
locus
three-point cross
genotype
wild type
phenotype
autosomes
Punnett square
sex chromosomes
Law of Segregation
Barr body
testcross
gene conversion
dihybrids
monosomics
Law of Independent Assortment
trisomics
continuous variation
Down syndrome
pleiotropic
amniocentesis
epistasis
chorionic villi sampling
13.1 Patterns of Inheritance
Did you know that diarrhea is hereditary? It runs in the ‘genes’!
A. Name 5 Dominant and 5 Recessive Traits
B. Which 7 traits did Mendel study in pea plants?
C. When Mendel crossed pure breeding purple flowering plants with pure
breeding white flowering plants, what were the results in the F1 generation?
In the F2 generation?
D. What is the difference between the law of Segregation and the law of
Independent Assortment?
E. In a dihybrid cross, how many parent genotypes are possible in the
gametes?
How many phenotypes are possible in the offspring?
F. What does a 9:3:3:1 ratio mean?
G. In reality, not all genes act as clearly as the 7 traits in Mendel’s studies.
Explain what is meant by each term below:
Continuous Variation, Epistasis, Pleiotropic Effects, Incomplete
Dominance, Environmental Effects
* There will be many opportunities in class to solve problems using your
understanding of genetics.
13.2 Human Genetics follows Mendelian principles.
H. Give an example of a disease caused by a dominant allele. How does
this disease remain in the population?
I. Describe Tay-Sach’s Disease.
J. Complete a Punnett Square for a man with type AB blood and a woman
with type O blood. Notice that the symbols are written differently, because
there are 3 different alleles.
K. Why is hemophilia more prevalent in men than in women?
(Related history: Do you know what became of Czar Nicolas and his family?)
How would you show 2 parents and three children (2 boys and a girl) on a
Pedigree?
L. Thoroughly describe sickle-cell anemia. What causes it, what are the
physical traits, the symptoms, and the benefit of having one copy of the
gene?
M. Explain what is meant by a vector. How were vectors expected to cure
cystic fibrosis? What problems occurred, and what is the current outlook in
using gene therapy?
13.3 Genes On Chromosomes
N. The chromosomal theory of inheritance states that it is on chromosomes
that Mendel’s “factors” reside. However, there are more characters that
assort independently than the number of chromosomes. Explain what this
means and how it was resolved. (Include the terms “crossing over” and
“genetic recombination”.
O. Explain, in one or two sentences, why none of the female drosophila in
Morgan’s F2 generation had white eyes. Could the next generation include
females with white eyes?
P. You made a genetic map in your meiosis lab. The units are now known
as centimorgans. What does a genetic map tell you? How is it made?
Q. An inactive X chromosome is called a Barr body. In a female, are all the
Barr bodies the same in all cells?
R. Read the section on “Why are X and Y Chromosomes so Different?”
Describe how editing works on the 22 autosomes and the X chromosome,
and compare with editing on the Y chromosome.
S. Which types of trisomics can survive? Name a defect caused by a
trisomy.
T. Copy the Punnett square shown in Figure 13.37. Additionally, name the
syndrome caused by nondisjunction of the Y chromosome.
U. Practice Problem: In tomato plants, red tomato color (R) is dominant to
yellow (r). How can a farmer be sure that the seeds from his red tomato
plants will breed true red, and not yellow?