Heredity - Chapters 14 and 15
Genes are the molecular unit of heredity. Sometimes a single gene codes for a single trait, but this is not
always the case. Sexually reproducing organisms pass on various combinations of their genes to their
offspring. Genetic variation in offspring is produced largely through crossing over, independent
assortment, and random fertilization. Genes are passed in a number of predictable patterns, which can
be tracked using a pedigree.
Learning Goals - Students will be able to…
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explain how the laws of probability govern Mendelian inheritance
describe the chromosomal basis of inheritance
identify and describe non-Mendelian patterns of inheritance
explain how gene linkage is used to determine a gene’s location on a chromosome
Vocabulary
character
trait
true-breeding
hybridization
P generation
F1 generation
F2 generation
Law of Segregation
dominant allele
recessive allele
allele
Punnett square
homozygous
heterozygous
phenotype
genotype
test cross
monohybrid
dihybrid
Law of Independent Assortment
Multiplication rule
complete dominance
incomplete dominance
codominance
multiple alleles
pleiotropy
epistasis
quantitative characters
polygenic inheritance
multifactorial character
norm of reaction
pedigree
carrier
amniocentesis
chorionic villus sampling (CVS)
chromosome theory of inheritance
wild type
sex-linked gene
X-linked gene
Barr body
linked gene
genetic recombination
parental types
recombinants
Analysis Questions
1.
What is the law of segregation? Law of independent assortment?
2.
What are quantitative characters? Discrete characters?
3.
Define pleiotropy and epistasis.
crossing over
genetic map
linkage map
map units
nondisjunction
aneuploidy
polyploidy
deletion
duplication
inversion
translocation
Down syndrome
genomic imprinting
4.
What is a recombinant?
5.
What is a linkage map?
6.
Define and provide three examples of multifactorial characters.
7.
In his research, Mendel found a 705:224 ratio of purple to white flowers in F2. Based on this,
explain the most likely genotypes of the P and F1 generations.
8.
In pea plants, yellow seeds (Y) are dominant over green seeds (y) and round (R) seeds are
dominant over wrinkled seeds (r). If a pea plant with the genotype YYRr is crossed with a pea
plant with the genotype yyRr, how likely is it that their offspring will have yellow, wrinkled seeds?
9.
A man with type A blood marries a woman with type B blood. Their child has type O blood.
What are the genotypes of these three individuals. What genotypes, and in what frequencies,
would you expect in future offspring from this marriage?
10.
In some plants, a true-breeding, red-flowered strain gives all pink flowers when crossed with a
white-flowered strain: C C (red) x C C (white) → C C (pink). If flower position (axial or
terminal) is inherited as it is in peas (see table 14.1), what will be the ratios of genotypes and
phenotypes of the F1 generation resulting from the following cross: axial-red (true breeding) x
terminal white? What will be the ratios in the F2 generation?
R
11.
R
W
W
R
W
What is the probability that each of the following pairs of parents will produce the indicated
offspring? (Assume independent assortment of all gene pairs).
(a) AABBCC x aabbcc → AaBbCc
(b) AABbCc x AaBbCc → AAbbCC
(c) AaBbCc x AaBbCc → AaBbCc
12.
In Labradors (labs), the gene for pigment deposition (E/e) is epistatic to the gene that codes for
black or brown pigment (B/b). What are the expected genotype and phenotype ratios for a cross
between a lab that is heterozygous for pigment deposition and homozygous dominant for pigment
and one that is heterozygous for pigment deposition and homozygous recessive for pigment?
13.
Red-color blindness is caused by an X-linked recessive allele. A color-blind man marries a
woman (a carrier) with normal vision. What is the probability that they will have a color-blind
child? What is the probability that they will have a color-blind daughter?
14.
Examine the pedigree below. Identify the genotypes of individuals I-1, II-1, and II-5. Is a
dominant or recessive trait portrayed? Explain.
15.
Determine the sequence of genes along a chromosome based on the following recombination
frequencies: A-B, 8 map units; A-C, 28 map units; A-D, 25 map units; B-C, 20 map units; B-D, 33
map units.