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Genetics
Kirsten Adams
National Cathedral School
AP Biology
Figure 14.0x Mendel
Figure 14.1 A genetic cross
Figure 14.2 Mendel tracked heritable characters for three generations
Figure 14.x1 Sweet pea flowers
Figure 14.3 Alleles, alternative versions of a gene
Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants
Figure 14.x2 Round and wrinkled peas
Figure 14.4 Mendel’s law of segregation (Layer 2)
Figure 14.5 Genotype versus phenotype
Figure 14.6 A testcross
Figure 14.7 Testing two hypotheses for segregation in a dihybrid cross
Figure 14.8 Segregation of alleles and fertilization as chance events
Problem #1
• In garden peas, tallness is dominant and
dwarfness is recessive. A heterozygous tall
plant is crossed with a dwarf plant. If 40
offspring are produced, how many will be
tall?
Problem #2
• In humans, brown eyes are dominant over
blue eyes. A brown-eyed man and a blueeyed woman have two blue-eyed children.
What are the chances that their next child
will have blue eyes?
Problem #3
• Cystic Fibrosis is inherited as a simple
autosomal recessive. Suppose a woman
who carries the trait marries a normal man
who does not carry it. What percent of their
children would be expected to have the
disease?
Problem #4
• Classical Albinism is a single-gene disorder
caused by the lack of an enzyme necessary
for the synthesis of melanin pigments.
Enzyme production requires the presence of
one normal allele. What progeny and what
proportions are expected from a normally
pigmented woman who has an albino
husband and an albino father?
Problem 5
• If two individuals with the genotype A/a
B/b C/c D/d mate, what is the probabilty of
getting an individual with the genotype A/A
B/b c/c D/d?
Problem #6
• In watermelons, the genes for green color
and for short shape are dominant over
alleles for striped color and long shape. A
plant that is heterozygous for green color
and homozygous for short shape is crossed
with a plant that is homozygous for striped
color and heterosygous for short shape.
What proportion of their offspring will be
striped and short?
Incomplete Dominance and
Codominance
Figure 14.9 Incomplete dominance in snapdragon color
Figure 14.9x Incomplete dominance in carnations
Problem #7
• In snap dragons, flower color and leaf color
are both controlled by partial dominance.
Pink flowers and light green leaves are the
intermediate conditions. Supposed you
crossed two plants, both of which had pink
flowers and light green leaves. If there
were 16 offspring, how many would you
expect to have both pink flowers and light
green leaves?
Multiple Alleles
Ex. Blood types
Figure 14.10 Multiple alleles for the ABO blood groups
Figure 14.10x ABO blood types
Problem 7
• A woman takes Mr. X to court for child
support, but Mr. X swears he is not the
father. The woman is blood type A and the
baby is blood type A. Which blood type
must Mr. X have to prove that he is not the
father?
Interactions Between Genes
Pleiotropy
Epistasis
Collaboration
Complementation
Modifier Genes
Multiple Gene Inheritance
Pleiotropy
Figure 14.15 Pleiotropic effects of the sickle-cell allele in a homozygote
Epistasis
Figure 14.11 An example of epistasis
Collaboration
Problem 8
• If the dominant allele K is necessary for
hearing, and the dominant allele M of
another gene results in deafness no matter
what other genes are present, what
percentage of the offspring produced by the
cross between k/k M/m and K/k m/m will
be deaf?
Complementation
Modifier Genes
Multiple Gene Inheritance
Figure 14.12 A simplified model for polygenic inheritance of skin color
Environment
Penetrance
Expressivity
Figure 14.13 The effect of environment of phenotype
Sex linked characteristics
Holandric
X-linked
Figure 15.3 Sex-linked inheritance
Figure 15.9 The transmission of sex-linked recessive traits
Figure 15.10 X inactivation and the tortoiseshell cat
Figure 15.10x Calico cat
Pedigrees
Figure 14.14 Pedigree analysis
Figure 14.16 Large families provide excellent case studies of human genetics
Human Disorders
Figure 14.17 Testing a fetus for genetic disorders
Figure 15.0 Chromosomes
Figure 15.0x Chromosomes
Figure 15.11 Meiotic nondisjunction
Figure 15.12 A tetraploid mammal?
Figure 15.x1 Translocation
Figure 15.13 Alterations of chromosome structure
Figure 15.14 Down syndrome
Figure 15.x2 Klinefelter syndrome
Figure 15.x3 XYY karyotype
Linkage
Figure 15.4 Evidence for linked genes in Drosophila
Figure 15.5a Recombination due to crossing over
Figure 15.5b Recombination due to crossing over
Figure 15.6 Using recombination frequencies to construct a genetic map
Figure 15.7 A partial genetic map of a Drosophila chromosome
Linkage Problem
• In rabbits, a dominant gene produces spotted body
color. Another dominant gene produces short hair
and its recessive allele long hair. Rabbits
heterozygous for both characteristics were mated
with homozygous recessive rabbits. The results of
this cross were as follows: 170 with spotted and
short; 30 with solid and short hair; 26 with spotted
and long; 174 with solid and long. What is the
map distance between these genese?
Figure 15.15 Genomic imprinting (Layer 3)
Figure 15.16 Cytoplasmic inheritance in tomato leaves