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Ch.15: Chromosome Mapping and Alterations of Chromosomes
Linkage Mapping: Using Recombination Data
Alfred Sturtevant, one of Morgan’s students,
constructed a genetic map, an ordered list of
the genetic loci along a particular
Sturtevant predicted that the _____________
two genes are, the ________________ the
probability that a ____________________
will occur between them, and therefore the
higher the recombination frequency
A linkage map is a genetic map of a
chromosome based on
Distances between genes can be expressed as
map units; one map unit, or _______________,
represents a _____ recombination frequency
Map units indicate _______________________
and order, not precise locations of genes
Sturtevant used recombination frequencies to
make linkage maps of fruit fly genes
Using methods like _____________________,
geneticists can develop cytogenetic maps of
Cytogenetic maps indicate the positions of
genes with respect to chromosomal features
Sex-linked genes exhibit unique patterns of inheritance
 In humans and other animals, there is a chromosomal basis of sex determination
 An organism’s sex is an inherited phenotypic character determined by the presence or absence of
certain chromosomes
 In humans and other mammals, there are two varieties of sex chromosomes, X and Y
 Other animals have different methods of sex determination
Inheritance of Sex-Linked Genes
 The sex chromosomes have genes for many characters unrelated to sex
 A gene located on either sex chromosome is called a _____________________________
 Sex-linked genes follow specific patterns of inheritance
Some disorders caused by recessive alleles on the X chromosome in humans:
o Duchenne muscular dystrophy
In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during
embryonic development (_______________________)
If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic
for that character (X chromosomes from both the father and the mother)
Large-scale chromosomal alterations often lead to spontaneous abortions (miscarriages) or cause a
variety of developmental disorders
Abnormal Chromosome Number
In _______________________, pairs
of homologous chromosomes do not
separate normally during meiosis
As a result, one gamete receives ____
of the same type of chromosome, and
another gamete receives no copy
____________________ results from
the fertilization of gametes in which
nondisjunction occurred
Offspring with this condition have an
_________________________ of a
particular ______________________
A _________________ zygote has
three copies of a particular
A _____________________ zygote has only one copy of a particular chromosome
_______________________ is a condition in which an organism has more than two complete sets of
Breakage of a chromosome can lead to four types of changes in chromosome structure:
o ___________________removes a chromosomal segment
o ___________________repeats a segment
o ___________________ reverses a segment within a chromosome
o ___________________ moves a segment from one chromosome to another
Human Disorders Due to Chromosomal Alterations
 Alterations of chromosome number and structure are associated with some serious disorders
 Some types of aneuploidy appear to upset the genetic balance less than others, resulting in
individuals surviving to birth and beyond
 These surviving individuals have a set of symptoms, or syndrome, characteristic of the type of
 Down syndrome is an aneuploid condition that results from three copies of chromosome
 It affects about one out of every 700 children born in the United States
 The frequency of Down syndrome increases with the age of the mother, a correlation that has not
been explained
 Nondisjunction of sex chromosomes produces a variety of aneuploid conditions
 Klinefelter syndrome is the result of an extra chromosome in a male, producing ______ individuals
 The most common symptom is infertility. Other symptoms may include:
o Abnormal body proportions (long legs, short trunk, shoulder equal to hip size)
o Enlarged breasts (gynecomastia)
o Sexual problems
o Less than normal amount of pubic, armpit, and facial hair
o Small, firm testicles
o Small penis
o Tall height
 _________________________, called Turner syndrome, produces ____ females, who are sterile; it
is the only known viable monosomy in humans
 Possible symptoms in young infants include:
o Swollen hands and feet
o Wide and webbed neck
 A combination of the following symptoms may be seen in older females:
o Absent or incomplete development at puberty, including sparse pubic hair and small breasts
o Broad, flat chest shaped like a shield
o Drooping eyelids
o Dry eyes
o Infertility
o No periods (absent menstruation)
o Short height
o Vaginal dryness, can lead to painful
Disorders Caused by Structurally Altered
 The cancerous cells in nearly all CML patients
contain an abnormally small chromosome 22 and a
long chromosome 9.
Some inheritance patterns are exceptions to the
standard chromosome theory
 There are two normal exceptions to Mendelian
 One exception involves genes located in the nucleus, and the other exception involves genes located
outside the nucleus
 For a few mammalian traits, the phenotype depends on which parent passed along the alleles for
those traits
 Such variation in phenotype is called _________________________________
Genomic imprinting involves the _________________ of certain genes that are
“_______________” with an imprint during gamete production
Extranuclear genes are genes found in _______________________ in the cytoplasm
The inheritance of traits controlled by extranuclear genes depends on the ___________________
because the zygote’s cytoplasm comes from the egg
The first evidence of extranuclear genes came from studies on the inheritance of yellow or white
patches on leaves of an otherwise green plant
Some diseases affecting the muscular and nervous systems are caused by defects in mitochondrial
genes, most of which come from the cytoplasm of the egg.
These mitochondrial genes help make up the protein complex of the ETC and ATP synthase which
leads to lower production of ATP.
The nervous system is impacted greatly by the reduced amount of ATP.
Leads to weakness, intolerance to exercise and muscle deterioration.