Advanced Biology
Chapter 14 & 15 Review
Punnett Squares
Pedigree analysis
Karyotype analysis
Chromosome mapping
How is sex determined? How do the sex chromosomes in some animals compare to
those in humans? In humans, sex is determined by the presence of X or Y chromosomes.
Females have 2 X chromosomes, males have an X and a Y. In other species, it is
determined by how many X chromosomes there are; in some insects, 2 X’s are females, 1 X
is male, etc. (see page 268). Primarily the difference in some species is that males are
haploid, females are diploid.
What is a Barr body? The inactive X chromosome in women. Even though women
have 2 X chromsomes, only the genes of one is active in each cell (which one is totally
random); the other inactivated one is usually found compacted near the nuclear
Calico cats are almost always female. How might you get a male calico?
The color gene in cats is located on the X chromosome, and Calico cats actually
proves that in each cell, only one X is active. A calico is heterozygous black-orange for
color (black allele on one, orange on the other X). During embryonic development, as the
cells divide, one of the X’s in each is inactivated; offspring of those cells will subsequently
have the same inactive x resulting in the patchy coloration of the active X allele in that cell.
Since 2 X chromosomes are needed, and males are XY, the only way to get a male calico is
in the event that the male has the genotype XXY (similar to Klinefelters in humans). There
are no “normal” male calicos
What is nondisjunction? When chromosomes fail to separate during meiosis
Identify the cause/effect of the following disorders:
Turner’s Syndrome
Nondisjunction; results in XO
--is the only viable monosomy
Klinefelter’s Syndrome
Nondisjunction; results in XXY, a male,
but sterile. Normal intelligence but taller
Than average, usually
Down Syndrome
Nondisjunction; results in trisomy-21
Retardation, “mongoloid” features, shorter
life span
considered a recessive mutation; brain
cells can’t metabolize some lipids, so
brain cells die
Huntington’s degenerative disease of the nerVous system; lethal dominant train not expressed until late in life
Phenylketonuria recessive; can’t break
down phenylalanine. Can result in retardation
Sex-linked “bleeders” disease or the
“King’s Evil” because it was common in
Royal families
Sickle-cell Disease
substitution of a single amino acid in
hemoglobin; results in an inability of
red blood cells to carry hemoglobin; is
treatable but there is not cure
Muscular Dystrophy
Sex-linked; weakening of muscles and
Loss of coordination. Rarely live past their
Fragile X Syndrome
related to genomic imprinting; more
common in males; retardation likely
What does it mean to be hemizygous? Refers to sex chromosomes that do not contain
the same genes, and therefore can’t be either homozygous or heterozygous
What could be considered good evidence for linkage of genes? When 2 traits are always
inherited together
Differentiate between a gamete and a zygote. A gamete is egg or sperm (a haploid cell).
The zygote is a union of the 2, and is diploid
What is a locus? An allele? Alleles are alternate forms of a gene (tall/short,
red/white). The locus is the specific location of the allele on a chromosome
What is genomic imprinting? The effect of a gene depending on whether or not it was
inherited from the mother or father. For example, Prader-Willi syndrome and Angelman
syndrome. Both seem to be caused by a deletion from chromosome 15. If the abberant
chromosome was inherited from the father, the result is Prader-Willi; if from the mother,
Discuss the possible results of the following alterations to a chromosome:
Deletion a nucleotide sequence is left out during transcription or translation
Inversion sequence is “flipped over”
Translocation sequence is moved to a new location
Duplication sequence is copied more than once
What is a tetrad? When homologous chromosomes pair up during Meiosis I and
recombination can occur
What are the Mendelian principles? Dominance and recessiveness, segregation, and
independent assortment
What is pleiotropy? The effect of one mutation on more than one traits
What is significant about the Rh factor when it comes to pregnancy? If mom is Rh- and
the baby ends up Rh +, a lethal condition may occur in the fetus called erythroblastosis
fetalis. If the baby’s blood leaks across the placental barrier, it may cause the mother’s
immune system to create antibodies to it, as it would if she had deliberately been given the
wrong blood type. The antibodies are able to cross the placental carrier, and attach the
baby’s own blood in the body
Explain the pattern of inheritance for each of the following, and how it affects might
affect phenotypic ratios where applicable:
incomplete dominance the heterozygote is an intermediate to the homozygotes
codominance both alleles are fully expressed
sex-linked traits on the X chromosome (most are x-linked); affects males more often,
as they have only on X
pleiotropy the ability of a gene to affect an organism in many ways (multiple
symptoms), i.e., sickle-cell disease
multiple alleles more than 2 possible alleles for a trait, though only 2 can be present
in a given organism (A-B-O blood system
epistasis a gene at one locus affects the expression of a gene at another locus, i.e.,
coat color in mice. Two genes contribute to the color—one by pigment (kind of pigment, B
or b) and one for the ability to produce a coat at all (C or c). Even if an organism has the
dominant color gene (B), it could not be produced if there is no C to let it happen.
What is a test cross? The mating of an unknown genotype to the homozygous
Given the parents PPTTIi x PpttIi, and assuming simple dominance and independent
assortment, what are the proportion of progeny that will be expected to phenotypically resemble
the first parent? ¾
1/1 x 1/1 x ¾ = 3/4