Chapter 13 Flashcards
Sutton and Boveri both proposed that
genes are present on chromosomes in
the early 1900s
homologous chromosomes
pair with each other during
meiosis
Chromosome Theory
Inheritance patterns of unlinked vs. linked genes. Linked genes do NOT segregate randomly during meiosis
Sex determination in Drosophila is based on the
number of
X Chromosomes
2 “X”
Female
1 “X”
Male
Sex determination in humans is based on the
Y Chromosomes
“Y” chromosome carries genes for
“maleness”
In many organisms, the Y chromosome is
greatly reduced or inactive
X-linked genes are present in only
1 copy in males, 2 copys in females
Sex-linked traits
controlled by genes on
the X or Y chromosome; show inheritance
patterns different than those of genes on
autosomal chromosomes
Dosage compensation ensures
equal gene
expression even though females have 2
“X”s and males have only 1
In female cells, 1 “X” is inactivated and
condensed into a
Barr Body
Genetic Mosiacs express
the dominant allele in some cells, the
recessive allele in other cells
DNA mutations can cause
altered proteins once the genes are transcribed and
translated
Altered proteins may not function correctly,
causing a
phenotypic change
Some genetic disorders are caused by
changes in
chromosome number
Nondisjunction during meiosis can create
gametes having too many or too few
chromosomes
Down syndrome is trisomy of chromosome
21
Fertilization of nondisjunction
gametes creates
trisomic or
monosomic
individuals
The incidence of
Down Syndrome
increases with
female age,
because non-
disjunction
during meiosis
increases with
ageing
Nondisjunction of sex chromosomes of
females can result in
XXX triple-X syndrome daughters
XXY sons (Klinefelter syndrome)
XO daughters (Turner syndrome)
XYY sons (Jacob syndrome)
OY nonviable zygotes
Cri-du-chat syndrome
occurs when a section
of
chromosome 5 is missing
Genomic imprinting occurs when the
phenotype
produced by a particular allele depends on which
parent contributed the allele to the offspring
