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Environment-induced disruptions in meiosis
BPA treated
Chromosome number error
(aneuploidy) rose from 1-2% to 40% in
mouse eggs!
Reason- bisphenol A (BPA),
a component of plastic..
….. results in meiosis errors in
mouse eggs
Meiosis
normal
Science 300:31 April 2003
Chromosomes and
Human Genetics
Chapter 11
Chromosomes and Cancer
Genes on chromosomes drive ___________
__________ is uncontrolled cell division
Philadelphia Chromosome
•First abnormal chromosome to be
associated with a cancer
•Associated with a chronic ________
•Overproduction of white blood
cells
•Due to _____________________
Genes
• Units of information about _______________
• Each has a particular __________
– Location on a _______________
•_______________ are identical in length,
size, shape, and gene sequence
Alleles
A
B
C
A
B
C
a
b
c
a
b
c
•Different __________ forms of a gene
•Arise through _____________
_______________- display of chromosomes
Fig. 11.4, p. 173
Blood sample
1000X magnification
1
2
3
4
13
14
15
16
5
17
6
7
8
9
18
19
20
21
10
22
11
12
XX (or XY)
Sex Chromosomes
• Discovered in late ______
• Mammals, fruit flies
– XX is _______, XY is _________
• In other groups XX is male, XY female
eggs
sperm
X
Sex determination
Y
X
X
Female germ cell
Male germ cell
X
X
X
XX
XX
Y
XY
XY
sex chromosome combinations possible
in new individual
The Y Chromosome
• < ____ genes
• Includes ____ gene- dictates ______
phenotype
The X Chromosome
• > ______ genes
• Most genes - _______ traits
• Genes expressed in both males and
females
Effect of Y
Chromosome
appearance of structures
that will give rise to
external genitalia
appearance of
“uncommitted” duct system
of embryo at 7 weeks
7 weeks
Y
present
Y
absent
Y
present
Y
absent
testes
ovaries
10 weeks
ovary
birth approaching
testis
• Thomas Hunt Morgan - first to associate a
specific gene with a specific chromosome in the
early 20th century.
• Morgan’s model-Drosophila melanogaster, a fruit fly
- have three pairs of __________ and a pair of
_____________ chromosomes (XX in females, XY in males).
Red eyes
White eyes
Normal is called “_________”
Non-normal is called “______”
Know these symbols
= _ _____ _
• Morgan’s experiments-
= _______ _
Red eye X White eye
F1
All Red eye
3:1 Red:white
F2
Conclude- classic _ ________ _ genetics
But- all __________were white,
all females red
Morgan concluded that a
fly’s eye color was linked to
the _ _____________ ___.
Fig. 15.3
Linked genes tend to be inherited together because they are
located on the same chromosome
15.3
15.2
15.1
14
13.2
13.3
13.1
12
11
11.1
11.2
12
Chromosome- 1.5 x 108 base pairs containing about ______ genes
13.1
13.2
13.3
14
15
21
22
23.1
23.2
23.3
31.1
31.2
31.3
32
33.2 33.1
33.3
34
35.2
35.1
35.3
0.4% of a chromosome, containing 10 genes
• Genes located on the same chromosome,___ ______
_______, tend to be inherited together because the
chromosome is passed along as a unit.
•Results of crosses with linked genes deviate from those expected
according to __ _____________________ __.
Linkage Groups
• Genes on one type of chromosome
• Fruit flies
– __ homologous chromosomes
– __ linkage groups
Crossover Frequency
-____________to the distance that separates genes
A
B
C
D
Crossing over will disrupt linkage between
_________ more often than _________
Frequencies can be used to construct a _______________
Incomplete Linkage
AC
A
C
Parents:
ac
c
x
A
a
a
c
C
F1 offspring
All AaCc
meiosis, gamete formation
Unequal ratios of
four types of
gametes:
C
A
c
a
Most
gametes
have parental
genotypes
c
A
a
C
A smaller
number have
recombinant
genotypes
Linkage Mapping in Humans
Called a “________”
• Chart that shows _____________ connections
among individuals
• Knowledge of probability and Mendelian
patterns used to suggest basis of a trait
Pedigree for
__________
Unusual
number of toes
or fingers
Genetic Disorders
•_________ conditions that
cause mild to severe medical
problems
Autosomal _________
•Many people are
_________
•Heterozygous parents-child will have a _____
chance of being affected
Autosomal __________
•Trait typically appears in
_______ generation
•Most of these ________
from population. WHY?
Autosomal dominant diseases
1. Huntington Disorder
• Causes involuntary movements, nervous system
deterioration, death
• Symptoms don’t usually show up until person is past
age ___
• People often pass allele on before they know they
have it
2. Acondroplasia
•In homozygous form usually leads to _______
• Heterozygotes display a type of _________
• Have short arms and legs relative to other body
parts
X-Linked Recessive Inheritance
• Males show disorder
_________ females
• Son _______ inherit
disorder from his
father
Examples
1. Color blindness2. _________, Blood-clotting disorder; 1/7,000 males
3. ________- Allele has repeated segments of DNA;
causes mental retardation
4. ____________________ - Appears to be dominant;
spontaneous mutation; premature aging effect, early death
The wrong number of chromosomes is bad
Usually due to ________________
n+1
n+1
n-1
chromosome
alignments at
metaphase I
n-1
nondisjunction
at anaphase I
alignments at
metaphase II
anaphase II
• Nondisjunction results in too many or to few
chromosomes termed ______________ .
– some gametes receive two of the same type of
chromosome and another gamete receives no copy.
– _______ cells - three copies of a particular chromosome
type and have _______ total chromosomes.
– _________ cells - one copy of a particular chromosome
type and have 2n - 1 chromosomes.
• Normally results in embryonic death, but some survive
Organisms with more than two _______ _sets of chromosomes, have
undergone _________, e.g. 3n or 4n (rare in ____________)
• Polyploids are more nearly normal in phenotype than ___________.
Other chromosome problems
A ________- a chromosome
fragment lacking a ________
is lost during cell division
A ___________- a fragment becomes attached as an
extra segment to a sister chromatid
Fig. 15.13c & d
• An inversion - a chromosomal
fragment ________ to the original
chromosome but in the reverse
orientation.
• In_ _______, a chromosomal
fragment joins a _________
chromosome.
•Some translocations are
___________ others are not.
Results of chromosome errors
• Homozygous embryos with a large ________ normally
die
• A deletion in the X chromosome is _______ in males
• A __ ________________ can alter phenotype because
a gene’s expression is influenced by its location.
Example- Leukemia is due to a growth gene being placed
next to an active region resulting in cancer
• Approx. _____ of human embryos are aneuploid and die early in
development
Some are viable• Chromosome 15 trisomy- die at birth
• Chromsome 21 trisomy- ________ syndrome
• Down syndrome- trisomy 21.
– One in 700 children born in the United States.
– result from ___________________ during
gamete production
• correlates with the age of the mother.
Fig. 15.14
Karyotype
Phenotype
Extra sex chromosomes are allowed
• _____________________ _an XXY male, occurs
once in every 2000 live births.
– Male sex organs, but are_ ________.
– Feminine characteristics; normal intelligence.
• Males with an extra Y chromosome (XYY) tend to
somewhat _______ than average.
• Trisomy X (XXX), which occurs once in every 2000
live births, produces _ ________ _ females.
• Monosomy X or _____________ (X0), which occurs
once in every 5000 births, produces phenotypic, but
immature females.
• XYY and XXYY- males often found in _________.
• In utero testing for genetic screening.
1. _____________ - beginning at the 14th to 16th week of
pregnancy to assess the presence of a specific disease.
Fig. 14.17a
•Fetal cells
extracted from
amniotic fluid are
cultured and
__________.
• 2. _____________
________(CVS)- performed
as early as the eighth to tenth
week of pregnancy.
– Extracts a sample of fetal
tissue from the chrionic
villi of the placenta are
karyotyped.
Fig. 14.17b
• Other techniques____________________________
allow fetal health to be assessed visually in
utero.
– usually reserved for cases in which the risk of
a genetic disorder or other type of birth defect
is relatively great.
• If fetal tests reveal a serious disorder, the parents
face the difficult choice of terminating the pregnancy
or preparing to care for a child with a genetic
disorder.