Download Biology 102A

Unit 6 – Genetic Abnormalities
Test Crosses, Pedigrees,
Mutations
Define mutation

Mutation: any
mistake of change in
the DNA sequence

Point mutation:
change in one
nitrogen base in
DNA; Ex: albinism
Describe common mutation
types.


Chromosomal mutation:
part of a chromosome is
lost, added, or moved to
another chromosome;
usually not passed on
because zygote dies
Crossing over: occurs
when chromosomes
exchange genes. Two
chromosomes overlap.
Some genes cross over
and switch places
Define nondisjunction and identify
the types of nondisjunction

Nondisjunction: occurs when a chromosome
pair fails to separate properly during meiosis
 Monosomy: when gamete has one less
chromosome than it should, when it joins
with another gamete the zygote would have
only 45 chromosomes
 Ex: Turner syndrome
Types of nondisjunction

Trisomy: when
gamete has one
more chromosome
than it should; when
it joins with another
gamete, the zygote
would have 47
chromosomes
 Ex: Down’s
syndrome, extra #21
Describe methods of detection
 Ultrasound:
sound waves are used to
generate an image of the unborn child.
Used to detect abnormalities of limbs,
organs, etc.
 Also called sonogram
 Amniocentesis:
fluid surrounding the
fetus is drawn out by needle, fetal cells
are collected and grown in a lab.
Chromosomes can be then karyotyped
 Chorion
villi sampling: a sample of the
chorion (membrane surrounding fetus)
is taken, chemical tests and karyotyping
are performed
 Karyotyping:
pictures of chromosomes
are matched up according to size
Quiz 1
A ___ mutation occurs when part of a
chromosome is lost.
a. chromosomal
b. crossing over
c.point
2. In ___ a gamete has one less chromosome than
it should .
a. disomy
b. monosomy
c. trisomy
3. ___ occurs when chromosomes overlap and
genes change places.
a. chromosomal
b. crossing over
c. point
4. In ___ a needle withdraws a small amount of fluid
from around the fetus for testing.
1.
a. amniocentesis
5.
b. chorion villi sampling
c. ultrasound
In ___ pictures of chromosomes are cut out and
matched up in pairs.
a. DNA fingerprint
b. karyotyping c. ultrasound
Interpret
testcrosses (14-1)





Testcross: way of
determining genotype
Cross individual of unknown
genotype with homozygous
recessive
If all offspring resemble
“unknown” then it is
homozygous dominant
If some offspring resemble
homozygous recessive
parent, unknown is a hybrid
Testcrosses are used in
breeding plants and
animals if a certain offspring
is needed
Interpret pedigrees

Pedigrees: graphic
representation of
family tree
 Symbols identify
sex, if they are
carriers, if they have
a certain trait, etc.
 May be used if
testcross cannot be
made