Transcript Academic Biology Chapter 12 Inheritance and Human

GENETIC PATTERNS
-Thomas Hunt Morgan –
breeding experiments with
DROSOPHILA - fruit fly
Studied because…
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easy to keep
generation time 10-15 days
produce hundreds of offspring
easy physical characteristics
only 8 chromosomes to look at
Observed that of 4 pairs of homologous
chromosomes :
- one pair different in male and female
Females:

pair were same
 longer was called the “X”
Males:
 pair
were different
 short and hook- shaped
 referred to as the “Y”
Discovery of the Sex
Chromosomes
*He correctly hypothesized that
the X & Y were SEX
CHROMOSOMES.
All others chromosomes are
referred to as AUTOSOMES
SEX-LINKED TRAITS
-Traits
determined by
alleles on the sex
chromosomes
Ex: fruit fly eye color
-Only males had white eyes
-The Allele for red was
carried on the “x”
LINKAGE GROUPS
Group of genes located on one
chromosome
-Morgan’s experiments showed that the
same traits are usually inherited together.
-The number of linkage groups equals the
number of chromosome pairs.
CROSS-OVER
The exchange of alleles between
homologous chromosomes
Alfred Sturtevant
Used crossing-over data
to construct a
CHROMOSOME
MAP.
-Maps are created by
comparing frequency
of cross-over for three
characteristics.
MAP UNITS
1 percent of cross-over is equal to
one map unit.
EX: if cross over happens 10% of
the time the alleles are separated
by 10 map units.
**Used to show the actual position
of alleles in chromosomes
MUTATIONS:
A
change in DNA at the genes or
in the chromosomes themselves.
GERM CELL mutationmutation of the sex cells, passed
to offspring
SOMATIC CELL mutationmutation of body cells, passed to
the daughter cells.
CHROMOSOME MUTATIONS
-Often
occur during cell division
-Mutations occur from…
A) changes in the chromosome
structure
B) loss of an entire chromosome
 *Most
mutations are harmful LETHAL MUTATION. They don’t
allow the organism to develop
beyond a zygote
MUTAGENS
 Described
as environmental factors
that damage DNA
 Ex:
4 ways
mutations occur
DELETION:
 Piece of
chromosome
breaks off and is
lost
1.
2. INVERSION:
chromosome
breaks off and
reattaches
itself in the
reverse
orientation
3. TRANSLOCATION:
A broken piece of chromosome
attaches to a non-homologous
chromosome
4. NONDISJUNCTION:
A replicated chromosome pair fails
to separate during cell division
(one daughter cell receives an extra
copy, other cell lacks chromosome)
GENE MUTATIONS
Involve single nitrogen
base within a
CODON, or larger
segment of DNA
1. POINT MUTATION:
The substitution ,
addition, or deletion
of a single nitrogen
base.
2. FRAMESHIFT
MUTATION:
A point mutation that
results only from an
addition or deletion
of a nitrogen base

Causes the genetic
message to be read
out of sequence
Mutations of the Genetic Code
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GLUTAMIC
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Gene Mapping
12-2: HUMAN GENETICS
Not as easily studied as
Morgan’s flies because…
1. Takes long time to
produce generations
2. Humans produce low #
of offspring
3. Some of the means of
study are unethical
MEANS OF STUDYING
HUMAN GENETICS
Population Sampling
 Study in which researchers
select a small # of individuals
to represent a whole
population
1.
2. Twin Studies
Study of identical
twins
 Used to
distinguish
between genetic
and
environmental
influences on
specific traits
3. Pedigree Study
A family record that shows how a trait is
inherited over generations.
*Reveals a CARRIER for specific traits they are Heterozygous
HUMAN GENETIC
TRAITS
1. Single Allele
Traits
 Trait is
controlled by a
single allele of a
gene.
EX: Sickle-Cell
Anemia
A. SICKLE-CELL ANEMIA

Change in the shape of the RBC:
 Results in anemia, clogs, pain,
decreased blood flow, death….
 Primarily effects African American
population
 1 in 500 births in USA
A = Normal
A’ = Sickle Cell
B. HUNTINGTONS DISEASE

Caused by dominant allele
 30-40’s, forgetfulness, loss of muscle
control, mental illness, death
 genetically programmed
degeneration of brain cells
*Can be detected by identifying short
sections of DNA known as
GENETIC MARKERS
C. TAY-SACHS DISEASE
Recessive Disorder
 fatty substance accumulate
in the nerve cells of the brain
 A child becomes blind, deaf,
and unable to swallow.
Muscles begin to atrophy and
paralysis sets in
 Children usually die by age 5

D. CYSTIC FIBROSIS
 Body
produces an abnormally
thick, sticky mucus
 Faulty transport of salt within
cells of organs such as the lungs
and pancreas
 very salty-tasting skin;
 persistent coughing,
 wheezing or pneumonia;
 excessive appetite but poor
weight gain
1
D. CYSTIC FIBROSIS
in 2500 people
are born with it
 More than 10
million people
2. Polygenic
Traits:
-Trait that is
controlled by two
or more genes.
Examples:
 skin color
 eye color
 fingerprints
3. Multiple Allele Traits:
-Trait that is controlled
by three or more alleles
for the same gene that
code for a single trait
Ex: Human blood type
-The combination of the
alleles determines the
ANTIGENS that are
produced by the body.
4. SEX-LINKED TRAITS
Traits with alleles found on the “X”
chromosome
-Males are more likely to express recessive
sex-linked alleles because the single “X”
has nothing to hide/mask the trait
Examples:
 Colorblindness
 Hemophilia
5. SEX-INFLUENCED TRAITS
-A trait that is expressed because of the
presence of male or female sex hormones
-Alleles that code for these are on the
autosomes
-Both males and females have same allele,
but the trait is only expressed in one of the
sexes
Ex: Pattern Baldness
B=dominant in males
B’=recessive in females
6. NONDISJUNCTION
Failure of chromatids
to separate during
cell division
 MEIOSIS
results in
an egg or sperm with
extra or missing
chromosomes
MONOSOMY
Condition where
the zygote has
only 45
chromosomes
Examples:
 Turner
Syndrome (XO)
 CRI-DU-CHAT
SYNDROME
TRISOMY

A condition where the
zygote has 47
chromosomes
Examples:
 Supermale
(XYY)
 Klinefelters
Syndrome (XXY)
DOWNE’S SYNDROME (trisomy)
Extra 21
PATAU SYNDROME (trisomy 13)
EDWARDS SYNDROME (trisomy 18)
DETECTING GENETIC
DISORDERS
Genetic Screening The examination of a persons
genetic make-up…
 Can determine genetic
disorders if they have a
history of problems in their
family
Fetoscopy

Tiny camera into the uterus
Karyotyping Picture
of a persons chromosomes
AmniocentesisRemoval
of amniotic fluid
Chorionic Villi Sampling
tissue
between
uterus
and
placenta
Ultrasound
High
frequency sound waves =
picture
Genetic Counseling