Transcript Chapter 12

http://worms.zoology.wisc.edu/zooweb/Phelps/karyo.jpeg
Inheritance Patterns
and Human Genetics
A. Trait coded for by an allele on a sex chromosome
1. Sex chromosomes B. The X and Y chromosomes
C. Diagram that shows the order of genes on a
2. Autosomes
chromosome
3. Sex-linked trait
D. Pairs of genes that are inherited together
4. Linked gene
E. All chromosomes except the X and Y
5. Chromosome map F. Type of mutation where one nucleotide replaces
6. Map unit
another
G. Chromosome piece breaks off, flips and reattaches
7. Deletion
H. Chromosomes fail to separate from their matching
8. Inversion
partner
9. Translocation
I. A piece of one chromosome breaks off and
10.Nondisjunction
attaches to another
11.Substitution
J. 1% frequency of cross-over in a chromosome
K. Loss of a piece of chromosome due to breakage
12.Germ-cell mutation
13.Somatic-cell mutation
14.Lethal mutation
15.Point mutation
16.Frameshift mutation
17.Insertion mutation
L. Genetic mutation that causes death
M. Genetic mutation in a body cell
N. Genetic mutation in a gamete cell
O. Mutation in which nucleotides are added
to a gene
P. Any mutation that affects the order and
grouping of all nucleotide bases that
occur after the mutation
Q. Any mutation that occurs in a single gene
1. Sex chromosomes
2. Autosomes
3. Sex-linked trait
4. Linked gene
5. Chromosome map
6. Map unit
7. Deletion
8. Inversion
9. Translocation
10. Nondisjunction
11. Substitution
12. Germ-cell mutation
13. Somatic-cell mutation
14. Lethal mutation
15. Point shift mutation
16. Frameshift mutation
17. Insertion mutation
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http://www.internetphotos.net/wp-content/uploads/2008/08/human-chromosome.jpg
To understand human genetics, we must first
understand chromosomes.
Chromosomes are structures made of DNA and
proteins that carry heredity information and direct
the activities of cells.
Humans have 23 matching pairs of chromosomes
(46 total)
Thomas Hunt Morgan
discovered that one
pair of chromosomes
determines the sex of
an animal while
studying fruit flies.
Called the X and Y
chromosomes, or sex
chromosomes.
XX = female
XY = male
Charts that show and individual’s full set of
chromosomes are called karyotypes
http://nuclearfamilywarhead.com/wp-content/uploads/2008/04/chromosomes.jpg
The other chromosomes are
known as autosomes.
The sex chromosomes
separate along with the
other 22 pairs of
chromosomes when sperm
and egg cells form during
meiosis.
Therefore, each egg cell
contains an X chromosome.
Sperm cells can contain an X
or a Y.
So, it is the father that
determines the sex of the
child.
http://www.zuniv.net/physiology/book/images/29-1.jpg
The Y chromosome
contains a gene called
SRY (Sex-determining
Region Y). It produces
a protein that causes
the development of
testes. Without this
protein, reproductive
organs will develop into
ovaries.
http://www.nature.com/scitable/nated/content/18935/pierce_4_10_mid_1.jpg
 During Morgan’s experiments he
discovered something odd. Examine
the diagram and try to figure out
what’s going on???
 Crossing a red eyed fly with a white
eyed fly produces all red eyed flies.
 What does this tell us about the genes
for red and white eyes??
 If white is recessive, then we should
get ¼ white eyes in the second
generation—and we do!!
 But…..they are all males!!!! Why???
 Answer: Sex-Linked Traits
http://knight.noble-hs.sad60.k12.me.us/content/exploringLife/text/chapter10/10images/10-16.gif
Sex-linked traits are traits that are carried on a
sex chromosome
Morgan called sex-linked traits:
 X-linked (carried on the X chromosome)
 Y-linked (carried on the Y chromosome)
Most are carried on the X chromosome and are
therefore more common in males.
This is because the matching information on the
Y chromosome is missing.
Examples: Color-blindness and Hemophilia
Normal woman marries a color blind man
XX
x
XcY
X
X
Xc
Xc X
XcX
Y
XY
XY
There is no chance any of their children will be colorblind.
However, any girl they have will be a carrier.
(Carrier = carries genetic information without showing the trait)
GgLl
 Once again, Morgan
discovered something odd
while studying his fruit
flies.
 He found two dominant
genes (gray body and long
wings) did not assort
independently as
predicted in Mendel’s pea
plant experiments.
 What’s going on???
 Answer: Linked Genes
 These genes are carried on
the same chromosome
X GgLl
Result: 3 Gray, long wings : 1 black, short wings
RrYy X RrYy
Result: 9:3:3:1 9 round/yellow
3 round/ green
3 wrinkled/yellow
1 wrinkled/green
 Chromosome map —
diagram that shows the
linear order of genes on a
chromosome.
 Developed by using the
results of breeding
experiments and by
looking for the percentage
of crossing-over for two
traits.
 The higher the percentage
of crossing-over, the
farther away two genes are
on a chromosome
 Map unit —frequency of
1% cross over
Mutation—a change in the nucleotide-base sequence
of a gene or DNA molecule.
Types:
Germ-cell mutation —occur in gametes/do not
affect the organisms/can be inherited
Somatic-cell mutation —occur in body cells/do
affect the organisms/can not be inherited
Lethal mutations —cause death, usually before
birth
Beneficial mutations —improve chance of
survival/provide variation in natural selection
http://www.montana.edu/wwwai/imsd/diabetes/mutation.gif
 Mutations that involve an entire
chromosome
 Types:
 Deletion—loss of a piece of
chromosome due to breakage
 Translocation—part of a
chromosome breaks off and
attaches to another
chromosome
 Inversion—part of a
chromosome breaks off, flips,
and reattaches
 Nondisjuction—a
chromosome fails to separate
from its partner during meiosis
 Point mutation —change
that occurs within a single
gene
 Types: Substitution,
Deletion, or Insertion
 Substitution—one
nucleotide replaces
another/result in the
production of a different
amino acid
 Deletions and Insertions
do not always result in
point mutations. More
commonly, they result in
Frameshift Mutatons.
DNA
mRNA
C
T
T
G
A
A
C
A
T
G
U
A
Amino acid
Glutamic
acid
Valine
DNA
 Frameshift mutation —
results after a deletion
has occurred. All
remaining codons are
incorrectly grouped
affecting all remaining
amino acids. This can
seriously damage the
protein.
 Can also occur after an
insertion of one or more
extra nucleotides occurs.
mRNA
Amino acid
A
C
Deleted G
U
G
C
C
T
C
G
A
G
Glutamic acid
G
T
C
C
A
G
Glutamine
Cysteine
T
DNA
A
C
C
A
mRNA
U
G
G
T
C
G
A
G
C
T
C
T
A
G
A
Amino acid
Tryptophan
Serine
Arginine
1. Pedigree
2. Carrier
3. Genetic disorder
4. Polygenic
5. Complex character
6. Multiple allele
7. Codominance
8. Incomplete dominance
9. Sex-influenced trait
10.Amniocentesis
11.Chronic villi sampling
12.Genetic counseling
13.Gene therapy
A. Characters influenced by both genes
and environment
B. Characteristics influenced by many genes
C. More than two alleles exist for a trait
D. Way of detecting genetic disorders by
extracting amniotic fluid
E. Intermediate traits (blending of two)
F. Way of detecting genetic disorders by
testing special cells derived from the zygote
G. Both alleles for a trait are expressed
H. Disabling conditions with a genetic basis
I. Diagram that shows inherited traits through
several generations
J. Have a recessive allele for a trait but do not
show the trait
K. Informing a person of their genetic makeup
L. Healthy genes replace defective genes
M. Male pattern baldness
1. Pedigree
2. Carrier
3. Genetic disorder
4. Polygenic
5. Complex character
6. Multiple allele
7. Codominance
8. Incomplete dominance
9. Sex-influenced trait
10.Amniocentesis
11.Chronic villi sampling
12.Genetic counseling
13.Gene therapy
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 Pedigree —diagram that
shows how a trait is
inherited over
generations.
 Can be used to trace the
occurrence of diseases as
well.
=male w/ trait
=female w/ trait
= carrier
Sex-linked
 Polygenic Inheritance —many genes control a single trait. Examples:
hair, eye and skin color, height, and fingerprint patterns
 Complex characters —characters that are influenced
strongly both by the environment and by genes
 Ex: skin color—both genetic and exposure to sun
 Height and weight—both genetic and diet or disease
 Some cancers
http://anthro.palomar.edu/adapt/images/skin_color_range.jpg
 Multiple alleles —more that two alleles exist for a trait in the population.
You still inherit only two—one from mom and one from dad.
 Ex: Blood type (Three alleles: IA, IB and i; produce four blood types: A,
B, AB, and O)
 IA and IB are codominant (both expressed in the phenotype)
 i is recessive
http://www.buzzle.com/images/blood-types/blood-types-chart.png
http://library.thinkquest.org/05aug/01576/images/bloodtypes.png
 Try to figure out the missing blood types. How many can
you determine for sure?
 Sex-influenced traits —males and females have the same genotype
but different phenotypes
 Ex: Male pattern baldness: The allele is dominant in men but
recessive in women due to different levels of testosterone
http://hairimplantsformen.com/pictures/male-pattern-baldness.jpg
 Genetic screening —examination of a person’s genetic makeup. Includes:
karyotypes, blood tests for proteins or DNA tests
 Genetic screening can be done even before birth:
 Amniocentesis —test of amniotic fluid
 Chorionic villi sampling —test of cells, derived from the zygote, that grow
between the uterus and the placenta
 Over 200 genetic disorders can be detected in a fetus using these techniques
Amniotic fluid sample
Chorionic villi sampling
 Genetic Counseling —medical guidance sought to determine
the likelihood of passing on a genetic disorder to a child.
Treating genetic diseases is difficult. Usually, we can only
treat symptoms.
 Gene Therapy is currently being studied as a way to cure
genetic diseases like Cystic Fibrosis. It has only been
somewhat successful in animal studies.
 Remove DNA core from a virus
 Inject good genetic material into the virus
 Allow virus to deliver the healthy DNA to cells