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Chapter 12
Mutations, Xs, and Inheritance
Mutations= changes in organisms
DNA
• Beneficial- lead to adaptations and aid
evolution of a species
• Harmful- the worst are lethal
Types of Mutations
1.cellular mutations;
a. germ cell mutation-change is in the gametes
so it affects the offspring and not the parent
organism
b. somatic cell mutation-change is in an
organism’s body cells will affect the organism
but not the offspring
ex; certain types of skin cancer, leukemia
Chromosome mutations
1. Deletion- loss of part of X so missing
genes and lack info
2. Inversion- one X breaks off a part and
attaches in a reverse pattern
3. Translocation- X part breaks off and
reattaches to a non-homologous X
4. Nondisjunction- Xs do NOT separate
during anaphase of meiosis so one
gamete gets too many Xs and gets too
few
Gene mutations(DNA---mRNA---aa---protein)
point mutation- if only 1 base is affected
1.
2.
3.
–
Substitution
Insertion
Deletion
#2 and #3 cause a change in the codon sequencecalled frameshifts
Ex. THE CAT ATE THE RAT
TTH ECA TAT ETH ERA T
TEC ATA TET HER AT
Genetics Traits
1. Single allele traits;
a. Dominant allele Ex- Huntington’s Disease
-HH or Hh will develop disorder
-hh is normal
-genetic marker used to ID
b. Recessive allele
-Heterozygous will give a carrier
Ex 1- cystic fibrosis
FF- normal Ff- carrier
ff- normal
Ex 2- sickle cell anemia
AA- normal Aa- carrier
aa- diseased
Genetic researcher Thomas
Morgan
•
Worked with fruit flies,
Drosophila melanogster
• Why fruit flies?
1. chromo. # = 8 (4 pairs)
2. Reproduce quickly
3. Males and females look
differentt
• Observations
1. males not like females
2. females had 2 XX and
males had 1 X and 1Y
3. called this the sex
determining pair
4. other 3 prs. alike in both
sexes (autosomes)
5. Had either red or white
eyes
Morgan’s experiment with eye color
• Took a male with white eyes and crossed
it with a red eyed female.
• Result was that ALL offspring had RED
eyes!!!(F1)
• Crossed 2 offspring together and got 3
Red eyed:1 white eyed; however ALL
white eyed flies were males this time!!!
• Why did that happen????
The Answer
• Sometimes a gene appears only on the X or Y
chromosome
• These genes are called sex linked genes
• Ex-Drosophila eye color, 2 possible alleles
red (R) or white (r)
• Allele only on the X chromo.
•
Genotypes= X R X R or X R Xr = red eyed females
XrXr = white eyed females
XRY = red eyed males
XrY = white eyedmales
Morgan’s 2nd Experiment
• Hypothesized that genes that are inherited
together are found on the same
chromosome
• Studied body color (GRAY vs. black) and
wing length (LONG vs. short)
• Crossed GGLL x ggll
• What do you think he got???
Answer to GGLL x ggll
• In the F1 all were GgLl (GRAY, LONG
wings)
• Morgan then crossed GgLl x GgLl
• Results were 3 GRAY, LONG :1 black,
short
• Expected 9:3:3:1, instead results are
always 3:1 for two characteristics
• So Morgan concluded that these were
“Linked Genes”
Linked Genes
• If known linked genes do NOT follow a predicted pattern
they may have crossed over during meiosis
• Ex.- pigmentation of human eye, hair, and skin color
• Chromosome maps• Determine how far apart genes are on a chromosome
• Geneticists use frequency
• (%) of cross-overs in offspring to determine distance
between genes
• called map unit
• Rule; for every 1% of crossovers the genes are 1 map
unit apart (p.224)
Chromosome Mapping
• Geneticists use
frequency(%) of
cross-overs in
offspring to determine
distance between
genes
• called map unit
• Rule; for every 1% of
crossovers the genes
are 1 map unit apart
(p.224)
12-2 Pedigrees
• used to study the inheritance of a trait
through many generations
• patterns of phenotypes can be followed
using a chart
Genetics Traits
2. X-linked Traits
Allele on X chromosome
• 2 needed for female phenotype
• 1 allele for male phenotype
• Ex- color blindness, hemophilia and
Duchenne MD
3. Sex Influenced Traits
• Phenotype affected by sex hormones
• Ex- Baldness
•
BB is bald in male and female
• Bb is bald only when testosterone present
• bb- no baldness
Genetic Traits
4. Multiple Allele Traits
• Determined by three or more alleles
• Ex- ABO blood type
• Alleles- A and B (codominant)
• O recessive
4 Phenotypes : Possible genotypes
Type O
OO
Type A
AO, AA
Type B
BO, BB
Type AB
AB
Genetic Traits
• 5. Polygenic Traits
Controlled by 2 or more genes
Ex- melanin amounts
In Hair, skin, eye color
Genotypes- AABBCC- darkest
AaBbCc- lt brown
aabbcc- lightest
Genetic Testing
• Before a fetus is born
A. Amniocentesis- takes sample of amniotic
fluid.
- can only be done week
14-16
B. Chorionic villi- taken from chorionic villi
- can only be done week
8-10
• Both require a karyotype be done after
cells are samples.
Genetic Diseases and Counseling
• Refer to page 246-247
• http://www.youtube.com/watch?v=goEZ7f
eoZVk
Gene Therapy
• Gene Therapy – a technique that replaces
a defective gene with a healthy gene.
-has been used to treat
cystic fibrosis
• 2 types of gene therapy
1. somatic cell- body cells are changed
2. germ cell- changes to egg and sperm