Genetic Variation and Mutation
Test Review
SEX CHROMOSOMES
XX---Female
XY---Male
Multiple Alleles
• Traits that have more than 2 phenotypes
• Example Blood Type
• A, B, O
• Sex-linked traits occur more often in males--ex hemophilia and colorblindness
•
•
•
•
How to find a genetic disorder?
a. analysis of pedigree
Genetic counseling
Prenatal testing
• Pedigree Basics… Squares are males
Circles are females….colored in shapes
have trait….non---colored do not have trait
Crossing Over
• When chromosomes exchange genetic
information that leads to more varations in
the population
Gives most variation in a population…
• Crossing over
• Recombination of parents genes through--Sexual reproduction (MEIOSIS)
• Mutations
• Organisms with different traits that cross
produce more variations in their offspring
• Populations with many different
traits/variations have a better chance to
survive---especial when the environment
changes
• Mutations can lead to variations in a
population because they change an organism’s
PHENOTYPE
Mutations
• A mutation is ANY change in the DNA that
causes a change in the phenotype or
appearance
• They can be harmful, helpful or neutral
Nonsense Mutation
• When the nucleotide/base of DNA is changed
and this causes the codon to be translated
into a STOP codon instead of amino acid
• Creates a protein we cant use
Silent Mutation
• When a nucleotide/base is changed but is
translated as the same amino acid….causeing
no problems
• Missense Mutation
• When a nucleotide/base is changed…causing
the codon to be translated into a DIFFERENT
amino acid causing problems
Frame shift Mutations
• When you insert one or more
nucleotides/bases into the DNA strand causing
the codons and reading of those codons to
shift
• Also can happen when one or more
nucleotide/base is deleted….
Nondisjunction
• Failure of chromosomes to separate during
Meiosis
• Causes Monosomy---one less chromosome in
cell
• Causes Trisomy---one more chromosome in
the cell
• Example Down Syndrome, Edward’s Syndrome
and Klinefelter’s
• Body cell mutations:
• Affect the person with it….such as mutated
skin cells…when they divide they pass on the
mutation to that new skin cell.
• Cant be passed on because they do not affect
the egg and sperm…AKA Gametes
• Germ cell mutations or mutations of the
gametes…results in the offspring’s phenotype
being changed.
Chromosomal Mutations
• Inversion----piece of chromosome breaks off and
reattaches to the SAME in the reverse order
• Deletion---piece of chromosome breaks off and is
gone
• Translocation---piece of chromosome breaks off
and reattaches to the DIFFERENT in the reverse
order
• OPEN ENDED
QUESTIONS….Know them….
X-linked Cross
• Normal Female----carrier
• Normal Male
• XN Xn
• XN Y
Results: XN XN 50% females normal
noncarriers
XN Xn 50% females normal carrier
Xn Y 50% All males with disorder
XN Y 50% All males normal
•
•
•
•
•
•
•
•
•
•
•
•
Sex-Linked Traits
Found on SEX CHROMOSOMES…usually X
Both sexes can have trait…males more likely
Hemophilia and Colorblindness
Sex Limited Traits
THIS IS THE CHART
Found on Autosomes
Only 1 sex expresses the trait
Beard growth or Milk Production
Sex-Influenced Traits
Found on Autosomes
Both sexes……
Baldness
• STUDY Nondisjunction Notes….
• GET OUT YOUR NOTES AND
LOOK AT THESE PICTURES
• KARYOTYPE Pictures for
• Monosomy, Trisomy and DIPLOID