Transcript Understanding Our Environment

Mutations
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Mutations and Genetic Disorders
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A mutation is a mistake in the DNA code.
Genetic disorders are the harmful effects
caused by mistakes in the DNA code.
 Most disorders are rare because affected
individuals often die at a relatively young
age, or cannot reproduce.
 Most, but not all mutations, are recessive.
- Huntington’s Disease is dominant
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Mistakes during Replication
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Frame shift
mutation-reading
frame is moved
up or down
depending on
whether a base is
added or removed
from the
sequence
 Base Insertion
 Base Deletion
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Substitution
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•
Substitutions
result when the
wrong nucleotide
base moves in to
the space
May or may not
result in a
genetic disorder
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Genetic Recombination
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Crossing Over
If 2 genes are located
far apart on a
chromosome, crossing
over is more likely to
occur than if they are
close together.
Frequency of crossings
can be used to
construct a genetic
map.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Abnormalities Due to Chromosome Number
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Failure of chromosomes to separate correctly
during meiosis I or II is called primary
nondisjunction.
 Down Syndrome caused by trisomy 21.
- 1 in 1700 for mothers < 20.
- 1 in 1400 for mothers >20<30.
- 1 in 750 for mothers >30<35.
- 1 in 16 for mothers >45.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Nondisjunction in Sex Chromosomes
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X Chromosome
 XXX or XXY yields Klinefelter syndrome
 XO yields Turner Syndrome
Y Chromosome
 XYY – Antisocial ?
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Gene Disorders Due to Protein Alteration
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Sickle-Cell Anemia is a recessive inherited
disorder in which afflicted individuals have
defective hemoglobin, and thus are unable to
properly transport oxygen to tissues.
 Homozygotes have Sickle-Cell.
 Heterozygotes usually appear normal, but
are resistant to malaria.
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Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Curable Defects
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Cystic Fibrosis
 Body cells of affected individuals secrete
thick mucus that clogs airways of lung and
affects digestion.
- Defect in cf gene.
 Researchers currently working on
methods of transmitting a working
copy of cf gene via viruses.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Pedigrees
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Mutations are accidental changes in genes.
 Rare, random, and usually result in recessive
alleles.
- Pedigrees used to study heredity.
 Hemophilia - Inherited condition where blood is
slow to clot or does not clot at all.
 Only expressed when individual has no
copies of the normal allele.
 Royal Hemophilia - Sex-linked
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Genetic Counseling
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Genetic counseling identifies parents at risk
of producing children with genetic defects
and assesses the state of early embryos.
High-Risk Pregnancies
 Couples with recessive alleles.
 Mothers older than 35 years.
- Amniocentesis
- Chorionic villi sampling
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies