BIOLOGY CH14 PPT OL
NAME__________________________
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CHAPTER 14: Genes in Action
Essential Questions:
What is A Mutation?
What Causes Mutation?
What is the origin of genetic differences among organisms?
What types of mutations are possible?
How can genetic change occur on a larger scale?
How will Modern Technology in DNA affect us?
Gene Mutations
A Mutation is a change in the _____________________________________ within a gene
Changes to DNA are called mutations
Change the DNA
Changes the mRNA
May change protein
May change trait
What Causes Mutations:
Mutations can be spontaneous or caused by environmental influences called___________________________
Mutagens include radiation (X-rays, UV radiation), and organic chemicals (in cigarette smoke and
pesticides).
Q1. WHICH MUTAGEN ARE YOU MOST LIKELY TO BE EXPOSED TO TODAY?
Origins of Genetic Difference
MUTATION is the origin differences among organisms
For the most part, genetic differences among organisms originate as some kind of mutation.
A genetic mutant is one whose DNA or chromosomes differ from some previous or ______________________state.
Every unique allele of every gene began as a mutation of an existing gene.
In genetics, a mutation is a change in the structure or amount of the protein produced
Q2. WHAT DOES IT MEAN TO BE NORMAL?
Effects of Mutations
–Because of the way DNA is translated, a mutation can have many possible effects.
–A small change in DNA may affect just one ______________________________ in the protein that results from a gene.
–A mutation may have no effect, or may harm or help in some way.
–The effect depends on where and when the mutation occurs.
–Mutations are noticed when they cause an unusual trait or disease, such as sickle cell anemia.
–Many mutations may go unnoticed.
Q3. NAME AN AMINO ACID?
2 Types of Mutations
There are essentially 2 types of Mutations
Point mutations & Frameshift Mutations
__________________________ mutation
change to ONE letter (base) in the DNA
may cause change to protein, may not
__________________________ mutation
addition of a new letter (base) in the DNA sequence
deletion of a letter (base) in the DNA
Both shift the DNA so it changes how the codons are read
BIG changes to protein
Q4. WHICH LETTER OF A CODON IS MOST IMPORTANT IN MUTATION?
3 Types of Point Mutations
1. A _______________________________________ mutation - the change in the codon results in the same amino acid
Ex: UAU  UAC both code for tyrosine
2. A ____________________________ mutation - a codon is changed to a stop codon; protein may be too short to function
Ex: UAC  UAG (a stop codon)
3. A ____________________________________ mutation - involves the substitution of a different amino acid, the result
may be a protein that cannot reach its final shape
Ex: Hbs which causes sickle-cell disease
Sickle cell anemia
Hemoglobin protein in red blood cells
strikes 1 out of 400 African Americans
limits activity, painful & may die young
Q5. WHAT DOES HEMOGLOBIN DO?
Frameshift Mutations
The reading frame of a sequence depends on the starting point for reading. An insertion or deletion can shift the
reading frame, or cause a frameshift.
In __________________________ mutations, the remaining sequence may be “read” as different codons.
Mutations as Changes in Results of Genes
–If an insertion or deletion is a multiple of 3, the reading frame will be preserved. However, the protein that
results may have a few more or less amino acids in it.
–An insertion or deletion of many codons is likely to disrupt the resulting protein’s structure and function.
Q6. IS A FRAMESHIFT MUTATION LIKELY TO PRODUCE A PROTEIN WITH ANY FUNCTION? WHY?
Frameshift Mutations
•
Add or delete one or more bases - changes the meaning of the whole protein
Frameshift Mutations
•
Addition = add one or more bases
Frameshift Mutations
•
Deletion = lose one or more bases
Deletion Mutation: Cystic Fibrosis
•
Mutated salt channel protein in cell
LARGE-SCALE GENETIC CHANGE
5. How can genetic change occur on a larger scale?
Very large-scale genetic change can occur by misplacement, recombination, or multiplication of entire
chromosomes.
Chromosomal Mutations
During meiosis, chromosomes pair up and may undergo crossover. Usually, the result is an equal exchange of
alleles between homologous chromosomes.
Errors in the exchange can cause chromosomal mutations.
Chromosomal Mutations
A deletion occurs when a piece of a ________________________________ is lost. At the end of meiosis, one of the cells will
lack the genes from that missing piece. Such deletions are usually harmful.
A duplication occurs when a piece remains attached to its homologous chromosome after meiosis. One
chromosome will then carry both alleles for each of the genes in that piece.
An inversion occurs when a piece reattaches to its original chromosome, but in a reverse direction.
A translocation occurs when a chromosome piece ends up in a completely different, nonhomologous
chromosome.
EFFECTS OF GENETIC CHANGE
What are the possible effects of mutations?
The results of genetic change may be harmful, beneficial, or __________________________; most changes are neutral
and may not be passed on to offspring.
Q7. ARE MOST CHANGES TO DNA BENEFICIAL- NEUTRAL – OR HARMFUL?
EFFECTS OF GENETIC CHANGE
Many genetic changes will cause no change in the appearance or function of organisms.
Mutations that occur in gametes can be passed on to offspring, but mutations in body
cells affect only the individual in which they occur.
The Formation of New Alleles
For a given gene, many alleles, or variations, may exist.
Any new allele must begin as a mutation of an existing allele.
Most new alleles are simply the result of silent mutations, so these changes make little difference to the
organisms in which they occur.
Sometimes a new allele can cause a change in a gene’s function, a result that may be harmful or
beneficial to the organism.
Q8. HOW MANY BLUE EYE GENES ARE THERE IN YOUR CLASSROOM?
Genetic Disorders
Harmful effects produced by inherited mutations (defective alleles) are called genetic _________________________.
Often, such a disorder results because a mutation has altered the normal function of a gene.
However, a person may still have one allele of the original, functioning gene.
Many disorders are recessive—that is, the disorder develops only in a person who is homozygous for the
mutated allele.
Two heterozygous people may be healthy, yet have children who develop a genetic disorder.
A person who is heterozygous for such an allele is said to be a carrier of the disorder.
LARGE-SCALE GENETIC CHANGES
How can genetic change occur on a larger scale?
Accidents can happen to entire sets of chromosomes.
Very large-scale genetic change can occur by misplacement, recombination, or multiplication of entire
chromosomes.
Recombination During Crossover
Genetic recombination through sexual reproduction has many important consequences.
During the crossover step of Meiosis in Prophase I the alleles from one parent are recombined with the alleles
from the other parent, creating new combinations of alleles in offspring.
Over time, sexual reproduction and meiotic recombination maintain genetic variety within a population.
Q9. WHEN DOES CHROMOSOMAL RECOMBINATION OCCUR
Some Common Genetic Diseases
Huntington’s Disease: Autosomal dominant
Neuromuscular disease; degeneration of muscle, onset in early 30’s.
Cystic Fibrosis: Autosomal Recessive;
Defective Protein is made that creates excess mucus; clogs lungs.
Color Blindness: Sex-linked recessive
Inablity to distinguish colors (8% of male population)
Hemophilia: Sex-linked recessive
Inablity of blood to clot
Muscular Dystrophy: Sex-linked recessive
Loss of muscle that begins in early childhood
Tay-Sach’s Disease : Autosomal Recessive
Degeneration of Central Nervous System; infant mortality
Q10. NAME A GENETIC DISEASE NOT LISTED ABOVE AND DESCRIBE SOME OF THE EFFECTS
Changes in Chromosome Number
•
Nondisjunction – occurs when:
– In meiosis I, homologous pair both go into the same daughter cell or
– In meiosis II, the sister chromatids both go into the same gamete.
•
The result:
– Trisomy (3 copies of a single chromosome) or
– Monosomy (1 copy of a single chromosome)
•
Nondisjunction in Meiosis I
Changes in Chromosome Structure
•
Chromosome mutation - a change in chromosome structure
•
Radiation, organic chemicals, or even viruses may cause chromosomes to break, leading to mutations.
•
Types of chromosomal mutations:
Inversion
Translocation
Deletion
Duplication.
Chromosomal Deletions
•
Deletions occur when a single break causes a lost end piece, or two breaks result in a loss in the
interior.
•
An individual inherits a normal chromosome from one parent and a chromosome with a deletion from
the other parent
•
No longer has a pair of alleles for each trait
•
A syndrome can result – type depends on chromosome(s) affected.
Chromosomal Deletion :Williams Syndrome
•
Chromosome 7 loses an end piece
•
Children have a pixie look (turned-up noses, wide mouth, small chin, large ears)
•
Poor academic skills, good verbal and musical abilities
•
Skin ages prematurely from lack of the gene that controls the production of elastin (also
affects cardiovascular health).
Chromosomal Duplication
•
Duplication results in a chromosome segment being ________________________ in the same chromosome
•
Ex: An inverted duplication in chromosome 15 causes inv dup 15 syndrome
•
Poor muscle tone, mental retardation, seizures, curved spine, and autistic characteristics
Chromosome Translocation: Alagille Syndrome
•
Translocation is exchange of chromosomal segments between two, non-__________________ chromosomes.
•
Ex: Alagille syndrome results from a deletion of chromosome 20 or a translocation that
disrupts an allele on chromosome 20.
•
Distinctive face, abnormalities of eyes & internal organs, and severe itching.
Chromosome Inversion
•
Inversion involves a segment of a chromosome being turned __________ degrees
•
The reverse sequence of alleles can alter gene activity.
•
Crossing-over between inverted and normal chromosomes can cause duplications and
deletions in resulting chromosomes.
DNA Technology and Modern Medicine
•
The Human Genome Project Decoded an entire length of DNA in 2003
•
The Genetic Sequencing allows for improvements in the detection and treatment of genetic disease and
cancer.
•
Gene Therapy is a technology in which good copies of a gene are introduced into those individuals
affected by genetic disease
BIOLOGY CH14 PPT OL
CHAPTER 14: Genes in Action Condensed Study Guide
Essential Questions:
NAME__________________________
1.What is A Mutation?
A Mutation is a change in the sequence of DNA within a gene
2. What Causes Mutation?
Mutations can be spontaneous or caused by environmental influences called mutagens.
Mutagens include radiation (X-rays, UV radiation), and organic chemicals (in cigarette smoke and pesticides).
3. What is the origin of genetic differences among organisms?
Genetic differences among organisms originate as some kind of mutation.
A genetic mutant is an individual whose DNA or chromosomes differ from some previous or normal state.
Every unique allele of every gene began as a mutation of an existing gene.
In genetics, a mutation is a change in DNA that results in a change in the structure of the protein produced
4. What types of mutations are possible?
There are essentially 2 types of Mutations- Point mutations & Frameshift Mutations
Point mutation
•
change to ONE letter (base) in the DNA
•
may cause change to protein, may not
1. Silent mutation - the change in the codon results in the same amino acid
Ex: UAU  UAC both code for tyrosine
2. Nonsense mutation - a codon is changed to a stop codon; resulting protein may
be too short to function
Ex: UAC  UAG (a stop codon)
3. Missense mutation - involves the substitution of a different amino acid, the
result may be a protein that cannot reach its final shape
Frameshift mutation
•
Addition of a new letter (base) in the DNA sequence
•
Deletion of a letter (base) in the DNA
•
Both shift the DNA so it changes how the codons are read
•
BIG changes to protein
5. How can genetic change occur on a larger scale?
LARGE-SCALE GENETIC CHANGES
Recombination During Crossover
Genetic Diseases
Changes in Chromosome Number
Changes in Chromosome Structure- Deletions , Duplication, Translocation, Inversion
6. How will Modern Technology in DNA affect us?
DNA Technology and Modern Medicine
The Human Genome Project
The Genetic Sequencing
Gene Therapy