Chapter 12 Patterns of Inheritance - wou.edulemastm/Teaching/BI102/Chapter 12 - Inheritance (2).pdf1...
Transcript of Chapter 12 Patterns of Inheritance - wou.edulemastm/Teaching/BI102/Chapter 12 - Inheritance (2).pdf1...
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Chapter 12
Patterns of Inheritance
Chapter 12: Inheritance
Modern Genetic Concepts:
Locus
Locus: Specific location of a gene on a
chromosome
Allele: Alternate form of a nucleotide
sequence for a single geneLocus
Heterozygous (“different pair”)
• Homologous chromosomes having
different alleles for a given gene
What is Inheritance?
Answer: The passage of genes from parent to offspring
Homozygous (“same pair”)
• Homologous chromosomes having
the same alleles for a given gene
Locus
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Who is the Father of Modern Genetics?
Answer:
Johann Gregor Mendel
Chapter 12: Inheritance
• Same flower provides pollen and eggs
• True-breeding (homozygous)
Chapter 12: Inheritance
Pea Plant Ideal for Genetic Work:
1) Normally undergo self-fertilization
• Different flower provides pollen and eggs
• Controlled experimentation
2) Can undergo cross-fertilization (manually)
Figure 12.3 – Audesirk2 & Byers
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• Mendel raised true-breeders
for different forms of a trait
and then cross-fertilized the
forms:
• Mendel then allowed F1 generation
to self-fertilize:
Chapter 12: Inheritance
Inheritance of Single Traits:
Figure 12.4 / 12.5 – Audesirk2 & Byers
1) Traits are determined by pairs of discrete physical units
• Physical units = genes
• One allele of each gene / homologous chromosome
3) Alleles of a gene segregate from one another during meiosis
• Law of Segregation
• Which allele enters which gamete occurs by chance
2) Differing alleles can mask one another if occupying same cell
• Dominant Allele: Allele expressed (observed)
• Recessive Allele: Allele mask (not observed)
4) True-breeding individuals have two of the same alleles
• Hybrids have two different alleles for the gene
Chapter 12: Inheritance
Inheritance of Single Traits – Mendel’s Findings:
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Phenotype:
Outward expression of a trait(e.g., appearance, behavior)
Chapter 12: Inheritance
Inheritance of Single Traits:
Genotype:
Actual combination of alleles
carried by an individual
Figure 12.8 / 12. 9 – Audesirk2 & Byers
=
Chapter 12: Inheritance
Inheritance of Single Traits:
Arrgghh!
Figure 12.10 – Audesirk2 & Byers
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Keep in Mind:
Predicted proportions
will fluctuate in real life
Phenotype:
3 purple : 1 white
Genotype:
1 PP : 2 Pp : 1 pp
Chapter 12: Inheritance
Punnett Square Method: (“Genetic Bookkeeping”)
Figure 12.11 – Audesirk2 & Byers
Mendel’s hypothesis can be used to predict cross outcomes:
Crossing a dominant phenotype individual with a homozygous recessive
individual to determine the genotype of the dominant individual
Test Cross:
PP or Pp
pp
P P
p
p
Pp Pp
Pp Pp
P p
p
p
Pp
Pp
pp
pp
100% Purple 50% Purple / 50% White
Chapter 12: Inheritance
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• Mendel then allowed F1
to self-fertilize:
YySs
YYSS x yyss
YySs x YySs
• Mendel raised true-breeders
for different forms of two traits
and then cross-fertilized the
forms:
Chapter 12: Inheritance
Inheritance of Multiple Traits:
Figure 12.13 – Audesirk2 & Byers
Resulting ratio of self-fertilization:
9 Yellow, smooth seeds
3 Yellow, wrinkled seeds
3 Green, smooth seeds
1 Green, wrinkled seeds
9 : 3 : 3 : 1
Yy = Seed Color
Y y
S s
y
Y
Ss = Seed Texture
s
S
YY Yy
Yy yy
SS Ss
Ss ss
3/4 yellow
1/4 green
3/4 smooth
1/4 wrinkled
9/16 Yellow, smooth seeds
3/16 Yellow, wrinkled seeds
3/16 Green, smooth seeds
1/16 Green, wrinkled seeds
9 : 3 : 3 : 1
Chapter 12: Inheritance
Inheritance of Multiple Traits:
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Figure 12.15 – Audesirk2 & Byers
Law of Independent Assortment:
• The alleles for one trait may be distributed to the gametes independently
of the alleles for other traits
• Traits located on separate
chromosomes
Chapter 12: Inheritance
Inheritance of Multiple Traits:
• Occurs via random assortment
of chromosomes during
meiosis I
YySs x YySsSperm
Egg
YS
Ys
yS
ys
YS Ys yS ys
Chapter 12: Inheritance
Punnett Square (Multiple Traits):
YYSS
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9 Yellow, smooth seeds
3 Yellow, wrinkled seeds
3 Green, smooth seeds
1 Green, wrinkled seeds
9 : 3 : 3 : 1
Punnett Square (Multiple Traits):
Figure 12.14 – Audesirk2 & Byers
Genes on the Same Chromosome Tend to be Inherited Together:
Linked Genes:
Genes on same chromosome
Chapter 12: Inheritance
Linked genes may be separated via crossing over:
Crossing Over:
Exchange of homologous chromosome segments(occurs during metaphase of meiosis I)
Genetic
Recombination
Figure 12.17-12.20 – Audesirk2 & Byers
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• Determine sex of individual:
• Humans = X and Y chromosomes
• Female = XX : Male = XY
• Birds / Reptiles = W and Z chromosomes
• Female = WZ : Male = ZZ
• Only one pair per individual in a species
Autosomes:
All other chromosome pairs other
than sex chromosomes
Chapter 12: Inheritance
Sex Chromosomes:
Sex-linked Genes: Genes present on one sex chromosome but not the other
• Human Y chromosome 20 unique genes
• Human X chromosome 1500 unique genes
• Examples: Color vision genes / Blood clotting factors
• Females = Normal dominant / recessive relationships exist for
alleles on X chromosomes
• Males = Fully express alleles on X chromosome
Example of Sex-linked Trait:
Chapter 12: InheritanceFigure 12.23 – Audesirk2 & Byers
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Heterozygous phenotype is
intermediate between
homozygous phenotypes
Assumption:
One allele is completely dominant
over another allele
Fact:
Alleles can display
incomplete dominance
Flower Color in SnapdragonsChapter 12: Inheritance
Variations on Mendelian Theme:
Assumption:
There are only two possible alleles
for each gene
Fact:
Genes can have multiple alleles
Chapter 12: Inheritance
Variations on Mendelian Theme:
AA or AO BB or BO
AB O
Table 12.1 – Audesirk2 & Byers
Codominance:
Both phenotypes expressed
equally in heterozygotes
• Most genes have > 10 alleles
• Alleles arise from mutation
Remember:
An individual will have only a
maximum of two unique alleles
for a gene (diploid organisms)
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Assumption:
Each trait is completely controlled
by a single gene
FactA:
Many traits are influenced by
several genes
Chapter 12: Inheritance
Variations on Mendelian Theme:
Polygenic Inheritance:
Interaction of two (2) or more genes
contribute to a single phenotype
Figure 12.25 – Audesirk2 & Byers
Assumption:
Each trait is completely controlled
by a single gene
FactB:
Single genes may have multiple
phenotypic effects (Pleiotrophy)
Chapter 12: Inheritance
Variations on Mendelian Theme:
Fertilization Sex Determining Region of the Y
Gonad FormationHormones
Sexual Differentiation of phenotype
SRY gene:
Codes for protein that
activates other
proteins in male cascade
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Assumption:
Each trait is completely controlled
by a single gene
FactC:
The environment can influence
gene expression
Chapter 12: Inheritance
Variations on Mendelian Theme:
Example:
Temperature in Himalayan rabbits
• Enzyme deactivated at
high temperature
• Skin color (exposure)
Humans:
• Height (nutrition)
• Intelligence (?)
How are Human Genetic Disorders Investigated?
Diagrams showing the genetic relationship
among related individuals:
Can reveal whether trait is
dominant, recessive, or sex-linked
Chapter 12: Inheritance
Answer: Pedigrees
Dominant Trait
Recessive Trait
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1) Recessive Alleles:
Sickle-cell Anemia(defective hemoglobin)
Chapter 12: Inheritance
Inheritance of Human Disorders (single gene):
Albinism (no pigmentation; pink eyes)
Carrier:
Heterozygous individual (not affected)
• Disease if individual inherits two recessive alleles
2) Dominant Alleles:
Chapter 12: Inheritance
Inheritance of Human Disorders (single gene):
• Potential effects: A) Produce abnormal proteins
B) Perform toxic reactions
C) Produce “overactive” proteins Huntington Disease:
Deterioration of brain(abnormal protein production)3) Sex-linked Alleles:
• Genes associated with the sex chromosomes
• Frequently in males; often skips a generation
Example 1:
Color blindness(defective receptors)
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Royal Families of Europe:
Chapter 12: Inheritance
Example 2:
Hemophilia(defective clotting proteins)
Nondisjunction:
Homologous pairs do not
separate during meiosis
1) Sex Chromosomes:
Chapter 12: Inheritance
Errors in Chromosome Number can Occur:
XO
Turner Syndrome
(♀; Infertile; lack 2° sexual char.)
Figure 12.32 – Audesirk2 & Byers
XXX
Trisomy X
(♀; Fertile; usually tall; potential IQ)
XXY
Klinefelter Syndrome
(♂; Fertile; often unnoticed)
XYY
Jacob Syndrome
(♂; Fertile; excess testosterone (violent?))
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Nondisjunction:
Homologous pairs do not
separate during meiosis
2) Autosomal Chromosomes:
Chapter 12: Inheritance
Errors in Chromosome Number can Occur:
Figure 12.32 – Audesirk2 & Byers
• Physical characteristics
• Mental retardation
• Heart malformations
Down Syndrome(Trisomy 21)
Frequency increase with
age at pregnancy