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Observable Patterns of Observable Patterns of InheritanceInheritance
Chapter 11Chapter 11
Earlobe Variation Earlobe Variation
Whether a person has attached or Whether a person has attached or detached earlobes depends on a single detached earlobes depends on a single genegene
Attached earlobes: two copies of the Attached earlobes: two copies of the recessive allele for this generecessive allele for this gene
Detached earlobes: either one or two Detached earlobes: either one or two copies of the dominant allelecopies of the dominant allele
Early Ideas about Heredity Early Ideas about Heredity
People knew that sperm and eggs People knew that sperm and eggs transmitted information about traitstransmitted information about traits
Blending theoryBlending theory Problem:Problem:
Would expect variation to disappearWould expect variation to disappear Variation in traits persistsVariation in traits persists
Gregor MendelGregor Mendel
Strong background Strong background in plant breeding and in plant breeding and mathematicsmathematics
Using pea plants, Using pea plants, found indirect but found indirect but observable evidence observable evidence of how parents of how parents transmit genes to transmit genes to offspringoffspring
GenesGenes
Units of information about specific traitsUnits of information about specific traits
Passed from parents to offspringPassed from parents to offspring
Each has a specific location (locus) on a Each has a specific location (locus) on a chromosomechromosome
AllelesAlleles
Different molecular forms of a gene Different molecular forms of a gene
Arise by mutationArise by mutation
Dominant allele masks a recessive Dominant allele masks a recessive
allele that is paired with itallele that is paired with it
Allele CombinationsAllele Combinations
Homozygous Homozygous having two identical alleles at a locushaving two identical alleles at a locus AAAA or or aaaa
Heterozygous Heterozygous having two different alleles at a locushaving two different alleles at a locus AaAa
Genetic TermsGenetic Terms
A pair of homologous chromosomes
A gene locus
A pair of alleles
Three pairs of genes
Figure 11.4Page 179
Figure 11.4Page 179
Question 1Question 1
1.1. An early idea about inheritance was the An early idea about inheritance was the “blending theory”. What was it and why “blending theory”. What was it and why was it deficient?was it deficient?
Answer 1Answer 1
1.1. An early idea about inheritance was the An early idea about inheritance was the “blending theory”. What was it and why “blending theory”. What was it and why was it deficient?was it deficient?
Traits from the male and female were Traits from the male and female were blended in the offspring.blended in the offspring.
If this were truth, then eventually, all If this were truth, then eventually, all individuality would disappear.individuality would disappear.
Question 2Question 2
2. What does the term “locus” mean?2. What does the term “locus” mean?
Answer 2Answer 2
2. What does the term “locus” mean?2. What does the term “locus” mean?
This is the location of a gene (which This is the location of a gene (which chromosome and where on the chromosome and where on the chromosome). Its “address”.chromosome). Its “address”.
Question 3Question 3
3. What are alleles?3. What are alleles?
Answer 3Answer 3
3. What are alleles?3. What are alleles?
These different molecular forms of the These different molecular forms of the same gene.same gene.
Question 4Question 4
4. If two genes are “homologous”, what 4. If two genes are “homologous”, what does that mean?does that mean?
Answer 4Answer 4
4. If two genes are “homologous”, what 4. If two genes are “homologous”, what does that mean?does that mean?
Homologous means “the same.” They are Homologous means “the same.” They are identical.identical.
Question 5Question 5
5. What does “heterozygous” mean?5. What does “heterozygous” mean?
Answer 5Answer 5
5. What does “heterozygous” mean?5. What does “heterozygous” mean?
Heterozygous means" different”. Heterozygous means" different”. Heterozygous for attached earlobes would Heterozygous for attached earlobes would mean that the individual carries a normal mean that the individual carries a normal gene and a mutant gene.gene and a mutant gene.
Question 6Question 6
6. If Sally is homozygous dominate for 6. If Sally is homozygous dominate for gene A, how would you write that in gene A, how would you write that in standard symbolic form? If she were standard symbolic form? If she were heterozygous for A? If she were heterozygous for A? If she were homozygous for the recessive form of A?homozygous for the recessive form of A?
Answer 6Answer 6
6. If Sally were 6. If Sally were (a)(a) homozygous dominate homozygous dominate for gene A, how would you write that in for gene A, how would you write that in standard symbolic form? standard symbolic form? (b)(b) If she were If she were heterozygous for A? heterozygous for A? (c)(c) If she were If she were homozygous for the recessive form of A?homozygous for the recessive form of A?
AA, Aa, aaAA, Aa, aa
Genotype & PhenotypeGenotype & Phenotype
Genotype refers to particular genes an Genotype refers to particular genes an individual carriesindividual carries
Phenotype refers to an individual’s Phenotype refers to an individual’s observable traitsobservable traits
Cannot always determine genotype by Cannot always determine genotype by observing phenotypeobserving phenotype
Tracking GenerationsTracking Generations
Parental generation Parental generation PP
mates to produce mates to produce
First-generation offspring First-generation offspring FF11
mate to produce mate to produce
Second-generation offspring Second-generation offspring FF22
Monohybrid CrossesMonohybrid Crosses
Experimental intercross between Experimental intercross between
two two FF11 heterozygotes heterozygotes
AA X aa Aa (F1 monohybrids)
Aa X Aa ?
Question 7Question 7
7. Define phenotype.7. Define phenotype.
Answer 7Answer 7
7. Define phenotype.7. Define phenotype.
Phenotype refers to an individual’s Phenotype refers to an individual’s observable traitsobservable traits
Question 8Question 8
8. Define genotype.8. Define genotype.
Answer 8Answer 8
8. Define genotype.8. Define genotype.
Genotype refers to particular genes an Genotype refers to particular genes an individual carriesindividual carries
Question 9Question 9
9. How do you represent the first 9. How do you represent the first generation of a cross?generation of a cross?
Answer 9Answer 9
9. How do you represent the first 9. How do you represent the first generation of a cross? Parental cross? generation of a cross? Parental cross? Second generation?Second generation?
FF11; P; F; P; F22
Question 10Question 10
10. What is monohybrid cross (how many 10. What is monohybrid cross (how many traits are being investigated)?traits are being investigated)?
Answer 10Answer 10
10. What is monohybrid cross (how many 10. What is monohybrid cross (how many traits are being investigated)?traits are being investigated)?
It is a cross where two true breeding It is a cross where two true breeding individuals are mated (individuals are mated (AA x aaAA x aa). Usually ). Usually they are homozygous dominant and they are homozygous dominant and homozygous recessive. One trait (two homozygous recessive. One trait (two alleles).alleles).
Mendel’s Mendel’s Monohybrid Monohybrid
Cross ResultsCross Results
787 tall 277 dwarf
651 long stem
207 at tip
705 purple 224 white
152 yellow428 green
299 wrinkled882 inflated
6,022 yellow 2,001 green
5,474 round 1,850 wrinkled
F2 plants showed dominant-to-recessive ratio that averaged 3:1
Figure 11.5Page 180
ProbabilityProbability
The chance that each outcome of a given The chance that each outcome of a given event will occur is proportional to the event will occur is proportional to the number of ways that event can be reachednumber of ways that event can be reached
Monohybrid Monohybrid CrossCross
IllustratedIllustrated
True-breedinghomozygous recessiveparent plant
True-breedinghomozygous dominantparent plant
An F1 plantself-fertilizesand producesgametes:
F1 PHENOTYPES
F2 PHENOTYPES
aa
Aa
AA
aaAa
Aa
Aa Aa
Aa Aa
Aa Aa
Aa Aa
Aa
Aa
AA
aa
A
A
A
A
a a
a
a
AA
Figure 11.7Page 181
Mendel’s Theory Mendel’s Theory of Segregationof Segregation
An individual inherits a unit of information An individual inherits a unit of information (allele) about a trait from each parent(allele) about a trait from each parent
During gamete formation, the alleles During gamete formation, the alleles segregate from each other segregate from each other
Test CrossTest Cross
Individual that shows dominant phenotype Individual that shows dominant phenotype is crossed with individual with recessive is crossed with individual with recessive phenotypephenotype
Examining offspring allows you to Examining offspring allows you to determine the genotype of the dominant determine the genotype of the dominant individualindividual
Punnett Squares of Punnett Squares of Test CrossesTest Crosses
Homozygous recessive
a a
A
a aa
Aa Aa
aa
Homozygous recessive
a a
A
A Aa
Aa Aa
Aa
Two phenotypes All dominant phenotype
Dihybrid Cross Dihybrid Cross
Experimental cross between individuals Experimental cross between individuals that are homozygous for different that are homozygous for different
versions of versions of twotwo traits traits
Dihybrid Cross: Dihybrid Cross: FF11 Results Results
AABB aabbx
AaBb
AB AB ab ab
TRUE-BREEDING PARENTS:
GAMETES:
F1 HYBRID OFFSPRING:
purple flowers, tall
white flowers,dwarf
All purple-flowered, tall
Figure 11.9 (1)Page 183
1/16aaBB
1/16aaBb
1/16aaBb
1/16Aabb
1/16Aabb
1/16AAbb
1/16AABB
1/16AABb
1/16AaBB
1/16AaBb
1/16AABb
1/16AaBb
1/16AaBB
1/16AaBb
1/16AaBb
1/4 AB 1/4 Ab 1/4 aB 1/4 ab
1/16aabb
1/4 AB
1/4 Ab
1/4 aB
1/4 ab
AaBb AaBbX
1/16 white-flowered, dwarf
3/16 white-flowered, tall
3/16 purple-flowered, dwarf
9/16 purple-flowered, tall
Dihybrid Cross: Dihybrid Cross: FF22 Results Results
Figure 11.9(2)Page 183
Question 11Question 11
11. Describe or define: dihybrid cross”.11. Describe or define: dihybrid cross”.
11. Describe or define: dihybrid cross”.11. Describe or define: dihybrid cross”.
Experimental cross between individuals Experimental cross between individuals that are homozygous for different that are homozygous for different versions of versions of twotwo traits traits
Example:Example:
AABB x aabbAABB x aabb
Independent AssortmentIndependent Assortment
Mendel concluded that the two “units” for Mendel concluded that the two “units” for the first trait were to be assorted into the first trait were to be assorted into gametes independently of the two “units” gametes independently of the two “units” for the other traitfor the other trait
Members of each pair of homologous Members of each pair of homologous chromosomes are sorted into gametes at chromosomes are sorted into gametes at random during meiosis random during meiosis
Independent AssortmentIndependent Assortment
Metaphase I:
Metaphase II:
Gametes:
1/4 AB 1/4 ab 1/4 Ab 1/4 aB
A A A A
A A A A
AAAA
B B
B B
BB
B B
BBBB
a a a a
aa aa
aaaa
bb b b
bb b b
b b b b
OR
Tremendous VariationTremendous Variation
Number of genotypes possible in Number of genotypes possible in
offspring as a result of independent offspring as a result of independent
assortment and hybrid crossing is assortment and hybrid crossing is
22nn
((nn is the number of gene loci is the number of gene loci
at which the parents differ)at which the parents differ)
Impact of Mendel’s WorkImpact of Mendel’s Work
Mendel presented his results in 1865Mendel presented his results in 1865
Paper received little noticePaper received little notice
Mendel discontinued his experiments in Mendel discontinued his experiments in 18711871
Paper rediscovered in 1900 Paper rediscovered in 1900
Dominance Relations Dominance Relations
Complete dominance Complete dominance
Incomplete dominanceIncomplete dominance
CodominanceCodominance
Incomplete Incomplete DominanceDominance
XHomozygous parent
Homozygous parent
All F1 are heterozygous
X
F2 shows three phenotypes in 1:2:1 ratio
Incomplete Dominance
Figure 11.10Page 184
Codominance: ABO Blood Codominance: ABO Blood Types Types
Gene that controls ABO type codes for Gene that controls ABO type codes for enzyme that dictates structure of a enzyme that dictates structure of a glycolipid on blood cellsglycolipid on blood cells
Two alleles (Two alleles (IIAA and and IIBB) are codominant ) are codominant when pairedwhen paired
Third allele (Third allele (ii) is recessive to others) is recessive to others
ABO Blood Type:ABO Blood Type:Allele CombinationsAllele Combinations
Range of genotypes:
Blood types:
IA IA
IA i IA IB IB i
IB IB
ii
A AB B O
or or
Figure 11.11Page 184
ABO and TransfusionsABO and Transfusions
Recipient’s immune system will attack Recipient’s immune system will attack
blood cells that have an unfamiliar blood cells that have an unfamiliar
glycolipid on surfaceglycolipid on surface
Type O is universal donor because it has Type O is universal donor because it has
neither type A nor type B glycolipidneither type A nor type B glycolipid
Question 12.Question 12.
12. What three types of dominance?12. What three types of dominance?
Question 12. What three types of Question 12. What three types of dominance?dominance?
12. What three types of dominance?12. What three types of dominance?
Complete dominance Complete dominance
Incomplete dominanceIncomplete dominance
CodominanceCodominance
Pleiotropy Pleiotropy
Alleles at a single locus may have effects Alleles at a single locus may have effects on two or more traitson two or more traits
Marfan syndrome - Mutation in gene for Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin system, lungs, eyes, and skin
Marfan SyndromeMarfan Syndrome
Epistasis Epistasis
Interaction between the products of gene Interaction between the products of gene pairspairs
Common among genes for hair color in Common among genes for hair color in mammalsmammals
Coat Color Coat Color inin
RetrieversRetrieversbbeeBBEE X
F1 puppies are all BbEe
BBEE
BBEe
BbEE
BbEe Bbee
BbEe
Bbee
BBEe BbEE BbEe
BBee BbEe
bbeebbEe
bbEE bbEe
BE Be bE be
BE
Be
bE
be
black
brown
yellow
F2 puppies
Figure 11.13Page 186
Comb Shape in PoultryComb Shape in Poultry
9/16 walnut 3/16 rose 3/16 pea 1/16 singlerrpp
RRpp(rose comb)
rrPP(pea comb)
RrPp (all walnut comb)
P:
F2:
F1:
X
RRPPRRPpRrPPRrPp
RRppRrpp
rrPPrrPp
Figure 11.15Page 187
Walnut CombWalnut Comb
http://www.longtail-fowl.com/images/sketches/minohiki_headstudy_1.jpg
Campodactyly: Campodactyly: Unexpected Phenotypes Unexpected Phenotypes
Effect of allele varies:Effect of allele varies:
Bent fingers on both handsBent fingers on both hands
Bent fingers on one handBent fingers on one hand
No effectNo effect
Many factors affect gene expressionMany factors affect gene expression
Continuous VariationContinuous Variation
A more or less continuous range of small A more or less continuous range of small differences in a given trait among differences in a given trait among individualsindividuals
The greater the number of genes and The greater the number of genes and
environmental factors that affect a trait, the environmental factors that affect a trait, the
more continuous the variation in versions more continuous the variation in versions
of that traitof that trait
Human VariationHuman Variation
Some human traits occur as a few discrete Some human traits occur as a few discrete typestypes Attached or detached earlobes Attached or detached earlobes Many genetic disordersMany genetic disorders
Other traits show continuous variationOther traits show continuous variation HeightHeight WeightWeight Eye colorEye color
Describing Continuous Variation Describing Continuous Variation
Range of values for the trait
Nu
mb
er o
f in
div
idu
als
wit
hso
me
valu
e o
f th
e t
rait
(line of bell-shaped curve indicates continuous variation in population)
Range of values for the trait
Nu
mb
er o
f in
div
idu
als
wit
hso
me
valu
e o
f th
e t
rait
Question 13.Question 13.
13. Define pleiotrophy.13. Define pleiotrophy.
Question 13Question 13
13. Define pleiotrophy.13. Define pleiotrophy.
Alleles at a single locus may have Alleles at a single locus may have effects on two or more traitseffects on two or more traits
Examples: Marfan’s syndrome and Examples: Marfan’s syndrome and Sickle Cell AnemiaSickle Cell Anemia
Temperature Effects Temperature Effects on Phenotype on Phenotype
Rabbit is homozygous for Rabbit is homozygous for an allele that specifies a an allele that specifies a heat-sensitive version of an heat-sensitive version of an enzyme in melanin-enzyme in melanin-producing pathwayproducing pathway
Melanin is produced in Melanin is produced in cooler areas of bodycooler areas of body
Figure 11.18Page 190
Environmental Effects on Plant Environmental Effects on Plant PhenotypePhenotype
Hydrangea macrophyllaHydrangea macrophylla
Action of gene responsible for floral Action of gene responsible for floral color is influenced by soil aciditycolor is influenced by soil acidity
Flower color ranges from pink to blueFlower color ranges from pink to blue