powerlecture: chapter 11 observing patterns in inherited traits
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PowerLecture:PowerLecture:Chapter 11Chapter 11
Observing Patterns in Inherited Observing Patterns in Inherited TraitsTraits
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
Gregor MendelGregor Mendel
The founder of modern geneticsThe founder of modern genetics
Fig. 11-2, p.170
a Garden pea flower, cut in half. Sperm form in pollen grains, which originate in male floral parts (stamens). Eggs develop, fertilization takes place, and seeds mature in female floral parts (carpels).
b Pollen from a plant that breeds true for purple flowers is brushed onto a floral bud of a plant that breeds true for white flowers. The white flower had its stamens snipped off. This is one way to assure cross-fertilization of plants.
c Later, seeds develop inside pods of the cross-fertilized plant. An embryo within each seed develops into a mature pea plant.
d Each new plant’s flower color is indirect but observable evidence that hereditary material has been transmitted from the parent plants.
Fig. 11-3, p.170
Gregor MendelGregor Mendel
Crossing garden pea plants
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 171
A pair of homologous chromosomes, each in the unduplicated state (most often, one from a male parent and its partner from a female parent)
A gene locus (plural, loci), the location for a specific gene on a chromosome. Alleles are at corresponding loci on a pair of homologous chromosomes
A pair of alleles may be identical or nonidentical. They are represented in the text by letters such as D or d
Three pairs of genes (at three loci on this pair of homologous chromosomes); same thing as three pairs of alleles
Fig. 11-4, p.171
Genetic TermsGenetic Terms
Genetic terms
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
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
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
33nn
((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
Codominance: ABO blood types
ABO Blood TypeABO Blood Type
Incomplete dominance
Incomplete DominanceIncomplete Dominance
Codominance: ABO Blood Types Codominance: ABO Blood 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 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
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
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
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
Fig. 11-17a, p.179
Environmental Effects on Plant PhenotypeEnvironmental Effects on Plant Phenotype
Fig. 11-17b, p.179
Environmental Effects on Plant PhenotypeEnvironmental Effects on Plant Phenotype
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 11.16Page 179
Fig. 11-16, p.179
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
Fig. 11-18, p.180
Continuous Continuous VariationVariation
Variation in human Variation in human eye coloreye color
The line of a bell-shaped curve reveals continuous variation in the population
Range of values for the trait
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mb
er o
f in
div
idu
als
wit
hso
me
valu
e o
f th
e tr
ait
Fig. 11-19a, p.180
Describing Continuous Variation Describing Continuous Variation