genetics
DESCRIPTION
Genetics. Which one of these is not like the other???. Mutants. Mutants. Contrasting Traits. Relationship of Phenotype to Genotype. The phenotype is the outward expression of all alleles governing a given trait The genotype is the alleles present in the genome - PowerPoint PPT PresentationTRANSCRIPT
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Genetics
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Which one of these is not like the other???
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Mutants
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Mutants
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Contrasting Traits
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Relationship of Phenotype to Genotype
• The phenotype is the outward expression of all alleles governing a given trait
• The genotype is the alleles present in the genome
• The gene products encoded by the gene (alleles) give rise to the phenotype
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A Controlled Cross between Two Plants
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Mendel’s Experiment 1 (Part 1)
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Mendel’s Experiment 1 (Part 2)
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Mendel’s Explanation of Experiment 1
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Phenotype
• Dominant trait One that appears exclusively in F1 generation
• Recessive trait One masked in the F1 but reappearing in some of F2
offspring
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Mendel’s Monohybrid Cross Results
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Mendel’s Law of Segretation
• Each parent contains two factors governing a particular trait
2 dominants 1 dominant + 1 recessive 2 recessives
• The factors are separated during reproduction and only 1 from each parent is passed to offspring
• Alleles of a gene segregate during meiosis
• Each somatic cell contains 2 alleles of each gene, while gametes contain only 1.
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Meiosis Accounts for the Segregation of Alleles
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Meiosis Accounts for the Segregation of Alleles
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Homozygosity vs Heterozygosity
• Homozygosity – alleles are same
• Heterozygosity alleles are different
• Homozygous dominant and heterozygous individuals have same phenotype (dominant)
• Homozygous recessive individuals have recessive phenotype
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Homozygous or Heterozygous?
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Dihybrid Crosses and Independent Assortment
• What is result of crosses between individuals differing in two traits?
• Do alleles of for different traits segregate together or separately?
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Meiosis Accounts for Independent Assortment of Alleles
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Relationships between Alleles
• In diploid organisms there are 2 alleles for every gene (locus) in the genome
• One allele was inherited from father and the other from mother
• Multiple alleles may exist in a population of organisms although only 2 are present at any one time in an individual
• Each gene encodes a gene product (protein or RNA)
• Alleles interact in following ways Complete dominance/recessiveness Co-dominance Incomplete dominance
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Phenotype vs Genotype
• Phenotype – appearance/function
• Genotype – set of alleles present in genome
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ABO Blood Types: Multiple Alleles Showing Complete Dominance or Co-dominance
• A dominant to O
• B dominant to O
• A co-dominant to B
• Co-dominance results when alleles each encode a functional enzyme, however, the encoded enzymes differ in their specificities
Phenotype
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Incomplete Dominance
• r encodes a non-functional protein
• R encodes a functional protein
• Rr makes ½ the amount of R-protein as an RR flower
• Rr flowers are less intensely colored
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Pedigree Analysis
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Pedigree Analysis
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Crossing Over Results in Genetic Recombination
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Linkage: When Alleles Do Not Sort Independently
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Recombinant Frequencies
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Steps toward a Genetic Map
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Map These Genes (Part 1)
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Map These Genes (Part 2)
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Figure 10.22 Map These Genes (Part 3)
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Figure 10.22 Map These Genes (Part 4)
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Figure 10.22 Map These Genes (Part 5)
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Eye Color Is a Sex-Linked Trait in Drosophila
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Figure 10.24 Red-Green Color Blindness is a Sex-Linked Trait in Humans
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Epistasis• Epistasis occurs when the alleles of one gene cover up
or alter the expression of alleles of another gene.
• Coat color in mice: B allele produces a banded pigment pattern, called
agouti, while the b allele results in unbanded hairs. genotypes BB or Bb produce agouti.
genotype bb is black. Alleles at the A locus
determine if any pigmentis made. The genotypes AA and Aa have color andaa are albino.
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Epistatic Gene Interaction
B is an enzyme that actively interupts deposition
AaNon-functional pigment producing enzyme
Functional pigment producing enzyme
A is an enzyme that actively synthesizes pigment
bBSequential pigment deposition
Constant pigment deposition
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EpistasisPigment producing
enzymepigment precursor molecule
pigment molecule
Deposition of pigment in hair pigmented
hair
aapigment precursor molecule
pigment molecule
BB or Bbpigmented
hair
AA or Aapigment precursor molecule
pigment molecule
bb Solid color hair
aapigment precursor molecule
pigment molecule
bbpigmented
hair
AA or Aapigment precursor molecule
pigment molecule
BB or BbStriped hair
genotype genotype
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Quantitative Traits• Traits exhibiting a range of phenotypic variance that can
be quantified (measured) Height, weight, seed yield, life span etc…
• Traits are simultaneously controlled by many alleles Additive alleles Proteins encoded by various alleles function in tandem
to influence trait
• Genes functioning in this manner are referred to as quantitative trait loci (QTLs)
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Quantitative Trait Loci• 2 genes control seed color for a given plant and each gene has 2
alleles
• Genes: A/a, B/b, Any given plant can be of one of the following genotypes
AABB, AaBB, aaBB, AABb, AAbb, AaBb, Aabb, aaBb, aabb Each allele of each gene can “add” a given amount of activity to
generating a color phenotype. A and B add the most color, a and b add less color
Therefore a range of colors can exist (5 categories) AABB – darkest AABb, AaBB – next darkest AaBb, aaBB, AAbb – mid range color Aabb, aaBb – very little color aabb – least color