Gregor Mendel: Father of modern genetics

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Gregor Mendel Father of modern genetics
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Genetic cross
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Mendel tracked heritable characters for three
generations
No Blending
White determinant still there, just masked in F1
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Alleles, alternative versions of a gene
1. Discrete genetic determinants for each trait
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Mendels law of segregation
Phenotype
2. Determinants for trait separate into different
gametes
Genotype
3. Some determinants dominant over others
(dominant and recessive traits)
4. Statistical occurrence of offspring supported
random fusion of gametes predicted by laws of
probability
Punnett square
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What experiment could you perform to determine
the genotype for flower color of a pea plant with
purple flowers?
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A testcross
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What happens when you follow 2 traits? Do two
traits assort together or independently?
Dihybrid cross
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What are Mendels 2 Laws of Inheritance?
Explain what each means as far as chromosomal
alignment and movement in meiosis.
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MENDELS LAWS OF INHERITANCE

• Segregation of alleles
• Independent assortment of different traits

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How many unique gametes could be produced by
independent assortment from an individual with
the genotype AaBbCCDdEE ?
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Solving Genetics Problems
Consider the following cross PpYyRr X
Ppyyrr What is the probability of the phenotype
Purple, Round, Yellow seed?
What is the probability of the genotype PpYyRr?
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What is the probability that each of the
following pairs of parents will produce the
indicated offspring? AABBCC x aabbcc AaBbCc AAB
bCc x AaBbCc AAbbCC
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In sesame plants, one-pod(P) condition is
dominant to 3-pod(p), and normal leaf (L) is
dominant to wrinkled leaf (l). Pod type and leaf
type are inherited independently. Determine
possible genotypes of parents for all possible
matings producing the following 318 one-pod,
normal leaf 98 one-pod, wrinkled leaf 323
three-pod, normal leaf 106 three-pod, wrinkled
leaf
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Mendel was not only smart, but extremely
lucky. All his traits were dominant/recessive and
on different chromosomes (or were far apart on a
chromosome) Many inheritance patterns are more
complex than simple dominant/recessive allele
interactions.
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Incomplete dominance in snapdragon color
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Knowledge of the molecular basis of gene
expression gives us a handle on understanding
these different types of gene (allele)
interaction and phenotypic expression.
Genes code for proteins!
Functional vs. nonfunctional enzymes, dosage
affects, etc.
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Multiple alleles for the ABO blood groups
A and B are codominant, O is recessive to A and B
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PLEIOTROPY One gene (or genotype) results in
multiple phenotypes. Many different outward
effects on the organism.
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Pleiotropic effects of the sickle-cell allele
in a homozygote
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Traits Determined by Multiple Genes
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EPISTASIS -More than one gene involved. -A gene
at one locus alters the phenotypic expression of
a gene at a second locus.
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Coat color in rats is an example of epistasis
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POLYGENIC INHERITANCE -Multiple genes resulting
in one phenotype. Ex. Skin color, eye color.
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A simplified model for polygenic inheritance of
skin color
Environmental effects also affect the range of
phenotype (multifactorial trait)
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The effect of environment of phenotype
Norm of reaction for a genotype is the range of
phenotype due to environmental influences.
Soil acidity effects the color of hydrangeas.
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HUMAN GENETICS
How do we study genetic traits in humans???
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Pedigree analysis
male
female
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HUMAN GENETIC DISORDERS WITH MENDELIAN
INHERITANCE
Recessive disorders Heterozygous carriers
are usually phenotypically normal. -Albinism -C
ystic Fibrosis most common lethal genetic
disease in U.S. (1/2500 white population) -Tay
Sachs 1/3600 in Jewish population -Sickle Cell
1/400 African Americans Example of balanced
polymorphism
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Dominantly inherited disorders Dwarfism
(Achondroplasia) 1/10,000 Dominant lethals rare
(usually dont survive to pass on
gene) -Huntingtons Disease