Blending Theory of Inheritance:

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Blending Theory of Inheritance
Parental traits are mixed in the offspring
Does NOT explain

• how population did not reach a uniform appearance

• how some inheritable traits skip a generation

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Mendels Particulate Theory
Parents transmit discrete factors (genes) that
remain separate from on generation to the next

• character

• trait

• true breeding

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Law of Segregation
Allele pairs segregate during meiosis and the
paired condition is restored by the random fusion
of gametes in fertilization
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Law of Segregation assumes

• alleles (alternate forms of same gene)

• an organism inherits two genes (one from each
  parent)

• if two alleles differ, one is dominant and the
  other recessive

• two genes for each allele segregate during
  gamete formation

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Pp x Pp
Purple flowers
Purple flowers
P
p
P
PP
Pp
Pp
pp
p
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Genetics Vocabulary

• homozygous

• heterozygous

• phenotype

• genotype

• test cross

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Inheritance as Probability
Event is certain to occur 1
Event is certain not to occur 0
Probabilities of all possible outcomes must
equal 1.
Random events are independent of one another
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Rule of Multiplication
Probability that independent events will occur
simultaneously is the product of individual
probabilities
Rule of Addition
Probability of an event that occur in two or more
independent ways is the sum of the probabilities
of the different ways
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(No Transcript)
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Law of Independent Assortment
Each allele pair segregated independently of gene
pairs during gamete formation
Incomplete Dominance
The dominant phenotype is not fully expressed in
the hetero-zygote, resulting in an intermediate
phenotype
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Codominance
There is full expression of both alleles on the
heterozygote
Pleiotropy
Ability of a single gene to have multiple
phenotypic effects
Epistasis
Interaction between two non-allelic genes in
which one modifies the genotypic expression of
the other
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Polygenic Inheritance
Mode of inheritance in which the additive effect
of two or more genes determines a single
phenotypic character
Multiple Alleles
There are more than two alternative forms of the
gene
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Norm of Reaction range of phenotypic
variability produced by a single genotype under
various environmental conditions
Nature vs Nurture
Multifactorial Disorders in-heritance of alleles
at a single locus (both genetic and
environmental)
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Human Pedigrees
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Recessively Inherited Disorders
a recessive gene that causes a disorder

• Usually a recessive allele causes a disorder
  that codes for a mal-functional protein or no
  protein at all

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• cystic fibrosis

• tay sachs

• sickle cell anemia

Dominantly Inherited Disorders

• achondroplasia

Lethal dominants are more rare than lethal
recessives.
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Late Acting Lethal Dominants

• Huntingtons disease

Can escape detection if it doesnt appear until
an advanced age
Consanguinity genetic relation-ship resulting
from shared ancestry
Higher probability of inheriting same harmful
alleles
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Risk Assesment

• genetic counseling

• carrier recognition

• amniocentesis

• chorionic villi sampling

• ultrasound and fetoscopy

• newborn screening