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

Mendel’s Particulate Theory:

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

• character• trait• true breeding

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

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

Pp x PpPurple flowers

Purple flowers

P

p

P p

PP

Pp

Pp

pp

Genetics Vocabulary:

• homozygous• heterozygous• phenotype• genotype• test cross

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

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

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

Codominance:There is full expression of both alleles on the heterozygotePleiotropy:Ability of a single gene to have multiple phenotypic effectsEpistasis:

Interaction between two non-allelic genes in which one modifies the genotypic expression of the other

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

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)

Human Pedigrees

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

• cystic fibrosis

• tay sachs

• sickle cell anemia

Dominantly Inherited Disorders:• achondroplasia

* Lethal dominants are more rare than lethal recessives.

Late Acting Lethal Dominants:• Huntington’s

disease* Can escape detection if it doesn’t appear until an advanced age

Consanguinity = genetic relation-ship resulting from shared ancestry* Higher probability of

inheriting same harmful alleles

Risk Assesment:

• genetic counseling

• carrier recognition

• amniocentesis

• chorionic villi sampling

• ultrasound and fetoscopy

• newborn screening