Multifactorial Inheritance Flashcards
Probability that a given member of a pair of chromosomes will be transmitted is _______
1/2, the other is 1/2
The multiplication Rule:
The probability of a given outcome in multiple trials is the product of the probabilities of each trial outcome
Ex. Probability of producing 3 girls 1/2x1/2x1/2=1/8
Addition Rule
The probability of either one outcome or another is the sum of the two probabilities
Probability of producing either 3 girls or 3 boys? 1/8 + 1/8=1/4
Gene Frequencies
Specify the proportions of each allele in a population
Genotype Frequencies
Specify the proportions of each genotype in a population
Remember that a genotype is one’s genetic make-up (i.e. allele pair) at a given locus
Hardy-Weinberg Principle
Specifies the relationship between Gene Frequencies and Genotype Frequencies
(p² + 2pq + q² = 1), p is defined as the frequency of the dominant allele and q as the frequency of the recessive allele for a trait controlled by a pair of alleles (A and a). In other words, p equals all of the alleles in individuals who are homozygous dominant (AA) and half of the alleles in people who are heterozygous (Aa) for this trait in a population.
Cystic Fibrosis example
In recessive disease, only the affected homozygotes with genotype aa are distinguishable
H-W tells us that the frequency of aa should be q^2
The frequency of the gene that contributes to the disease is 2%
98% is the good gene
2pq=1/25
*So…1/25 Europeans carry the allele for Cystic Fibrosis
The incidence of Cystic Fibrosis (in European population) is 1/2500=q^2
Thus…
q=√1/2500=0.02
p=0.98
2pq=1/25, suggesting a lot of recessive disease alleles are effectively “hidden”
Autosomal Dominant
Every generation (vertical transmission) has disease
Roughly equal numbers of affected males and females.
Father-to-son transmission may be observed
Consanguinity and the Frequency of Recessive Diseases
“Blood relation”
Consanguineous mating’s are more likely to produce offspring affected by rare Autosomal Recessive Disorders
Studies show that mortality rates among offspring of first-cousin mating’s are somewhat higher than those of the general population (up to 9% greater mortality)
Shown on pedigree with a double line…. =
Multifactorial Inheritance: The Basic Model
“Blending”
Bell-shape curve
B/c the traits are caused by the additive effects of many genetic and environmental factors, they tend to follow a normal, or bell-shaped, distribution in populations
Polygenic
Traits in which variations is thought to be caused by the combined effects of multiple genes…“many genes”
Multifactorial
When environmental factors cause variation in the trait
Multifactorial Disease: caused by the simultaneous influence of multiple genetic and environmental factors
Threshold Model
The further to the right of the bell curve, the more risk genes you inherit–>greater change of getting disease
If you pass the threshold limit, you’ll get the disease. Can be different amounts for men/women
Below the threshold, the person appears normal
Pyloric Stenosis
****Make sure to understand
Muscular hypertrophy between stomach and duodenum-leading to vomiting and obstruction
5x more common in males than females
Males need less risk genes to show disease
The least affected sex (females) has a higher risk threshold and transmits the condition more often to the most frequently affected sex
-Children of women with pyloric stenosis are more likely to be born with condition (especially males)
Multifactorial Disease
Caused by the simultaneous influence of multiple genetic and environmental factors
