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Flashcards in Multifactorial Inheritance Deck (19)
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1
Q

Probability that a given member of a pair of chromosomes will be transmitted is _______

A

1/2, the other is 1/2

2
Q

The multiplication Rule:

A

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

3
Q

Addition Rule

A

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

4
Q

Gene Frequencies

A

Specify the proportions of each allele in a population

5
Q

Genotype Frequencies

A

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

6
Q

Hardy-Weinberg Principle

A

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.

7
Q

Cystic Fibrosis example

A

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”

8
Q

Autosomal Dominant

A

Every generation (vertical transmission) has disease

Roughly equal numbers of affected males and females.

Father-to-son transmission may be observed

9
Q

Consanguinity and the Frequency of Recessive Diseases

A

“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…. =

10
Q

Multifactorial Inheritance: The Basic Model

A

“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

11
Q

Polygenic

A

Traits in which variations is thought to be caused by the combined effects of multiple genes…“many genes”

12
Q

Multifactorial

A

When environmental factors cause variation in the trait

Multifactorial Disease: caused by the simultaneous influence of multiple genetic and environmental factors

13
Q

Threshold Model

A

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

14
Q

Pyloric Stenosis

A

****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)

15
Q

Multifactorial Disease

A

Caused by the simultaneous influence of multiple genetic and environmental factors

16
Q

Genetic Drift

A

Genetic Drift: A random evolutionary process that produces LARGER changes in gene frequencies in SMALLER populations (i.e.island/isolated populations)

Founder effect: Populations that have started from a small group of individuals that mix with few newcomers, preferring to mate within the population) is a special case of genetic drift

Ex. Albinism (autosomal recessive) among the Cuna indians in Panama is 1/200 versus European Caucasians at 1/20,000

17
Q

Albinism (autosomal recessive) among the Cuna indians in Panama is 1/200 versus European Caucasians at 1/20,000. What is frequency of heterozygous individuals in Cuna indian population?

A

1/200=q^2
q=√1/200=.07
p=.93

What is frequency of heterozygous carrier? =2pq

=13% of population are heterozygous or carry the gene

*For heterozygous, or carriers in wording

18
Q

Autosomal Recessive inheritance

A

Clustering of disease phenotype among siblings, but disease is not usually seen among parents or other ancestors

Equal numbers of affected males and females

Consanguinity may be present

19
Q

Recurrence Risks and Transmission Patterns

A

Multifactorial diseases can change substantially from one population to another. This is because gene frequencies as well as environmental factors can differ among populations