Session 7 & 8 - Polygenic Inheritance in Humans and Brassica Rapa & PCR and Genetic Variation in Humans (P.1 of 2)

Question 1

Polygenic traits

Answer 1

• Exhibit a wide and continuous range of expression that is measurable – therefore, know as quantifiable traits
• Many exhibit continuous variation – demonstrating a seemingly infinite number of variations over a wide range
• referred to as multifactorial if the environment also impacts the expression of these traits

Question 2

Explain the relevance of the trichome number trait in Brassica Rapa

Answer 2

It is an inherited trait that is influenced by an unknown number of genes. The “hairiness” of a given population of plants does exhibit continuous variation, ranging from no trichomes to many on a given plant

Question 3

Fingerprint patterns of dermal ridges can be classified into these groups:

Answer 3

arches, loops and whorls

Question 4

Explain the characteristics of the arch pattern

Answer 4

It’s the simplest and least frequent pattern
Can be subclassified as plain if ridges rise slightly over the middle of the finger or tented when the ridges rise to a point

Question 5

What is a triradius?

Answer 5

A point at which 3 groups of ridges coming from 3 directions meet at angles of about 120 degrees

Question 6

What is a core?

Answer 6

Essentially a ridge that is surrounded by a field of ridges which turn back on themselves at 180 degrees

Question 7

What comprises the loop pattern?

Answer 7

A triradius and a core

Question 8

What are the subclasses of loops?

Answer 8

Either radial or ulnar;
A finger possesses a radial loop if its triradius is on the side of the little finger for the hand in question, and the loop opens toward the thumb.
A finger has an ulnar loop if its triradius is on the side of the thumb for that hand and the loop opens toward the little finger.

Question 9

What comprises the whorl pattern?

Answer 9

2 triradii, with the ridges forming various patterns inside. And a core.

Question 10

What is the frequency of the arch pattern in the general population?

Answer 10

5%

Question 11

What are the frequencies of the loop patterns in the general population?

Answer 11

radial loop: 5.4%

ulnar loop: 63.5%

Question 12

What is the frequency of the whorl pattern in the general population?

Answer 12

26.1%

Question 13

What is the ridge count for an arch?

Answer 13

0

Question 14

The ridge count on a finger with a loop is determined by

Answer 14

counting the # of ridges between the triradius and the center/core of the pattern.

Question 15

The ridge count on a finger with a whorl is made from

Answer 15

each triradius to the center of the fingerprint, but only the higher of the two possible counts is used.

Question 16

To obtain your total ridge count (TRC):

Answer 16

Add all 10 ridge counts together to obtain TRC

Question 17

How did we study genetic variation in humans?

Answer 17

Extracted DNA from cheek cells isolated from a sterile saline mouthwash; use PCR to amplify a region within the Tissue Plasminogen Activator (TPA) on Chromosome 8 to look for an insertion of a short DNA sequence called an ‘Alu’ element

Question 18

Describe Alu elements

Answer 18

a family of transposable elements of ~300 bp in length; derive their name from a single recognition site for the endonuclease Alu I located near the middle of the sequence. This family of short, interspersed, repeated DNA Alu elements are distributed throughout primate genomes and over 2000 different elements are thought to exist

~1 million copies of Alu elements in the human genome; comprising an estimated 10.7% of the genome. A few appeared relatively recently, and are not present in all individuals–such as TPA-25, which is found within an intron of the TPA gene.

Question 19

Regions of the human genome that exhibit a great deal of diversity are known as…?

How is this relevant to the TPA-25 Alu element?

Answer 19

variable sequences that are polymorphic;

The TPA-25 Alu element insertion is dimorphic, meaning that it is present in some individuals and not in others. PCR can be used to screen individuals for presence/absence.

Question 20

How will PCR be used in this experiment?

Answer 20

Oligonucleotide primers flanking the insertion site will be used to amplify a 100bp intronic region of the TPA gene. Thus, it’s expected if the TPA-25 Alu element insertion is present a 400bp PCR product will be produced; if absent, a 100bp fragment will be produced.

Question 21

How many alleles are in this analysis? What are the genotypes & phenotypes?

Answer 21

two allels, having the TPA-25 Alu element insertion or not, which gives us 3 possible genotypes:

• homozygous TPA-25 (400bp only)
• homozygous absent (100bp only)
• heterozygous (400 and 100bp)

Question 22

What was added to the cheek cell pellet (or what was the cheek cell pellet added to)?

Answer 22

The cells were suspended in a solution containing ‘Chelex (beads)’, a resin that binds metal ions (which can inhibit a PCR reaction); this solution was then boiled to lyse the cells and centrifuged to remove debris

Question 23

What’s in the PCR mix (Alu AMP mix)?

Answer 23

oligonucleotide primers (2), dNTPs (the 4 deoxynucleotides), Taq DNA polymerase, buffers/magnesium chloride cofactor.

Question 24

What temperatures does the thermal cycler (PCR machine) cycle?

Answer 24

1st cycle: 94℃, 5 min
\+ 30 more cycles:
- 94℃ for 1 min
- 58℃ for 2 min
- 72℃ for 2 min

Question 25

Hardy-Weinberg Equilibrium Principle

Answer 25

States that both ALLELE and GENOTYPE FREQUENCIES in a POPULATION remain CONSTANT; i.e. they are in EQUILIBRIUM from generation to generation as long as these 3 criteria are satisfied:

1) Population size is “large” (INFINITE)
2) NO IMMIGRATION & NO EMIGRATION
3) RANDOM mating; NO SELECTION forces

⊨ p ≔ allele A frequency
∧ q ≔ allele B frequency
⇒ you can calculate/predict genotypes:
{ p² = AA ∧ 2pq = AB ∧ q² = BB : p² + 2pq + q² = 1 }