Mol Lecture #23

Question 1

Dihybrid Crosses and Independent Assortment

Answer 1

• Build on monohybrid crosses: focussing on one character
  -The dihybrid cross is a cross of F1 individuals

Question 2

Definition of dihybrid

Answer 2

• the F1 resulting from a cross of 2 parents that have different traits with respect to 2 characters.
  -The parents are true breeding individuals

Question 3

Dihybrid Crosses and Beyond

Answer 3

• P1 generation (or P generation) is going to be 2 individuals (RRYYxrryy (F1))
• Ratio: 9:3:3:1
• Each box corresponds to a 1/16 chance, and use the sum rule in order to calculate
  the probability. (1/8th)

Question 4

Phil Problem

Answer 4

• Look at each character individually and multiply that character out
• Broken down into punnett squares and multiplied individually

Question 5

Principle of Independent assortment

Answer 5

• States that when 2 or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together.

Question 6

Chromosome behavior during meiosis

Answer 6

• During meiosis I we randomly assort parental versions into different positions
  –>This is repeated in meiosis II

Question 7

Chromosome behavior during meiosis

Answer 7

• During meiosis I we randomly assort parental versions into different positions
  –>This is repeated in meiosis II

Question 8

Modifications to Mendelian Inheritance

Answer 8

• Mendel’s work involved single gene characters where there were 2 alleles (traits), one dominant while the other recessive.
  –>As genetics research progressed, the need to have new ways to explain more complex situations became apparent.

Question 9

Incomplete Dominance

Answer 9

• When one allele of a gene is not completely dominant to another
• F1: looks like blended inheritance, but original parental phenotypes reappear.
• F2: 1:2:1

Question 10

How does incomplete Dominance work?

Answer 10

• The C gene codes for a transcription factor that induces transcription of the color-producing enzyme
• C → Red enzyme
• If you have the white allele, you don’t have this transcription factor at all
• The more R allele, the redder it will be
• Therefore, R & W will make it pink (half the amount of transcription factor)

Question 11

Multiple alleles and Codominance (Blood Group systems)

Answer 11

• Governed by glycoproteins on the surface of red blood cells (RBCs)

Question 12

Transfusion rejection:

Answer 12

• when foreign or nonself glycoproteins are on the surface of recipient RBCs, antibodies attack and destroy the RBCs

Question 13

Blood Group System

Answer 13

• Antigens= glycoproteins
• AB represents codominance
• All cells have protein, but the types of sugars attached are different.
• Gene- codes for glycosyltransferase (adds sugars to the site), which has different activities or no activity

Question 14

ABO and Disease

Answer 14

• There are different susceptibilities to infectious diseases depending on your blood types. (Malaria and Cholera)
• A,B and AB have increased susceptibility to malaria
• O has increased susceptibility to cholera.

Question 15

Incomplete Dominance v.s. Codominance

Answer 15

• Co: both expressed at the same time (red and white) (1:2:1)
• Incomplete: mixed expression (1:2:1)
• Dominant, recessive: 3:1 ratio
  (On F1 self-cross)