Polygenic

1
Polygenic

• Many traits have a quantitative nature.
• IQ, length, width, skin colour, etc.
• These traits are governed by many (poly) genes.

2
Example

• If skin colour in humans is determined by 3 gene
  pairs and each gene contribute 15 colour to a
  basic colour of 10, is it possible for 2 lightly
  pigmented people (each with 25 colour) to have a
  black child (gt70 colour)?

3
Example

• To get 25 colour each parent should have 1
  dominant gene. Let us assume they have different
  dominant genes
• Aabbcc x aaBbcc

4
Problem

• Two pure breeding Sorghum lines with lengths of
  75 cm and 55 cm respectively, are crossed. The
  F1s were 65 cm. Self-pollination of the F1s
  result in plants with lengths of 35, 45, 55, 65,
  75, 85 and 95 cm. In nature plants with lengths
  of 15 and 25 cm were observed. What type of
  inheritance is present? What are the genotypes of
  the parental lines and the F1s?

5
Problem

• 15, 25, 35, 45, 55, 65, 75, 85 95 cm
• 8 genes (4 gene pairs).
• Each gene contributes 10 cm to a basic length of
  15 cm.
• 15, 25, 35, 45, 55, 65, 75, 85 95
• 4 6 dominant genes respectively.
• AABBccdd x aaBBCCDD
• AaBBCcDd

6
KC 5.6 (p125)

• Harvy ? 6 cm Erma ? 30 cm
• F1 ? 18 cm
• F2 ? 6, 10, 14, 18, 22, 26, 30
• Polygenic inheritance
• 3 gene pairs
• Harvy ? aabbcc Erma ? AABBCC
• Basic length of 6 and each dominant gene
  contributes 4 cm

7
aabbcc (6) x AABBCC (30)

• AaBbCc (18)
• 0 (6) 1
• 1 (10) 6
• 2 (14) 15
• 3 (18) 20
• 4 (22) 15
• 5 (26) 6
• 6 (30) 1