Backcross Method

Question 1

What is the main objective of the Backcross Method?

Answer 1

Qualitative improvement, by focusing on ONE trait.

Question 2

What is the fundamental process of the Backcross Method?

Answer 2

Repetitve crosses of outlying progeny with specific parent… 2nd donor parent only used once in initial cross.

Question 3

What is the general formula for recovery of recurrent parental of selected genotype?

Answer 3

1 - (1/2)^(N + 1)

where N = # of backcrosses

Question 4

Why do procedures differ in Backcross Methods?

Answer 4

Exact procedures depend on:

• Inheritance of trait of interest
• How trait is evaluated.

Question 5

Discuss steps of Backcrossing a dominant gene.

Answer 5

1. Recurrent parent A (aa) x Donor parent B (AA) -> F1 = Aa
2. aa x F1 Aa -> BC1F1 = 1/2 Aa : 1/2 aa … evaluate / eliminate aa!
3. aa x BC1F1-> BC2F1 = 1/2 Aa : 1/2 aa … evaluate /eliminate aa!

… repeat …

4. BC6F1 Aa, selfed. -> BC6F2 = 1/4 AA : 1/2 Aa : 1/4 aa … evaluate / elimate aa!
5. Self AA’s and Aa’s -> BC6F2:3 rows = 1/3 AA : 2/3 segregate.
6. Bulk AA’s and release!

Question 6

Discuss steps of Backcrossing a recessive gene.

Answer 6

1. Recurrent parent A (AA) x Donor parent (aa) -> F1 = Aa
2. AA x F1 Aa -> BC1F1 = 1/2 Aa : 1/2 AA

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