Table I.

Breeding for β-null mice.

Parents	Target genotype	Target frequency of offspring (1/4 expected)
Hbb^th^–3/+, γ^lo/γ^lo × Hbb^th^–3/+, γ⁻/γ⁻	Hbb^th^–3/Hbb^th^–3, γ^lo/−	0 of 35
Hbb^th^–3/+, γ^lo/γ^lo × Hbb^th^–3/+, γ^lo/γ^lo	Hbb^th^–3/Hbb^th^–3, γ^lo/γ^lo	0 of 68
Hbb^th^–3/+, γ^hi/γ^hi × Hbb^th^–3/+, γ^hi/γ^hi	Hbb^th^–3/Hbb^th^–3, γ^hi/γ^hi	1 of 29^*

Died at 2 months of age.