poisson mixture model

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I'm a doctor trying to understand Bayesian stats because I'm tired of poking needles in patients when I know that tests don't have excellent specificities and sensitivities.

I need help with a mixture model:

y_a ~ Poisson(θ_a)

y_b ~ Poisson(θ_b)

where θ_a = θ and θ_b = γ and γ is the ratio θ_a/θ_b

θ ~ gamma(a_θ,b_θ)

γ ~ gamma(a_γ,b_γ)

What is the full conditional of θ given y_a, y_b and γ? What is the full conditional of γ given y_a, y_b and θ?

I'm told that p(θ|y_a, y_b, γ) ≡ p(θ|y_a) but I don't understand how that is possible under this parameterization. Or is that wrong?

Thanks for help.