How do genes have an additive effect in polygenic inheritance?

The traits that are determined by polygenic inheritance are not an effect of dominance and recessivity, and do not exhibit complete dominance as in Mendelian Genetics, where one allele dominates another. Instead, polygenic traits exhibit incomplete dominance so the phenotype displayed in offspring is a mixture of the phenotypes displayed in the parents. Each of the genes that contributes to a polygenic trait has an equal influence and each of the alleles has an additive effect on the phenotype outcome. Hope this helps!

Explanation:

tsd is temerature dependent sex determination.

tsd: it is a type of environmental sex determination in which the temperature experienced during embryonic/ larval development (ambient temperature for development) determine the sex of the offspring.

crocodile displays the tsd where the ambient temperature of the developing egg determines the individual's sex. for example in the american alligator's eggs, incubation at 33 ºc produces mostly males, while incubation at 30 ºc produces mostly females. so if the american alligator's egg will get the ambient temperature (33 degree celcius)during embryonic development from egg, the offspring will be male and same for the female sex determination.

human-caused climate hope this