How do scientist predict the patterns of heredity?

The classic tool to predict the patterns of heredity is using a Punnett Square.

Explanation:

In genetics, a trait can be considered dominant or recessive. Since the important discoveries of Gregor Mendel, scientists use a capital letter (D) to indicate a trait is dominant, and a lowcase letter (d) to show a trait is recessive.

Assuming that a scientist knows the genotype for the desired trait they want to predict on the offpsring, a Punnett Square is a reliable tool and a graphic representation that permits them to visualize the potential features of the offspring by showing how the alleles may be exhibited and passed on the offspring and will determine the possible combination of genotypes.

How does it work?

For example, as we can observe in the image below, both parents are homozygous for a trait PP=Purple; pp=white. P is dominant and p is recessive (the color purple will be dominant, and the white will be recessive). So, we put one parent's genotype in the top row (PP) and the other parent's genotype in the left column (pp) and combine one of each letters on the squares, i.e. one of each parent's alleles. Then, we can observe in the results that 3 of the offspring will exhibit the purple color (PP, Pp, Pp) and only one will exhibit the white recessive color (pp); or more properly known as a genotypic ratio of 3:1.

as resources become scarce because of population growth, the growth decreases after few years due to lack of resources and food.