How do you know that individual 1 is heterozygous for trait

you know they are heterozygous for a trait because they have it as jj or jj.

explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.