What causes genetic variation in a population? environmental changes random mutations favorable adaptations

Many farmers prefer cattle without horns because it is safer for their herds. the allele for no horns (n) is dominant to the allele for the presence of horns (n). a farmer mates a male with horns to a heterozygous female without horns. what is the chance that the offspring will have horns?

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?

Which substance contains thylakoids? a) nadph b)atp c)stroma d)chloroplast