Using Fig. 4.2, describe how air temperature and milk yield change from April through August.
In tropical regions, many dairy farmers choose cattle breeds that are tolerant to heat stress (heat-tolerant cattle). These heat-tolerant cattle can cope with higher air temperatures than Holstein Friesian cattle before heat stress begins, and they show milder symptoms of heat stress than Holstein Friesian cattle when the air temperature is equally high. If heat stress is absent, heat-tolerant cattle produce a lower milk yield than Holstein Friesian cattle under the same conditions. Scientists compared the DNA sequences of Holstein Friesian cattle and heat-tolerant cattle for several genes known to affect body temperature. They identified twenty genes with alleles found only in heat-tolerant cattle. Using the information given, including Fig. 4.2: state the type (pattern) of phenotypic variation shown by milk yield in cattle; identify the factors that cause phenotypic variation in milk yield in cattle. In each case, give a reason for your choice.
Using Fig. 4.3, describe how the $SLICK$ allele affects milk yield in Holstein Friesian cattle.
Compare gene editing with selective breeding for introducing the $SLICK$ allele into Holstein Friesian cattle. Include both similarities and differences in your response.