one parent is heterozygous dominant in earlobe & the other parent is homozygous recessive in earlobe & crossing a heterozygous dominant organism with a homozygous recessive organism causes their offspring to be homozygous recessive of 50% probability ->  the offspring will have a 50% probability to be homozygous recessive  an attached earlobe is a recessive trait in human & if both recessive genes are present , then the recessive trait will be visible / expressed ->  to have an attached earlobe requires the human to have both recessive genes  to have an attached earlobe requires the human to have both recessive genes & a homozygous recessive organism contains only recessive genes ->  to have an attached earlobe requires the human to be homozygous recessive  the offspring will have a 50% probability to be homozygous recessive & to have an attached earlobe requires the human to be homozygous recessive -> the offspring will have a 50% probability to have an attached earlobe