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If only one parent has sickle cell allele, then the child won’t get sickle cell disease. However, if both parents have sickle cell allele, then the probability of their child having the disease is pretty high
The tetrad occurs during the first phase of meiosis. It is the foursome of chromatids that forms when replicated homologous chromosomes align. It must be formed for crossing over to occur. It is broken apart when the homologous chromosomes separate in meiosis I
