Whether or not the earlobe is attached is a genetically inherited trait and so you would need to look at earlobes in your, and your partner's, families.
Nowadays it is approximately 0.5169
The probability is zero! There is no such thing as "normal". Every child (and adult) has some unique characteristics and that makes them not normal - in that respect.
It's used commonly to estimate the traits of a child of two parents. For example, the probability of the child having blue eyes, or curly hair, or even having genetic disease.
Since having a child to a child is an independent event (assuming no outside intervention), the probability is still about 50 / 50 boy or girl.
The probability of having a blue-eyed child depends on the genetic makeup of the parents. If both parents carry the recessive allele for blue eyes (Bb), where "B" represents the brown eye allele and "b" represents the blue eye allele, there is a 25% chance of having a blue-eyed child (bb). If one or both parents have brown eyes but carry the blue eye allele, the probability may vary. If neither parent has the blue eye allele, the probability of having a blue-eyed child is 0%.
Attached earlobes are a recessive trait. When one parent has attached earlobes and the other is heterozygous for free earlobes, the chances of any particular offspring having attached earlobes is fifty percent.
The parents would each have the genotype Ee (heterozygous for earlobe attachment) and the phenotype for hanging earlobes. The child inherited the attached earlobe allele from both parents, resulting in the AA genotype and the phenotype for attached earlobes.
Nowadays it is approximately 0.5169
The probability is zero! There is no such thing as "normal". Every child (and adult) has some unique characteristics and that makes them not normal - in that respect.
It's used commonly to estimate the traits of a child of two parents. For example, the probability of the child having blue eyes, or curly hair, or even having genetic disease.
Since having a child to a child is an independent event (assuming no outside intervention), the probability is still about 50 / 50 boy or girl.
It is always 50/50.
1/4
1/2
1/32
By showing the history of genetics in the family
50-50. In the circumstances you list, each child of theirs has an equal chance of having- or not having- HD.