Answer:100% offspring has extra finger
Let say that the dominant gene for extra finger is F and the recessive gene if f. That means the parent genetic would be:
Mother: homozygous dominant = FF
Possible allele: 100% F
Father: homozygous recessive= ff
Possible allele: 100% f
Since the father has 100% chance to give f allele and the mother has 100% of giving F allele, then the offspring would be:
100% Ff (heterozygous). Since the extra finger condition is dominant, a heterozygous individual will express the extra finger condition.