Hemophilia is a sex-linked trait which is carried on the X chromosomes. Females who have two X chromosomes need to gain 2 alleles with hemophilia in order to get the disease. Males, however, only have one X chromosomes which they get from their mother. If their mother was a carrier and passed on the allele for hemophilia, then her son who doesn't have another X-chromosome will get the disease.

When you do a punnet square you will see the portion of genotypes being 25% AA, 50% Aa and 25% aa. The AA allele is not viable, however, so only the Aa and aa genotypes would make it to term. Since 1 out of 3 children would have aa then the percentage would be 33%.

Since the father has only dominant alleles for the brown phenotype, all of the litter will be brown. However, half the litter should carry the recessive allele. The punnet square below shows the dad's genotype on top and the mom's genotype on the left. The outcome is that half the progeny will have the genotype BB and half will have the genotype Bb. Therefore, all offspring will have the brown phenotype.

      B      B

B  BB    BB

b  Bb     Bb

In order for an offspring to be affected, it must receive an affected allele from both its parents. Hence, the parents can be either carriers or affected. This would give the affected offspring a homozygous recessive genotype (only possibility).

Mitochondrial inheritance only involves mother-to-offspring (son or daughter) transmission. Hence, both those choices can be eliminated. Both mitochondrial and X-linked inheritance do not include father-to-son transmission. Hence, the only differentiating transmission is father-to-daughter (not seen in mitochondrial).

In conventional usage, each individual on the "family tree" that a pedigree represents is shown using a single shape. Males get square shapes; females get circular shapes. (Sometimes, individuals whose sex is not known or not specified will be shown with triangular shapes.)

Since pedigrees are often used to study genetic disorders, it is important to track who was affected by the disorder of interest across the family history. Affected individuals are shown with shaded, colored, etc. shapes, while individuals who did not have the disorder are shown with unfilled, "clear" shapes.

This question asks about an affected male. Since the individual is male, the shape is square; since the individual is affected by the genetic disorder, the shape is solid/filled.

The correct answer here is Marfan's syndrome. If you chose any of the other options, remember what it means to have an autosomal dominant disease vs. an autosomal recessive disorder. If a child has one of their alleles marked for the an autosomal dominant disease, they will exhibit the symptoms of this disease. This is correct for Marfan's disease. For all the other syndromes listed, a child must have both of their alleles marked with disease to exhibit the disease.