Chart 1 - Autosomal Recessive Inheritance

1. Carrier × Carrier cross produces a 1:2:1 ratio - 25% affected (homozygous recessive), 50% unaffected carriers, and 25% unaffected non-carriers. The disease only manifests when two abnormal alleles are inherited (one from each carrier parent).
2. The trait skips generations - Because carriers show no symptoms, the condition can remain hidden in a family for multiple generations before two carriers happen to have children together, at which point affected offspring can appear unexpectedly.

Chart 2 - X-Linked Recessive Inheritance

1. Sons have a 50% chance of being affected - Males inherit only one X chromosome (from their mother), so if that X carries the recessive allele, they have no second X to mask it. Sons are either unaffected (XY normal) or fully affected (XY with recessive X). Daughters, by contrast, need two copies to be affected, so they are either unaffected or unaffected carriers.
2. Carrier mothers are phenotypically normal but transmit the condition - The mother has one normal and one recessive X allele. She shows no disease but passes the recessive allele to 50% of her sons (who become affected) and 50% of her daughters (who become carriers like her). This is why the trait appears to "jump" from grandfather to grandson via an unaffected carrier mother.

Chart 3 - X-Linked Dominant Inheritance (Affected Mother)

1. Both sons and daughters can be affected - Because the mutation is dominant and located on the X chromosome, an affected heterozygous mother passes the disease allele to 50% of her sons (XY - affected) and 50% of her daughters (XX - affected). This distinguishes it from X-linked recessive, where daughters are typically only carriers, not affected. The chart shows affected daughter, affected son, unaffected son, and unaffected daughter as the four possible outcomes.
2. The note that some X-linked dominant disorders are embryonic lethal in males - A homozygous dominant (X^D X^D) state is often lethal in utero, and hemizygous affected males (X^D Y) may also be lethal in certain disorders (e.g., Incontinentia pigmenti). This means affected females outnumber affected males in the population, and the male-to-female ratio among affected individuals skews female.

Chart 4 - X-Linked Dominant Inheritance (Affected Father)

1. All daughters of an affected father will be affected; no sons will be affected - An affected father (X^D Y) passes his only X chromosome to ALL his daughters, meaning every daughter receives the dominant disease allele and is affected. He passes his Y to all his sons, none of whom receive the disease allele, so all sons are unaffected. This father-to-all-daughters, no father-to-sons pattern is the hallmark distinguishing feature of X-linked dominant inheritance with an affected father.
2. Females are typically less severely affected than males - As shown in the bottom note of the chart ("most affect females less severely"), daughters who inherit the dominant allele are heterozygous (X^D X), so the normal second X provides partial compensation. Affected sons, when they do survive (in non-lethal X-linked dominant conditions), are hemizygous (X^D Y) and show a more severe phenotype because there is no second normal X to buffer the effect.

Summary Table