Y-Linked Inheritance Probability Calculator for Sons and Daughters

Enter whether the father has the trait, and the calculator reports separate probabilities for biological sons and biological daughters. The result follows the defining rule of Y-linked inheritance: a father gives his Y chromosome to every son and gives an X chromosome, not a Y chromosome, to every daughter. The calculation is deterministic and intended for clear genetics exercises and inheritance explanations.

How Y-linked inheritance works

A Y-linked trait is associated with a gene or variant on the Y chromosome. In the usual human chromosomal model used for basic inheritance problems, a biological father has one X chromosome and one Y chromosome, while a biological mother has two X chromosomes. The father contributes either an X or a Y chromosome to a child. A child who receives the father's Y chromosome is a biological son in this model, and a child who receives the father's X chromosome is a biological daughter. Because the relevant trait is on the Y chromosome, it follows the Y whenever that chromosome is transmitted. An affected father therefore passes the Y-linked trait to all of his biological sons. He cannot pass that Y chromosome to a biological daughter, so the probability for daughters is zero. This calculator applies that direct transmission rule. It does not average sons and daughters together, because the sex-specific probabilities answer different inheritance questions and have different results.

How to read the calculated probabilities

Set `father_has_trait` to true when the biological father carries and expresses the Y-linked trait described by the problem. The calculator then returns a son inheritance probability of 1, equivalent to 100 percent, and a daughter inheritance probability of 0, equivalent to 0 percent. Set the field to false when the father does not have that Y-linked trait. In that case, neither sons nor daughters inherit the trait from him, so both reported probabilities are zero. The decimal probability fields are convenient for software and further calculations, while the percentage fields are easier to read in homework, counseling notes, or teaching material. These are conditional probabilities: the result for a son assumes the child is a biological son, and the result for a daughter assumes the child is a biological daughter. The calculator does not predict whether a future child will be a son or daughter, and it does not combine that separate event with inheritance.

Scope, assumptions, and responsible use

Use this calculator for traits that are genuinely Y-linked and for problems that explicitly use father-to-son Y-chromosome transmission. It is not a general Mendelian genetics calculator. X-linked, autosomal dominant, autosomal recessive, mitochondrial, sex-limited, and multifactorial traits follow different rules and require different inputs. The result also does not estimate whether a person has been correctly diagnosed, whether a variant is fully penetrant, or how strongly a trait will be expressed. Real genetic findings can involve mosaicism, structural chromosome differences, uncertain variant classification, incomplete clinical information, and other factors that a one-rule educational calculator cannot represent. For a classroom pedigree, the output provides a quick check of the expected father-to-son pattern. For personal health or reproductive decisions, treat it as an explanation of the simplified inheritance model rather than medical advice, and discuss laboratory findings and family history with a qualified genetics professional who can evaluate the specific evidence.