Can use chi-squared to compare with expected results >0.05
Led to Mendel's law of random assortment
"Each member of a pair of alleles may combine randomly with either of another pair"
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Sex-linkage - haemophilia
Any gene on the X or Y gene is sex-linked
The x chromosome is much longer than the Y chromosome
For a lot of the X chromosome, there is no equivalent on the Y chromosome
The characteristics controlled by recessive alleles will appear more frequently in males as there is no homologous portion on the Y chromosome that may have the dominant allele which would stop the expression of the recessive allele
Haemophilia is on the X chromosome which causes blood clots to form slowly which can lead to persistent internal bleeding - especially in joints - can be lethal
Only 1 in 20,000 in Europe
Nearly always males, as females need both copies of the recessive allele and females, would usually die during menstruation at puberty
One cause is a recessive allele that makes a faulty protein required for clotting
This protein can be produced by genetically modified organisms to give haemophiliacs near-normal lives
Males only obtain the Y chromosome from their father the X comes from their mother so males only inherit the disease through their mother
Affected fathers' daughters will always be carriers of the disease as they take the defective X chromsome
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