How is genetic information inherited? - OCR 21st CenturyUse probability, direct proportion and ratios
Our genes are inherited from our parents, and the different combinations of these genes make us unique. Genetic inheritance controls the characteristics of all living things.
Mathematics - Use probability, direct proportion and simple ratios
You can express the outcome of a genetic cross using probability, direct proportion or ratios.
Worked example
Two parents are both carriers of phenylketonuria (PKU). This means that they are both heterozygousThis describes a genotype in which the two alleles for a particular characteristic are different..
P = normal
p = phenylketonuria
P
p
P
PP
Pp
p
Pp
pp
P
P
PP
p
Pp
p
P
Pp
p
pp
Direct proportion
A quarter of the offspring would develop phenylketonuria (pp), a quarter would be completely normal (PP) and half would be carriers (Pp).
Probability
The probability of the offspring being PP is 25%.
The probability of the offspring being Pp is 50%.
The probability of the offspring being pp is 25%.
Ratio
The ratio of the genotypes PP:Pp:pp is 1:2:1
It is important to remember during the process of fertilisation, the allele combinations created are a random process, and that is why probability is used - nothing is guaranteed.