6.2.4 Predicting Inheritance: Monohybrid Crosses Flashcards
What is monohybrid inheritance?
Monohybrid inheritance looks at how the alleles for a single gene are passed on from one generation to the next
Known information about the genotypes, phenotypes and the process of meiosis are used to make predictions about the phenotypes of offspring that would result from specific breeding pairs
When two individuals sexually reproduce there is an equal chance of either allele from their homologous pair making it into their gametes and subsequently the nucleus of the zygote
This means there is an equal chance of the zygote inheriting either allele from their parent
How are monohybrid crosses presented?
Genetic diagrams are often used to present this information in a clear and precise manner so that predictions can be made
These diagrams include a characteristic table called a Punnett square
The predicted genotypes that genetic diagrams produce are all based on chance
There is no way to predict which gametes will fuse so sometimes the observed or real-life results can differ from the predictions
What happens if there are multiple alleles?
Many genes have more than two alleles
However, a diploid individual will still only inherit two of the possible alleles
Human blood groups provide a good example of multiple allelism as there are three different alleles:
Alleles IA and IB are codominant, but both are dominant to IO
I represents the gene and the superscripts (A, B or O) represent the alleles
IA results in the production of antigen A in the blood
IB results in the production of antigen B in the blood
IO results in no antigens being produced in the blood
These three possible alleles can give us the following genotypes and phenotypes:
IAIA or IAIO= phenotype A
IBIB or IBIO=phenotype B
IAIB= phenotype AB
IOIO= phenotype O
How are genetic diagrams used with codominance?
When working with codominant alleles the genetic diagrams can be constructed in a similar way, however the genotypes are represented using a capital letter for the gene and superscript letters for the alleles (e.g. IAIA)
There will be more possible phenotypes and so the predicted ratios will be different
