Monohybrid and dihybrid inheritance, codominance and multiple alleles Flashcards
What is monohybrid inheritance?
The inheritance of a single gene.
Give an example of monohybrid inheritance.
- Mendel bred two green pods repeatedly which produced pure breeding for the character of green pods
-This means that the green pods were homozygous - Mendel then bred pure green pods with pure yellow pods and all of the offspring produced green pods
- This means that the allele for green was dominant and yellow was recessive
- When the heterozygous plants were then crossed together, the ratio of green to yellow was 3:1
Why might real life events match ratios calculated?
- Each crossing is independent of each other
- A large sample must be used which makes it more likely that actual results will match the theoretical ratios
What is dihybrid inheritance?
When two characters determined by different genes located on different chromosomes are inherited
Give an example of dihybrid inheritance?
- Mendel crossed two pure breeding types of plants
- one that was round and yellow (dominant) and one that was wrinkled and green (recessive)
- In F1 all of the plants were round shaped and yellow
- In F2 he crossed two of the offspring
- This produces offspring in the ratio 9:3:3:1
9 = round and yellow
3 = round and green
3 = wrinkled and yellow
1 = wrinkled and green - Diagram in books
What is codominance?
When both alleles are equally dominant and both are both expressed in the phenotype
Give an example of codominance
Cw = No pigment
CR = red pigment
As these two alleles are codominant, there are 3 possibilities
1. Cattle that are homozygous for red pigment
2. Cattle that are homozygous for white pigment
3. Cattle that are heterozygous and are light red
What are multiple alleles?
A gene that has more than two alleles
Give an example of multiple alleles?
ABO blood groups
IA = leads to antigen A
IB = leads to antigen B
IO = no antigen
There are 3 alleles but only can be used, therefore there 6 possibilities
