Monohybrid vs dihybrid inheritance

What is monohybrid inheritance

It is the inheritance of a characteristic controlled by a single gene that depending on the cross may lead to contrasting traits in two different things eg. Plant height

What is discontinuous vs continuous variation

Discontinuous is when the characteristic is controlled by one gene so there are distinct categories with no intermediate values for alleles for the phenotypes - less influenced by the environment

Continuous variation is when the characteristic is controlled by multiple genes with many alleles polygenic so it has many variations and phenotypes and is especially influenced by interaction with the environment

Explain Mendel’s Monohybrid experiments and his conclusion

Mendel did experiments on pure breed peas which has distinct different characteristics so that they could be easily compared. The characteristics he also choose to look at were monohybrid and discontinuous.

He chose peas because

• They are easy and quick to grow

• They produce many seeds to compare - statistically significant

• They have many variation

• They can cross and self fertilize

From crossing them he created his ‘law of inheritance’ = The characteristics are determined by alleles in pairs and a pair is present in each gamete

Explain the steps for doing a monohybrid genetic cross diagram

1. Pick allele letter that are different in upper and lower case eg. T and t

2. Then show the parents phenotype

3. Then show the parents genotype

4. Then show the parents gametes

5. Then cross them to show all the F1 generation (1st gen) possible outcomes in a matrix - Punnet square

6. Then put out the genotypes and phenotypes of offspring

7. Ratios

Explain the test cross

To determine whether a sample is homozygous or hetero

1. Cross the sample with homozygous recessive

2. If heterozygous 50% will be recessive and if homozygous Dominant it will be 25% recessive

What is the difference between co-dominance and incomplete dominance

co-dominance = The alleles in the heterozygote are presented individually so the phenotype bpth the alleleds expressed eg. AB blood group etc.

incomplete dominance = The alleles in the heterozygote are presented as a combination rather both being expressed

What is dihybrid inheritance

The simultaneous inheritance of two unlinked genes resulting in two contrasting traits being inherited together

Explain how Mendel tested dihybrid inheritance and his conclusion

He crossed peas with two contrasting genes eg. Round R vs wrinkled r and yellow Y vs green y and Found the ratio to be 9:3:3:1 = crossing in square

It lead to his second law that chromosomes are segregated during meiosis

Explain how a dihybrid cross differs

1. Create one letter for each inherited characteristic eg. RY ry

2. Parents phenotypes

3. parents genotypes

4. create all gamete possibilities

5. cross them in the Punnet square

6. Give genotype, phenotype and ratio of generation