BIOL 2500 - Topic 3 (part 3)

Mendel’s pure lines

He bred two pure-line parental plants, thereby forming a monohybrid cross:

Yellow seeded pea plants (AA) x Green seeded pea plants (aa)

Seed colour phenotype of F1 generation

They all had yellow colour seeds

Confirming the F1 results

He did reciprocal crosses to confirm his results, where he ended up getting the same thing.

Reciprocal crosses use

1.) It determines if the gene is autosomal or sex-linked

2.) If the gene is inherited equally in both males and females then it is autosomal

Generating the F2 generation

The F1 plants self-fertilized to obtain the F2 generation

F2 generation (phenotypes)

A 3:1 phenotypic ratio was seen (yellow:green)

Replicate crosses results

It produced hundreds of F1 plants and thousands of F2 plants

Reciprocal crosses

Plants with the same phenotypes were crossed, but the sexes of the donating parents were swapped, such that the plant donating the egg in one cross, donated the pollen in another and vice versa.

Test-crosses

1.) Crosses designed to identify the alleles carried by an organism whose genotype is unknown

2.) It is usually to determine whether it is homozygous or heterozygous, so you would cross AA and Aa with aa (the homozygous recessive)

AA x aa (phenotypic results)

100% A (it means the unknown genotype is homozygous dominant)

Aa x aa (phenotypic ratio)

1:1 (it means that the unknown genotype is heterozygous)

Heritable factors

1.) Mendel proposed that traits had heritable factors, otherwise known as genes

2.) In the case of the pea plant, which is diploid, it has a pair of each type of gene

The two different forms of genes are called

Alleles

If a plant has a pair of alleles, it has ___ alleles

2

Genotype alleles

YY, Yy, yy

/ between A/a

It signifies that the two alleles can be found on different homologs, but within the same homologous chromosome

Phenotype alleles

YY and Yy produces the dominant phenotype, while yy produces the recessive phenotype

Homozygous

Individuals with a pair of identical alleles

Heterozygous

Individuals with a pair of different alleles (the phenotype presents as the dominant trait)

Homozygous dominant

Both alleles are dominant alleles and present the dominant trait

Homozygous recessive

Both alleles are recessive alleles and present the recessive trait

Phenotypic ratio

The relative proportions between organisms with different phenotypes

ex.) Mendel’s yellow:green peas —> 3:1

Genotypic ratio

Relative proportions between organisms with different genotypes

ex.) Mendel’s peas —> 1:2:1