Mendels Genetics

Law of Dominance

This law states that in a pair of alleles, one allele can be

dominant over the other, determining the organism's phenotype.

Law of Segregation

According to this law, every individual possesses two alleles

for a trait, but only one allele is passed on to the offspring. The alleles segregate

during gamete formation.

Law of Independent Assortment

This law explains that the inheritance of one

gene is independent of the inheritance of the other. Different traits have an

equal opportunity to occur together due to independent assortment

Homologous chromosomes

Same order of genes, but many are

different versions (alleles)

genes arranged along…..

Chromosomes

Different alleles may make different…….

Proteins

Gene mutations may influence the activity of the……

Protein

Examples of differences in

protein function

more/less/loss of enzymatic

activity

• loss/gain of binding partner

Example: Mendel’s pea seed coloration For functional and non-functional enzyme

non-functional enzyme:

can NOT break down

chlorophyll

functional enzyme:

breaks down

chlorophyll

Transmission of recessive alleles between generations

o Q: Why does green reappear in the F2 plants?

Meiosis

Cross (or self) the F1 plants

o In the F2 The green comes back!

o The F2 progeny will segregate in a 3:1 phenotypic ratio dominant:recessive

Test cross, outcome 1: the individual is homozygous

Progeny will all have dominant trait (yellow), and be heterozygous

Test cross, outcome 2: the individual is heterozygous

Progeny will be half YY and half yy (1:1 genotypic ratio)

Functional enzyme and non functional enzyme with synthesizing sugars?

non-functional enzyme:

Can NOT synthesize starch

functional enzyme:

synthesizes starch

from sugars

This is what you get for F2 for dihybrid cross

This is what you get for F2:

o You get a 9:3:3:1 phenotypic ratio in your F2

o However, it’s still just 3:1 each!

What these phenotypic ratios tell us?

o The two traits are transmitted across generations independently from each

other. They are not linked together.

o Mendel called this “independent assortment”

Why do they exhibit “independent assortment”

It is because the two genes are located on separate chromosomes.

Double heterozygotes can make … gamete combos

Four

Why is there 4 instead of 2?

Random orientation and segregation of chromosomes

Four gamete types means ….possible fertilation combos

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