Mendel and the basis of inheritance

Studied only one phenotype in each experiment

i.e, HEIGHT, COLOR

When he crossed homozygous plants TALL x SHORT all of the offspring in F1 where TALL

When he crossed F1 with each other, he ended up getting 3 to 1 ratio of TALL to SHORT.

This told him that the characteristic in F1 was dominant and that what we saw in F2 (SHORT) was recessive.

These characteristics were each controlled by a homologous pair of factors (one pat, one mat)

Alleles (Allelomorphs) are the individual members of each pair of factors. Factors are the genes. Gene for height has alleles TT, Tt or tt...etc.

Mendel's breeding experiments

 Breeding 2 homozygotes together yields all heterozygotes in first generation progeny.

All will express the dominant allele.

GENES are not described as dominant or recessive, only phenotypes

The second filial generation gave:

genotype = 1:2:1

phenotype = 3:1

Mendels Laws of Heredity

1. Uniformity: TT x tt = all Tt (Heterozygous)

2. Segregation: Each individual carries two genes for a characteristic but only one is passed on to the next generation at each mating.

3. Independent assortment: Members of different gene pairs segregate to offspring independently of each other (this law is broken by linkage)

example: Tall n smooth

Tall n wrinkled.

The Genome

Has ~5% sequence conserved (under selection), therefore only 5% of the seqeunce is being read

Of the 5%, only 1.5% of genome codes for protein, 3.5% regulates expression of those proteins.

Huntington Disease

- Choreiform movements (involuntary jerky movements, grimacing)

- Forgetful & depressed; restless

AUTOSOMAL DOMINANT

How to determine if phenotype is dominant or recessive:

If the Heterozygote is affected the phenotype is DOMINANT.

(DO NOT describe alleles or genes are being dominant or recessive).