NON-MENDELLIAN PATTERNS OF INHERITANCE

HETEROZYGOATS

According to Mendel’s law, phenotypical characteristics are

determined by pairs of factors (alleles) that

separate independently in gametes.

Lack of Dominance

A genetic condition in which the heterozygous individual has a different phenotype from the homozygous individual.

Multiple Alleles

The phenomenon in which the same gene has more than two different alleles

Pleiotropy

Pleiotropy (or pliotropy) is the phenomenon in which a single gene conditions several different phenotypical traits.

Pleiotropy

Pleiotropy

Lethal Genes

Lethal genes are genes with at least one allele that, when present in the genotype of an individual, cause death.

Sex-linked Inheritance

A type of non-Mendelian inheritance because it opposes Mendel’s first law, which postulates that each trait is always conditioned by two factors (alleles).

Sex-linked Inheritance

Sex-linked traits are genetic characteristics determined by genes, which are located on sex chromosomes.

Sex-linked Inheritance

Sex-linked Inheritance

Gene Interactions

Gene interactions are the phenomenon in which a given phenotypic trait is conditioned by two or more genes

Gene Interactions

The three main types of gene interaction are: complementary genes, epistasis and polygenic inheritance (or quantitative inheritance).

Complementary Genes

Complementary genes are different genes that act together to determine a given phenotypic trait.

Epistasis

Gene interaction in which a gene (the epistatic gene) can disallow the phenotypical manifestation of another gene (the hypostatic gene).

Epistasis

In dominant epistasis, the inhibitor allele is the dominant allele (for example, I) of the epistatic gene and, as result, inhibition occurs in dominant homozygosity (II) or in heterozygosity (Ii).

Epistasis

In recessive epistasis, the inhibitor allele is the recessive allele of the epistatic gene (i) and, as a result, inhibition occurs only in recessive homozygosity (ii).

Polygenic Inheritance

Gene interaction in which a given trait is conditioned by several different genes with alleles that may or may not contribute to increasing the intensity of the phenotype.

Gaussian Curve

Pedigree Analysis

Hemophilia is a recessive, sex-linked disorder which causes an inability to clot when bleeding. Ray and Elaine Smith were married in 1970. Neither Ray nor Elaine had hemophilia. They had two daughters and then a son. Both daughters, Alicia and Candace, had normal clotting abilities and never had any children of their own.

Pedigree Analysis

The son, Mike, had hemophilia and married Beth, who did not. They had two children of their own, first Gregory and then Victoria. Surprisingly, Victoria had hemophilia but Gregory did not. Draw the pedigree that traces hemophilia in the Smith family, shade in the circles/squares of the individuals with the blood disorder.

Pedigree Analysis

a.) Why is it surprising that Victoria had hemophilia but Gregory did not?

b.) If Victoria has children, what do you automatically know about her… Daughters? Sons?

Very Short Quiz!

Briefly explain the following terms:

1. Incomplete Dominance2. Codominance3. Lethal Genes4. Gene Interaction5. Pedigree Analysis