Gene action and Non-Mendelian Inheritance

1. Non-additive

2. Additive

Types of gene action

Non-additive

1. limited genes involved

2. affects qualitative traits (descriptive)

3. produces distinct phenotype

Additive

1. many genes are involved

2. affects quantitative traits (measurable)

3. gradual differentiation in the phenotype of different genotypes

Dominant gene

hides or prevents the expression of its recessive allele when gene pair is heterozygous.

Recessive allele

is only expressed in homozygous recessive pairing.

Lack of Dominance

Both alleles are expressed in the phenotype when the genotype is heterozygous.

Over Dominance

• The heterozygote is superior to both homozygote genotypes.

• Effect of hybrid vigor due to heterosis

• Ex: Sickle cell anemia

Epistasis

• interaction of non-alleles or inter-allelic interaction

• epistatic gene influences the expression of genes which are not their allelic pair.

Additive Gene Action

• Several genes affecting the same trait

• Involve quantitative traits (measurable)

1. Monohybrid cross

2. Dihybrid cross

Types of Genetic Crosses

Monohybrid cross

• cross involving a single trait

• e.g. coat color in cattle

Dihybrid cross

• cross involving two traits

• e.g. coat color and polledness

Punnett Square

Used to help solve genetics problems

Phenotypic Ratios

Shows ratio of what is seen

Genotypic Ratios

Shows what is not seen (Genotype)

Linkage

characters or traits carried in the same chromosome tend to stay together during gamete formation.

Sex-linkage

Happens in the sex chromosomes

Mammals: XY male (heterogametic)

XX female (homogametic)

Birds: ZZ male (homogametic)

ZW female (heterogametic)

Autosomal Linkage

Linked genes or genes located in the same chromosomes tend to be inherited together.

crossing over

linked genes are separated by — which happens during the prophase stage in meiosis 1.

parentals

Individuals appearing like the parents are called the

recombinants

Those appearing less frequently are called the —which are products of crossing over.

Extra-nuclear Inheritance

• Extra-nuclear Inheritance

• Cytoplasmic or extra-chromosomal inheritance

• Ex: mitochondrial DNA

Dam

The eventual phenotype of the progeny is largely

influenced by the __

Height

An individual’s __ is influenced by the mother’s health and condition during pregnancy