Epitasis, Penetrance & Lethal Alleles

What is gene action?

Interaction of alleles at a single locus

What is multiple alleles?

More than two possible alleles at a locus in a population but only 2 alleles ever occur in any one individual

What is epistasis?

Inter loci allelic interaction or interaction of genes at different loci

What are the types of 2 loci interactions?

Masking effect: Gene at one locus masks the expression of gene at second locus and expresses its phenotype instead (epistasis)

Modifying effect: Modifies an expression rather than masking it

Penetrance #ff00c2

• What

• AKA

• Depends on

• When is penetrance 100%

What: Percentage with which a (certain genotype) dominant or homozygous recessive gene expresses itself in phenotype

AKA: Reduce or incomplete penetrance

Depends on: Genotype and environment

When is penetrance 100%: If all individuals of genotype show the trait

Incomplete Penetrance

• What

• Percentage of penetrance

• Formula

• Example: find the penetrance

  • Fufu (heterozygous) = distortion and fusion of tail

  • FuFu (homozygous) = very badly fused tails

  • Test cross: Fufu (heterozygous) x fufu (normal)

    • 87 fused tails

    • 129 non-fused tails

  • Problem: 21 non-fused mice had Fufu genotype

What: Not all individuals who carry a specific genotype show the expected trait

Percentage of penetrance: <100%

Formula: Number showing the trait / Total number with the genotype

Example penetrance: 87 / (87 + 21) x 100 = 80.6%

What is expressivity?

Intensity of expression of a given phenotype among those individuals expressing that phenotype

What are lethal genes?

Genes on the chromosome that lead to death

What are the 3 types of lethal genes?

• Aneuploidy #ff9d00

• Monosomy #00c0ff

• Trisomy #9800ff

Lethal Genes: Aneuploidy

• What

• Most observed type of

What: Condition of having less or more than normal diploid number of chromosomes

Most observed type: Cytogenetic abnormality

Lethal Genes: Monosomy #00c0ff

• What

• Example

• Most common during

What: Lack of one of a pair of chromosomes

Example: Turner’s syndrome (females have only 1 X chromosome)

Most common during: Prenatal development

Lethal Genes: Trisomy #9800ff

• What

• Example

What: Having an extra chromosome (three chromosomes)

Example: Down syndrome (trisomy 21)

• Has 3 chromosomes 21 instead of 2

Mitochondrial (cytoplasmic) Inheritance

• Location

• Do eggs and sperm head have mitochondria

Location: Nuclei or mitochondria

Do eggs and sperm head have mitochondria: Only eggs have mitochondria so disease inherited from mom