Twins - Genetics

Monozygotic (MZ) twins

Twins that arise from a single fertilized egg that splits into two embryos, sharing 100% of their genes.

Dizygotic (DZ) twins

Twins that arise from two separate eggs fertilized by two separate sperm, sharing 50% of their genes.

Concordance

The percentage of twins both showing a specific trait, used to determine genetic vs. environmental influence.

Heritability estimate formula

2 × (concordance rate in MZ twins) − (concordance rate in DZ twins).

Amniocentesis

A procedure that can be done later in pregnancy (15-20 weeks) to obtain genetic information, providing a reliable sample but taking longer for results.

Chorionic villus sampling (CVS)

A procedure that can be done earlier in pregnancy (10-13 weeks) for faster results, but has a slightly higher risk of miscarriage.

Genetic Information Nondiscrimination Act (GINA)

A law that prohibits discrimination by employers and health insurance providers based on genetic information.

Genetic anticipation

The phenomenon where a genetic disorder presents earlier or with increased severity in successive generations.

Trinucleotide Repeat Disorders

Genetic disorders characterized by excessive repetitions of a sequence of three nucleotides, often showing genetic anticipation.

Genetic counselor pedigree

A family tree used to analyze inheritance patterns and identify genetic risks in families.

Epigenetics in identical twins

Explains differences in traits due to environmental factors and lifestyle despite sharing the same genetic sequence.

Identical vs. Fraternal Twins in genetic anticipation

Identical twins may show differences due to epigenetic factors, while fraternal twins share 50% of genes and may exhibit less pronounced differences.