03a Errors in Meiosis & Their Impact

Nondisjunction

Failure of homologous chromosomes to separate during meiosis, causing gametes with extra or missing chromosomes

Meiosis I Nondisjunction

Error during Anaphase I where all gametes have an extra or missing chromosome

Meiosis II Nondisjunction

Error during Anaphase II where half of gametes have an extra or missing chromosome

Monosomy

Having only one copy of a chromosome (e.g., Monosomy X)

Trisomy

Having three copies of a chromosome (e.g., Trisomy 21)

Chromosomal Inversion

Reversal of a chromosome segment end-to-end during crossing over

Chromosomal Deletion

Loss of a chromosome segment and its genes

Genetic Testing

Analysis done to detect or predict genetic disorders

Cytogenetic Testing

Examines entire chromosomes to detect abnormalities

Molecular Testing

Examines DNA sequence for genetic mutations

Biochemical Testing

Examines proteins to assess gene function

Amniocentesis

Sampling of amniotic fluid to analyze fetal chromosomes

Chorionic Villus Sampling

Sampling of placental cells for fetal chromosome analysis

Karyotype

Total number and appearance of chromosomes in an individual

Karyogram

Chart showing paired chromosomes used to detect chromosomal disorders

Down Syndrome

Genetic disorder caused by Trisomy 21

Down Syndrome Traits

Short stature, round face, enlarged tongue, stubby fingers/toes, cognitive impairment

Down Syndrome Frequency

Occurs in about 1 in 750 births; risk increases with maternal age

Down Syndrome Life Expectancy

Over 40 years; about 50% develop Alzheimer’s disease