05 Non-Disjunction - Mitosis and Meiosis

Down Syndrome

Also known as Trisomy 21, causes developmental challenges.

Trisomy 21

Extra chromosome 21 leading to Down Syndrome.

Maternal Age Effect

Older mothers have higher risk for Trisomy 21.

Nondisjunction

Failure to separate chromosomes during meiosis.

Gamete Formation in Males

Begins at puberty, producing 1 billion sperm daily.

Sperm Production

Approximately 2.56 x 10^13 sperm in 70 years.

Genetic Combinations

Humans can produce 8,388,608 unique gametes.

Spindle Fibers

Formed during meiosis, critical for chromosome separation.

Meiosis Duration

Takes about three days in human males.

Prophase I Duration

Roughly 48 hours in male meiosis.

Anaphase I Timing

Spindle fibers about 48 minutes old in 48-year-old male.

Prophase II Duration

Approximately 90 minutes in male meiosis.

Anaphase II Timing

Spindle fibers about 90 minutes old in males.

Female Meiosis Complexity

Begins in utero, paused at Metaphase I until puberty.

Spindle Fiber Age in Females

In Anaphase I, spindle fibers are 1-2 days old.

Oogenesis

Egg formation, more complex than spermatogenesis.

Spermatogenesis

Sperm formation, continuous process in males.

Risk Factors for Nondisjunction

Older women and men equally likely to produce extra chromosome.

Nondisjunction Timing

Most likely during Anaphase I and II in egg formation.

Mitosis vs Meiosis

Mitosis does not form tetrads; meiosis does.

Crossing Over

Occurs during meiosis, increasing genetic variation.

Chromosome Count

Humans have 23 pairs of chromosomes.

Chromosome Abnormalities

Can lead to conditions like Down Syndrome.

Cell Cycle Regulation

Critical for normal cell division and cancer prevention.