GENETICS: 3.4 - errors in meiosis

What is meiosis?

The process of making gametes (egg/sperm) with two divisions, resulting in 4 unique cells

What are the two main purposes of meiosis?

Genetic recombination and genetic reduction

How is genetic recombination achieved in meiosis?

Through crossing over and independent assortment

How is genetic reduction achieved in meiosis?

Through separation of homologous chromosomes in anaphase I

What can go wrong during meiosis?

Errors in chromosome structure or chromosome number

What is an error in chromosome structure?

An incorrect exchange of DNA during crossing over, often involving non-homologous chromosomes

When do errors in chromosome structure usually occur?

During crossing over in Prophase I

What is an error in chromosome number?

When chromosomes fail to separate properly during anaphase I or II

What is non-disjunction?

The failure of homologous chromosomes or sister chromatids to separate during meiosis

What does non-disjunction lead to?

An incorrect number of chromosomes in gametes

What is monosomy?

When a gamete has only 1 chromosome from a homologous pair instead of 2

What is trisomy?

When a gamete has 3 chromosomes in a homologous pair instead of 2

What is aneuploidy?

A condition of having an incorrect number of chromosomes

What happens when a gamete with an abnormal number of chromosomes is fertilized?

The resulting zygote will also have an abnormal number (monosomy or trisomy)

How does an incorrect chromosome number affect the body?

Every cell will inherit the error after mitosis, so all cells will have the wrong chromosome number

What determines whether a monosomy or trisomy results in a live birth?

The chromosome number on which the error occurs

Which trisomies can result in live births?

Trisomy 13, 18, and 21

What usually happens with trisomies of other chromosomes?

They result in miscarriage

Can monosomy result in live birth?

Only if it occurs in the sex chromosomes; otherwise, it results in miscarriage