Chromosomal Disorders

Chromosomal disorders

Having mild to severe (fatal) mental and/or physical deformities due to:

1.Adding or deleting part of a chromosome

1.Having extra or missing chromosomes

How do these disorders happen?

Mistakes before and during

Parents never have the disorders! Can happen to anyone. Family history does not matter!

Must follow:

*Replication rules: Make an exact copy of the DNA with A-T and G-C

*Law of segregation: homologous chromosomes must separate into different gametes

*Crossing over- homologous chromosomes exchange pieces DNA

meiosis!!!

TelophaseII

AnaphaseII

MetaphaseII

ProphaseII

AnaphaseI

MetaphaseI

TelophaseI

Starting cell Interphase

Meiosis

ProphaseI

The cell grows bigger and a copy of each chromosome is made

Interphase

Chromosomes condense and crossing-overoccurs

ProphaseI

The homologous pairs line up in the middle

MetaphaseI

The homologous pairs are pulled away to opposite sides

AnaphaseI

Cell has split in two

TelophaseI

New spindle fibers begin to form

ProphaseII

Chromosomes line up in the middle

MetaphaseII

Sister chromatids are pulled apart

AnaphaseII

Each cell separates leaving 4 unidentical haploid cells

TelophaseII

How do these disorders happen?

1. Adding or deleting part of a chromosome

Causes:

Mistakes during DNA replication Or

Mistakes during Crossing over

How do these disorders happen?

2. Having extra or missing chromosomes

Causes:

Nondisjunction: homologous chromosomes pairs or sister

chromatids do not separate during

meiosis.

This leads to gametes (sperm or egg) that contain more or less than 23 chromosomes

Common Chromosomal Disorders

Down Syndrome = an extra 21st chromosome

Turners Syndrome = Missing X or Y chormosome

Klinefelters Syndrome =having extra X chromosomes XXY or XXXY