Chromosomal Disorders What happens when meiosis goes wrong? - PowerPoint Presentation

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Chromosomal Disorders

What happens when meiosis goes wrong?

Karyotype

Human Chromosomes

Humans have 46 chromosomes arranged in 23 pairsTwo sex chromosomes- determine an individual’s sexFemales have two copies of the large X chromosomeMales have one X and a smaller Y chromosome

Human Chromosomes

The remaining 44 chromosomes are known as autosomal chromosomes or autosomesMales and females are born in a roughly 50:50 ratioAll human egg cells carry a single XHalf of all sperm carry an X and the other half carry a Y

Male or Female

???

Types of Mutations

Mutations effects vary. One factor is the type of cell if affects…

GERM CELLS-

Cells that undergo meiosis to produce egg and sperm cells (in ovaries and testes)

SOMATIC CELLS-

All the “other” body cells that only do mitosis

How would this affect the person differently?

Types of Mutations

Chromosomal mutations involve changes in the number or structure of chromosomesCan lead to diseases or disorders… or (more rarely) can be beneficial

Chromosomal Mutations

Examples: Entire chromosome mutation = nondisjunction“chunk” of a chromosome mutation= listed to the right in diagram (insertion, deletion…)

Gene/DNA Mutations

Gene/DNA mutations involve changes in ONE nucleotideEx’s- Point and Frameshift Mutations

Chromosomal Mutations

Entire chromosomes encounter mutations as wellThere are four types:DeletionInversionInsertionTranslocation

A B C

D E

Chromosome

Gene

Deletion

Before mutation

After mutation

A B C

D E

A C

D E

Occurs when a single break causes a chromosome to lose an end piece or when two simultaneous breaks lead to loss of internal segment

Inversion

Before mutation

After mutation

A B C

D E

A B C

E

D

Occurs when a part of the chromosome breaks off and is reinserted backwards

Insertion

Before mutation

After mutation

A B C

D E

A B C B C

D E

Occurs when a part of the chromosome breaks off & re-attaches to the same chromosome resulting in a duplication of genes

B C

Translocation

Before mutation

After mutation

A B C

D E

F G

H

F G

H

F G

H

F G

H

F A B C

D E

G

H

Occurs when a part of one chromosome breaks off & attaches to a non-homologous chromosome

Can you spot what is wrong with this

karyotype?

Nondisjunction

Homologous chromosomes fail to separate during meiosis ISister chromatids fail to separate during meiosis II

OR

Creates gametes with the wrong number of chromosomes!

Changes in chromosome structure

DeletionPart of a chromosome is lost during cell divisionChromosome is missing genesDuplicationRegion of chromosome is repeatedTranslocationPiece of a chromosome moves to another chromosome