27.3 Genetic Disorders

•Errors in the chromosome number•Genetic Disorders and sex chromosomes•Genetic Disorders and autosomes•Genetic Counseling

Errors in Chromosome Numbers

• Less than 46 chromosomes

• OR

• More than 46 chromosomes

• Due to mistakes in meiosis

• Anaphase, chromosomes do not get pulled appart

Errors due to Meiosis

*Normal *Normal *Too many *Too few

4 Possible Gametes

Sperm or Egg

Trisomy

• Inheriting three copies of a chromosome instead of two

• Too many

• 47 chromosomes

Down syndrome

• Outwardly slanted eyes • Exaggerated fold of skin

on the inside of the eye • Flat ears set low on the

head • Flattened face • Small teeth • Relatively short arms and

legs.

Edward syndrome • Defects of the kidneys,

ureters, heart, lungs and diaphragm.

• Cleft lip or cleft palate. • Small skull

(microcephaly). • Malformations of the

hands and feet • Neural tube defect, where

the spinal cord, meninges and blood vessels protrude through a gap in the vertebrae

• Malformations of the sex organs

Patau syndrome

• Small skull (microcephaly). • An abnormal opening in the skull. • Malformations of part of the brain. • Structural defects of the eyes. • Cleft lip or cleft palate. • Additional toes or fingers • Congenital heart disorders, such as

ventricular septal defect. • Neural tube defect, where the spinal

cord, meninges and blood vessels protrude through a gap in the vertebrae

• Malformations of the sex organs.

Monosomy

• Inherit one copy of a chromosome instead of two

• Too few

• 45 chromosomes

Monosomy Disorders

• Turner Syndrome

Turner Syndrome

• condition in females (XX)• Due to an absent X-chromosome• short stature• sexual underdevelopment• physical abnormalities

Types of Chromosomes

1. Autosome: a non-sex chromosomes pairs 1 -22 on a karyotype

2. Sex chromosomes: the XX or XY pair 23 on a karyotype

Genetic Disorders

Carried by Sex Chromosomes:

• Hemophilia

Carried by Autosomes

• Dyslexia

• PKU

Hemophilia

• Disorder

• Blood can not form clots

• Found on recessive gene

Dyslexia

• A learning disorder

• Can not see or write letters and or words

• Appear backwards

• Dominant gene

PKU

• Body lacks the enzyme necessary to metabolize phenylalanine to tyrosine.

• Causes brain damage and progressive mental retardation

Genetic Counseling

• Provide information and support to families who have members with birth defects or genetic disorders

• Or

• to families at risk for a variety of inherited conditions.

Counselors

• They identify families at risk, investigate the problem present in the family, interpret information about the disorder, analyze inheritance patterns and risks of recurrence, and review available options with the family.

Pedigree

• a diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships.

• Determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases.

Pedigree

• A series of symbols are used to represent different aspects of a pedigree.

Pedigree

Dominant traits:

• Never skips a generation

• Two affected individuals can give rise to unaffected individuals

Recessive traits:

• may skip a generation

• two unaffected individuals can give rise to affected individuals

I

II

III

IV

Marriage Line

Children line

Siblings