1

2

Chromosome NumberChromosome NumberAll cells in the human body (SOMATIC CELLS) have 46 or 23 pairs of chromosomes

Called the DIPLOID or 2n number

GAMETES (eggs & sperm) have only 23 chromosomes

Called the MONOPLOID or 1n number

3

NondisjunctionNondisjunctionChromosomes may fail to separate during meiosis

Resulting gametes may have too few or too many chromosomes

Examples of chromosomal disorders:Down Syndrome – three #21 chromosomesTurner Syndrome – single X chromosomeKlinefelter’s Syndrome – XXY chromosomes

4

KaryotypeA picture of a person’s chromosomes

62n = 46

72n = 46

82n = 47

92n = 47

Downs SyndromeSet of symptoms that can range from mild to

severeSlower mental and physical developmentFlat face with an upward slant to the eye,

short neck, and abnormally shaped ears Poor muscle tone, loose ligaments Heart disease Eye problems Intestinal problems

122n = 47

Klinefelter’s syndromeMaleDon’t produce enough testosteroneSmaller testesBreast enlargementReduced body and facial hairMost infertileIncreased risk of breast cancerMay have learning disabilities1 in 500 births

15

2n = 45

Turner SyndromeShort statureOvaries don’t function correctlyWon’t go through puberty unless

treated with hormones1/3 have extra folds on the neck1/3 have heart defects1 in 2500 births (many miscarry,

though)

Pedigree ChartsThe family tree of genetics

What is a Pedigree?A pedigree is a chart of the genetic

history of family over several generations.

Scientists or a genetic counselor would find out about your family history and make this chart to analyze.

Constructing a Pedigree

Male

Female

Connecting Pedigree Symbols

Married Couple

Siblings

Examples of connected symbols:Examples of connected symbols:

ExampleWhat does a pedigree chart look

like?

Interpreting a Pedigree Chart1. Determine if the pedigree chart shows

an autosomal or X-linked disease.

If most of the males in the pedigree are affected the disorder is X-linked

If it is a 50/50 ratio between men and women the disorder is autosomal.

Example of Pedigree ChartsIs it Autosomal or X-linked?

AnswerAutosomal

Interpreting a Pedigree Chart2. Determine whether the disorder is

dominant or recessive.

If the disorder is dominant, one of the parents must have the disorder.

If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

Example of Pedigree ChartsDominant or Recessive?

AnswerDominant

Example of Pedigree ChartsDominant or Recessive?

AnswerRecessive

Examples of recessive traitsAlbinism – lack of hair and skin

pigmentationTay-Sachs – fatal disease that causes

nerve damageCystic fibrosis – defective protein

needed for lungs and digestion

Examples of dominant traitsAchodroplasia – dwarfism – 1 out of

25,000Huntington’s disease – degeneration

of nervous system leading to death