Human Heredity

• 1) Autosomes– all the chromosomes

except the sex chromosomes (in humans, there are 22 pair)

2) Sex chromosomes– The sex-determining

chromosomes, the X & Y

• 3) Karyotype– Pictures of paired

human chromosomes arranged by size, used to identify abnormalities in fetuses

– Cells from an amniotic fluid sample are cultured, stained & photographed

• 4) Nondisjunction– Failure of chromosomes to separate– May cause a variety of birth defects, including

trisomy 21 or Down syndrome

• Turner’s syndrome

XX

XX O

•Only 1 sex chromosome is present.

*Associated with underdeveloped ovaries, short stature, webbed neck, and broad chest.

*Individuals are sterile, and lack secondary sexual characteristics.

*Mental retardation typically not evident .

• Klinefelter’s syndrome

• 5) Pedigree5) Pedigree Chart showing family history of a traitChart showing family history of a trait– Solid lightSolid light = homozygous dominant, = homozygous dominant, – solid darksolid dark = homozygous recessive, = homozygous recessive, – half-circlehalf-circle = heterozygous = heterozygous

• 6) Genetic disorders– Harmful effects produced by mutated genes,

most are recessive and few are lethal– Example: sickle cell anemia

Genotypes

SS

Ss

ss

Normal, with malarial resistance

Same as parents ; normal, no resistance; sickle-cell anemia

• 7) Sex-linked traits– A recessive gene on the X chromosome– Examples: color-blindness & hemophilia

– Genotypes:Phenotypes:– XNY normal male– XnY colorblind– XNXN normal female– XNXn carrier female– XnXn colorblind

normal vision

“weak red”

“weak green”

Phenotypes???

Cross of carrier female & normal male

XN

Xn

XN XNXN XNY

XN Xn XnY

Y

HY

X H Xh XHXh

XHXh

XHXH XHXh XHY XhY

Carrier Mom

Royal Hemophilia

Sex linkage & calico cats

Polydactyly(multiple fingers and toes)