Unit 4--Genetics

Chapter 14

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. Turner syndrome is associated with underdeveloped ovaries, short stature, webbed neck, and broad chest. Individuals are sterile, and lack expected 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 light = homozygous dominant, Solid light = homozygous dominant,

solid dark = homozygous recessive, solid dark = homozygous recessive, half-circle = heterozygoushalf-circle = heterozygous

• 6) Blood groups

% of U.S. population

Serum

Universal recipient

Universal donor

• 7) 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

• 8) 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

Y

XNXN XNXn

XNY XnY

HY

X H Xh XHXh

XHXh

XHXH XHXh XHY XhY

Carrier Mom

Royal Hemophilia

Sex linkage & calico cats

Polydactyly(multiple fingers and toes)