Transcript X c Y - inetTeacher.com

Human Heredity
14.1 and 14.2
Human Chromosomes
• The 46 human chromosomes can be arranged
as a karyotype (picture of chromosomes
arranged in homologous pairs):
Female
Male
Human Chromosomes
• Two of the 46 are sex chromosomes
(female = XX , male = XY)
• ALL egg cells carry a single X; sperm
carry either an X or a Y
• Women can only contribute X’s, while men
contribute half X and half Y
• The other 44 are autosomes
Human Pedigrees
• Some human traits are inherited like traits
in Mendel’s garden peas, with simple
dominance and recessivity
• We can construct a pedigree to trace the
inheritance of traits through a family.
Constructing Human Pedigrees
• Rule One: Use a square for males and a
circle for females.
• Rule Two: Use a horizontal line to link
parents
• Rule Three: Use a vertical line to link
parents to children
• Rule Four: Color in all members with the
trait
Constructing Human Pedigrees
• Let’s trace a white lock of hair above the
forehead through a family:
• 1. Draw two parents; the male has the trait
• 2. They have three children; one male that
has the trait, one female who doesn’t, and
one female who does
• 3. The male has two girls with a female
with the trait; only one child gets the trait
Constructing Human Pedigrees
• 4. The female without the trait has no
partner or children
• 5. The female with the trait has a partner
with the trait; they have two boys and a
girl. One boy and the girl have the trait.
IS THIS TRAIT DOMINANT OR RECESSIVE?
- Predict the genotypes, starting at the top…
Sex Linked Traits (14.2)
• Some alleles for non-gender traits are
found on the X Chromosome
• Men are more likely to have disorders from
these alleles because they have one X
• All alleles on the man’s X chromosome will
physically show up!
• Women can just be carriers of a disorder if
one X is normal
Sex-Linked Trait Problem
XC = normal vision Xc = color blind
Mom is carrier of color-blindness
allele, but is not color blind (XCXc)
Dad has normal vision
XC
Y
XCXC
XC Normal
XCY
Normal son
daughter
Xc
XCXc
XcY
Carrier
Daughter
Color blind
son
Sex Linked Traits
Hemophilia and Muscular Dystrophy are
also common sex-linked traits
Hemophilia: lack protein for normal blood
clotting
Muscular Dystrophy: progressive weakening
and loss of muscle