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John Quincy Adams
Sexy!
Sex Linked and Sex Influenced
Heredity
Sex Determination
 Sex Chromosomes
 X and Y
 Autosomes
 Other 22 pairs
Sex Determination
If female, your 23rd
pair are XX.
X
If male XY.
X
Female
X
Y
Male
Sex Determination
XY
Male
 Male gamete
that determines
sex of offspring.
X
XX
Female
X
Y
XX
Female
XY
Male
XX
Female
XY
Male
X
Sex-Linked Inheritance
Traits controlled by genes located on sex
chromosomes.
The alleles written as superscripts of X
or Y.
Some traits ONLY found on the X and
not on the Y (and a very few vice-versa).
Sex Linked Inheritance
White-eyed
male (XrY)
F2
Females:
all red eyed
Redeyed
female
(XRXR)
Males:
1/2 red eyed
1/2 white eyed
F1 All red eyed
Sex Linked Inheritance
First sex-linked trait discovered in a male
fruit fly. Turned out it was on the X
chromosome.
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Sex-Linked Traits in Humans
 Males pass X to daughters and Y to sons.
 Father CANNOT pass X linked traits to son.
 Females pass one X chromosome to each
offspring.
 The only X boys get is from their mom.
 Girls get one X from mom and one from dad.
Sex-Linked Traits in Humans
Male
Female
Female
Sperm
Eggs
Eggs
Female Female
Male
Male
Female
Male
Sperm
Male
Female
Male
Boy’s Versus Girls
Boys are either dominant for a sex linked
trait, or recessive, only one X.
Girls can be homozygous dominant,
homozygous recessive, OR
heterozygous and carry but not show the
trait.
Red-Green Color Blindness
 Red and green look
the same.
 Caused a recessive
allele on the X.
Red-Green Color Blindness
Red-Green Color Blindness
5 with color vision
2 with color blindness
Red-Green Color Blindness
 Man who is
Colorblind = XcY
Normal sight = XCY.
5 with color vision
2 with color blindness
 What would be the
genotype for a
woman who was
heterozygous?
Hemophelia: An X-Linked Disorder
 Causes a problem with
blood clotting.
 Clotting stops bleeding
 SERIOUS problem with
any kind of bleeding:
 External scrapes and cuts
 Internal bleeding
 Bruises
Hemophelia: An X-Linked Disorder
 Can’t make clotting-factor protein.
 Treated by intravenous injections of clotting
factor even done at home.
 Hemopheliacs can now live fairly normal lives.
Hemophelia: An X-Linked Disorder
 About one male in every 10 000 has
hemophilia, but only about one in 100 million
females.
 If a mother is a carrier for hemophelia but does not
have the disease (heterozygous) and she has
childrent with a father that does not have the
disease, what are the chances that their child with
have hemophelia? Does it matter if the kid is a boy
or a girl?
Hemophelia: An X-Linked Disorder
Sex-Influenced Traits
 Male pattern baldness is the
most commonly known sexinfluenced trait.
 The gene for baldness is
NOT found on one of the sex
chromosomes.
 The trait is INFLUENCED by
the different hormones
present in males and
females.
Sex-Influenced Traits
 B is for bald, b is for normal.
 Male
 Genotype
 bb
 Bb or BB
Phenotype
Normal
Bald
 Female
 Genotype
 bb or Bb
 BB
Phenotype
Normal
Thin Hair