Transcript Sex Linked Traits

Human Heredity
14.1
& Sex Linked Traits
2/22/2011
Human Genome
A genome is a full set of
information that an organism
carries in its DNA
Studying genomes means studying
chromosomes
When would it be possible to “see” the
chromosomes in order to study them?
Karyotypes
 Pictures are taken of cells
during mitosis, the
chromosomes are cut out of
the pictures and arranged
into another picture
 Show the complete diploid
set of chromosomes,
grouped together in pairs,
and arranged in order of
decreasing size
Sex Chromosomes
2
of the 46 CHX in the human genome
are the sex CHX
What
ALL
do these CHX determine?
human egg cells contain an X
chromosome (designated: 23, X)
½ of all sperm cells contain an X (23,
X) and ½ all sperm cells contain a Y
(23, Y)
Sex Chromosomes
X chromosomes
(about 1,200 genes)
are larger than Y
(about 140 genes)
Human Genome
The other 44 CHX are
called autosomes, and
pairs are numbered 1-22
So the complete human
genome consists of 44
autosomes and 2 sex
chromosomes
Cells are labeled as:
 46, XX (females)
 46, XY (males)
Gene Linkage
Think about the karyotype - Can
two alleles from different genes be
inherited together?
Yes! Alleles of different genes tend
to be inherited together when they
are on the same CHX
Gene Linkage con’t…
 These genes are said to be “linked”
 Each CHX is actually a group of
linked genes
 The closer together they are, the
more likely they are linked
 The further apart they are, the less
likely
Transmission of Human Traits
• Human genes follows the same patterns of
inheritance as the genes of other organisms
 Dominant / recessive alleles
 Rh blood group (+ or -)
 Codominant alleles
 Blood types
 Multiple alleles
 Blood types
 Polygenic traits
 Skin color, height, metabolism, eye color,
intelligence
 Sex – linked inheritance
Sex Linked Traits
 Because the X and Y chxs determine sex,
the genes located on them show a
pattern of inheritance called sexlinkage
 A sex-linked gene is a gene located on
a sex CHX
 Genes on Y chx are found only in males
and passed directly from father to son
 Genes on X chx are found in both sexes
Sex Linked Traits
 In humans, three genes control color
vision
 All three genes are located on the X
chx
 Color blindness is a recessive trait
 1 in 12 males are red-green color blind
 1 in 200 females are red-green color blind
 Why the difference?
END