Transcript Sex Linked Traits

• Humans have 23 pairs
of chromosomes.
• One pair of
chromosomes is
related to the sex of
an individual , these
chromosomes are
called sex
chromosomes
• The other 22 pairs of chromosomes
are called autosomes (1-22)
• Genes that are located on the X
chromosome are called sex-linked genes.
• Traits determined by sex-linked genes are
called sex-linked traits
(c = colorblind, C = normal)
Ex. Color blindness
female Xc Xc
male Xc Y
• Sex linked traits are recessive, this
means both x chromosomes must have
the gene in order for the trait to be
expressed.
• If only one x chromosome is present
(in males)and has the sex linked gene,
then the trait will be expressed
• A carrier is a person that has the
trait on only one chromosome and
does not express the trait. Carriers
of sex linked traits are always women.
(C= normal, c= colorblind)
Ex. Color blind carrier XC Xc
•
A colorblind male marries a normal
female. What are the offspring genotypes
and phenotypes?
(C = normal, c = colorblind)
Xc
XC
XC
Y
• A normal male (not colorblind) marries a
carrier. What are the offspring genotypes
and phenotypes?
XC
Y
XC
Xc
• A normal male (not colorblind) marries a
colorblind female. What are the offspring
genotypes and phenotypes?
XC
Y
Xc
Xc
• Hemophilia is
characterized by
uncontrolled bleeding
• It is a sex linked
disorder caused by
errors in the DNA that
codes for the proteins
involved in clotting
Linked Genes
• Some traits seem to be inherited together.
– Example Gray bodied fruit flies also have long
wings.
Genes that tend to be inherited together are on the
same chromosome and called Linked Genes.
Mutations
• Germ-Cell Mutations are changes in your
sex cells. They do not affect the person, but
can be passed on.
• Somatic- Cell Mutations are changes to
your body cells and can affect you.
Mutations
• A Chromosome Mutation is a change in the
structure of a chromosome or the loss or
gain of a chromosome.
• Four main types of mutation.
–
–
–
–
Deletion
Inversion
Translocation
Duplication
Mutations
• Deletion: The loss of a
piece of a
chromosome due to
breakage.
• Inversion: a
chromosomal segment
breaks off flips around
backwards and
reattaches.
Mutations
• Translocation: A piece
of a chromosome
breaks off and
reattaches to a non
homologous
chromosome.
• Duplication: A certain
section of the
chromosome gets
copied twice.
Mutations
• Another mutation that
can occur is when
sister chromatids fail
to separate correctly
during meiosis.
• This is called Nondisjunction.
Chromosome Map
• Scientists are able to
locate individual genes
on a chromosome.
• Due to chromosome
mapping scientists are
able to tell if certain
genes are damaged
and the resulting
disorder.
Pedigrees
• Some Mutations are
inherited.
• Scientists can use
Pedigrees to show
how a trait is inherited
over generations.