Transcript X-linked Traits

staff.tuhsd.k12.az.us
 Tell
the difference between sex
chromosomes and autosomes
 Define different types of mutations
 Evaluate and create pedigree charts
 In
the early 1990’s a researchers noticed that
Drosophilia melanogaster (fruit flies) had 4
chromosomes

3 were the same in both males and females and 1
was different
house-flies.net
exploratorium.edu
 Sex
chromosomes contain genes that
determine the sex of an individual (“X”
or “Y”)
 Males
decide the gender
 Autosomes-all
the other chromosomes
that are not involved in gender
determination
 Cause
about half of all genetic diseases
 Pair
of genes that are inherited together
 They are located in the same chromosome
and very close together.
graphicshunt.com
 Refers
to a trait that is coded for by an allele
on a sex chromosome (X or Y)



More X-linked traits than Y-linked traits because
the of the size difference
Males who have an X chromosome that carries a
recessive allele will exhibit the sex-linked trait
Females have less of a chance expressing an X
linked disease because they have 2 Xchromosomes
karakalpak.com
 Germ-cell

– occur in the gametes
Effect the offspring
 Somatic-cell
– occur in an organisms body
cells

Can not be inherited-results in things like
leukemia or skin cancer
 Lethal
– cause death, often before birth
 Beneficial – help the organism survive and
reproduce
photography.nationalgeographic.com
 Change
the structure of the chromosome
 Deletion and Insertion
 Loss of nucleotide bases or an addition of
them
biology-online.org
A
piece of the chromosome
breaks off and flips
around backward
activars.com
•A piece of one
chromosome
breaks off and
attaches to a
nonhomologous
chromosome
http://www.youtube.com/watch?v=XAGxp
9j5rtc&feature=related
staff.jccc.net
 The
chromosomes don’t separate during
meiosis so one gamete receives 2 copies and
the other receives none.
 Trisomy
– an extra chromosome in every
cell
Most of these disorders make it very difficult
for the individual to survive
 Trisomy 21-down syndrome
 Trisomy 18 &13-normally die before age 1

 Monosomy
– absence of 1 chromosome
Typically lethal to embryonic
development
 Turner’s syndrome

cdadc.com
 Point
mutation – change within a single gene
 Substitution – one nucleotide replaces
another
 Frameshift mutation – if some nucleotides
are deleted the entire segment of DNA moves
down changing the codons for amino acids

Detrimental to the proteins function
 Insertion
mutation – one or more nucleotides
are added which can result in a frameshift
mutation
 Sickle
Cell Anemia: only 1 amino acid is
substituted to produce the sickle shape
 Recessive trait that prohibits
Hemoglobin from binding correctly
To the red blood cell
unitedhealthdirectory.com
 Changing
one letter completely alters the
codon sequence
staff.um.edu.mt
 Substitution:
 Original
– the fat cat ate the wee rat.
 Mutation - The fat hat ate the wee rat.
 Insertion:
 Original: The fat cat ate the wee rat.
 Mutation: The fat cat xlw ate the wee
rat.
 Frameshift:
 Original: The fat cat ate the wee rat.
 Mutation: The fat caa tet hew eer at.
1. Below is the base sequece for the normal protein for
normal hemoglobin and sickle cell:
Normal: GGG CTT CTT TTT
Sickle: GGG CAT CTT TTT
Is this a point or frameshift mutation? Explain.
2. Delete the first H in the following sequence and regroup
the letters in groups of three. Does the sentence still make
sense? What type of mutation is this
THE FAT CAT ATE THE RAT
3. Name 2 chromosome mutations. How are they alike? How
are they different?
4. Using the sequence ATT GCA AAG GGT. Give an example of a
deletion, insertion, and substitution. Circle the change you
have made.
5. What is the difference between sex chromosomes and
autosomes?
 Huntington’s
Disease
 Down’s Syndrome
 Cystic Fibrosis
 Duchenne muscular
dystrophy
 Sickle
Cell Anemia
 Trisomy 18 (Edwards)
 Tay-Sachs disease
 Color blindness
 PKU (Phenylketonuria)
 Fragile X syndrome
•Thalassemia
•Marfan syndrome
•Breast Cancer
•Hemophilia
•Cri du Chat
•Polydactyly
•Maple Syrup urine disease
•Turner Syndrome
•Klinefelter's syndrome,
•(XXY syndrome)
•Super males (XYY)
•Patau syndrome
•Albinism
 Diagram
that shows how a trait is inherited
over several generations
http://www.uic.edu/classes/bms/bms655/gfx/pedigree1.gif
Reading Pedigrees
•A
circle
represents a
female
•A square
represents a male
• If the circle or
square is filled in
that means the
individual has the
trait
• Horizontal lines
indicate marriage
or having children
• Vertical lines
show offspring
Practice Problems
Is the mom or dad in generation I affected by a trait?
How many offspring are shown in generation II?
How many daughters & sons in generation II?
How many have the trait?
How many offspring does daughter #1 have?
How many have the trait?
 Autosomal
Dominant Traits
 Passed on to sons or daughters even if only
one parent has the gene
 Affected individuals who mate with an
unaffected individual have a 50% chance of
passing on the gene as long as they are not
homozygous for the trait
 Can appear in males and females equally
 What
must the
genotype of the
parents be to produce
a child #7 who is
unaffected?
 What is the genotype
of #9?
 What are the
genotypes of the 3
children in the third
generation?
 In
order to be passed on both parents must
have the gene
 Traits can be passed on if both parents are
“carriers” of the trait

Have the trait but it isn’t expressed because they
also have the dominant trait
 An
individual who is infected may have
parents who are not
 If both parents are affected, all of their
children will be affected
•If individuals 2 + 3 in generation 3 have more
children- will they be affected?
•Can Individual #8 in gen. 3 have any
unaffected children?
•Can individual #9 in gen 3 have affected
children?
 Located
only the sex chromosomes (X and Y)
 More frequently expressed on males than
females
 Y-linked is male only
 X-linked –passed from mother to son


Mainly expressed in males
Daughters are carriers
 Traits
that are on the X chromosome
 Males are affected more than females
 Color blindness is an X-linked recessive
disorder passed from mother to son
 Evident
in males because they only have 1 X
chromosome
 Women are rarely affected because they
have 2 X chromosomes-better chance of not
getting it
 If the father has the mutated gene all of his
daughters will have it
 No
transmission from father to son
 All daughters of the affected male will have
it
 Only 1 dominant allele is needed for the trait
to be expressed
 What is the genotype of #2 in generation II?
 Diseases
that have a genetic basis
 Researchers have found that most traits are
Polygenic – influenced by several genes

Skin color – combination of 3-6 genes which
control the amount of melanin in the skin
 Complex
characters – influenced by both
genes and environment

Height, certain diseases such as breast cancer
cosbiology.pbworks.com
 Displaying
a trait that is intermediate of
the two parents
Wavy hair comes from one parent having
straight hair and one parent having curly hair
 Red flower and a white flower produce a pink
flower

doctortee.com
 Males
and females can show different
phenotypes even when they share the same
genotype
Ex: Male pattern baldness – the allele is
dominant in males but recessive in females
due to the higher testosterone levels in
males
 Trait
controlled by 1 allele-dominant or
recessive
Dominant Examples
Huntington’s Diseasedegradation of the brain
Polydactly- presence of a
sixth digit
Achondroplastic
dwarfism-dwarf size
Recessive Examples
Cystic Fibrosis-most
common lethal disease
Sickle-cell anemia-blood
disorder
Albinism- lack of color
pigment in skin, hair, and
eyes
 Amniocentesis
– technique used to detect
genetic disorders in a fetus
 Chrionic villi sampling – takes some cells
derived from the placenta
 Treatments
depend on the specific disease