Transcript X chromosome - Fort Bend ISD

Human Heredity
• There are traits that are controlled by one
gene with 2 alleles. Often, one is
dominant and the other is recessive
• Example:
widow’s peaks and dimples.
Some traits are controlled by a gene with
multiple alleles – 3 or more for a single
trait.
For example: blood types and skin color in
humans.
• There are 44 chromosomes that we call
autosomal chromosomes.
• However, there are 2 chromosomes that
determine our sex and we call them sex
chromosomes.
• These 46 chromosomes all carry genes on
them that determine our traits.
• Out of our 23 pairs of chromosomes, 1
pair is the sex chromosomes (X and Y).
•
Female = XX
•
Male = XY
• Question: What is the probability
that your parents will have a boy
or girl?
• XY (dad) x XX (mom)
X
X
XX
Y
XY
Phenotype:
50% boy
50% girl
X
Genotype:
XX
XY
50% XX
50% XY
Question?
If my parents have 5 boys in a row, what is
the chance they will have a girl the next
time?
50%
Sex-linked gene:
• Some traits are carried on the sex
chromosomes. Genes on the X or Y
chromosomes are sex-linked genes.
• These traits are passed on from parent to
child. Sex- linked genes can be recessive or
dominant.
• MALES are more likely to have a sex-linked
trait because they only have ONE X and Y. The
allele is USUALLY on the X chromosome.
• Ex. colorblindness, hemophilia, hairy ears,
muscular dystrophy
Are you colorblind?
What numbers do you see?
Carrier – person who has one recessive
allele and one dominant allele for a trait or
heterozygous for that trait (only women
can be carriers).
Example
Hemophiliac carrier XHXh
Colorblind carrier XBXb
• Carriers do not show that particular trait
phenotypically but have a chance to pass
the trait on to their child.
Carrier – half colored
Reading a Pedigree
Task 1: Genotyping a pedigree chart
Task 2:
Take out your pedigree sheet and some paper.
Lets do the first one together.
Do # 2.
Come see me to get your paper starred.
Sex linked Punnett Squares:
Question:
What is the probability that a carrier female and a
colorblind male will have a girl who is colorblind
(b = colorblind, B = normal)?
Xb
Y
Phenotype:
XB
XBXb
XBY
25% normal boy
25% colorblind boy
25% normal girl
Xb
25% colorblind girl
XbXb
XbY
Try this one on your own
Question:
What is the probability that a homozygous
(normal vision) female and a colorblind male will
have a girl who is colorblind (b = colorblind, B =
normal)?
Parents: XBXB x
Xb
X bY
Y
Phenotype:
XB
XBXb
XBY
XB
XBXb
XBY
50% normal girls
50% normal boys
Genetics Disorders and
Mutations
Mutations …
• are changes in the
genetic material
• can be good or bad
• can be on a single
gene or the whole
chromosome
Genetic Disorder –
abnormal condition that a person inherits
through genes or chromosomes.
They are caused by mutations or changes
in a person’s DNA.
Write down 3 disorders that have
affected someone you know.
Cystic Fibrosis
• Genetic disorder where the body produces abnormally thick mucus
in the lungs and intestines making respiration and digestion difficult
• caused by a mutation in a gene. The product of this gene is a
chloride ion channel important in creating sweat, digestive juices
and mucus.
• One in four babies are born with cystic fibrosis
• Most common among Northern European descent
Sickle Cell Anemia
•
•
•
•
Sickle cell is a genetic disorder that affects the
blood’s hemoglobin. Hemoglobin is the protein in
your blood that carries oxygen.
Sickle-cell anemia is caused by a point mutation in
protein chain of hemoglobin, replacing the amino
acid glutamic acid with the amino acid valine
The ‘sickle shape’ of the cell doesn’t allow the red
blood cell to carry very much oxygen.
Most common among African American descent
Famous People with Sickle Cell Disease
Miles Davis, jazz musician.
Paul Williams, singer (The Temptations)
Georgeanna Tillman, singer (The Marvelettes)
Tionne "T-Boz" Watkins, singer (TLC)
Hemophilia
•
•
•
Hemophilia is a genetic disorder in which a person’s
blood clots VERY slowly or not at all.
A person with hemophilia can bleed to death from a
paper cut or scrape.
This is sex-linked disorder on the X chromosome.
– Queen Elizabeth suffered from this disorder.
This man received a
vaccine. This is what having
hemophilia did to is body.
Down Syndrome
•
•
Down Syndrome is a genetic disorder that
occurs when an individual receives an extra
copy of a chromosome.
A mistake occurs during Meiosis I: the
chromosomes failed to separate correctly
(non-disjunction) therefore leaving an extra
copy of chromosome #21.
• Doctor’s use tools like amniocentesis and
karyotypes to help detect most diseases.
What is a karyotype?
• Picture of your
chromosomes
• Arranged from largest
to smallest
• quickly identify
chromosomal
changes
Sex-linked-Practice on your own:
• What is the probability of a female carrier
of hemophilia and a normal male having a
boy with hemophilia?
• What is the probability of a man with hairy
ears and a normal female (not a carrier)
having a child with hairy ears?
• What is the probability of a carrier woman
and a male with muscular dystrophy
having a girl with muscular dystrophy?
Quiz time!
• Get in your same groups as earlier.
• Put together the Genetics magic squares
puzzle.