14-2 Human Chromosomes

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14-2 Human Chromosomes
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• A human diploid cell contains more than 6 billion
  base pairs of DNA
• All DNA is packed into 46 chromosomes.

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Human Genes and Chromosomes

• Chromosomes 21 and 22 are the smallest human
  autosomes.

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• Chromosome 21 contains 225 genes
• Contains associated amyotrophic lateral sclerosis
  (ALS) Lou Gehrigs disease.
• Many regions have no genes at all.
• Chromosome 22 contains as many as 545 different
  genes
• Disorders can cause leukemia and
  neurofibromatosis
• Long stretches of repetitive DNA are unstable
  sites.

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Remember

• Genes located close together on the same
  chromosome are linked, meaning that they tend to
  be inherited. It is true for many genes but they
  might be divided by crossing over.

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Sex- Linked Genes

• There is a special patter of inheritance for
  genes located on the X chromosome or the Y
  chromosome because they determine the sex.
• Many sex-linked genes are found on the X-
  chromosome

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SEX CHROMOSOMES CAN CARRY OTHER GENES TOO
___________________
SEX LINKED TRAITS
These traits show up in different
_______________ in males and females because
they move with the sex chromosomes
percentages
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• Y-LINKED GENES
• Genes ______________ chromosome

carried on Y
EXAMPLEHairy pinna
ONLY
Y linked
in males
________genes _____ show up _______
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X-LINKED

• ____________ GENES
• are carried on the X chromosome

X-linked recessive disorders show up
_____________ in ______ than females because
males only have ______ X chromosome.
MORE frequently
MALES
ONE
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• Males ONLY HAVE ONE X

DEFECTIVE
NORMAL
They either have the disorder
They are normal
Or
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• FEMALES HAVE TWO X CHROMOSOMES

DEFECTIVE
NORMAL
DEFECTIVE
Females have one normalgene that works.
Females __________defective recessive alleles to
show the disorder
need 2
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• The X chromosome in males . . .
• flies WITHOUT a copilot!
• . . . theres NO BACK UP X to help them!

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X-LINKED RECESSIVE

• Examples of ____________________
• DISORDERS
• ____________________
• ____________________
• ____________________

HEMOPHILIA
COLORBLINDNESS
DUCHENNE MUSCULAR DYSTROPHY
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COLORBLINDNESS

• CAUSE Mutation in one of three genes for
  _______________ carried on X chromosome
• Persons with this disorder have trouble
  distinguishing colors.
• _________________
• colorblindness is most common
• Seen in 1 in 10 males
• 1 in 100 females

Color vision
Red-green
http//gizmodo.com/gadgets/peripherals/samsung-dev
elops-lcd-for-colorblind-036306.php
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http//www.beavton.k12.or.us/sunset/academics/gene
tics.htm
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HEMOPHILIA

• CAUSE Mutation in genes for
  __________________ carried ______ chromosome
• Blood clotting proteins are missing so person
  with this disorder cant stop bleeding when
  injured can ________________ from minor cuts or
  suffer internal bleeding
• from bruises or bumps.

Blood clotting proteins
on X
bleed to death

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HEMOPHILIA

Treatment Need ____________ of normal clotting
proteins to stop bleeding _____________ in
______ because it is X-linked, but females with
______ recessive hemophilia alleles will also
show the trait. 1 in 10,000 males has
hemophilia
injections
More common
males
TWO
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http//www.ikm.jmu.edu/Buttsjl/ISAT493/Hemophilia/
hemophiliaeurope.html
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Duchenne Muscular Dystrophy

• CAUSE
• deletion in gene
• that codes for a
• _______________
• Results in
• ____________________
• and loss of ___________________

muscle protein
progressive weakening
skeletal muscle
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Duchenne Muscular Dystrophy (DMD)

• SYMPTOMS
• 1 in 3000 male births
• Appears before age 5
• Progressive muscle weakening
• Most in wheelchair by age 13
• Eventually lethal

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Whats the pattern ________ traits show up
_______ in _______ __________________
traits ________________________ than females.
________________ can be ________. _____________
__________ traits BOTH ______ _________ can be
________
Y-linked ONLY
males
X-linked recessive
more common in males
ONLY FEMALES _______ carriers
AUTOSOMAL RECESSIVE
MALES FEMALES carriers
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CAT COLOR

• In cats, a gene that
• controls the _____________
• is carried on the
• ____________________

SPOT COLOR
X chromosome
In some female cells the X with the allele for
orange spots is switched off and in some cells
the X with the allele for black spots is
switched off, so cat has different colored
spots.
See a video
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CAT COLOR
_________ cats have only one X chromosome, so
they can only have ____________ of spots!
Male
one color
THINK ABOUT IT? How many colors of spots could a
male cat with Klinefelter syndrome have?
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________________ Abnormalities
CHROMOSOMAL

• 1 infant in 200 newborns has a
  chromosomal abnormality
• 28 of first trimester miscarriages have
  a chromosomal abnormality
• Abnormalities in larger chromosomes dont
  usually survive

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CHROMOSOMAL MUTATIONS
____________________________ Change in the
______________ or ____________ of chromosomes
structure number
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• Homologous chromosomes ________________ during
  MEIOSIS
• _________________________
• One cell gets 2 copies of
• the chromosome the
• other cell gets none.

fail to separate
NONDISJUNCTION
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Normal Meiosis

• Nondisjunction

http//web.udl.es/usuaris/e4650869/docencia/gen_et
ica/meioferti2.html
http//www.tokyo-med.ac.jp/genet/anm/domov.gif
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Nondisjunction
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Nondisjunction

• Since it happens to a
• sperm or egg, the new
• baby can end up
• with _____________ of a
• chromosome
• __________________
• OR
• only ___________ of a
• chromosome
• ___________________

3 copies
TRISOMY
one copy
MONOSOMY
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Human Abnormalities caused by Non-Disjunction____
________________________________________________
__
Down syndrome
Klinefelter syndrome
Turner syndrome
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Down syndrome ( ____________)
TRISOMY 21
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Down syndrome (Trisomy 21)

• 1 in 800 births
• Similar facial features
• Slanted eyes
• Protruding tongue

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Down syndrome (Trisomy 21)

• Simian line on palm

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Down syndrome (Trisomy 21)

• Most common chromosomal abnormality
• 50 have heart defects that need surgery to
  repair
• Mild to severe mental retardation
• Increases susceptibility to many diseases
• Risk of having a child with Down syndrome
  increases with age of mom

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Sex Chromosome Disorders
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Turner syndrome
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Turner syndrome ____
XO

• 1 in 5000 births
• Females have only one X chromosome (45,X)
• Small size
• Slightly decreased intelligence
• 35 have heart abnormalities
• Hearing loss common
• Broad chest
• Reproductive organs dont develop at puberty
• Cant have children

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Klinefelter syndrome XXy
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Klinefelter syndrome

• 1 in 1000 births
• Males have extra X chromosomes
• (Can be XXy, XXXy, or XXXXy) (46,XXY)
• Average to slight decrease in intelligence
• Small testes/cant have children
• Usually not discovered until puberty when dont
  mature like peers

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Karyotype (need cells from baby)
Can tell __________________ chromosomes __________
Some _____________________ Cant see
_______________ mutations
MISSING/EXTRA
GENDER
DELETIONS/INSERTIONS
single gene
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If having extra chromosomes causes genetic
problems, how come having two X chromosomes in
females and one X in males is not a problem?
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X-chromosome Inactivation

• In female cells ______ chromosome is randomly
  ________________
• It condenses and forms a dense region in the
  nucleus called a
• _____________

ONE X
SWITCHED OFF
BARR BODY