11.3 CHROMOSOMES & HUMAN HEREDITY
WHAT YOU WILL LEARN
-The role of telomeres
-How nondisjunction leads to Down syndrome and other abnormalities
-The benefits and risks of fetal testing
JUST LIKE ME VIDEO – DOWN’S SYNDROME
http://www.youtube.com/watch?v=5M--xOyGUX4
READING Q’s
APPLY:
Examine the karyotype.
Are these chromosomes for a male or female?
-MALE
READING Q’s
DEFINE
-What happens during nondisjunction?
-homologous chromosomes do not separate during meiosis 1
-sister chromatids do not separate properly during meiosis 11
NON-DISJUNCTION
READING Q’s
EVALUATE
-Does nondisjunction during meiosis produce any normal gametes?
-YES
EXPLAIN-nondisjunction during meiosis II produces
two normal and two abnormal gametes
READING Q’s
LABEL
-Circle the pictures that show a trisomy in the sex
chromosomes
READING Q’s
STATE
-The purpose of fetal testing
-test for genetic disorders in the fetus
-determine course of action
BACKGROUND INFO
KARYOTYPE
-method of identification of chromosomes
HOW
WHY
-identify abnormalities in
-picture taken during mitosis
chromosomes/genes
-image enlarged
-identify sex of fetus
-individual chromosomes cut up
-chromosomes matched based on:
-size
-centromere position
-gene banding
-pairs arranged from largest smallest
KARYOTYPE: EXAMPLE
A mess of chromosomes…
KARYOTYPE: EXAMPLE
After karyotyping- male or female?
NORMAL MALE
NORMAL FEMALE
NON-DISJUNCTION
WHAT
-chromosome pair or sister chromatids fails to separate during meiosis
-as a result, the gamete that forms has wrong # chromosomes
-TRISOMY: 1 extra
-MONOSOMY: 1 less
FACTS
-occurs quite often in humans
-impact so severe to zygote: miscarriage occurs very early in pregnancy
-if baby survives, develops a set of traits we call a syndrome
NON-DISJUNCTION
Nondisjunction during Meiosis I
Metaphase I
Anaphase I
Failure to
separate
homologous
pairs
NON-DISJUNCTION
Nondisjunction during Meiosis II
Metaphase II
Failure to
separate
Chromatids
Anaphase II
NON-DISJUNCTION: trisomy
Trisomy 21- Down’s Syndrome
-most commonly known trisomy
-extra chromosomes #21
-1:700 births
-distinguishing facial features:
flat nose/face, slanted eyes
-lowered IQ
-short stature
-stubby fingers/toes
-large tongue: difficult speech
-heart/respiratory problems
*chances  as mother’s age 
Trisomy 21—Down’s syndrome
NON-DISJUNCTION: trisomy-13
Patau Syndrome
-extra chromosomes #13
-1:1500 births
-most fetuses don’t develop to term
-serious eye, brain, and circulatory defects
Trisomy 13—patau’s syndrome
NON-DISJUNCTION: trisomy-18
Edward’s Syndrome
-extra chromosomes #18
-many complications
-severe psychomotor growth/retardation
-malformed ears
-distinctively clenched fingers
•95% of conceptions with trisomy 18
don’t survive to term
•only 10% born survive beyond 1st year
Trisomy 18—Edward’s syndrome
NON-DISJUNCTION
These are the only known trisonomy genetic
disorders that result in offspring surviving for a short
period of time
NON-DISJUNCTION OF SEX CHROMOSOMES
These can be fatal
Most do survive just fine
NON-DISJUNCTION: SEX CHROMOSOMES
Klinefelter’s Syndrome - XXY
-1:500 males
-XXY
-tall, sterile male
-normal intelligence
-some female characteristics
NON-DISJUNCTION: SEX CHROMOSOMES
Jacob’s Syndrome (super male) - XYY
-1:1000 males
-XYY
-taller than average
-slightly below normal intelligence
-extra testosterone
XYY
NON-DISJUNCTION: SEX CHROMOSOMES
super female - XXX
-1:1000 female births
-XXX
-no physical problems/fertile
-weakened muscle tone
-may have delayed learning
-taller than average
-most super females unaware they
have an extra X chromosome
XXX
NON-DISJUNCTION: monosomy
Turner’s Syndrome - XO
-1:2700 births
-XO
-females live normal lives
-do not mature sexually at puberty
-sterile
-short stature, short broad neck, broad chest
Monosomy XO
GROUP WORK: GUIDED NOTES
-As a cooperative group complete the guided note sheet
using your knowledge from the reading.
VOCABULARY
REVIEW: gamete
-egg or sperm produced during Meiosis
1- micrograph of chromosomes
-KARYOTYPE
2- abnormal number of chromosomes
-NONDISJUNCTION
3- withdrawal of amniotic fluid from the placenta
-AMNIOCENTESIS
4- extra chromosome 21
-DOWN SYNDROME
5- protective cap at the end of a chromosome
-TELOMERE
KARYOTYPES
EXPLAIN: how chromosomes are arranged in a karyotype
-in homologous pairs LARGEST to SMALLEST
KARYOTYPES
SEQUENCE: how a scientists make a karyotype
1-chromosomes removed during metaphase
2-chromosomes stained
-reveals banding patterns
3-chromosomes pairs arranged: largestsmallest
4-microscopic picture taken
KARYOTYPES
INDICATE: the parts of a karyotype of a child born with Down syndrome.
XX
XXX
XX
TELL: why this karyotype is called trisomy
-THREE CHROMOSOMES of ONE KIND
RECALL term for chromosomes failing to separate
-nondisjunction
STATE: does risk increase with mothers who are younger/older
-older
KARYOTYPES
COMPARE/CONTRAST
TELOMERES
DESCRIBE
DNA
PROTEIN
-Telomeres are made of ____________&______________.
-They are located at the
END of chromosomes
_____________________________________________.
-Their function is to
PROTECT the chromosomes
________________________________________________.
HYPOTHESIZE
-protection of chromosomes during cell
division & against cellular enzymes
NONDISJUNCTION
MODEL
ANALYZE
-Klinefelter’s XXY
-nondisjunction in meiosis 1 or 2 :
-Klinefelter’s results when an XX egg is
fertilized with a Y sperm.
FETAL TESTING
SUMMARIZE the following facts about fetal testing.
-How an abnormal number of chromosomes is identifiedA sample of cells is taken from the individual / fetus
-amniocentesis / chorionic villi sample / fetal blood sample
-four possible results of abnormal chromosome numbers
Embryo death
1-_________________________
Down’s syndrome
2-_________________________
Turner’s syndrome
3-_________________________
Klinefelter’s syndrome
4-_________________________
FETAL TESTING
INFER
What might be the benefits of fetal testing? What might be the risks?
BENEFITS
RISKS
Discovery of genetic problems
-________________
Harm to fetus
-________________
Prepare / make informed decisions
-________________
infection
-________________
REVIEW
1- What could explain a human karyotype showing 47 chromosomes
trisomy
2- Why does nondisjunction occur?
The sister chromatids do not separate
3- Which statement concerning telomeres is not true?
They consist of DNA and sugars