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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 SYNDROMEhttp://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?-YESEXPLAIN--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 chromosomesHOW-picture taken during mitosis-image enlarged-individual chromosomes cut up-chromosomes matched based on:
-size -centromere position-gene banding
-pairs arranged from largest smallest
WHY-identify abnormalities in chromosomes/genes-identify sex of fetus
KARYOTYPE: EXAMPLE
A mess of chromosomes…
KARYOTYPE: EXAMPLEAfter 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
Failure to separate
homologous pairs
Anaphase IMetaphase I
NON-DISJUNCTION
Nondisjunction during Meiosis II
Metaphase II
Anaphase II
Failure to separate
Chromatids
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 CHROMOSOMESThese can be fatalMost 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 karyotype1--chromosomes removed during metaphase 2--chromosomes stained-reveals banding patterns3--chromosomes pairs arranged: largestsmallest4--microscopic picture taken
KARYOTYPES
INDICATE: the parts of a karyotype of a child born with Down
syndrome.
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
XX XXX XX
KARYOTYPES
COMPARE/CONTRAST
TELOMERES
DESCRIBE
-Telomeres are made of ____________&______________.
-They are located at the
_____________________________________________.
-Their function is to
________________________________________________.
HYPOTHESIZE
DNA PROTEIN
END of chromosomes
PROTECT the chromosomes
-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 TESTINGSUMMARIZE the following facts about fetal testing.-How an abnormal number of chromosomes is identified- -four possible results of abnormal chromosome numbers1-_________________________2-_________________________3-_________________________4-_________________________
A sample of cells is taken from the individual / fetus-amniocentesis / chorionic villi sample / fetal
blood sample
Embryo deathDown’s syndromeTurner’s syndrome
Klinefelter’s syndrome
FETAL TESTING
INFER
What might be the benefits of fetal testing? What might
be the risks?BENEFITS RISKS
-________________ -________________
-________________ -________________
Discovery of genetic problemsPrepare / make informed decisions
Harm to fetus
infection
REVIEW1- 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