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