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

LABEL -Circle the pictures that show a trisomy in the sex chromosomes 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 -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…

After karyotyping- male or female? KARYOTYPE: EXAMPLE After karyotyping- male or female? NORMAL MALE NORMAL FEMALE

NON-DISJUNCTION WHAT FACTS -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

Nondisjunction during Meiosis I Metaphase I Anaphase I Failure to separate homologous pairs

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. 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

PROTECT the chromosomes 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 TESTING SUMMARIZE the following facts about fetal testing. -How an abnormal number of chromosomes is identified-   -four possible results of abnormal chromosome numbers 1-_________________________ 2-_________________________ 3-_________________________ 4-_________________________ A sample of cells is taken from the individual / fetus -amniocentesis / chorionic villi sample / fetal blood sample Embryo death Down’s syndrome Turner’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 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