Chapter 11.3 – Nondisjunction I.Nondisjunction – the failure of homologous chromosomes to...
-
Upload
julius-patrick -
Category
Documents
-
view
264 -
download
3
Transcript of Chapter 11.3 – Nondisjunction I.Nondisjunction – the failure of homologous chromosomes to...
Chapter 11.3 – Nondisjunction
I. Nondisjunction – the failure of homologous chromosomes to separate properly during meiosis
A. Normal Meiosis – one chromosome of each homologous pair moves toward opposite sides of the cell
B. Nondisjunction Meiosis – both chromosomes in 1 or more
homologous pair move to the same side of the cell
1. Forms of Nondisjunction – 2 different types of
gametes (egg or sperm)a. +1 chromosome –
human gamete with 24 chromosomes instead of the normal 23
b. -1 chromosome – human gamete with 22
chromosomes instead of the normal 23
II. Karyotype – an arrangement of homologous chromosomes
normal karyotype shows 23 pairs of each chromosomes #1-23 (46 total)
A. Procedure:1. Amniocentesis – a large
needle is inserted into mother’s placenta to collect amniotic fluid, which
contains baby’s cells
2. Baby’s cells are searched
for cells in metaphase
3. Metaphase cell is photographed & enlarged on film
4. Chromosomes are arranged in homologous pairs, according to size & structure
B. Autosomes – chromosomes 1-22C. Sex Chromosomes – 23rd pair
Female = XX, Male = XY
III. Disorders Seen on KaryotypesDisorder Condition Total # Effects
Down Syndrome 3 of #21 47 Mental disability, heart defects, respiratory
problems, early death (40s)
Edwards’ Syndrome
3 of #18 47 Severe mental disabilty, deformed skull, pelvis, feet,
die in early infancy
Patau’s Syndrome
3 of #13 47 Severe mental disabilty, deformed face, die in early
infancy
Turner’s Syndrome
1 X in females
45 sterile, webbed neck, short, slight mental disability
Klinefelter’s Syndrome
Extra X in males
47 Normal appearance, tall, sterile
XYY Syndrome Extra Y in males
47 Normal appearance, low mental ability
XXX Syndrome Extra X in females
47 Normal appearance, only some are sterile
Down syndrome
Turner’s syndrome
Patau’s syndrome
Edwards’ syndrome
Klinefelter’s syndrome