KARYOTYPING AND NON-DISJUNCTION Please take out your Gizmo worksheet and vocabulary sheet
Learning Goals Understand what a karyotype is and how to analyze it Learn about symptoms of various syndromes Understand the process of nondisjunction and how it explains the genetic basis of various syndromes
Agenda for Today Take up Gizmo Lesson on Karyotyping Playdough activity Lesson on nondisjuction Nondisjunction worksheet Reading on Gregor Mendel
What is karyotyping? A picture of a cell’s complete set of chromosomes grouped together in pairs and arranged in order of decreasing size Pictures of chromosomes are taken as the cell undergoes mitosis (metaphase)
Types of Chromosomes Sex Chromosomes Autosomal Chromosomes One of two chromsomes that determine an individuals sex In humans and most mammals the two sex chromosomes are the X and Y Females: XX Males: XY Autosomal Chromosomes A chromosome that is not a sex chromosome Humans have 22 pairs of autosomal chromosomes
How do the X and Y Chromosomes Compare? X is larger than Y X chromosome contains about 1,000 functioning genes while the Y chromosome only has about 80 WHY??
How do the X and Y Chromosomes Compare? They Y chromosome is only carried by approximately 50% of the population. Therefore, it cannot carry genes that are necessary for an individual's survival. The genes on the Y chromosome code for only male-specific traits
Preparing A Karyotype Harvested cells are first cultured The cells are then treated with colchicine which arrests the cells in metaphase, and then treated and stained to observe the chromosomes Chromosomes can be photographed or visualized using a computer, and then analyzed Chromosomes are identified by size, position of the centromere, and banding and staining regions
Preparing A Karyotype
A mess of chromosomes…
Analysis of a Karyotype The analysis involves comparing chromosomes for their: Length Placement of centromeres (areas where the two chromatids are joined) Banding pattern.
After karyotyping… a normal male
After karyotyping… a normal female
What is wrong with this picture?
Down’s syndrome
Down’s Syndrome Most commonly known trisonomy 21 1:700 births; 1 in 6 die within 1st year Average age is 16.2 years Common facial feature Short stature Stubby fingers and toes Large tongue – makes speech difficult
Down’s Syndrome Odds of having a Down’s child increases with the age of the mother 1 in 1500 if mom is in early 20’s 1 in 70 if mom is over 35 1 in 25 if mom is over 45
What is wrong with this picture?
Edward’s Syndrome Only 10% survive past one year All die early in infancy Many complications
What is wrong with this picture?
Klinefelter’s Syndrome Affects 1:500 males XXY Tall, sterile males Normal intelligence Has female characteristics
Klinefelter’s Syndrome
What is wrong with this picture?
Monosomy – Turner’s Syndrome (XO) 1:2700 births Live normal lives but do not mature sexually at puberty Sterile Short stature Short broad neck Broad chest
Jacob’s Syndrome (super male) XYY Somewhat taller than average Slightly below normal intelligence 1:1000 males Extra testosterone
XXX (super female?) 1:1000 live births Normal intelligence Fertile No physical problems What is the sex of this person?
How Do These Disorders Occur? You have 10 minutes to complete the following activity. Working in your table groups: Obtain a handful of 2 colours of playdough (do not mix them) Build 2 different coloured homologous, replicated chromosomes Using your chromosomes simulate meiosis Where does meiosis need to go wrong in order to end up with a monosomic or trisomic disorder. There are two possibilities.
Non-disjunction Non-disjunction is a failure of chromosomes to properly separate during either Stage 1 or Stage 2 of meiosis Upon fertilization the zygote may have one too many chromosomes ( trisomy) or one too few chromosomes (monosomy)
Non-disjunction Non-disjunction occurs quite often among humans Impact is so severe to the zygote that miscarriage occurs very early in the pregnancy If the baby survives, it develops a set of traits that we call a syndrome