Errors in Meiosis

What is Karyotyping? A method of identification of chromosomes Pictures of chromosomes are taken as the cell undergoes mitosis (metaphase) The image is enlarged Individual chromosomes are cut up Chromosomes are matched up based on: Size (largest to smallest) Centromere postion G-banding

Normal Male Normal Female

What is Non-Disjunction? Process where homologous chromosomes or sister chromatids do not separate during meiosis (anaphase I or anaphase II). Non-disjunction produces gametes that have too many (trisomy) or too few chromosomes (monosomy).

Non-Disjunction 22 23 23 24 45 47 monosomy trisomy

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

Down Syndrome Most commonly known as trisomy 21 1:700 births; 1 in 6 die within 1st year Average age is 16.2 years

Down Syndrome Prone to heart defects, respiratory problems and leukemia Odds of having a Down’s child increased 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

Down Syndrome Common facial feature Short stature Stubby fingers and toes Large tongue – makes speech difficult Mental disability (IQ is in the 25-75 range)

XXX (Super Female) 1:1000 live births Normal intelligence Fertile (able to have children) No physical problems

Klinefelter’s Syndrome XXY Affects 1:500 males Tall, sterile males (not able to produce children) Normal intelligence Has female characteristics

Jacob’s Syndrome (super male) XYY Somewhat taller than average Slightly below normal intelligence 1:1000 males Extra testosterone

Homework Read pg. 161-166 Pg. 166 #1, 3, and 9 Study for Meiosis Quiz