ABNORMAL MEIOSIS Nondisjunction occurs when two homologous chromosomes
ABNORMAL MEIOSIS • Nondisjunction occurs when two homologous chromosomes fail to separate during meiosis or mitosis. • Daughter cell forms with too many or too few chromosomes
• More serious effects if occurs during production of gametes • Nondisjunction occurs during anaphase I or anaphase II
ABNORMAL MEIOSIS • Nondisjunction in humans produces: • Gametes with 22 and 24 chromosomes. • If the gamete with 24 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 47 chromosomes is produced. • The zygote will have three chromosomes rather than a pair. – This condition is referred to as trisomy
• Nondisjunction results in gametes with too many or too few chromosomes. • Nondisjunction may take place during anaphase I (A) or anaphase II (B).
ABNORMAL MEIOSIS • If the gamete with 22 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 45 chromosomes is produced. • The zygote will have one chromosome rather than a pair – This condition is referred to as monosomy. • Once the cells of trisomic or monosomic zygotes begin to divide, each cell of body will be one plus or one minus a chromosome.
NONDISJUNCTION DISORDERS • Male & Female – Down Syndrome – Patau • XYY • Gender Specific – Turner Syndrome (female) • X 0 – Triplo-X Syndrome (female) • XXX or XXXX – Klinefelter Syndrome (male) • XXY or XXXY – Jacob’s Syndrome (male)
Down Syndrome – Trisomy 21 – Physical signs: • • Flat face Upward slant eyes Abnormal ears Thick tongue – Symptoms: • 40 % congenital heart defects Zhou is also a famous conductor
DOWN SYNDROME
Patau Syndrome – Trisomy 13 – Physical Signs: • • Very small eyes Extra digits Cleft lip Cleft palate – Symptoms: • Heart defects • Brain/spinal cord abnormalities • 5 -10% survive to 1 st birthday
Edward Syndrome – Trisomy 18 – Physical Signs: • Small head & jaw • Clenched hands, crossed legs – Symptoms: • Congenital heart disease • 50% do not survive beyond 7 days
Turner Syndrome • Absence of all or part of the second X chromosome • Symptoms: – Small <4’ 9’’ – Extra skin folds at neck – Failure to develop secondary sex characteristics • Health Conditions: – Infertile – Heart abnormalities
TURNER SYNDROME
Triple X Syndrome • Trisomy X • Symptoms: – Taller than average – Few unusual symptoms • Health Effects – Learning disabilities – Delayed motor skills
Klinefelter Syndrome • XXY • Symptoms: – Taller, leaner – Less body & facial hair • Health Effects: • 90 -95% infertile
Jacob’s Syndrome • XYY • Symptoms: – Learning disabilities – Delayed motor skills – Motor tics (tremors)
JACOBS SYNDROME
NONDISJUNCTION DISORDER STATS • The chances of nondisjunction disorder increases with age • Chances of having a child with Down’s Syndrome – Conceiving between 20 and 24 years, 1 in 1490 – Conceiving at age 40, 1 in 106 – Conceiving at age 49, 1 in 11
KARYOTYPES • A chart of chromosomes. • Obtained by mixing a small sample of tissue with a chemical that stimulates mitotic division. – Division is stopped during metaphase. – Chromosomes are stained – A picture is taken and chromosomes are paired up with their homologue. • Homologue chromosomes are similar in size, length, centromere location and banding pattern. • They are organized in decreasing size with the sex chromosome placed at the end.
Karyotype Info • The karyotype of a normal human female contains 23 pairs of homologous chromosomes: – 22 pairs of autosomes – 1 pair of X chromosomes • The karyotype of a normal human male contains: • The same 22 pairs of autosomes – one X chromosome – one Y chromosome
NORMAL MALE
Practise • Answer questions 1 -6 on Pg. 586
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