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) X0 Triplo-X Syndrome (female) XXX or XXXX Klinefelter Syndrome (male) XXY or XXXY Jacob’s Syndrome (male)

Down Syndrome Trisomy 21 Physical signs: Symptoms: Flat face Upward slant eyes Abnormal ears Thick tongue Symptoms: 40 % congenital heart defects Zhou Zhou is also a famous conductor

DOWN SYNDROME

Patau Syndrome Trisomy 13 Physical Signs: Symptoms: Very small eyes Extra digits Cleft lip Cleft palate Symptoms: Heart defects Brain/spinal cord abnormalities 5-10% survive to 1st birthday

Edward Syndrome Trisomy 18 Physical Signs: Symptoms: 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: Health Effects Taller than average Few unusual symptoms Health Effects Learning disabilities Delayed motor skills

Klinefelter Syndrome XXY Symptoms: Health Effects: 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