1. Mistakes in Meiosis
Nondisjunction

2. Nondisjuction
Nondisjunction ("not coming apart") is the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2, specifically in the anaphase.

3. Nondisjuction
This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II. The result of this error is a cell with an imbalance of chromosomes.
Such a cell is said to be aneuploid.

5. Results
Loss of a single chromosome (2n-1), in which the daughter cell(s) with the defect will have one chromosome missing from one of its pairs, is referred to as a monosomy.
Gaining a single chromosome, in which the daughter cell(s) with the defect will have one chromosome in addition to its pairs is referred to as a trisomy.

6. Syndromes
In the event that an aneuploidic gamete is fertilized, a number of syndromes might result.
The only known survivable monosomy is Turner Syndrome, where the individual is monosomic for the X chromosome.
Examples of trisomies include Down Syndrome (trisomy 21), Edwards Syndrome (trisomy 18), and Patau Syndrome (trisomy 13).

8. Down’s Syndrome (Trisomy-21)
Short stature
Round face
Developmental Delays
Eyelids that cover inner corner of eyes

10. Edward’s syndrome (Trisomy 18 )
Growth deficiency
Feeding difficulties
Breathing difficulties
Developmental delays
Underdevelopped organs
Small head
Low-set, malformed ears
Cleft lip/palate
Overlapped, flexed fingers

12. Patau syndrome (Trisomy 13)
heart defects
sloping forehead,
small or missing eyes,
low set ears,
cleft palate
extra fingers and toes
Developmental delays

14. Klinefelter’s syndrome
Affects only males
Sterile
Varying affects
Extra X Chromosome

16. Turner Syndrome Monosomy of X chromosomes. All female
Varying Characteristics
Mostly Infertile