Mistakes in Meiosis

Nondisjunction Nondisjunction The failure of homologous chromosomes to separate properly during meiosis. What should happen Nondisjunction

The results If the abnormal gametes is fertilized the results

Polyploidy the condition where cells have multiple sets of chromosomes usually 3-4 sets Most often found in plants, rare in animals Polyploidy is the condition where cells have more than one set of chromosomes, as supposed to haploidy. In most organisms which reproduce by sexual reproduction the usual state of cells is diploidy. Some plants (especially flowering plants) exibit triploidy and tetraploidy, or even octoploidy e.g. in strawberry plants and sugar cane. Plants are more likely than animals to exhibit polyploidy because their gametes are produced from somatic cells rather than germ-line cells, and therefore go through more cell cycles, but polyploidy can also occur in some animals. Polyploidy has been observed in insects, fish, amphibians, reptiles, and once in mammals (a rat), though it was once thought polyploidy would be fatal to mammals. Polyploidy is a route by which plants could increase their chromosome numbers, and the size of their genome. Over time changes in the duplicated chromosomes are liable to build up until they can be distinguished as different chromosomes, and the organism can once again be described as diploid ('diploidisation', during which the haploid chromosome number of the organism becomes difficult to define). Polyploidy will duplicate the genes on each chromosome, and during the subsequent changes many copies will be 'turned off', increading pseudogenes and the proportion of 'Junk DNA' in the genome. Polyploid plants are often larger and have other accentuated charactoristics, making them useful in agriculture and horticulture. Polyploidy can be artificially induced in plants by botanists and horticulturalists, e.g. with the chemical colchicine, which provents chromosomes from separating during mitosis.

Examples of Polyploidy Diploid & tetraploid many plants Octoploidy strawberries Triploid seedless watermelon Seedless watermelon is the result of a cross between 4n and 2n – 3n offspring is sterile

Trisomy The zygote has an extra chromosome Organisms with an extra chromosome sometimes survive

Examples of trisomy in humans Trisomy 21: Downs Syndrome Trisomy 18: Edwards syndrome Trisomy 13: Patau syndrome XXY: Klinefelter's syndrome Trisomy 1: rare Trisomy 2: associated with loss of pregnancy Trisomy 3: lethal Trisomy 4: lethal Trisomy 5: lethal Trisomy 6: rare, no heath concerns in know cases (six total cases) Trisomy 7: never reported in live birth childern Trisomy 8: Trisomy 9: Trisomy 10: lethal Trisomy 11: Trisomy 12:majority have normal outcomes Trisomy 13: Patau syndrome 0.03 Trisomy 14: Trisomy 15: lethal Trisomy 16: lethal Trisomy 17: not reported Trisomy 18: Edwards syndrome .2% Trisomy 19: Trisomy 20: not viable Trisomy 21: Downs Syndrome Trisomy 22: Trisomy 23: Trisomy x: XXY: normal development, slightly taller, decreased sperm quality Trisomy X: super female syndrome

Trisomy 21: Downs Syndrome Decreased muscle tone at birth Separated sutures (joints between the bones of the skull) Asymmetrical or odd-shaped skull Round head with flat area at the back of the head (occiput) Small skull (microcephaly) Upward slanting eyes, unusual for ethnic group Small mouth with protruding tongue (see tongue problems) Broad short hands Single crease on the palm Retarded growth and development Delayed mental and social skills (mental retardation) Iris lesion (an abnormality of the colored part of the eye called Brushfield spots)

Trisomy 18: Edwards syndrome Most children die in the first year of life, some have lived 10 years Growth deficiency Feeding difficulties Breathing difficulties Developmental delays Mental Retardation Undescended testicles in males Prominent back portion of the head Small head (microcephaly) Low-set, malformed ears Abnormally small jaw (micrognathia) Small mouth Cleft lip/palate Upturned nose Narrow eyelid folds (palpebral fissures) Widely-spaced eyes (ocular hypertelorism) Dropping of the upper eyelids (ptosis) Overlapped, flexed fingers Underdeveloped or absent thumbs Underdeveloped nails Webbing of the second and third toes Clubfeet Small pelvis with limited movements of the hips Short breastbone Kidney malformations Structural heart defects at birth (i.e., ventricular septal defect, atrial septal defect, patent ductus arteriosus)

Trisomy 13: Patau syndrome Mental retardation, severe Seizures Small head (microcephaly) Scalp defects (absent skin) Small eyes (microphthalmia) Cleft lip and/or palate Eyes close set (hypotelorism) -- eyes may actually fuse together into one Iris defects (coloboma) Pinna abnormalities and low set ears Simian crease Extra digits (polydactyly) Hernias: umbilical hernia, inguinal hernia Undescended testicle (cryptorchidism) Hypotonia Micrognathia Skeletal (limb) abnormalities

XXY: Klinefelter's syndrome Klinefelter Syndrome is probably the most common chromosomal variation found in humans. In random surveys, it is found to appear about once in every 500 to one in every 1,000 live born males. sterility, breast development, incomplete masculine body build, and social and/or school learning problems

Monosomy The zygote is lacking a chromosome Organisms lacking one or more chromosomes rarely survive

Examples of monosomy in humans Monosomy X: Turners Syndrome

Monosomy X: Turners Syndrome Short height Webbed neck Drooping eyelids A "shield-shaped", broad, flat chest Absent or incomplete development at puberty, including sparse pubic hair and small breasts Infertility Dry eyes Absent menstruation Absent normal moisture in vagina; painful intercourse

Karyotyping a picture showing the number and type chromosomes in a cell Chromosomes are arranged in order from largest to smallest Shows major chromosomal abnormalities i.e. pieces of chromosomes are missing of extra copies (will not show defective gene)

Human Karyotype