this occurs when an organism has more than 2 set of chromosomes is not a desirable occurrence in...
TRANSCRIPT
This occurs when an organism has more than 2 set of chromosomes
Is not a desirable occurrence in humans but is common in plants (ex. Wheat and potatoes)
3n or even 4n are possibilities
Polyploidy
karyotype is the display that is formed when the chromosomes are arranged in pairs according to size with the X and Y chromosomes coming last
Karyotype
homologous chromosomes - chromosomes that make up a pair - have the same length, centromere position, and staining pattern
both carry genes controlling the same inherited characteristics
Chromosomes
Example - the homologous chromosomes from the mother and father both carry information about eye color at the same locus
exception to rule in humans - the X and Y chromosomes
females have a homologous pair of X chromosomes, males have XY
Nondisjunction - happens when two homologous chromosomes move to the same pole during meiosis
one daughter cell is missing a chromosome and another has an extra
Meiosis gone wrong
Normal number of chromosomes in gamete is 23
gamete with the extra chromosome will have 24 chromosomes
gamete lacking one will have 22
What happens next?
Gamete with 24 chromosomes joins with a gamete that has 23 chromosomes making a zygote that contains 47 chromosomes
remember: normally the zygote has 46 chromosomes
has 3 copies of one chromosome when it should only have 2
condition is called trisomy
What happens next?
Trisomic disorder in which a zygote receives three homologous chromosomes for chromosome pair number 21
happens in 95% of Down syndrome cases Philippines example
Down syndrome
Called a syndrome because there are a number of traits that are associated with the condition regardless of race
round, full face, enlarged and creased tongue, short
height, large forehead rate of Down Syndrome increases with
the age of the mother
Down Syndrome cont...
Nondisjunction of the sperm or egg cell child inherits two X chromosomes and 1 Y
chromosome appears to be male at birth but produces
large amounts of female sex hormones at puberty
males are sterile
Klinefelter Syndrome (XXY)
Gamete with 22 joins with 23 gamete, final number is 45 (normal is 46)
zygote only has one copy of the lacking chromosome when it should have 2
resulting condition is called monosomy
Or?
Monosomic disorder when sex chromosomes undergo nondisjunction
female with single X chromosome 45 chromosome zygote produced traits - do not develop sexually, short,
widened necks most miscarried before 20th week can grow to lead highly productive lives
Turner’s Syndrome