17.4 Abnormal Meiosis

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?

Nondisjunction in Meiosis I or II

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...

Trisomy 18 Faun like ears Small ears Dies within the first few weeks

Edward’s Syndrome

Trisomy 13 Hairlip Small Head 130 day life span

Patau Syndrome

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)

Tall Aggressive Acne Too much testosterone

Super Male (XYY)

Has 3 X chromosomes

Trisomic Female

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

Do questions 1-6 on page 586 as a class Do questions 1-12, 18, 21-25 on page 593

to be handed in

To Do: