C-Notes: Chromosomal Abnormalities(Errors of Meiosis)

Stnd: 2c2/14/2014

Objective: SWBAT explain the problems with meiotic spindles not separating properly during Meiosis, which causes abnormalities in offspring.

How can genetic material be changed?

Incorrect number of chromosomes1. Non-Disjunction (Chromosomal

Aberration) – Problems with meiotic spindle causes the

homologous chromosomes NOT to separate properly during Meiosis I

– Or sister chromatids fail to separate during Meiosis II

– Leading to TOO MANY or TOO FEW chromosomes in one daughter cell.

• either an extra or missing chromosome causing Aneuploidy (wrong # of chromosome. Ex: XXX)

• Found in Chromosomes # 8,12,13,14,15,18, & 21)

2. Breakage of Chromosomes– Deletion– Duplication– Inversion – translocation

Changes in chromosome structure• deletion

– loss of a chromosomal segment

• duplication– repeat a segment

• inversion– reverses a segment

• translocation– move segment from one chromosome to

another

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How do changes in the genetic material (alteration of chromosomes) of an organism lead to changes in the traits of that organism?

This leads to gametes with irregular numbers of chromosomes.

How does these alteration of chromosomes effect an organism?

Baby has wrong number of chromosomes“SOMY” means Mutations

– Involve individual extra/missing chromosomes– Usually result in early miscarriage

Why is the extra # 21 chromosomemore tolerated by organisms ? (Down Syndrome)

Because it does NOT result in miscarriage• 3 copies of Chromosome 21

– Characteristic of facial appearance and other varying effects

– Varying levels of retardation– Frequently correlates with age of mothers.

 

Down syndrome & age of motherMother’s age

Incidence of Down Syndrome

Under 30 <1 in 1000

30 1 in 900

35 1 in 400

36 1 in 300

37 1 in 230

38 1 in 180

39 1 in 135

40 1 in 105

42 1 in 60

44 1 in 35

46 1 in 20

48 1 in 16

49 1 in 12

Rate of miscarriage due to amniocentesis: 1970s data

0.5%, or 1 in 200 pregnancies

2006 data<0.1%, or 1 in 1600 pregnancies

What are the Sex Chromosomes abnormalities?

• Human development (body cells/ Autosomes) (chromosome #1-22) are more tolerant of wrong numbers than Sex Chromosome (pair #23/ X & Y)

• But abnormalities in Sex Chromosomes produces a variety of distinct syndromes in humans– XXY = Klinefelter’s syndrome male – XXX = Trisomy X female– XYY = Jacob’s syndrome male– XO = Turner syndrome female

What is Turner’s Syndrome: Monosomy X?

• XO Females• Phenotypically female (short stature, swelling,

broad chest, webbed neck, los set ears, etc)

• Sterile (cant have kids)

• Associated with heart defects

What is Klinefelter’s syndrome?

XXY Male– one in every 2000 live births– have male sex organs, but are sterile– feminine characteristics

• some breast development• lack of facial hair

– tall– normal intelligence

Klinefelter’s syndrome

What is Jacob’s syndrome?

XYY Males– 1 in 1000 live male births– extra Y chromosome– slightly taller than average– more active– normal intelligence, slight learning

disabilities– delayed emotional immaturity– normal sexual development

What is Trisomy X?

XXX Females– 1 in every 2000 live births– produces healthy females

• Why?• Barr bodies

– all but one X chromosome is inactivated