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SBI 3U0 09/03/2011. Mistakes in Meiosis. Karyotype Non-disjunction disorders (examples) Mutations (examples). 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

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mistakes in meiosis

SBI 3U0 09/03/2011

Mistakes in Meiosis

Karyotype

Non-disjunction disorders (examples)

Mutations (examples)

karyotyping
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)
slide4

Preparation of a karyotype

Fixative

Packed red

And white

blood cells

Hypotonic solution

Blood culture

Stain

White

Bloodcells

Centrifuge

3

2

1

Fluid

Centromere

Sisterchromatids

Pair of homologouschromosomes

4

5

alternations of chromosome number
Alternations of Chromosome Number
  • Non-disjunction (p. 116-118*)
    • Monosomy (i.e. Williams Syndrome)
    • Trisomy (i.e. Down`s Syndrome)
  • Abnormal Number of Sex Chromosomes

(p. 363-364)

(i.e. Turner Syndrome)

  • Mutations (p. 408-409)

(i.e. Huntington`s Disease; Cystic Fibrosis; Leukemia)

slide6

Nondisjunctionin meiosis I

Normalmeiosis II

Gametes

n + 1

n + 1

n – 1

n – 1

Number of chromosomes

Non-Disjunction

Alterations of Chromosome Number

1. Homologous chromosomes fail to move apart properly

during meiosis 1

slide7

Alterations of Chromosome Number

2. Sister chromatids don't separate during meiosis II

Normalmeiosis I

Nondisjunctionin meiosis II

Gametes

n + 1

n – 1

n

n

Number of chromosomes

slide9

Alterations of Chromosome Number

Monosomy – fertilized cell is missing a chromosome

Trisomy – fertilized cell has an extra copy of a chromosome

Ex. Down's Sydrome: 3 copies of chromosome # 21 (trisomy 21)

slide10

Alterations of Chromosome Number

  • Fertilization after nondisjunction in the mother results in a zygote with an incorrect number of chromosomes

Eggcell

n + 1

Zygote2n + 1

Spermcell

n (normal)

slide11

Alterations of Chromosome Number – Example:

Down syndrome is caused by an extra copy of chromosome 21

This karyotype shows three number 21 chromosomes

slide12

The chance of having a Down syndrome child goes up with maternal age

  • Down Syndrome occurs in about 1/700 live births.
slide13

Alterations of Chromosome Number

  • It is possible to have trisomy of chromosomes 13, 15, 18, 21 & 22
  • This happens infrequently
  • Is it usually fatal if the embryo has trisomy of any of the other autosomal chromosomes
  • = spontaneous abortion
slide15

Poor beardgrowth

Breastdevelopment

Under-developedtestes

  • A man with Klinefelter syndrome has an extra X chromosome, genotype XXY
slide17
A woman with Turner syndrome lacks an X chromosome, genotype X0, or X.

Characteristicfacialfeatures

Web ofskin

Constrictionof aorta

Poorbreastdevelopment

Under-developed

ovaries

slide19

Sickle Cell Anemia

  • Autosomal recessive blood disorder (ss)
  • Red blood cells have an abnormal “sickle” shape cause by an abnormal type of hemoglobin
  • Cells can clog up blood vessels
  • Caused by just one amino acid that is different from what it is supposed to be!
slide20

Cystic Fibrosis

  • Autosomal recessive mutation (cc)
  • Effects lungs - excessive mucus production
  • Breathing is very difficult
slide21

Huntington’s Disease

  • Autosomal dominant mutation (HH, Hh) – child of an affected parent has 50-100% chance of inheritance
  • Causes certain nerve cells in the brain to waste away or degenerate
  • Chromosome # 4 - causes a part of DNA to have a CAG repeat
  • Noticeable between age 30 – 40 years old
homework

Homework

Read pp. 358-362