Karyotype and genetic disease
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Karyotype and genetic disease. The number of chromosome per species is fixed. Each species has a characteristic number of chromosomes which is constant for that species: Examples: Human: 46 chromosomes Mouse: 40 chromosomes Onion: 16 chromosomes.

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Karyotype and genetic disease

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Karyotype and genetic disease

Karyotype and genetic disease


The number of chromosome per species is fixed

The numberof chromosome per species is fixed

  • Each species has a characteristic number of chromosomes which is constant for that species:

    Examples:

  • Human: 46 chromosomes

  • Mouse: 40 chromosomes

  • Onion: 16 chromosomes


The shape of a chromosome is characteristic

The shapeof a chromosome is characteristic

  • Length

  • Position of the centromere (constriction that can occur anywhere along the chromosome, but always in the same position on a given chromosome)

Size of the arms depends on the position of the centromere

Centromere in the center

Centromere close to the end


Karyotype picture of a person s chromosomes

karyotype (picture of a person's chromosomes):


Karyotyping

Karyotyping:

Examination of the chromosomes:

Number

structure


To obtain a karyotype

To obtain a karyotype:

Chromosomes are isolated, stained, and examined under the microscope.

A picture of the chromosomes is taken through the microscope. 

The picture of the chromosomes is cut up and chromosomes are arranged as homologous pairs in descending order of size.


Karyotype

Karyotype

Chromosomes are numbered:

each chromosome has been assigned a number based on its size;

the largest chromosome is chromosome 1.

The 23rd pair of chromosomes are sex chromosomes which determine the gender:

Female: two X chromosomes

Male: an X and a Y chromosome. 

22 numbered pairs of human chromosomes, called autosomes (autosomal chromosomes)


Karyotyping1

Karyotyping

  • The test can be performed on almost any tissue, including:

  • Amniotic fluid *

  • Placenta (chorionic villus sampling) *

  • Blood

  • Bone marrow

  • *the genetic material in the amniotic fluid and chorionic villus cells is the same as that in the baby's cells.


Amniocentesis

Amniocentesis

  • Allows:

  • Pre-natal diagnosis of chromosome abnormalities

  • Gender determination


Karyotype and genetic disease

  • http://learn.genetics.utah.edu/content/chromosomes/karyotype/


Human abnormalities due to alterations in chromosome number

Human abnormalities due to alterations in chromosome number

A pair of homologues chromosomes may not separate during meiosis I

or

sister chromosomes fail to separate properly during meiosis II:

Non-disjunction

Result: formation of gametes with too many chromosomes or too few (aneuploid);

Baby is born with genetic disease


Error in meiosis and genetic disease

Error in meiosis and genetic disease

Nondisjunction of chromosome 21 during egg formation:

Down syndrome(trisomy 21), individual has 3 copies of chromosome 21 (47 chromosomes)

Mental retardation and distinct physical traits;

Probability increases with age of the mother

Under 20 years: risk about 1:1700

20-30 years: risk about 1:1400

30-35 years: risk about 1:750

45 years: risk about 1:16


Error in meiosis and genetic disease1

Error in meiosis and genetic disease

Loss of a chromosome is always lethal


Human abnormalities due to non disjunction of sex chromosomes

Human abnormalities due to non-disjunction of sex chromosomes

XX do not separate: resulting gametes: XX and O

If an XX gamete combines with an X gamete, the resulting zygote is a female XXX, usually sterile (XXX Syndrome);

If an XX gamete combines with a Y gamete, the resulting zygote is XXY, infertile male with enhanced female characteristics (breast) and diminished mental capacities (Klinefelter syndrome)

If a O gamete combines with a Y gamete, the resulting zygote is nonviable

If a O gamete combines with an X gamete, the resulting zygote is XO, sterile female, does not mature sexually (Turner syndrome)


Human abnormalities due to alterations in sex chromosome number

Human abnormalities due to alterations in sex chromosome number

Nondisjunction of XY chromosomes: YY gamete

If a YY gamete combines with an X gamete, the resulting zygote is XYY, fertile male, with learning difficulties and violent tendencies


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