Karyotypes

IB1 BiologySong Hee Bae

Karyotypes• Karyotype: the number and

appearance of the chromosomes in an organism.

• Karyotype is always found in a photograph of the chromosomes found in a cell arranged according to a standard format.

• Organisms that are same species usually have the same karyotype.

• Can detect:o Gendero Chromosome abnormalities

Karyotyping

1. Fetal cells obtained2. Cells are stimulated to divide by

mitosis.3. Stops mitosis in stage of metaphase,

because chromosomes are mostly visible in metaphase.

4. Chromosomes in the photograph are cut out and arranged into pairs according to their size and structure.

• Two Methods of Karyotypingo Amniocentesis: a sample of amniotic fluid is removed from the

amniotic sac around the fetus.o Chorionic villus sampling: obtaining a tissue sample from the

placenta’s finger-like projections into the uterus wall.

Examining Karyotypes

Gender• Sex chromosomes.

o XX – femaleo XY - male

• Women - X chromosomes• Men - either X or Y chromosomes

Chromosome disabilities• sometimes, chromosomes do not split during meiosis - non-

disjunction.• Gametes are produced with either specific chromosome too

many or too few.• Gametes with one chromosome too few usually quickly die.• Gametes with one chromosome too many sometimes survive.

= down syndrome

Down Syndrome• 47 Chromosomes in total• Three chromosomes of type 21, rather than two.• Can be due either to non-disjunction during the formation of the

sperm or egg.• Can’t deduce the extent of affect.• The chance of down syndrome increases with the age of the parents.

Vocabulary

• Karyotype: the number and appearance of the chromosomes in an organism.• Karyotyping: the process of cutting the chromosomes in the photograph and

arranging into pairs.• Amniocentesis: a method of extracting fetus cell by removing a sample of

amniotic fluid from the amniotic sac around the fetus, using a hypodermic needle.

• Chorionic villus sampling: a method of extracting fetus cell by obtaining a tissue sample from the placenta’s finger-like projections into the uterus wall.

• Non-disjunction: non-separation of chromosomes.

Reference

• IB Biology Study Guides (page 25)• Pearson Biology (page 97)• Human Karyotype image linked• Mitotic metaphase image linked• Sex chromosome image linked• Down Syndrome Karyotype image linked