Karyotype = a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells.

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2 Karyotype = a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells. Homologous chromosomes are arranged by size, banding patterns, and centromere placement.

3 Extra, missing, or abnormal positions of chromosome pieces can cause problems with a person's growth, development, and body functions. 2 types of chromosomes: 1)Autosomal (autosomes) = chromosome pairs ) Sex = 23 rd chromosome pair; determines the sex of the individual

4 Normal FEMALE Normal MALE

5 1. Determine whether the chromosomes of an adult have an abnormality that can be passed on to a child. 2. Determine whether a chromosome defect is preventing a woman from becoming pregnant or causing miscarriages. 3. Determine whether a chromosome defect is present in a fetus.

6 4. Determine the cause of a baby's birth defects or disability. 5. Identify the sex of a person by determining the presence of the Y chromosome. This may be done when a newborn's sex is not clear.

7 1) Human Karyotypes are usually prepared from photographs of chromosomes that have been spread, fixed, and stained to highlight banding patterns. 2) The chromosomes in the photograph are cut apart and then arranged in homologous pairs just as you will be doing in an upcoming activity.

8 3) Chromosomes are obtained through various tests: blood, bone marrow, amniotic fluid, or tissue from the placenta (the organ that develops during pregnancy to feed a growing baby). White blood cells are used most frequently because they are easily induced to divide and grow in culture. To test amniotic fluid, an amniocentesis is done. A long needle fluid is withdrawn which contains cells shed by the fetus. A bone marrow specimen requires a bone marrow biopsy.

9 4) The sample is placed into a special dish and allowed to grow in the laboratory. 5) Various chemicals are added to stop the cell s growth during prophase and metaphase. 6) The cells are placed on microscope slides and treated so they swell and their chromosomes spread apart. 7) Then various stains are used to highlight banding patterns.

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11 8) The treated chromosomes can then be photographed, enlarged if desired, and cut out to do a karyotype.

12 9) Experienced geneticists observe the karyotype for chromosomal abnormalities.

13 1. Differences in sizes of chromosomes Missing pieces or additional pieces 2. Differences in the position of centromeres This is brought about by translocations. 3. Differences in basic number of chromosomes

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15 Cause = nondisjunction of the 21 st pair of chromosomes

16 Characteristics: Happens equally in males and females since it does not involve the sex chromosomes Individuals are mentally handicapped but the severity varies with the individual. The probability of giving birth to a child with Down syndrome increases with age of the mother, increasing significantly after age 35.

17 Cause = nondisjunction of the sex chromosomes during meiosis so individuals are missing one copy of the X chromosome. They have 22 pairs of autosomal chromosomes and only one X chromosome.

18 Characteristics: Affects ONLY females. Women are usually short, sexually underdeveloped and sterile. Women with this syndrome function well within society and are not diagnosed until they are assessed for infertility as adults.

19 Cause = nondisjunction of the sex chromosomes during meiosis so individuals have an extra X chromosome The person has 22 autosomal chromosomes and 3 sex chromosomes (XXY).

20 Characteristics: Affects ONLY males. Males are often tall, sexually underdeveloped and may have slight intellectual impairment. Recognition of this syndrome before puberty usually does not occur. Many males with this syndrome function well within society and are not diagnosed until they are assessed for infertility as adults.

21 Cause = occurs when a male inherits two Y chromosomes from his father instead of one. The exact cause of why this occurs is unknown.

22 Individuals with Jacob s syndrome have 22 autosomal chromosomes and 3 sex chromosomes (XYY). He is an XYY male. Remember most males are XY.

23 Characteristics: Affects ONLY males. The most common symptoms are learning problems at school and delayed emotional maturity. Males are tall, thin, have acne, speech problems, and reading problems.