Karyotypes Karyotype A display picture of all the

Karyotypes

Karyotype = A display (picture) of all the chromosomes in the nucleus of a cell.

How do you make a karyotype? 1. Cell cycle is stopped in mitosis Why? – So you can see the chromosomes 2. Put cells on microscope slide 3. Stain cells so the chromosomes can be seen 4. Take a picture of what is seen under the microscope 5. Enlarge picture

What do Doctors do with karyotypes? 1. Cut out chromosomes 2. Pair up homologous chromosomes – according to size starting with the largest, position of centromere and banding pattern 3. Glue them down with their homologous partner

Enlarged picture of chromosomes in prophase Completed karyotype

Remember. . . Normal humans have 2 of each chromosome No more -- no less

Sex chromosomes the X & Y –Always the last set of chromosomes Males = XY Females = XX

Autosomes All chromosomes except for the X & Y (sex chromosomes) Pairs 1 -22

What can a Dr. determine from a karyotype?

¶ Sex of a person ¶determined by the 23 rd pair of chromosomes (in humans) ^Females have 2 “large” X chromosomes ^Chromosomes will be the same size Males have 1 “large” X and a smaller chromosome – Chromosomes will not be the same size y

What else can a doctor determine? · The presence of a chromosomal number defect …

Disjunction Normal separation of Chromosomes and Chromatids during Meiosis I and Meiosis II (Anaphase I & II)

Normal Karyotypes Has 46 chromosomes for humans Arranged in 23 pairs

Nondisjunction- failure to separate

What does nondisjunction cause? Missing Chromosomes – Monomy Embryo/Fetus will not survive Means 45 chromosomes Exception is this can occur on 23 rd chromosome pair Extra Chromosomes – Trisomy Means 47 chromosomes – – – Down Syndrome (Trisomy 21) Patau Syndrome (Trisomy 13) Klinefelter’s Syndrome (XXY) Turner’s Syndrome (X-) XYY Syndrome And many more………….

47, XX or XY, +13 Serious eye, brain, circulatory defects as well as cleft palate. 1: 5000 live births. Children rarely live more than a few months. Patau Syndrome

Cleft Palate

Klinefelter’s Syndrome

Symptoms of Klinefelters Sterile male Testes abnormally small Later in life feminine contours may develop

Characteristics of Cri-du-chat Has only 1 chromosome at locus 5 Mentally retarded Small head

Characteristcs of Cri-du-chat Unusual facial features Cry sounds like a cat meowing

Characteristics of Turner Syndrome Only 1 X no y Female Sex organs and secondary sex characteristics do not develop

Characteristics of Turner Syndrome Sterile Short of stature Mentally “normal”

Characteristics of Down Syndrome Has 3 chromosomes at locus 21 Characteristic facial features Mentally retarded short

Characteristics of Down Syndrome Heart defects Webbed fingers Generally do not live to be much older than 30

Amniocentesis