Karyotypes copyright cmassengale

Meiosis copyright cmassengale

What happens when things go wrong? If chromosomes don’t separate during Meiosis I, aneuploidy can occur. This is when a cell has one extra chromosome or is missing one chromosome.

Down Syndrome The most common example of aneuploidy. One of the two gametes carries 2 copies of chromosome 21. When the zygote forms, it carries 3 copies of chromosome 21. AKA Trisomy 21.

What causes it? Sperm cells develop in males constantly (beginning at puberty). Female gametes develop before birth. At birth, they are called primary oocytes in Prophase I. They stay in this phase until ovulation. For a 20 year old woman, her egg cells have collected 20 years of damage (chemicals, radiation, etc.) For a 40 year old woman, the cells have 40 years of damage and the chance of non-disjunction is increased.

To analyze chromosomes, scientists photograph cells during mitosis.

Then they cut out the photographs of the chromosomes and group them in pairs. These chromosomes have been stained with Giemsa

A completed Karyotype

copyright cmassengale Karyotype * A picture of the chromosomes arranged in pairs by size * First 22 pairs are called autosomes * Last pair are the sex chromosomes * XX female * XY male copyright cmassengale 9 9

Using karyotypes. Scientists use karyotypes to help diagnose genetic disorders. They take embryonic cell samples copyright cmassengale

Prenatal Testing – 2 tests Chorionic villus sampling Done at 11-12 weeks of pregnancy Takes a sample of the chorionic villi (they have cells that originally came from the zygote). Amniocentesis Done at 16 weeks Takes a sample of amniotic fluid (it contains fetal cells) copyright cmassengale

copyright cmassengale

Genetic Disorders Down Syndrome – an extra 21st chromosome. Turner Syndrome – only one X chromosome Klinefelter’s Syndrome – XXY chromosomes

Genetic Disorders Problem Name of Disorder Results Extra #13 Patau Syndrome Brain defects; 1:5000 live birth Extra #18 Edward’s Syndrome All organ abnormalities, 1:10,000 live birth Extra #21 Down Syndrome Unique facial features, shorter limbs, mild mental retardation Only one X X Turner’s Low fertility, many health issues Extra X XXY Klinefelter’s Low fertility, lanky body, many health issues copyright cmassengale

Normal Male copyright cmassengale 2n = 46

Normal Female 2n = 46 copyright cmassengale

Female Down’s Syndrome copyright cmassengale

Down Syndrome (extra 21) Decreased cognitive development Shorter limbs Eyelid fold Flatter nose More common for mothers over 40 years old.

Klinefelter’s Syndrome copyright cmassengale

Klinefelter Syndrome (extra X) The most common sex chromosome disorder. Males get it. Low fertility Less testosterone production Lower language development Tend to be lanky.

Turner’s Syndrome 2n = 45 copyright cmassengale

Turner’s Syndrome (one X) Occurs in females. Low fertility Many health problems.

Patau Syndrome (extra #13)

Patau Syndrome Most embryos do not survive Very few survive past 1 year. Mental/motor retardation Brain, heart, anatomy problems.

Edward’s Syndrome (extra #18)

Edward’s Syndrome Very low survival rate. Heart abnormalities Affects all internal organs.

You are going to be the scientist! You will make a karyotype! You will need: 1. one set of chromosomes 2. a blank piece of paper (put both names on it). 3. scissors 4. glue 5. Reference Sheet copyright cmassengale

Procedure: Label the blank paper 1 through 23. Cut out ONE chromosome at a time. Glue them on the blank paper, by size and shape, using the reference sheet. You will have 2 for each number. Remember there are 46 chromosomes, or 23 pairs. Determine the genetic disorder and the gender. copyright cmassengale

Make sure you’ve written down: a. the disorder b. the gender c. ALL your names! copyright cmassengale

Summary How does a karyotype help scientists determine genetic disorders? Write at least 5 complete sentences. copyright cmassengale