Hemophilia • Read the passage about hemophilia in dogs • Answer the following questions in your Bell Ringer journal • Do sex-linked disorders happen in humans only? • Is it important to know if a trait is sex-linked or not? Why or why not? • Does it surprise you to find that there are similar genetic disorders in dogs as humans? Explain.
There are traits that are controlled by one gene with 2 alleles. Often, one is dominant and the other is recessive • Example: widow’s peaks and dimples.
Some traits are controlled by a gene with multiple alleles – 3 or more for a single trait. For example: blood types and skin color in humans.
There are 44 chromosomes that we call autosomal chromosomes. • However, there are 2 chromosomes that determine our sex and we call them sex chromosomes. • These 46 chromosomes all carrier genes on them that determine our traits.
Out of our 23 pairs of chromosomes, 1 pair is the sex chromosomes (X and Y). • Female = XX • Male = XY
Each egg produced by an ovary contains one X chromosome • Each sperm produced by a testicle contains either one X chromosome OR one Y chromosome • The X chromosome is larger than the Y chromosome and holds more genes • Each animal has its own sex chromosomes and sex determination based on those chromosomes
Question: What is the probability that your parents will have a boy or girl? • XY (dad) x XX (mom) Y X Phenotype: 50% boy 50% girl X XX XY Genotype: 50% XX 50% XY X XX XY
Question? If my parents have 5 boys in a row, what is the chance they will have a girl the next time? 50%
Sex-linked gene: • Some traits are carried on the sex chromosomes. Genes on the X or Y chromosomes are sex-linked genes. • This term is historically used to describe traits housed on the X chromosome • These traits are passes on from parent to child. Sex- linked genes can be recessive or dominant.
MALES are more likely to have a sex-linked trait because they only have ONE X and Y. The allele is USUALLY on the X chromosome. • Fathers pass on to daughters only; mothers pass to sons and daughters • Ex. colorblindness, hemophilia, hairy ears, muscular dystrophy
Are you colorblind? What numbers do you see?
Sex linked Punnett Squares: Question: What is the probability that a carrier female and a colorblind male will have a girl who is colorblind (b = colorblind, B = normal)? Xb Y Phenotype: 25% normal boy 25% colorblind boy 25% normal girl 25% colorblind girl XBXb XBY XB Xb XbXb XbY
Try this one on your own Question: What is the probability that a homozygous (normal vision) female and a colorblind male will have a girl who is colorblind (b = colorblind, B = normal)?
Parents: XBXB x XbY Xb Y Phenotype: 50% normal girls 50% normal boys XBXb XBY XB XB XBXb XBY
X-Inactivation • Since females have 2 X chromosomes, one is inactivated • During development, each cell of the embryo randomly inactivates one • Every cell may have a different X inactivated (ex. Tortoiseshell Cat) • Barr-bodies - inactive X chromosomes lies along the inside of the nuclear envelope
Carrier – person who has one recessive allele and one dominant allele for a trait or heterozygous for that trait (only women can be carriers). Example Hemophiliac carrier XHXh Colorblind carrier XBXb
Carriers do not show that particular trait phenotypically but have a chance to pass the trait on to their child. Carrier – half colored
Reading a Pedigree Task 1: Genotyping a pedigree chart • Task 2: • Go to the lab tables. • Each person should have one answer sheet. • Lets do the first one together. • As a group, finish analyzing the pedigrees. If you have extra time, work on conclusion questions (homework if not completed in class).
Ticket Out • Obtain a paper with a problem that asks you to create your own pedigree… due on your way out of the classroom.
What is a karyotype? • Picture of your chromosomes • Arranged from largest to smallest • quickly identify chromosomal changes • http://www.biology.arizona.edu/human_Bio/activities/karyotyping/karyotyping2.html
Diagnose the karyotypes in the back of the room at your table. • Make sure to include: • Case number • Boy or girl • Number of chromosomes • Normal or abnormal • (if abnormal, what is the problem?)
Mutations … • are changes in the genetic material • can be good or bad • can be on a single gene or the whole chromosome
Genetic Disorder – abnormal condition that a person inherits through genes or chromosomes. They are caused by mutations or changes in a person’s DNA. Write down 3 disorders that have affected someone you know.
Cystic Fibrosis • Recessive genetic disorder where the body produces abnormally thick mucus in the lungs and intestines making respiration and digestion difficult • Caused by a mutation in a gene. Body produces mucus which builds up in the breathing passages of lungs and pancreas (the organ that helps to break down and absorb food) • One in four babies are born with cystic fibrosis • Most common among Northern European descent
Sickle Cell Anemia • Sickle cell is a recessive genetic disorder that affects the blood’s hemoglobin. Hemoglobin is the protein in your blood that carries oxygen. • Sickle-cell anemia is caused by a point mutation in protein chain of hemoglobin, replacing the amino acid glutamic acid with the amino acid valine • The ‘sickle shape’ of the cell causes it to form clots easily and the protein doesn’t allow the red blood cell to carry very much oxygen. • Most common among African American descent Famous People with Sickle Cell Disease Miles Davis, jazz musician. Paul Williams, singer (The Temptations) Georgeanna Tillman, singer (The Marvelettes) Tionne "T-Boz" Watkins, singer (TLC)
Hemophilia • Hemophilia is a genetic disorder in which a person’s blood clots VERY slowly or not at all. • A person with hemophilia can bleed to death from a paper cut or scrape. • This is a recessive sex-linked disorder on the X chromosome. • Queen Elizabeth suffered from this disorder. This man received a vaccine. This is what having hemophilia did to is body.
Down Syndrome • Down Syndrome is a genetic disorder that occurs when an individual receives an extra copy of a chromosome. • A mistake occurs during Meiosis I: the chromosomes failed to separate correctly (non-disjunction) therefore leaving an extra copy of chromosome #21.
Doctor’s use tools like amniocentesis and karyotypes to helpdetect most diseases.
4 Types of Genetic Disorders 1. Single gene • Change in the DNA sequence • More than 6000 known disorders • Autosomal or sex linked • 1 in 200 births Examples: cystic fibrosis, sickle cell anemia, Marfan syndrome, Huntington’s disease
Types of Genetic Disorders 2. Multi-factoral • combination of environmental factors and mutations in multiple genes • more complicated Examples: heart disease, high blood pressure, Alzheimer’s disease, arthritis, diabetes, cancer, and obesity
Types of Genetic Disorders 3. Chromosomal • abnormalities in chromosome structure as missing or extra copies or gross breaks and rejoining Example: Down Syndrome
Types of Genetic Disorders 4. Mitochondrial • rare type of genetic disorder • caused by mutations in the non-chromosomal DNA of mitochondria
Here are some genetics disorders, some you have heard about and some you haven’t.
Turners Syndrome 1 in 5,000 births 45 chromosomes X only #23 MonosomyNondisjunction
Turners Syndrome 96-98% do not survive to birth No menstruation No breast development No hips Broad shoulders and neck
Cri-Du-Chat Syndrome 1 in 216,000 births 46 chromosomes XY or XX #5 Deletion of lower arm
Cri-Du-Chat Syndrome Moon-shaped face Heart disease Mentally retarded Malformed larynx Normal lifespan
Aniridia-Wilms Tumor Syndrome 1 in 50,000,000 births 46 chromosomesXY or XX #11 Deletion of upper arm
Aniridia-Wilms Tumor Syndrome Mentally retarded Growth retarded Blindness Tumors on kidneys Short lifespan
Thirteen Q Deletion Syndrome 1 in 500,000 births 46 chromosomesXY or XX #13 Deletion of lower arm
Thirteen Q Deletion Syndrome Mentally retarded Deformed face No thumbs Heart disease Short lifespan
Prader-Willi Syndrome 1 in 5,000,000 births46 chromosomes XY=97% XX=3% #15 Deletion of lower arm
Prader-Willi Syndrome Small bird-like head Mentally retarded Respiratory problems Obesity Short lifespan
Eighteen Q Deletion Syndrome 1 in 10,000,000 births 46 chromosomesXY or XX #18 Deletion of lower arm