Genetic Disorders, Pedigrees, and Advances in Genetics

Review…Pattern baldness is sex-linked.If a carrier female marries a pattern-bald man,

what are the chances of their children having pattern baldness? Show the Punnett Square.

Use XB

There would be a 2/4 chance that the child would have pattern baldness.

XB Y

X XXB XY

XB XBXB XBY

Genetic DisordersA genetic disorder is an abnormal

condition that a person inherits through genes or chromosomes. Some genetic disorders are caused

by mutations in the DNA of genes. Other disorders are caused by

changes in the overall structure or number of chromosomes.

    

Cystic Fibrosis Cause- Recessive allele on Chromosome 7      How do people get the disorder?- The

recessive allele has to be inherited from BOTH parents. (Parents are Heterozygous)

Symptoms- Affects the respiratory and digestive

systems. A protein does not work correctly so thick

sticky mucus is produced in excess. Coughing, wheezing, respirator illness,

weight-loss, salty tasting skin, infections

Cystic Fibrosis cont’d Diagnosis- Sweat test, because people who

have the disorder have 2-5 times as much salt in sweat as a normal person. Or Blood Sample

Treatment- No cure, but new treatments help people live longer. Chest physical therapy helps clear mucus, prevent infections, antibiotics, gene therapy

Incidence- 2,500 babies per year in US. 10 million people are carriers and do not know.

Sickle Cell Cause- Recessive allele on Chromosome 11      How do people get the disorder?- The

recessive allele has to be inherited from BOTH parents. (Parents are Heterozygous)

Symptoms- Prevents oxygen from reaching organs

causing damage. Red blood cells are not a normal shape Frequent infections, red blood cells don’t live

as long, low red blood cell count (anemia), Pain, delayed growth,

Sickle Cell cont’d Diagnosis- Newborns are usually screened at

birth with a Blood Test

Treatment- Daily antibiotics, take folic acid, get rest, drink plenty of water, avoid to much physical activity, blood transfusions or bone marrow transplant in extreme cases

Incidence- 1 out of every 500 African-Americans born in US.

Hemophilia Cause- Recessive allele on the X-Chromosome   How do people get the disorder?-

Boys- receive the X chromosome with the allele from mom,

Girls- receive the X chromosome with the allele from mom and dad.

Symptoms- Blood clotting disorder, so person will not

normally clot when cut. Deep bruises, prolonged bleeding, joint

pain/swelling, pain

Hemophilia cont’d Diagnosis- Family history and tests during

pregnancy. Mild hemophilia isn’t usually diagnosised until after a major event. Blood tests.

Treatment- No cure, drugs can help blood to clot, blood transfusions, avoid inquiry, pressure or ice packs can help slow bleeding, wear med-alert bracelet.

Incidence- 1 in 5,000 male births. About 400 babies born each year in US.

Down Syndrome Cause- Extra copy of chromosome 21 (trisomy 21)      How do people get the disorder? During

meiosis the chromosomes get crossed and fail to separate so the egg or sperm end up with an extra copy. (Non-disjunction)

Symptoms- Distinct facial features: flat face, small nose,

abnormally shaped ears, larger tongue, increased risk for other health concerns

Have trouble learning and communicating compared to peers.

Down Syndrome cont’d Diagnosis- Screening tests by looking for

physical characteristics or blood tests can be done on pregnant women. Confirmed with a Karyotype.

Treatment- No cure, but physical and speech therapy can help develop skills, some corrective surgeries are done if there are other medical conditions.

Incidence- 1 out of every 800 to 1,000 babies. Mostly likely to occur due to mom’s egg and

most likely with older mothers.

Huntington’s Disease Cause- Dominant allele on Chromosome 4     How do people get the disorder?- Dominant

pattern, so everyone who inherits the allele has the disorder.

Symptoms- Affects the part of the brain used for thinking

talking, reasoning, emotion and movement. Symptoms start between 30-50 (or later)get

worse over time. Poor memory, depression, mood swings, lack

of coordination, twitching, difficulty moving, speaking walking etc.

Huntington’s Disease cont’d Diagnosis- Pregnant women can have testing

done to find out if the baby has the disease but you cannot tell when the person will get sick.

Treatment- Treatments make the person comfortable but do not cure the disease. (Medicines or Therapies)

Incidence- 1 out of 30,000 people in US.

Phenylketonuria (PKU) Cause- Recessive allele on Chromosome 12      How do people get the disorder?- The recessive

allele has to be inherited from BOTH parents. (Parents are Heterozygous)

Symptoms- Person with PKU cannot break down an amino acid

so it will build up in the blood and poison cells. Babies usually have no symptoms at first but left

untreated can develop severe brain damage and other issues.

Stunted growth, eczema, musty body odor, small head, fair skin

PKU cont’dDiagnosis- Newborns are screened at

birth with a Blood Test, so that treatment can be started early

Treatment- Must eat a protein-free diet and avoid phenylalanine in all foods

Incidence- 1 out of every 15,000 babies born in the US.

PedigreesA tool used to trace the inheritance of traits in humans.Chart or family tree that can trace the

inheritance of a genetic disorder or train in a family.

Can show possibilities of children inheriting traits or where certain traits come from.

Can be used to diagnosis conditions/genetic disorders.

Pedigree Symbols Circle represents - Female Square represents- Male Horizontal line represents- marriage Vertical line and bracket represents- connect

parents to children Shaded all the way represents- person has the

trait Not shaded represents- person does not have the

trait Shaded half-way represents- person is a carrier

of the trait

A Family Puzzle

Joshua and Bella Kimax have a son named Ian. Ian has been diagnosed with the recessive genetic disorder, cystic fibrosis. Joshua and Bella are both healthy. Bella’s parents (Paul and Bev) are both healthy. One of Joshua’s parents (Steve and Erica) is not healthy. Joshua’s sister, Sara, has cystic fibrosis. Bella is an only child. Use this information to make a pedigree for the Kimax family. HINT: Start with Ian and his alleles.

What were the genotypes of Joshua’s parents?

What are the genotypes of Bella’s parents?

Joshua also has a brother. What is the probability that he has cystic fibrosis? Explain/ Show the Punnett Square.

Review the pedigree that you just studied. What data suggests that the trait is not sex-linked? Explain using the families names and genotypes.

Imagine you are a genetic counselor. A couple asks why you need information about many generations of their families to draw conclusions about a hereditary condition. Write an explanation you can give them.

A man and a woman marry. They have 5 children, 2 girls and 3 boys. The mother is a carrier of hemophilia, an X-linked disorder. She passes the gene on to two of the boys who died in childhood and one daughter is also a carrier. Both daughters marry men without hemophilia and have 3 children each (2 boys and a girl). The carrier daughter has one son with hemophilia. One of the non-carrier daughter’s sons marries a woman who is a carrier and they have twin daughters. What is the percent chance that each of the twin daughters will be a carrier.