Pedigree Analysis - Lecture 8

Question 1

Hutchinson-Gilford Syndrome

Answer 1

Appear healthy at birth, by age 2 show features of accelerated aging. Many die from CAD by age 13.
Usually inherited as an autosomal dominant trait. Caused by mutations in the lamin A gene (LMNA) on chromosome 1.

Question 2

Human genetics as organism for genetic study

Answer 2

Best - know most about humans, keep detailed records back many generations
Bad - controlled mating not possible, long generation time, family size is small

Question 3

Proband

Answer 3

The affected person for whom the pedigree is initiated.

Question 4

Autosomal Recessive

Answer 4

Both sexes equal frequency
Tends to skip generations
Affected born to unaffected
When both parents are heterozygous, approx. 1/4 offspring affected
More frequently in consanguine

Question 5

Autosomal Dominant

Answer 5

Both sexes equal frequency
Both sexes transmit trait to offspring
Does not skip generations
Affected must have an affected parent.

Question 6

X-Linked Recessive

Answer 6

More males than females affected
Affected sons usually born to unaffected mothers, so it skips generations
Affected fathers pass to all daughters

Question 7

Y-Linked Recessive

Answer 7

Only males affected
Passed from father to all sons
Does not skip generations

Question 8

Concordance

Answer 8

The percentage of twin pairs in which both members of the pair express a trait.
Ex. Obesity - genetic

Question 9

Concordance and Genetic Influence

Answer 9

Higher concordance in monozygotic than dizygotic twins indicates a genetic influence.
Less concordance indicates enviro influence on trait

Question 10

Any discordance in monozygotic twins due to

Answer 10

Environmental factors since they are genetically identical

Question 11

Adoption Studies

Answer 11

Use to analyze the inheritance of human characteristics. Similar between adopted and bio indicates genetic factors. Similar between adopted and adopted indicates enviro factors.

Question 12

Genetic Counseling

Answer 12

Genetic disease in family
Couple has given birth to child with genetic disease, defect or child is MR
Older woman gets pregnant, usually >35
First cousins
Known carriers for recessive

Question 13

Ultrasonography

Answer 13

High frequency sound beamed into uterus, when they encounter dense tissue, they bounce back and are transformed into a picture

Question 14

Amniocentesis

Answer 14

A sample of amniotic fluid is obtained, contains fetal cells that can be used for genetic testing.

Question 15

Chorionic Villus Sampling

Answer 15

Can be performed earlier than amniocentesis and collects larger amt of fetal tissue so cells do not have to be cultured. Go through cervix into uterus. Suction off small piece of chorion, outer layer of placenta. *This and amnio can be used to make a karyotype

Question 16

Maternal Blood Testing

Answer 16

Don’t determine presence of genetic problem, indicate increased risk – Screening

Question 17

Fetal Cell Sorting

Answer 17

You can detect and separate fetal cells from maternal blood with use of lasers and automated cell-sorting machines. Can be cultured for chromosome analysis or used as source of fetal DNA for molecular testing. Not as accurate and only mutated genes from father can be detected.

Question 18

Preimplantation Genetic Diagnosis

Answer 18

Genetic testing combined with IVF allows implantation of embryos that are free of a specific genetic defect. IVF embryos allowed to divide to 8 or 16 cell stage, one cell removed and tested for genetic abnormalities. Healthy embryo selected and implanted in uterus. Testing made possible through PCR

Question 19

Disorders that may be detected prenatally

Answer 19

Cleft lip and palate, CF, dwarfism, Lesch-Nyhan syndrome, neural tube, Chromosome abnormalities, osteogenesis imperfecta, PKU, sickle-cell anemia and Tay-Sachs

Question 20

3 Types Postnatal Genetic Testing

Answer 20

1. Newborn Screening - Collect drop of blood soon after birth
2. Heterozygote Screening - Members of population are screened to identify heterozygous carriers
3. Presymptomatic Testing - Testing healthy adults for genes that might predispose them to a genetic condition in future.

Question 21

Autosomal recessive traits often appear in pedigrees in which there have been consanguine matings, because these traits:

Answer 21

Appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related.

Question 22

When might you see an autosomal dominant trait skip generations?

Answer 22

When a new mutation arises or the trait has reduced penetrance

Question 23

How can you distinguish between an autosomal recessive with higher penetrance in males and an X-linked recessive trait?

Answer 23

If X-linked recessive trait, it will not be passed from father to son

Question 24

A male affected with an X-linked dominant trait will have what proportion of offspring affected with the trait?

Answer 24

All daughters and no sons

Question 25

What features of a pedigree would distinguish between a Y-linked trait and a trait that is rare, autosomal dominant and sex-limited to males?

Answer 25

If the trait were Y linked, an affected male would pass to all sons. If autosomal and sex-linked, affected heterozygous would pass to only half of their sons

Question 26

Why are monozygotic twins genetically identical, whereas dizygotic twins have only 1/2 of their genes in common on average?

Answer 26

Monozygotic from single embryo

Dizygotic from two embryos

Question 27

A trait exhibits 100% concordance for both mono and di twins. Conclusion?

Answer 27

Genetic factors are not important

Question 28

What assumptions underlie use of adoption studies in genetics?

Answer 28

All of above

• no contact with bio after birth
• foster parents and bio parents are not related
• the enviro of bio and adopted parents are independent.

Question 29

How does preimplantation genetic diagnosis differ from prenatal genetic testing?

Answer 29

Done on embryo at early stage