How to solve Pedigree problems
- Identify the aa individuals
- Identify all the parents of the aa individuals. Must be Aa or aa. Children much be aa or Aa
- Identify any other individuals entering the pedigree that are assumed to be AA
- Determine all other possible genotypes and calculate the probability of each
- When you do the punnet square, take out the aa individuals. Your value will not sum up to 1.
- To get the ratio of normal phenotypic children divide by that value
- Cross the two.
- Calculate the probably of other gametes by calculating the probability of a and the probability of A
Autosomal recessive
- two copies of an abnormal gene must be present in order for a disease to trait to develop
- traits normally appear with equal frequency in both sexes and tend to skip generations
- more likely to appear among progeny of related parents
Autosomal dominant
- if you inherit the abnormal gene from only one parent, you can get the disease.
infected dad Dd. Normal mom dd. Progeny are Dd and dd. The Dd individuals will be infected
- traits normally appear with equal frequency in both sexes and do not skip generations
- affected individuals have at least 1 affected parents
- unaffected do not transmit trait
X linked recessive
females need two recessive X’s in order to get the disease.
Males need one from their mom.
Appear more often in males in females and are not passed from father to son
- affected male must have unaffected father
- ex: hemophilia
X linked dominant
females only need one recessive X in order to get the disease. Males only need one.
affect both males and females
affected male passes it to all daughters and no sons
affected male needs an affected mother
Y linked
appear only in males and are passed from a father to all his sons
Exploratory Pedigrees
- Determine genotypes
- Assume complete penetrance
- Make sure alleles are consistent with inheritance
- If there are any inconsistencies, you can excuse the mode of inheritance
Cytoplasmic inheritance
affected mother passes to all of her children
Monozygotic (identical) twins
Result when a single fertilized egg splits into two separate embryos
Dizygotic (nonidentical) twins
result when two separate eggs are fertilized by two sperm
concordance
the percentage of twin pairs that are the same fit for a given trait
If both members of a twin pair have a trait, the twins are
concordant
If only one member of the twins has the trait, they are said to be
discordant
Adoption studies
assess genetic and environmental effects on trait variation
overweight biological parents have overweight children
no association between the weight of adopted children and that of their adoptive parents
consanguinity
- mating between related persons
- usually goes as far as first cousins
Amniocentesis
- used for obtaining fetal cells for genetic testing. 15-18 weeks pregnant (disadvantage)
1. sterile needle inserted through the abdominal wall into the amniotic sac
2. small amount of amniotic fluid is withdrawn through the needle
3. the amniotic fluid contains fetal cells, which are separated from the amniotic fluid
4. and cultured
5. test are then performed on the cultured cells
Chorionic Villus Sampling
- used for obtaining cells for genetic tests. (10-11 weeks in). - - Somewhat higher risk than amniocentesis
- Karyotype can be performed
1. CVS can be performed early in pregnancy
2. Under the guidance of ultrasound, a catheter is inserted through the vagina and cervix and into the uterus
3. where it is placed in contact with the chorion, the outer layer of the placenta
4. Suction removes a small piece of the chorion
5. Cells of the chorion are used directly for many genetic tests, and culturing is not required
Maternal Blood Screening Tests
- screening for certain substances (proteins and hormones) in the mother’s blood. These substances are produced by the fetus and are present in fetal blood, amniotic fluid, and maternal blood during pregnancy
- abnormal levels of these may indicate an increased for NEURAL TUBE DEFECTS or CHROMOSOMAL ABNORMALTITIES in the fetus.
- Ex. alpha-fetoprotein when a baby has a neural tube defect
Fetal DNA diagnosis
- during pregnancy, some fetal cells are released into the mother’s circulatory system. Also contains free floating fetal DNA derived from the breakdown of fetal cells
- about 3-10% of cell-free DNA in a mother’s blood belongs to her baby.
10-15 weeks of pregnancy. as early as 10
Preimplantation Genetic Diagnosis
combines genetic testing with in vitro fertilization. One cell is removed from 8- to 16-cell embryo and tested before implantation
Newborn screening
- allows for detection of metabolic diseases so that early intervention can prevent problems
- 34 in NC
Heterozygote screening
tests on adults to identify heterozygous carriers of recessive disease-carrying alleles before they have children
Presymptomatic testing
evaluating healthy people before onset of disease, especially in families carry autosomal dominant diseases when early intervention can save lives
Proband
the first affected family member coming to attention of a geneticist
