Chapter 7: Human Genetics Flashcards
Reasons why man is an unsuitable research subject (3)
a. Man has a long life cycle.
b. Man can not be made to interbreed randomly and can only bear a comparatively small number of progeny.
c. He can not be subjected to rigorous experimental conditions. ( i.e. Closely controlled matings and standardized experiments)
Methods used to study human genetics (2)
- Pedigree Analysis
- Karyotyping
- or family histories; Mode of transmission can be revealed
- to determine if the mode of inheritance is recessive, dominant, partial dominant, autosomal, mitochondrial or sex-linked. Moreover, it also determines the probability of an individual or offspring being affected in the given cross.
pedigree analysis
- stained preparations of mitotic metaphase chromosomes are photographed, individual chromosomes are cut apart and arranged in pairs
- Through it, one can detect numerical and structural abnormalities.
Karyotyping
Inheritance of traits can be observed in __.
families
A pedigree indicates the structure of a __ schematically.
family
Pedigrees give information on: (2)
- Dominance or recessiveness of alleles
- Risks (probabilities) of having affected offspring
modes of transmission of hereditary traits
- autosomal dominance
- autosomal recessive
- sex-linked dominance
- sex-linked recessive
- never skips a generation
- affected individuals may either be homozygous dominant or heterozygous for the trait.
- unaffected individuals are all homozygous recessive
autosomal dominance
- Marriage between affected individuals produces offsprings who are also affected by the trait.
- Affected progenies may also result from mating between unaffected parents if they are heterozygous for the gene pair
autosomal recessive
- CAN (but don’t have to) skip generations
- shaded individuals are homozygous recessive
- unshaded individuals that have shaded children must be heterozygous
autosomal recessive
- Every affected person must have at least 1 affected parent
- Both males and females are affected and capable of transmitting the trait
- No skipping of generations
- No alternation of sexes: we see father to son, father to daughter, mother to son, and mother to daughter
autosomal dominant
- Because most matings are with homozygous normal individuals and no offspring are affected
- Expect increased consanguinity between the parents.
autosomal recessive
Autosomal disorders (2)
- Phenylketonuria
- cystic fibrosis
- A hereditary disorder due to an autosomally recessive allele
- Most common disease in the U.S (1 in every 2000 births)
- Affected individuals die before reproductive age
- occur as a result of matings between heterozygotes.
- no homozygotes reproduce.
cystic fibrosis
a hereditary disorder characterized by lung congestion and infection and malabsorption of nutrients by the pancreas
cystic fibrosis
High frequency of carriers due to overcompensation; average number of children in families with CF child is 25% higher than in normal families (__ of normal children are carriers)
2/3
CF gene was identified and sequenced in 1989; encodes a large protein (about 1500 aa) that functions in cell membranes to regulate __ __ inside cells.
water balance
- Defective CF protein prevents __ __ from exiting cells, resulting in excess water inside the cell.
- All __-__ glands malfunction especially those in the __ and __ systems.
- chloride ions
- mucus-producing
- respiratory
- digestive
Cystic Fibrosis
- Leads to the buildup of thick dry mucus in the __ causing persistent cough and breathing difficulty. Residual mucus also good medium for __ __(pneumonia and other infections)
- lungs
- bacterial growth
Cystic fibrosis
* Mucus also clogs ducts of the __, blocking the passage of important enzymes; food can not be digested=malnutrition
- pancreas
Cystic fibrosis
* unusually high concentration of __ in sweat (2-5 times); detected when parents kiss their babies
* Clinically detected using the __ __- measures concentration of __ in a sample taken from a warmed patch on the child’s back or forearm
- salt
- sweat test
- salt
__ has no cure; therapeutic abortion the only way
* Possibly gene therapy
Cystic fibrosis
- Act as recessive traits in females, but dominant traits in males
- An affected male cannot pass the trait on to his sons, but passes the allele on to all his daughters, who are unaffected carriers
- A carrier female passes the trait on to 1/2 her sons
X-linked Recessive Disorders
