Clear and orderly summary of Chapter 25 of the book "Genetics: Analysis and Principles, 6th Edition by Robert Brooker". Together with all my other summaries of Genetics I got an 8,5 for this course.
Genetics Summary Chapter 25 – Medical Genetics and Cancer
25.1 Inheritance Patterns of Genetic diseases
Genetic Basis for human disease may be suggested by a variety of different
observations
Several observations consistent with idea that disease is caused by inheritance of
mutant genes and thus has genetic basis
1. Individual who exhibits disease is more likely to have genetic relatives (familie
connecties) with the disorder than people in general populations
2. Identical twins share the disease more often than nonidentical twins
Monozygotic (MZ) twins; eeneiige hetrozygotic (DZ) twins/fraternal twins; twee
eiige
Concordance; degree to which a trait is inherited, in which both twins exhibit
the disorder.
Concordance in identical twins; 100%
Concordance in fraternal twins for dominant; 50%. For recessive; 25%
3. Disease does NOT spread to individuals sharing similar environmental
situations.
4. Different populations tend to have frequencies of the disease
5. Disease tend to develop at a characteristic age
6. Human disorder may resemble (lijken op) a disorder that is already known to
have a genetic basis in an animal
7. A correlation is observed between a disease and a mutant human gene or a
chromosomal alternation
Inheritance patterns of human diseases
Human diseases follow simple Mendelian patterns of inheritance. So, mutation in
single gene.
Autosomal recessive
Features of autosomal recessive
1. Frequently, affected offspring, has 2 unaffected parents.
2. 2 unaffected heterozygote parents have children, percentage of affected
children is 25%
3. Two affected individuals have 100% affected children
4. Trait occurs with same frequency in both sexes
Caused by loss-of-function alleles
Autosomal dominant
Features of autosomal dominant
1. Affected offspring has 1 or 2 affected parents
2. Affected individual with 1 affected parent is expected to produce 50% acted
offspring
3. 2 affected, heterozygous individuals have 25% unaffected offspring.
4. Trait occurs with the same frequency in both sexes
5. Dominant homozygote is more affected with the disorder, it may be lethal
Caused by gain-of-function alleles, haploinsufficiency or dominant-negative
mutations
, - Haploinsufficiency/incomplete dominance; phenomenon in which person has
only a single functional copy of a gene and this this single copy doesn’t
produce normal phenotype. 50% is not enable to produce a normal
phenotype.
- Gain-of-function mutations; mutation that change gene product so it gains a
new or abnormal function,
- Dominant-negative mutations; mutation that produces an altered gene product
that acts antagonistically (tegengesteld) to the normal gene product.
X-linked recessive
Features
1. Males are much more likely to exhibit the trait
2. Mother of affected males often have brother or father who are also affected
3. Daughters of affected males produce, on average, 50% affected sons
X-linked dominant
Features
1. Only females exhibit the trait when it is lethal to males
2. Affected mothers have 50% change of passing the trait to daughters.
Genetic disorders exhibit locus heterogeneity
Locus heterogeneity; phenomenon in which a particular type of disease or trait may
be caused by mutation in 2 or more different genes.
Mutations in more than one gene can cause the same disorder
25.2 Detection of Disease-Causing Alleles via Haplotypes
Haplotype; linkage of alleles or molecular markers along a single
chromosome. See bottom of 2 pictures
Haplotype do not dramatically change from one generation to the
next, more likely to change over course of few generations due to
crossing over. Cross over happens if the distance is far.
Haplotype are conducted (uitgevoerd) to identify disease-causing alleles
How do genetics identify genes that cause disease when they are mutant?
Begins with family pedigrees. Localize disease causing allele, that is distinguished by
its haplotype.
1. Disease-causing allele had its origin in a single individual known as founder
2. Disease-causing allele originated in the founder, occurred in a region of a
chromosome with a specific haplotype. If the disease-causing allele and
markers in this region are very close then it is not likely
to have changed over several generations
Linkage disequilibrium; alleles and molecular markers
associated with each other at a frequency that is higher than
expected by random chance.
Disease-causing allele is close to molecular markers. Do
not likely to have change over several generations
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