-
Allele:
different versions of a gene
-
Gene:
A unit of heredity in a living organism
Is the region that produces a protein plus the promoter to make sure it can be produced
-
Heterozygote:
an individual with two different alleles at a given gene
-
Homozygote:
the two alleles are identical
-
Hemizygote:
has only one allele
almost all X-linked genes are hemizygous in males
-
Gamete:
either egg or sperm, dependent on the sex of the person in which the meiosis occurs
-
Phenotype:
characteristics of a person, effects of genes + environment
-
In a person heterozygous for a gene on Chr. 7, Meiosis will distribute the two alleles
to two different gametes
-
There is no such thing as a male hidden carrier in
Sex linked diseases
-
Autosomes are
The chromosomes 1-22 excluding the sex chromosomes
-
Dominant Disease are
These are rare 1/500
By chance alone, two heterozygotes rarely have children; one heterozygote + one homozygous normal is the rule
Therefore homozygotes are extremely rare
-
Fitness Definition:
the number of offspring that reach reproductive age divided by the average number for the population
-
Recessive Disease
Only the homozygous carriers show symptoms (and homozygotes are rare)
Normal occurrence is that patients are offspring of two heterozygous carriers
New mutations are rare
-
What are the pedigree symbols
-
Autosomal dominant inheritance:
phenotype shows presence of allele also in heterozygote; gene on autosome (not X or Y)
-
Autosomal recessive inheritance:
phenotype only present when two bad alleles are present
-
Individuals with a Recessive normally don't have
have affected parents; average of ¼ affected in each sibship; the parents are often related (sometimes quite distantly)
-
Individuals with a Dominant disease all have
one affected parent (except new mutations and reduced penetrance); average of 50% affected in a sibship
-
Autosomal diseases are found to be:
In equal number of affected males and females (except sex limited)
-
Sex-linked Inheritance X-linked recessive:
Express the phenotype if there is no other allele present, i.e., in hemizygous males [or homozygous females]
-
Sex-linked Inheritance with an X-linked dominant:
always shows phenotype
-
Y-linked phenotypes have shown to express
male fertility; reports of non-syndromic hearing impairment
-
In X-linked recessive is expressed normally with
many more males than females affected; never father-to-son transmission
New mutations happen
-
In an X-linked dominant circumstance:
more females than males affected; never father-to-son transmission
-
Y-linked individuals are only transmitted what way
Only father-to-son transmission
-
Transmission of X-linked Traits chart
-
Sex-limited Inheritance charecteristics
- This is not the same as Sex-linked!
- Genes on autosomes
- Can be dominant or recessive
- Typically influences traits expressed in one sex only or traits influenced by the sex hormones
-
What are some examples Sex-limited Traits
- Male pattern baldness
- Autosomally inherited infertility
- Milk-related traits
- Breast and ovarian cancer
- Testicle cancer
-
Penetrance of a disease-causing mutation is
The proportion of individuals with the mutation who exhibit clinical symptoms
A non-penetrant person is one who has the predisposing genotype but does not show symptoms
-
Reduced Penetrance used to only occur in dominant diseases
But now similar observations have been found in recessive diseases
-
Variable Expressivity
Difference in severity or in age of onset for seemingly identical genotype (mostly seen in dominant diseases)
-
Heterogeneity
- Similar -> identical phenotype, but:
- Causes can be involvement of different loci (locus heterogeneity)
- Or involvement of different alleles at the same locus (allelic heterogeneity)
-
Allelic heterogeneity can mean
different alleles at the same locus produce different diseases
-
Phenocopies:
looks like a known genetic disorder, but is caused by environmental influence
-
Pleiotropy:
mutation in one gene has more than one effect, effects in more than one physiological system
-
Contiguous gene disorders:
Typically in deletion or duplication of part of a chromosome
|
|
