Unit 2 Day 1 Flashcards
What does a family history consist of information wise?
- Biological relationships between family members
- any medical conditions they may have
What can a family history reveal?
- Patterns of inheritance
- what type of inheritance may be part of a condition
- distinguishing btw. conditions with similar presentations
How many generations should be included in a family history?
3 (if in doubt)
genotype
- an individual’s collection of genes. The term also can refer to the two alleles inherited for a particular gene. The genotype is expressed when the information encoded in the genes’ DNA is used to make protein and RNA molecules.
- the DNA sequence*
phenotype
- an individual’s observable traits, such as height, eye color, and blood type. The genetic contribution to the phenotype is called the genotype. Some traits are largely determined by the genotype, while other traits are largely determined by environmental factors.
- refers to observed traits*
dominance
- the phenomenon whereby, in an individual containing two allelic forms of a gene, one is expressed to the exclusion of the other.
- phenotype that is expressed in the heterozygous state*
recessive
- relating to or denoting heritable characteristics controlled by genes that are expressed in offspring only when inherited from both parents, i.e., when not masked by a dominant characteristic inherited from one parent.
- a phenotype that is expressed only in homozygotes or hemizygotes*
semidominant
One of a series of terms applied to the phenotypic effect of a particular allele in reference to another allele (usually the standard wild-type allele) with respect to a given trait. An allele “A” is said to be semidominant with respect to the allele “a” if the A/A homozygote has a mutant phenotype, the A/a heterozygote has a less severe phenotype, while the a/a homozygote is wild-type. An example is Pmp22(Tr-J) in mouse. Pmp22(Tr-J)/Pmp22(Tr-J) animals display a myelination defect associated with a “trembler” phenotype, while Pmp22(Tr-J)/Pmp22(+) animals are less severely affected, and Pmp22(+)/Pmp22(+) animals are wild-type.
when the heterozygous phenotype is intermediate btw the 2 homozygous phenotypes
single-gene disorders
When a certain gene is known to cause a disease, we refer to it as a single gene disorder or a Mendelian disorder. For example, you may have heard of cystic fibrosis, sickle cell disease, Fragile X syndrome, muscular dystrophy, or Huntington disease.
Mendel’s First Law
The principle of segregation (First Law): The two members of a gene pair (alleles) segregate (separate) from each other in the formation of gametes. Half the gametes carry one allele, and the other half carry the other allele.
Mendel’s Second Law
The principle of independent assortment (Second Law): Genes for different traits assort independently of one another in the formation of gametes.
penetrance***
the percentage of individuals with a given genotype who exhibit the phenotype associated with that genotype. For example, an organism may have a particular genotype but may not express the corresponding phenotype, because of modifiers, epistatic genes, or suppressors in the rest of the genome or because of a modifying effect of the environment.
the fraction of individuals with a trait genotype who show manifestations of the disease
expressivity***
measures the extent to which a given genotype is expressed at the phenotypic level. Different degrees of expression in different individuals may be due to variation in the allelic constitution of the rest of the genome or to environmental factors.
the degree to which a trait is expressed in an individual (severity)
pleiotropy***
occurs when one gene influences two or more seemingly unrelated phenotypic traits, an example being phenylketonuria, which is a human disease that affects multiple systems but is caused by one gene defect. Consequently, a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously.
some mutations–>multiple and different phenotypes. different than variable expressivity
homozygous
2 identical alleles at a given locus (wt or mutant)
heterozygous
2 different alleles at a given locus
hemizygous
mostly refers to males (XY) who have just a single copy of each X-chromosomal gene
autosomal dominant
pattern of inheritance characteristic of some genetic diseases. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the disease-associated mutation is enough to cause the disease.
autosomal recessive
one of several ways that a trait, disorder, or disease can be passed down through families. An autosomal recessive disorder means two copies of an abnormal gene must be present in order for the disease or trait to develop.
mitochondrial inheritance
They are maternally inherited because they are supplied by the egg at fertilization. Mitochondria contain their own their own DNA, including 39 genes that are susceptible to mutations at a rate 10-20 times higher than nuclear DNA.
x-linked dominant
a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.
x-linked recessive
a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males (who are necessarily heterozygous for the gene mutation because they have one X and one Y chromosome) and in females who are homozygous for the gene mutation, see zygosity.
not male-to-male transmission
What are the major patterns of Mendelian inheritance?
autosomal dominant
autosomal recessive
sex linked/x-linked recessive
age dependent penetrance
the likelihood of manifesting the disease in mutation carriers is dependent on age
