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Chapter 4 - Genetics

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gene interaction
a situation in which a single phenotype is affected by more than one set of genes
X-linkage
a case where genes are present on the X chromosome
loss-of-function
mutations that produce alleles that encode proteins with reduced or no function
if the loss is complete from a loss-of-function mutation, the mutation results in
a null allele
gain-of-function
mutation that produces a phenotype different from that of the normal allele and from any loss-of-function alleles
incomplete dominance
expressing a heterozygous phenotype that is distinct from the phenotype of either homozygous parent (aka partial dominance)
Tay-Sachs disease
homozygous recessive individuals are severely affected with a fatal lipid-storage disorder and neonates die during their first one to three years of life
threshold effect
normal phenotypic expression occur anytime a certain level of gene product is attained
codominance
when two alleles of a single gene are responsible for producing two distinct, detectable gene products
multiple alleles
three or more alleles of the same gene
H substance
the connection of sugars by which one and/or two sugars can be added resulting in the A, B, or AB blood types
bombay phenotype
a rare variant of the ABO antigen system in which affected individuals do not have A or B antigens and thus appear to have blood type O, even though their genotype may carry unexpressed alleles for the A and/or B antigen
recessive lethal allele
mutations that result in the synthesis of a gene product that is non functional can often be tolerated in the heterozygous state
one wild-type allele may be sufficient to produce enough of the essential product to allow survival
gene interaction
term used to express the idea that several genes influence a particular characteristic
epigenesis
the idea that an organism or organ arises trhoguht eh sequential appearance and development of new structure, in contrast to preformationism
hereditary deafness
mutations that interrupt many of the steps of ear development lead to a common phenotype called this
epistasis
the expression of one gene pair masks or modifies the effect of another gene pair
complementation group
all mutations determined to be present in a ny single gene are said to fall into this group
pleiotropy
condition in which a single mutation caused multiple phenotypic effects
marfan syndrome
a human malady resulting from an autosomal dominant mutation in the gene encoding the connective tissue protein fibrillin
X-linkage
genes present on the X chromosome exhibit patterns of inheritance that are very different from those seen with autosomal genes
chromosome theory of inheritance
the correlation between mendel's work and the behavior of chromosomes during meiosis
sex-influenced inheritance
phenotypic expression conditioned by the sex of the individual. a heterozygote may express one phenotype in one sex and an alternate phenotype in the other sex
sex-limited inheritance
a trait that is expressed in only one sex even though the trait may not be X-linked