Genes & Gene Action Flashcards
gene definition
a unit of information, coded in DNA on a chromosome
all genes make ___ mostly for the reason of ____. Some genes make it just as an _____
RNA, making proteins
end product
each gene has a specific location on a _____
chromosome
gene location is called
locus (plural: loci)
alternative versions of the same gene are called
alleles
gene map definition
the loci of all the genes on a chromosome
ie. all normal copies of chromosome 15 in humans have the same ____
map of loci
they are homologs (have the same genes)
homologs may have the same genes in the same places, but maybe different ____
alleles
each homolog can have its own ____ of the same gene
version
allele definition
different version of the same gene
sister chromatids in regard to alleles
have the same alleles b/c they are identical
different alleles of the same gene may only have ____ differences in their effects
small
how many alleles can there be for the same locus?
in a whole species … infinite
in an individual diploid… one or two different alleles at the same time
how many differences do these infinite alleles in a species cause?
smaller than you would think b/c many alleles have similar effects
5-alpha-reductase type 2 gene
codes for a protein enzyme called 5-alpha-reductase type 2 that converts testosterone –> dihydrotestosterone
many different mutated/nonfunctional alleles of this gene have turned up
when a male has no functional copy of 5-alpha-reductase type 2 gene
develops externally as a female, at least until puberty
CFTR gene
cystic fibrosis transmembrane conductance regulator
causes cystic fibrosis when mutated to non-functional form
in allele G551D of CFTR….
glycine in position 551 is replaced by aspartic acid (4%)
a drug can cure this!!
a single base change in a gene may….
destroy its ability to make a working product
have no effect
cytogenetic definition
chromosomal
genotype definition
set of alleles carried by an organism at one or more loci
homozygote
individual with a homozygous genotype
heterozygote
individual with a heterozygous genotype
homozygous
both alleles at the locus are the same (AA or aa)
heterozygous
both alleles are not the same (Aa)
phenotype
the effect of a genotype on an organism
wild-type
a phenotype that is typical or normal
recessive phenotypes are not seen unless…
the recessive allele is homozygous
example of a genetic condition that is recessive
albinism
for recessive genetic conditions…
a good copy of the gene for an enzyme is usually enough to give the wild-type phenotype
a mutated gene for an enzyme is usually involved
dominant phenotypes are seen…
in heterozygotes for the dominant allele
example of a genetic condition that is dominant
achondroplastic dwarfism
inactivates fibroblast growth factor receptor 3
this protein is a membrane signal receptor for growth factor hormone
for dominant genetic conditions…
one bad allele is enough to give an abnormal phenotype
the homozygote is lethal
do not often involve a mutated gene for an enzme
a recessive allele has to be ____ to cause its phenotype
homozygous
a dominant allele causes its phenotype if ___
just one allele is present
many dominant alleles cause the same ____
phenotype in heterozygotes and homozygotes
Incomplete dominance definition
The phenotype of the heterozygote is intermediate between the two homozygotes
Codominance
The phenotype of a heterozygote shows the effects of both alleles at the same time
ie. blood type AB
