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Genetics 1.3: Genes and Alleles
Terms in this set (112)
the specific location where a gene is located
fundamental unit of heredity
sequence of DNA that gives rise to products
a location on a chromosome
old concept of gene
1 gene = 1 enzyme
most mutations that affect gene function are ...
recessive loss of function
genetic makeup (DNA sequence itself)
long ds DNA helix
different forms of the same gene
How many different alleles are possible? Why?
1000s, due to number of nucleotides in a gene
2 copies of each gene
1 copy of each gene
test to determine whether mutations are different alleles of the same gene, or 2 different genes
mutations are in the same gene = offspring have mutant phenotype
mutations are in different genes = offspring will have normal phenotype
way of representing a gene
1 gene = many functions, many traits
How are genes defined functionally?
Steps of complementation test
1. cross 2 homozygous mutants together (with different mutations
2. observe phenotype
mutant = fail to complement = 2 alleles, same gene
wildtype = complement = 2 different genes
how are the terms dominant & recessive defined?
operationally with a genetic test
only appears when both copies have the same allele
always expressed (even with only 1 copy)
Leber's Congenital Amaurosis
caused by mutations in 18 genes
Leber's Congenital Amaurosis
The production of the same or similar phenotypes by different genetic mechanisms
a technique that places a gene into a cell to correct a hereditary disease
only current example of a forever fix
reduced or complete lack of gene products from a gene
new, increased, or altered function of a gene
function of gene is completely eliminated
product with new activity
An allele that produces a weakly active product, or a reduced amount of product
product from one allele works against product from another alleles of the same gene (poisons a protein complex)
recessive alleles are _________ _________ of function
dominant alleles are ___________ ___________ of function
dominant loss of function
a LOF gene that is always expressed. Due to Haploinsufficiency
one copy of a gene does not product enough product to produce a normal phenotype
one copy is enough for a normal phenotype
A & B both encode a functional protein that attaches antigen . A & B are dominant to O, but co-dominant to each other
The A gene
attaches N-Ac-Gal sugars to surface proteins on RBC's
The B gene
attaches Gal sugars to surface proteins on RBC's
The O gene
does not produce a functional product
enzyme that transfers a functional group from one molecule to another
alleles will both be completely expressed
process of making gametes
cells with a haploid number of chromosomes
pair of chromosomes that have the same size, appearance & genes
process by which chromosomes undergo breakage and reunion
genes that are closely linked on the same chromosome are ____ likely to recombine
can recombination occur within a gene?
2 closely linked genes are ____ apart
2 far apart linked genes are ____ apart
the closer the 2 genes =
fewer cross-overs =
fewer recombinant classes
How many reading frames for DNA?
How many reading frames for mRNA?
In higher eukaryotes, how many ORF's are there?
Open Reading Frame
recombination distance =
number of recombinant classes/total x 100%
1 centimorgan =
1% recombination = 1 map unit
genetic recombination map unit
3 nucleotide sequence that codes for an amino acid
open reading frame
the reading frame that encodes a functional product
the strand that is complementary to the template strand and carries the actual code
the strand that will be read by the polymerase
The DNA constituting the genome of a cell or an organism, as distinguished from extra chromosomal DNAs, such as plasmids.
Complementary DNA, synthesized from RNA by reverse transcriptase.
the joining of complementary base pair sequences
at least one strand of nucleotides must be short.
stretches of DNA that are excised (spliced) prior to translation
stretches of DNA that are translated
1. never jumbled in order
2. can be skipped
exon splicing is
the RNA sequences as it is originally transcribed
the finished RNA sequence after the introns have been spliced out
alternative promoter use
when different starts are used on the same gene to produce different proteins
use of splicing to produce different products from the same mRNA
the stretch of DNA that is transcribed into an RNA molecule
groups of related multigene families
a protein segment with a distinct function that folds independently
How has the concept of a gene changed over the last 100 years?
old: 1 gene = 1 enzyme/ protein
next: 1 gene = 1 polypeptide/ product
now: 1 gene = 1 transcription unit = 1+ products
genes linked =
allele combo preserved
case study for LCA
experienced gradual loss of sight after age 5
wtRPE65 gene treatment
retinal degeneration continues
many disease are classified by
What is the difference between a protein and a polypeptide:?
A polypeptide is a sequence of amino acids linked by peptide bonds
All proteins are polypeptides.
Proteins tend to have a well defined 3D structure.
The term polypeptides is often reserved for the shorter, unstructured polypeptides that do not fold into a protein structure.
leaky LOF mutation
Which genetic tests are used to classify mutation?
start codon also codes for
the wrong reading frame will contain
numerous stop codons
usually loss of function
ancestral DNA sequence
allele with most function that confers and advantage
most common allele
why is a wildtype gene difficult to define?
sometimes a gene has an allele set with more than one fully functional allele (ex ABO)
How are linkage maps created?
by evaluating recombination frequencies
3 differences between eukaryotes and prokaryotes genes
prokaryotes = circular chromosome, introns rare
eukaryotes = linear chromosomes, introns common, telomerase needed
What is the difference between preRNA and mRNA
preRNA has introns
mRNA does not
intron lengths and position can be use to deduce ...
3 different ways to producing different polypeptides from the same gene
1. alternative splicing
2. alternative reading frames
3. alternative control elements
overall, length of a gene is determined by ...
the size of it introns
how does the transcription unit relate to the modern concept of a gene?
gene = transcription unit
however 1 transcription unit can equal many products
How are genes and proteins grouped into families and superfamilies?
Proteins in a family descend from a common ancestor, ave similar 3-D structures, functions, and significant sequence similarity.
Superfamilies have structural and mechanistic similarity but may have no sequence similarity
do exons from allele join with the exons from another allele during splicing?
process in which homologous chromosomes exchange portions of their chromatids during meiosis
RNA polymerase reads the template strand from
3' to 5'
The RNA that is synthesizes is the same as the
standard notation for a published gene sequence:
message strand only
Suppose in a given pair of homologous chromosomes all the alleles are different on the two homologues. If there is no crossing over at what stage of meiosis do the different alleles present in the homologous chromosomes separate?
The rate at which certain events occur (number of new cases of a trait) is known as
From whom does a male child inherit colorblindness?
If an individual has a genotype RR for a proto-oncogene (both functioning alleles), then one allele becomes mutated (ie: RR*), what is the likely outcome? In this case, why is heterozygosity a bad thing compared to #10?
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