6.Genomes, genes and alleles & Genetics I + 2 Flashcards
RNA Polymerase function
RNA polymerase is an enzyme, RNA polymerase binds to the promoter region, which is located directly upstream of the gene.
definition: An enzyme that is responsible for producing a transcript (pre-mRNA) of a gene by joining free RNA nucleotides via complementary base pairing.
upstream vs down stream of the gene
upstream-towards the 5’ end of the coding strand
downstream-towards the 3’ end of coding strand
genome
all the genetic information (DNA) in an individual (organism) or cell
in which direction does RNA Polymerase move
3’ to 5’
start and end product of transcription
start-DNA
end-mRNA
Function of 5’ methyl cap
-5’ methyl cap is added to protect the mRNA from enzyme degradation (enzymes breaking down the code)
-it also helps the ribosome bind to mRNA to begin translation
what is the 3’ poly-A-tail
addition of multiple adenine nucleotides to 3’ end of mRNA
Function of 3’ Poly-A-tail
-protects the mRNA from enzyme degradation (prevents enzyme breaking it down)
-also makes the molecule more stable
-allows mRNA to leave the nucleus
Splicing
process by which the introns are removed
introns vs exons
introns are sections of DNA that do not directly code for proteins whereas exons are sections of DNA that are able to code for proteins.
start and end product of RNA processing
start-pre mRNA
end- (mature) mRNA
start and end product of translation
start-mRNA
end-polypeptide
name of 3 nucleotide bases in mRNA
codon
name of 3 nucleotide bases in tRNA
anticodon
how many possible mRNA codons
64
how many possible tRNA codons
61
site of translation
in the cytosol at ribosomes
where are intracellular protein synthesised
at free floating ribosomes
where are extracellular proteins synthesised
proteins for secretion (extracellular function) are synthesised at the rough endoplasmic reticulum (on ribosomes)
tRNA function
carries a group of three RNA nucleotides called an anticodon which is specific and complementary to a particular mRNA codon.
what is meant by the ‘degenerate code’
multiple codons can code for the same amino acid, one amino acid may be encoded for by multiple different codons
stop codon function
-does not code for an amino acid
-has no associated tRNA therefore causes mRNA to be released from the ribosome and the ribosome to disassociate
Post translational modification
-polypeptides can be modified by having other groups (eg carbohydrate chains) added to them. This will change the way the protein is folded
-occurs at rough endoplasmic reticulum (for export) or at a chaperone protein (for use in cell)
define mutation
random changes in genetic code, leading to new alleles
-can occur through mutagens eg UV light or chemicals in cigarette smoke
point mutation
point mutation-where one base is changed in the DNA code
identify the types of point mutations
substitution
insertion
deletion
duplication
substitution (point mutation)
base change
insertion (point mutation)
base added
deletion (point mutation)
base removed
duplication (point mutation)
base repeated (same base added)
what does ‘transcribe’ suggest
-we are given the template strand
-hence must make use complementary base pairing
what is the start codon for DNA
ATG-hence given the coding strand
what is done when given the coding strand
replace ‘T’ with ‘U”
silent mutation
change in single nucleotide base codes for the same amino acid(the code is redundant)
missense mutation
change in single nucleotide base codes for another (different) amino acid
nonsense mutation
change in single nucleotide base codes for a STOP codon
what is meant by ‘frameshift’
mutation leads to a change in not just one amino acid but the sequence of amino acids from that point onwards (as the code is read in groups of three)
Sickle cell
Sickle cell anaemia Is caused by a point mutation in the beta goblin chain of haemoglobin. Glutamic amino acid is therefore replaced by valine.
how to identify the 5’ end
end of DNA attached to phosphate group to 5th carbon
purpose of alternate splicing
alternate splicing allows for cells to produce many different versions of a protein using a single gene.
define a gene
-a hereditary unit
-it occupies a specific location on a chromosome
-it determines the characteristic(s) of an organism by directing the formation of a protein (s)
what is Gregor Mendel’s law of inheritance
genes are inherited to the offspring from each parent
define alelle
variation of a gene at a particular gene locus
define genotype
the allele combination of an individual
-eg Bb
what is meant by homozygous
two of the same alleles for a gene at specific gene locus
eg BB or bb
what is meant by heterozygous
two different alleles for a gene at a specific gene locus
eg Bb
another name for homozygous
pure breeding
another name for heterozygous
hybrid
what is a dominant trait
allele will be expressed in a heterozygous genotype
what is a recessive trait
only expressed in the phenotype when the genotype is homozygous
define phenotype
the physical, behavioural or physiological characteristics of an organism which are a result of the combination of the genotype and environment
what are epigenetics
the study of how your behaviour and environment can cause changes that affect the way your genes work
what is a test cross
To figure out an unknown genotype, a test cross is carried out between an individual that expresses the recessive trait (homozygous recessive trait) and the unknown genotype.( complete two crosses to show the potential options)
what is meant by co-dominance
where both alleles are equally expressed in the phenotype
eg blood type AB
define discontinuous variation(+extra info)
Variation in a population where phenotypes fall into discrete groups
-involves one gene(monogenetic inheritance)
-represented as a bar chart
define continuous variation(+extra info)
Variation in a population where phenotypes fall across a range between two extremes
-controlled by multiple genes(polygenetic inheritance)
- scale of traits=continuum
-represented as a histogram
define genetics
genetics is the study of inheritance
genetic diagram criteria
-allele key
-parents: phenotype, genotype, gametes(circled)
-punnett square
-f1: phenotypes(with percentages), genotypes(with percentages), phenotypic ratio(with percentages)
blood types alleles
I^A, I^B, i
what is sex linked inheritance
-This is when alleles are present on the sex chromosomes
polygenic inheritance
-there is no complete dominance; however, there is incomplete dominance (phenotypes in offspring is a mixture of parents phenotypes)
-each gene roughly has an equal influence and alleles have an additive affect on the phenotype outcome
-inherited traits that are controlled by two or more genes
melanin production
the protein pigment melanin responsible for skin colour
-at least 3 genes which control for human skin colour
what is height controlled by
Height is controlled by many genes (>400) as well as the environment (eg. diet) so is considered a multifactorial trait, not just a polygenic trait.
gene regulation
The process by which cells can either turn on or off gene expression.
gene expression
The process by which functional products, such as proteins, are produced through two stages: Transcription and Translation.
What are independent genes
genes found on different chromosomes
What are linked genes
genes that are found on the same chromosome and alleles therefore inherited together (unless crossing over occurs)
What are parental gametes
gametes containing chromosomes unchanged from the parent
what are recombinant gametes
gametes made as a result of crossing over containing allele/chromosome combinations not found in the parent
how can you determine if genes are linked
-test cross, crossing an individual who is heterozygous at both gene loci with a homozygous recessive individual at both gene loci
-if genes are linked it would produce a 1:1 phenotypic ratio or many:many:few:few phenotypic ratio
what is the phenotypic ratio produced when two linked genes undergo crossing over
many:many:few:few
-many parent gametes and few recombinant gametes
what is the phenotypic ratio when two linked genes don’t undergo crossing over
1:1
what is the phenotypic ratio when two heterozygous are crossed (monohybrid cross)
3 dominant : 1 recessive
what is the unknown phenotype if a test cross produces 100% of the dominant trait (monohybrid cross)
homozygous dominant
eg AA x aa
what is the unknown phenotype if a test cross produces a 1 to 1 ratio (monohybrid cross)
heterozygous dominant
eg Aa x aa
what is the unknown genotype if a test cross produces 100% dominant (Independent-dihybrid cross)
homozygous dominant at both gene loci
eg AABB x aabb
what is the unknown phenotype if a test cross produces 1:1:1:1 ratio (Independent-dihybrid cross)
heterozygous dominant at both gene loci
eg AaBb x aabb
what makes the mode of inheritance recessive
an effected individual (that expresses the trait) has two unaffected parents
what makes the mode of inherence likely dominant
all effected individuals have an affected parent
what makes the mode of inheritance dominant
-all effected individuals have an affected parent
-two affected parents have an unaffected child
what makes the mode of inheritance x linked recessive
-an affected individual has two unaffected parents
-an affected mother passes the trait on to all sons
what makes the mode of inheritance autosomal recessive
-an effected individual has two unaffected parents
-an affected mother does not pass on the trait to ALL sons
what makes the mode of inheritance x linked dominant
-every affected individual has an affected parent
-two affected parents have an unaffected child or all affected individuals have an affected parent
-affected father passes trait on to ALL daughters
what makes the mode of inheritance autosomal dominant
-every affected individual has an affected parent
-two affected parents have an unaffected child
-affected father does NOT pass trait on to ALL daughters
can females express Y linked traits
no, only males (XY) can
-females don’t carry a Y chromosome
why are sex linked traits more common in males
if males possess the recessive allele it will be expressed (as there is no allele on the Y chromosome)
