Chapter 4 Flashcards
Extension of Mendelian Genetics
What is the central dogma?
DNA is used as instructions to make RNA (transcription) -> RNA is then used as instructions to make a protein (translation)
How do genes influence our phenotype?
Genes produce proteins, proteins are machines that carry out biological functions. These biological functions are our phenotype.
Define mutations
Change in nucleotide sequences of a gene.
What do mutated genes produce?
Produce defective proteins, altering an organism’s phenotype.
Why do we have the 3:1 phenotype ratio in mendelian genetics?
Due to mutated alleles. Since we have 2 copies of each gene, one good copy is enough to have a normal phenotype.
How is seed shape of peas influenced?
Protein normally produces rigid polysaccharides.
Mutated gene = defective protein = no rigid polysaccharides = wrinkly seed shape
Define WT allele
Wild type allele. Natural, normal, unmutated allele. Usually whichever is most common in a population.
Can be denoted as + in genotypes
Define LOF mutation
Loss of function mutation. Reduces function of the protein.
Typically recessive.
Define GOF mutation
Gain of function mutation. Increases function of protein.
Typically dominant due to gaining something extra from mutation which drowns out/masks the WT allele.
Define neutral mutation
Nucleotide change occurs, but doesn’t damage protein / protein structure.
Define incomplete dominance
When the phenotype is a cross between parent phenotypes. This is caused by an intermediate level of protein function
White + Red = Pink !!
Define codominance
2 phenotypes appear simultaneously in distinct areas of the same organism. When one allele is active in one area, and the other is active in another.
What is an example of a gene with more than 2 alleles?
ABO gene - blood type gene. (A, B, or O)
What is an example of a lethal mutation?
Agouti and yellow mice.
Mice that are homozygous dominant for yellow do not survive. This is due to the mutation affecting the MERC gene, which is essential for embryonic development.
Define recessive lethal allele
When you need BOTH alleles to die
Define dominant lethal allele
When you only need ONE copy of an allele to die.
What type of lethal allele is the agouti mutation?
Recessive lethal allele
Define polygenic traits
Traits controlled by more than one gene
Define gene interaction
When products of different genes influence the same trait
Define epistasis
When one gene influences the effect of another gene
What is an example of epistasis?
Bombay blood phenotype
How does the bombay blood phenotype function?
The FUT1 gene influences the activity of the ABO gene. When FUT1 is homozygous recessive, the ABO gene does NOT produce antigens.
FUT1 produces the chemical precursor for the antigen, so without this precursor the ABO gene can’t build antigens.
Define epistatic
Overrides the other gene
Define hypostatic
Overriden by the other gene.
Define pleiotropic
More than one function in the body. One mutation can cause several health issues.
What is an example of a pleiotropic mutation?
Marfan syndrome affects the fibrillin gene, affecting connective tissue, bone length, the increased risk of aortic aneurysms, and eye problems.
Define hemizygous
Only one copy of a gene in a diploid cell
Typically for male sex chromosomes.
A mothers X-mutation results in…
Her son’s disorder
X-Linked inheritance
Inheritance resulting from the X-chromosome. Results in a gendered pattern of inheritance (male-dominated inheritance in a pedigree)
Define sex-influenced inheritance
Expression of autosome genes being influenced by the sex chromosome. Alters phenotypes in a sex-dependent manner & dependent on sex-specific hormones.
How does temperature affect expression? What is an example?
Some enzymes function only at a certain temperature.
Some pigments for fur are only produced at color extremities.
How does nutrition affect expression? What is an example?
Some mutations only cause problems in specific nutritional contexts.
Lactose intolerance mutation only causes issues when consuming lactose.
How does development affect expression? What is an example?
Some genes are only expressed later in development, so the mutation only causes issues during certain points of life.
Duchenne muscular dystrophy. Normal infancy, but a mutation causes the muscles to begin wasting away at 3-5 years old, and fatalities by their 20s.
What would the genotype ratio be of an F1 cross of 2 pink-flowered plants?
RrRr, 2 RrRw, 1 RwRw
What would the phenotype ratio be of an F1 cross of 2 pink-flowered plants?
1 red: 2 pink: 1 white
What conclusion can we drawn about the genotype and phenotype ratios in incomplete dominance?
Every unique genotype has a unique phenotype in incomplete dominance.
