Flashcards in Ch 12 - Genetics & Evolution Deck (67)
What is a chromosome?
What all genes are arranged into
This is to ensure that all genetic material is passed on from mother to daughter cell during mitosis and meiosis
What are alleles?
Alternative forms of a gene
Emailed: ABO blood group has three alleles for the same gene (Ia, Ib, i)
What is a genotype?
The genetic combination that an individual has
What is a phenotype?
The MANIFESTATION of of a given genotype via observable traits
What are homologues?
What is the one exception to this?
Homologues are two copies of each chromosome - humans have 2 copies of each chromosomes.
The exception is the male sex chromosome which has one X chromosome and one Y chromosome
What is the LOCUS of a chromosome?
A specific place for the gene to be
The normal locus of each gene is the same among all humans, so that a gene can be found based on the description of it's location
Since there are two of each chromosome, what does this mean for alleles?
There are hence two alleles present for each gene.
These can be the SAME allele - HOMOZYGOUS
Or can be two different alleles - HETEROZYGOUS
HEMIZYGOUS means that only one allele is present for a given gene, for example the X chromosome in men
What are alleles categorized based on?
Dominant versus Recessive
Based on their expression (via phenotype)
Dominant: if only one copy of an allele is needed to express a phenotype
Recessive: if two copies of the allele are needed to express a phenotype
What is complete dominance?
When there is one dominant allele and one recessive allele
What is co dominance?
Two dominant alleles
Ie: someone with an allele for A antigen and an allele for B antigen = AB blood type
What is incomplete dominance?
No dominant alleles
When a heterozygote (two diff alleles) express a phenotype that is intermediate between the two homozygous genotypes
Ie: a red flower with a white flower = a pink flower
What is penetrance?
A population measure
The proportion of people in a population who carry the allele and express the phenotype
(Given that someone has the allele, the likelihood that they will express the phenotype)
An example of penetrance
People with 40 sequence repeats have FULL PENETRANCE meaning that 100% of individuals with this allele show symptoms.
Fewer sequence repeats: HIGH penetrance, aka most but not all of the people who have this allele will express the disease
With fewer sequence repeats, the gene has REDUCED PENETRANCE aka very few people with the allele express the phenotype
What is expressivity?
On the individual level. The different manifestations of the same genotype.
Varying PHENOTYPE despite identical GENOTYPE
It is either CONSTANT (given genotype always results in one phenotype) or VARIABLE (same genotype but different phenotypes)
What is a gene?
A DNA sequence that codes HERITABLE TRAITS that can be passed from one generation to the next
Four tenets of Mendel's first law of SEGREGATION
1. Genes exist in alternate forms (alleles)
2. Two alleles for each gene (one from each parent)
3. Two alleles segregate during meiosis, making gametes that have only 1 allele for any inherited trait
4. Two diff alleles means one will be silent and one will be fully expressed (dominant and recessive) *with the exception of complete and co- dominance
Mendel's first law (of segregation) applies to which phase of meiosis
What genetic material (re: alleles) does each gamete carry ?
ONE ALLELE for any given trait
What do segregation and independent assortment lead to in gametes?
GENETIC DIVERSITY of the gametes and eventually of the offspring as well
Imrpove ability of a species to evolve and adapt to environmental stresses
Why phases of meiosis do Mendel's first and second laws most closely take place?
Mendel's first law (segregation) - Anaphase 1
Mendel's second law (independent assortment) - Prophase 1
Mendel's second law of INDEPENDENT ASSORTMENT
What is it
How does it happen
The inheritance of one gene does NOT affect the inheritance of another
This happens during PROPHASE if meiosis 1, where a tetras is created by homologous chromosome pairs. (2 chromatids in each of the chromosomes)
RECOMBINATION takes place, swapping of small segments of emetic material - results in novel combinations of alleles that were not present in the original chromosomes.
*recent findings of LINKED GENES make this theory questionable
What is a gene pool?
All of the alleles that exist within a species.
Mutations, genetic leakage, and genetic drift allow the species to evolve and adapt to environments
What is a mutation?
Give 3 examples
A change in DNA sequence
Ionizing radiation (can damage DNA)
DNA polymerase can make mistakes during DNA replication (proof reading mechanisms help prevent this)
Transposons (can insert and remove themselves from the genome)
*transposon going into the MIDDLE of a code can disrupt the gene
What are other ways that flawed proteins can happen, unrelated to damage in DNA?
Indirectly pairing nucleotides during transcription and translation
tRNA put with incorrect amino acid for it's anticodon
(These cause de arrangements to the normal amino acid sequence)
What are point mutations?
Occur when one nucleotide is swapped for another (A, T, C, G)
Silent (no change in amino acid)
Missense (diff amino acid)
Nonsense (results in STOP codon)
What are frameshift mutations?
When nucleotides are added or deleted from the genome (and shift everything over by one)
"Insertion" or "deletion" frameshift mutations
Results in either a change in the amino acid sequence, or truncating of the protein due to a nonsense mutation
What is a chromosomal mutation?
On a larger scale - affects large segments of DNA
Insertion (DNA from another chromosome)
Translocation (swapped segment of DNA between chromosomes)
How can mutations be advantageous?
If the mutation has few side effects but some resistance to something
Ie, people who are heterozygotes for sickle cell disease have minor symptoms but have natural resistance to malaria because their RBC's have a slightly shorter lifespan (short enough that malaria can't reproduce)
What are inborn errors of metabolism?
A class is deleterious mutation (detrimental = bad!)
Where the defects affect the genes requires for metabolism - results in a buildup of metabolite a in various pathways