BIO- Genetics Flashcards
Gene
Sequence of DNA that codes for a given trait
Alleles
Variations of a gene
Dominant or recessive
Homologues
Copies of the same chromosome
Same set of genes
Can have different alleles
Locus (loci)
Specific place on a chromosome where a gene occurs
Recessive
Both alleles must be recessive for the phenotype to be expressed
Gain of function mutations
Mutated protein can do something the original protein could not
Usually dominant
Doesn’t mean advantageous –> Huntington’s Disease
Loss of function mutation
Mutated protein can no longer perform the function of the original protein
Usually recessive
Homozygous
2 copies of the same allele
Ex: RR or rr
Homozygous dominant
RR
Homozygous recessive
rr
Heterozyogous
Have one copy each of two different alleles
Ex: Rr
Hemizygous
Only one copy of a give allele i present
Can occur due to nondisjunction in an organism with aneuploidy
Ex: can occur with regard to genes on the X and Y chromosome in male humans
Parent generation homozygous dominant (RR) and homozygous recessive (rr) –>
F1 generation –> all heterozygotes –> Rr
Cross F1 generation with itself (Rr x Rr)
Genotypes 1:2:1 ratio
25% homozygous dominant (RR)
50% heterozygous (Rr or rR)
25% homozygous recessive (rr)
Phenotype 3:1 ratio
Test Cross
Used to tell whether an organism with a dominant trait is Homozygous dominant (RR) or Heterozygous (Rr) by test crossing it with a Homozygous recessive (rr) organism
Homozygous dominant (RR) offspring --> 100% dominance Heterozygous (Rr) offspring --> 50% dominance
Wild-Type
Refers to the default phenotype or genotype that is present in most members of a species, in contrast to mutation
Complete Dominance
One copy of the dominant gene is enough to induce the dominant phenotype
No phenotypic difference between homozygous dominant individuals and heterozygotes
Codominance
When two dominant alleles can be expressed at the same time
Ex: ABO blood typing –> AB
Ex: B for black fur, W for white –> BW for black and white spots
Incomplete dominance
Occurs when a heterozygote displays a blended phenotype
Ex: Snapdragon flower
Homozygous snapdragon flower (red or white)
Heterozygotes have blended phenotype of pink
Penetrance
Refers to the likelihood that the carrier of a given genotype will manifest the corresponding phenotype
Ex: BRCA1 gene –> 80% risk of developing breast cancer –> BCRA1 gene has an 80% penetrance
Expressivity
The intensity or extent of variation in the phenotype
Mutations of human diseases –> could be thought of as the severity of the condition
Penetrance vs. Expressivity
Penetrance: yes/no question, does an organism express a certain phenotype or not?
Expressivity: grey area question, how much of an effect does a mutation have on the phenotype?
Law of Independent Assortment
No link between inheritance of an allele of the R gene and inheritance of the allele of the P gene
Alleles of genes on different chromosomes will be inherited independently due to the random orientation of the homologous pairs on the metaphase plate in Metaphase I of meiosis
Alleles of genes on the same chromosome will be inherited independently assorted due to crossing over during Prophase I of meiosis
Chiasmata
points of crossing over on the chromosome
Obey the Law of Independent Assortment
When the recombination frequency (theta) is greater than 50% then the genes in questions
Recessive mutations
Can skip generations, but don’t have to
Dominant mutations
Cannot skip generations
Sex-linked Inheritance
takes place for genes located on the X chromosome
X-linked Inheritance
Asymmetry in the sex of affected individuals
Affect males much more since only one X from mother
