Patterns of Inheritance Flashcards
what 3 things did mendel learn from monohybrid crosses?
- Diploid organisms inherit 2 alleles for each gene,
one allele from each parent - The dominant allele determines the phenotype in
a heterozygous individual - Two alleles of a gene separate during meiosis =
Law of Segregation
what are dihybrid crosses? what kind of offspring (F1 gen) do they produce?
are a cross of homozygous organisms with different alleles at two genes
-Generate heterozygous offspring (F1 generation)
what is the Law of Independent Assortment? what condition is needed for this to be true?
states that the alleles of two (or more) different genes get sorted into gametes independently of one another
- aka: the allele a gamete receives for one gene does not influence the allele received for another gene
- condition: the genes must be located on non-homologous chromosomes
what is the Law of Segregation?
states that allele pairs separate (or segregate) during gamete formation (meiosis) and randomly unite at fertilization
How would you determine which allele is dominant
and which is recessive for each gene?
look at phenotype of F1 generation
what are the phenotypic frequencies you will see in the F2 generation of a dihybrid cross?
9 : 3 : 3 : 1
9/16 –> will express both dominant alleles (A and B)
3/16 –> will express dominant A and recessive b (A and b)
3/16 –> will express recessive a and dominant B (a and B)
1/16 –> will express both recessive alleles (a and b)
what are the three degrees of dominance? what does this mean?
- Complete dominance
- Incomplete dominance
- Codominance
-it means that alleles show different degrees of dominance and recessive in relation to each other
what is complete dominance? what does this mean for heterozygote and homozygous phenotypes?
- it is when one allele of a gene is completely dominant over the other
- Phenotypes of heterozygote and homozygous dominant are indistinguishable –> ie. both PP and Pp will look the same
what is incomplete dominance? what does this mean for the heterozygote phenotype?
- it is when neither allele of a gene is completely dominant
- means that the phenotype of the heterozygote falls somewhere between the two homozygous organisms that cross –> ie. red flower and white flower cross and produce pink flower
when determining gentoypes of incomplete dominance organisms, why do you not use upper case and lower case letters? what do you use instead?
- do not use upper case/lower case letters because neither allele is dominant or recessive
- from slide * –> use two different uppercase letters. eg C^R (for red) and C^W (for white)
what are the incomplete dominance genotypic and phenotypic ratios? give example
genotypic ratio : 1:2:1
phenotypic ratio : 1:2:1
flower example: P gen --> C^R C^R (red) & C^W C^W (white) F1 gen --> C^R C^W (pink) F2 gen (can make punnet square) --> 1 : C^R C^R (red) 2 : C^R C^W (pink) 1 : C^W C^W (white)
what is codominance? what does this mean for the phernotype of the heterozygote?
- when two alleles both affect the phenotype in separate, distinguishable ways
- means the phenotype of the heterozygote exhibits both alleles
what is multiple allelism? give example
is when a gene has more than 2 alternative alleles
e.g. ABO blood group
-Single gene with 3 alleles = I^A, I^B, i
meaning blood cells may have carbohydrate A, carbohydrate B, both, or neither
what are alleles variations of? what does the recessive allele code for?
variations in a gene’s nucleotide sequence
-the recessive allele codes for a defective enzyme
what happens to the heterozygote phenotype if just having one copy of a functional enzyme is enough? what will we see when we look at the organism level? what about at the enzyme level?
- in this case the heterozygote phenotype will be the same as the homozygous dominant phenotype
- organism level will appear like complete dominance
- enzyme level we see that both proteins are expressed = codominant
-b/c one enzyme id defective and therefore not producing any effect, but it is still present, even though not expressed
