Belyaev – artificially bred foxes ... happy foxes vs. Aggressive foxes
Laws of inheritance
Experimented with garden peas
Why Garden peas?
Easy to cross fertalize
Large numbers of offspring
Short growing season
Phenotype – observable characteristic, can also be behaviour, referred to as a trait
Genotype- genetic make-up, version of the gene
Monohybrid cross – matings between individuals that only differ one trait. Example tall
vs short, yellow vs green.
Gene - unit of inheritance. Example: one gene in humans for eye colour.
Allele – alternative form of a single gene. Example: ^ multiple versions of eye colour.
Polymorphic – more than one wiltype allele, allele frequency greater than 1%, several
alleses that occurs normally in a population.
Monomorphic – only one wild type alle, only one allele above 1%, one alle that is
normally present in a population. Example: sickle cell anemia.
Used selective breeding to produce true-breeding lines of peas
Found a consistent pattern of inheritance
Mendel’s Law of Segregation:
The two alleles for each trait separate (segregate) during gamete formation, then unite at
random, one from each parent at fertalization.
At the DNA level, alleles vary in nucleotide sequence. This can result in:
o New amino acid sequence
o Change in amount of protein o Example: garden peas. R gives the pea a round shape because the version of starch
branching enzyme is normal. The r allele as a different amino acid sequence and the
enzyme is non-functional (ie. No branched starch)
Mendel’s Law of Independent Assortment
During gamete formation, different pairs of alleles segregate independently of each other.
Dominant allele G does not always travel and pair with dominant W.
Law of Segregation describes how different alleles of a gene behave. Law of independant
assortment describes how different genes behave.
Phenotypic ratio: 3:1
Genotypic ratio 1:2:1
To determine genotype, use a test cross.
Test crosses – breeding an unknown genotype with a homozygous recessive indivudal
will reveal it’s genotype. If it was homozygous dominant, all offspring would be
heterozygous and have the same phenotype. If it was heterozygous, we would see a 1:1
The law of product: The probability of two or more independent events occurring
together is the product of the probabilities that each event will occur by itself. AND IS
Example: coin toss – chance of heads twice in a row. Probability of a head and a head. ½
x ½ = ¼
The law of sum: The probability of either of two mutually exclusive events occurring is
the sum of their individual probabilities. OR IS KEY WORD.
Example: dice throw – chance of an even number = probability of a 2, 4, or a 6. 1/6 + 1/6
+ 1/6 = ½.
Dihybrid Crosses – Matings between individuals that differ in two traits. There are more
phenotypic classes seen because there are more allele combo’s for independant
assortment. 9:3:3:1 phenotypic ratio.
Multihybrid Cross – Matings between individuals that differ in three or more traits. Eg.
Aa Bb Cc Dd x Aa Bb Cc Dd ... branching diagram, or... probability of an AA bb Cc Dd
offspring : ¼ x ¼ x ½ x ½ = 1/64
-Modifications of Mendels Ratios
Crossing – When a gene has more than 2 alleles, reciprocal crosses help determine
dominance relationships by crossing pure breeding lines. Modifications of Mendelian Ratios
Types of Dominance:
Incomplete Dominance – The F1 hybrid doesn’t resemble either purebred parent. There is
often an intermediate phenotype. It doesn’t look like dominant or recessive phenotype.
Example: flower pigments. A red flower and a white flower produce all
Pink F1s. The F2s will have a genotypic and phenotypic ratio of 1:2:1 –
one AA (red), two Aa (pink) and one aa (white).
Codiminance – alternative traits are both visible in F1 hybrid. F2 generation also
genotypic and phenotypic ratio of 1:2:1.
Blood type is also an example of codominance.
IB= makes enzyme to add sugar A
I = makes enzyme to add sugar B
I or I = no ezymes = no sugars added
I I = makes both enzymes to add sugars A and B
I and I are codiminant to each other, but they are both dominant to the I allele.
Note: A gene may have more than two alleles
Reciprocal crosses cna be done between pure breeding lines (homozygous) representing
all phenotypes to establish the dominance series.
Ex. Bunnies: cc = albino, c c = Himalayan, c c = chinchilla, and c c = wildtype.
Wild is dominant over Himalayan, wild is dominant over albino. Himalayan is dominant
C (wildtype) has a frequency of greater than 99% therefore is a monomorphic gene
Alleles and Inheritance
Allele frequency – percentage of total number of copies of a gene in a population
represented by a particular allele.
Wild type allele: greater than 1%
Mutant allele: less than 1%
Monomorphic: gene with only one wild type allele, all other mutant.
Polymorphic: gene with more than one wild type allele.