Biology Chap 14 Essay

Chapter 14: Genetics
Mendel
Heredity- “blending process”
He documented how inheritance might work
He used garden peas
You can get peas in a ton of varieties
Could strictly control which pea plant mated with pea plant
**We cant always study what we want to study so we work in a model system- something we can work in easily and has certain advantages**
Tracked in an “either or manner”
True breeding (how he started his experiments)
P generation
After crossing they are called the F1 (filial generation)
When F1 self pollinates, F2 is produced
1. Alleles- variations in inherited characteristics
Could be as simple as a change on the DNA strand
2. For every character, an organism inherits two alleles (one from each parent)
3. If two alleles at a locus are different, the dominant determines the organism’s appearance
4. Law of Segregation copies segregate during gamete formation
2 laws of inheritance

Punnett Square
(this is F1 generation) Pp x Pp (F2 generation)
Heterozygous- Pp
Has a pair that are different for that gene
Homozygous- PP, pp
Identical alleles
Characteristic: a heritable feature, such as flower color
Trait: a variant of a character; such as purple or white color
Phenotype
Physical appearance
What does it look like?
Ex. Purple flowers
You can readily observe
Genotype
Has to do with genes
Its genetic make up
What alleles does it have?
Ex. “Homozygous dominant”
Phenotypic ratio 3:1
Genotypic Ratio 1:2:1
Test Cross
Allows us to determine the genotype of an organism with the dominant phenotype, but an unknown genotype
Cross is with homozygous recessive
P__ X pp
Figure 14.7
Law of Segregation
Alleles separate during gamete formation
Monohybrids **
One characteristic being followed
Law of Independent Assortment
Identified his second law of inheritance
Followed two characteristics at the same time
Produces dihybrids in the F1 generation
4 different phenotypes in F2

9:3:3:1  phenotypic ratio
Each pair of alleles segregate independently
Threes another way!
Utilize the rule of probability
Mendel’s laws follow the rules of probability
1. The multiplication rule
The probability two or more independent events will occur together is the product of their individual probabilities
Figure 14.9
2. The rule of addition the probability that any one od two or more exclusive vents will occur is calculated by adding together their individual probabilities
A dyhbrid or other multichracteristic cross is equivalent to two or more independent monohybrid crosses occurring simultaneously
Multiplication
aabbccdd
AaBBCCDd
Inheritance are often more complex than just crossing
The phenotype may deviate than what we predicted (Medelian Process)
Complete Dominance
Occurs when the phenotypes of the heterozygote and dominant homozygote are identical
Codominance
Two dominant alleles to their full extinct in their pehotype
Blood group MN (MM, NN is only one do only one is dominant)
Incomplete Dominance
Snapdragons
The phenotype of F1 hybrids is somewhere between the two phenotypes of the two parental varieties
Dominance and Phenotype
Don’t really interact; they just lead to different forms of the same protein
Dominant Alleles
Are not necessarily more common in populations than recessive
Ex
Polydactyl is dominant but we don’t have 6 fingers
Most genes exist in populations in more than just two different alleles
Ex. Blood Type
Table 14.2
ABO
Pleiotrophic (multiple effects)
Multiple phenotypic effects
Ex. Sickle Cell
Deformed blood cells
Weaknesss
Pain and organ damage
You can have multiple genes that determine a trait
Epistasis
Gene at one location alters the phenotypic expression alters a gene at another location
Masking of one genotype by the phenotypic expression of another
Black Lab example
Figure 14.11
The genotype of a place effected the phenotype of the lab
Even though it should

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