1. Chap 9/11 : Fundamentals of Genetics
Mendel
-- Gregor Mendel – “Father of Genetics” – worked with pea plants. Discovered inheritance (passing of traits from parents to offspring)

2. A. Terminology
1. Pure or Strain – trait that’s always passed to offspring.
2. P1 generation – parents
3. F1 generation – 1st filial generation – offspring of P1
4. F2 generation – offspring of F1

3. B. 3 Principles of inheritance
1. Principle of Dominance and Recessiveness – says that traits that mask other traits are called dominant traits (R) and those that don’t are recessive traits (r).
2. Principle of Segregation – each trait is expressed by 2 factors – one from each parent
Ex. RR x rr = Rr
(mom) (dad) (offspring)

4. C. Chromosomes and Genes gene – piece of DNA
3. Principle of Independent Assortment – says traits are independent from each other. Ex. Eye color and hair color are independent of each other.
C. Chromosomes and Genes
gene – piece of DNA
calling for a specific
trait – like eye color
allele – that form of a
gene. Ex. Blue, brown,
or green
gene
chromosome

5. II. Genetic Crosses
A.1. Genotype – genetic makeup of an organism. Expressed with letters. (Rr)
2. Phenotype – physical appearance of an organism (ex. Blue eyes)
3. Homozygous – when both alleles of a pair are the same. (RR or rr)
4. Heterozygous – when the alleles of a pair are not the same. (Rr)

6. Ex. B- black b - blonde Bb (dad) x bb (mom)
Geneotype: Bb bb
Phenotype: black blonde
heterozygous homo. Rec.
Homozygous dominant – BB
Homozygous recessive – bb
5. Multiple alleles – when 3 or more alleles control 1 trait.
ex. Blood type : A, B, O

7. 18 heads, 32 tails. What is the probability of tossing a head ?
6. Probability – the likelihood of something occurring. #of 1 kind of event / # of events
Ex. 50 tosses of coin
18 heads, 32 tails. What is the probability of tossing a head ?
18/50 = 36 %
B. Monohybrid crosses – cross between 1 trait

8. Types of Monohybrid Crosses
--- Punnett Square – tool used to predict the probability from genetic crosses.
Types of Monohybrid Crosses
In rats brown fur is dominant over white fur. If a homozygous dominant and homozygous recessive parent produced offspring, what would be their genotypes and phenotypes ?
B- brown b-white
BB x bb G: 100% Bb
b b P : 100% Brown
B Bb Bb

9. 2. If two of the offspring from #1 were mated what would be the outcome ?
B- brown b- white
Bb x Bb G : 1 BB
B b Bb
B BB Bb bb
b Bb bb P : 3 brown
1 white

10. R- round r – wrinkled Rr x rr r r R Rr Rr r rr rr
3. In pea seeds round is dominant over wrinkled. If a heterozygous seed is mated with a wrinkled one what percentage would end up wrinkled ?
R- round r – wrinkled
Rr x rr
r r
R Rr Rr
r rr rr
50 % would be wrinkled

11. 4. Test Cross – used to determine the genotype of a dominant phenotype.
In mice red eyes are recessive to blue. A mouse has blue eyes and you want to know if red eyes “run in the family line”, how can you determine this ?
--- Perform a test cross – cross the mouse with a homozygous recessive (one with red eyes). B? X bb = ?. If any offspring have red eyes you would know the allele in question was for red eyes.

12. 4. Codominance – when one or more alleles is considered dominant
4. Codominance – when one or more alleles is considered dominant. The result produces a blend of the alleles.
Ex. Flower petals exhibit codominance.If a red flower was crossed with a white flower describe the genotype and phenotype of the offspring.
R – red R’ – white
RR x R’R’
R’ R’
R RR’ RR’
R RR’ RR’ G: all RR’
P : all pink

13. C. Dihybrid Crosses – cross between individuals that involves 2 different traits.
In Peas, round seeds are dominant to wrinkled and yellow is dominant to green. What would be the genotype and phenotye of the offspring of a homo.rec. and homo.dom. parents ?
R – round G- yellow
r – wrinkled g – green
RRGG x rrgg

14. RG(1+3) RG(1+4) RG(2+3) RG(2+4)
(1+3) rg RrGg RrGg RrGg RrGg
(1+4) rg RrGg
(2+3) rg
(2+4) rg
G : all RrGg
P : all round and yellow

15. Ex. If two offspring from above were to be mated what would be the phenotypes of the offspring ?
RrGg x RrGg
RG(1+3) Rg(1+4) rG(2+3) rg(2+4)
RG RRGG RRGg RrGG RrGg
Rg RRGg RRgg RrGg Rrgg
rG RrGG RrGg rrGG rrGg
rg RrGg Rrgg rrGg rrgg
Phenotypes :
9 round and yellow (R_G_)
3 round and green (R_gg)
3 wrinkled and yellow (rrG_)
1 wrinkled and green (rrgg)