Read and review notes

1. CHAPTER 11 FUNDAMENTALS OF GENETICS
Early Concepts in Genetics
Genetics Prehistory - domestication of wolves into dogs of specific specialization of traits; breeding
of plants.
BLENDING HYPOTHESIS – this explanation is developed by Aristotle.
- it says that the traits of the parents were blended in their offspring producing a form of
intermediate between the two parents and the blended traits are passed on to the next
generation.
- Example: Parents: Tall and Short
Children: Medium
GREGOR MENDEL – he is the father of Modern Genetics. He is an Austrian monk who studied and
bread pea plants. His observations helped him to understand the patterns of heredity.
GENETICS – the scientific study of heredity.
Mendel’s Investigations
Mendel’s Experiments:
1. He cross-bred pea plants with different traits like (tall with short; wrinkled seed with smooth;
green with yellow; etc.)
2. Observations: Mendel did several generations of breeding of pea plants
P : parents; F1: first generation offspring; F2: 2nd
gen. offspring from self fertilization of F1
DOMINANT TRAIT – a trait that masks the appearance of a recessive gene
- a trait that can be showed in a hybrid.
RECESSIVE TRAIT – a trait that is masked by the dominant trait.
- a trait that did not show in a hybrid.
p. 131 shows us the summary of F1 results:
Plant Height Seed shape Seed Color
P TT x tt
tall x short
RR x rr
round wrinked
YY x yy
yellow x green
F1 Tt
tall
Rr
round
Yy
Yellow
After self pollination
of F1:
Tt x Tt
After self pollination
of F1:
Rr x Rr
After self pollination
of F1:
Yy x Yy
F2 3 tall, 1 short 3 round, 1 wrinkled 3 yellow, 1 green
Mendel’s Hypothesis: that each trait is controlled by something called a “factor” within the
organism.
GENE – the term used by scientists to indicate a genetic factor that controls a trait

2. Modern Genetics
ALLELES: are different versions of a gene for the same trait.
- Example: T and t are alleles of the gene that controls height.
MENDEL’S LAWS:
1. LAW OF SEGREGATION – states that each pair of alleles segregates, or separates during
meiosis.
2. LAW OF DOMINANCE – when the 2 alleles are different, like Hybrid, one allele can control a
trait (Dominant allele), and an allele that is hidden (Recessive allele).
3. LAW OF INDEPENDENT ASSORTMENT – states that gene pairs segregate or separates into
gametes randomly and independently for each other.
Genotype VS Phenotype:
GENOTYPE – the actual genetic make-up of an organism. It shows the alleles.
- Examples: TT; Yy
PHENOTYPE – is the form of the trait that is observed
- Examples: tall; yellow
Homozygous VS Heterozygous
HOMOZYGOUS – the 2 alleles of a trait is identical or the same
- Examples: TT; RR; rr; yy
HETEROZYGOUS – the 2 alleles of a trait is not the same
- Examples: Tt; Rr; Yy
** Recessive is always homozygous and dominant can be homozygous or heterozygous.
Probability and Genetics
Using a PUNNET SQUARE – is a grid for organizing genetic information
Steps on How to Use the Punnet Square
1. Determine the alleles in the gametes of parents
2. Place the alleles on one parent along the top of the grid and those of the other parent along
the left side.
3. Combine the 2 alleles inside the boxes, the dominant or BIG letter comes first
4. Determine the genotypes and phenotypes of the offspring inside the boxes.
MONOHYBRID CROSS – only 1 trait at a time
Example: Seed color: (Y) yellow vs. (y) green
Yy x Yy
Y y Y y Offsprings:
Genotypes
1 YY – yellow
2 Yy – yellow
1 Yy – green
Phenotypes
3 yellow
1 green
Y
y
Y
y
YY Yy
Yy yy

3. DIHYBRID CROSS: 2 traits at a time
Example: Seed color: (Y) yellow vs. (y) green AND
Seed shape: (R) round vs. (r) wrinkled
RrYy x RrYy
RY Ry r Y ry
RY Ry r Y ry
RRYY RRYy RrYY RrYy
RRYy RRyy RrYY Rryy
RrYY RrYy rrYY rrYy
RrYy Rryy rrYy rryy
** Exercises: Determine the genotypes and phenotypes of the
following cross:
1. RRYy x Rryy
2. rrYY x Rryy
TEST CROSS – use a homozygous recessive to cross with an unknown genotype. If the result is half
dominant and half recessive trait, then the unknown genotype is heterozygous.
RY
Ry
rY
ry
RY
Ry
rY
ry
Offsprings:
Genotypes
1 RRYY; 2RRYy; 1
RRyy; 3 RrYY; 3
RrYy; 2Rryy; 1 rrYY; 2
rrYy; 1 rryy
Phenotypes
9 round, yellow
3 round, green
3 wrinkled, yellow
1 wrinkled green

4. 8.4 Other Patterns of Heredity
1. Intermediate Inheritance – there is no completely dominant allele over a recessive allele.
A. INCOMPLETE DOMINANCE – the heterozygote shows a phenotype that is
intermediate the two homozygous phenotypes
- Example: (R)red petals (r) white petals
RR x rr
Red x white
R R Offsprings:
Genotypes Phenotypes
4 Rr 4 Pink
1 green
B. CODOMINANCE – both alleles in the heterozygote express themselves fully
- Example: blood type (IA
IB
) this is blood type AB
C. POLYGENIC TRAITS – traits that are controlled by 2 or more genes.
- Example: skin color, eye color
2. MULTIPLE ALLELES – these are genes that have more than 2 alleles.
- Example: blood type has 3 alleles: IA
IB
and i
3. Environmental Effects – genes adjust to accommodate environmental changes.
- Example: fur and feather colors of ptarmigans and rabbits.
r
r
Rr
Rr Rr
Rr