GENETICS

Why do you look like that?!?

A little background…

• Gregor Mendel- “Father of Genetics”– Austrian monk and biologist in the mid-1800s– Used pea plants to figure out how traits were

inherited (passed down)

Vocabulary

Genetics:

the study of heredity, or how genes are inherited

Allele:

variation of a trait; form of a gene

ex. Trait- pod color / Alleles- yellow, green

• Dominant:

allele that can mask the other

(uppercase letters- A)

• Recessive:

allele that can be masked by the other (lowercase letters- a)

• Homozygous:

both alleles in the pair are the same

(AA or aa)

• Heterozygous:

both alleles in the pair are different

(Aa)

• Genotype:

genetic make-up (the genes) of an organism

Ex. Uu or UU

• Phenotype:

physical appearance expressed by the genes

Ex. Unibrow

G – green pea pods g – yellow pea pods

(Dominant) (Recessive)

Genotypes GG Gg gg

Terms

Phenotypes

Homozygous dominant

Homozygous recessive

Heterozygous

Green pea pods

Green pea pods

Yellow pea pods

Mendel’s Work

Laws of Heredity

• Law of Segregation:

Two alleles for a trait separate during gamete formation

Laws of Heredity

• Law of Independent Assortment:– Alleles from different genes separate

independently of one another during gamete formation

Punnett Squares

• Used to figure out the possible genotypes and phenotypes (ratios)

• Monohybrid cross:

one trait of an individual is crossed with the same trait of another individual

Monohybrid Cross Example

Let’s look at pea pod color:– Green is dominant (G) and yellow is recessive (g)– Example: Homozygous dominant (GG) crossed with

homozygous recessive (gg)

G G

g

g

Genotype ratio 4 Gg: 0 GG: 0 gg 100% Gg

Phenotype ratio 4 green: 0 yellow 100% green

Gg Gg

Gg Gg

Punnett Squares

• Dihybrid cross:

two traits of an individual are crossed with the same two traits of another individual

Dihybrid Cross ExampleMust find all possible allele combinations:

Traits - seed shape and seed color

Alleles: R = Round r = Wrinkled

Y = Yellow y = green

Female: RrYy Male: RrYy

both are round and yellow

All combinations for each:

Female: RY, Ry, rY, ry Male: RY, Ry, rY, ry

Dihybrid Cross Example

Cross these combinations to find possible genotypes/phenotypes of offspring:

RY

RY

Ry rY ry

Ry

rY

ry

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Dihybrid Cross ExampleCross these combinations to find possible genotypes/phenotypes of offspring:

Genotype ratio: RRYY 1/16 RRYy 2/16 RrYY 2/16 RrYy 4/16

Rryy 1/16 Rryy 2/16

rrYY 1/16 rrYy 2/16

rryy 1/16

Round and Yellow 9/16

Round and Green 3/16

Wrinkled and Yellow 3/16

Wrinkled and Green 1/16

Phenotype ratio:

Types of Dominance:

• 1) Complete Dominance-

One allele can completely mask another

RR- Red Rr- Red rr- white

Types of Dominance

• Incomplete Dominance:

one allele is partially covered by another

RR- RED RR’- PINK R’R’- WHITE

Types of Dominance

• Co-dominance:

Both alleles are dominant, so they both show through

RR- RED RW- Red & White WW- White

Types of Dominance

• 4) Multiple Alleles- when a trait has more than two alleles

• Ex. Blood Type– IA- Type A– IB- Type B– i- Type O

• Both complete and co-dominance are shown in creating phenotypes

• Type A- IAIA, IAi• Type B- IBIB, IBi• Type AB- IAIB

• Type O- ii

Types of Dominance

5) Sex-linked- Allele for trait is found on a sex chromosome

• Ex. Hemophilia– Normal- XH

– Hemophilia- Xh

– Nothing at all- Y