Mendelian GeneticsMendelian Genetics

Gregor MendelGregor Mendel

IntroductionIntroduction

• Genetics is the study Genetics is the study of heredityof heredity

• Gregor Mendel used Gregor Mendel used mathematics to mathematics to study the inheritance study the inheritance of traitsof traits

Phenotypes

• These are features you exhibit physically

( your looks)

Example: Eye color - green

Alleles

• The different versions of a characteristic

• Example: blue, green, and brown eyes

Inheritance

• Occurs when traits are passed down from parent to child.

• Gametes (sex cells like sperm or ovaries) carry traits to offspring.

Genes

• Bits of information passed down from parent to child.

• Made of chemicals called DNA.

HeredityHeredity

• The chromosome theory of heredity states that the inheritance of traits is controlled by genes, located on chromosomes

Key TermsKey Terms GenotypeGenotype - - gene combination for a gene combination for a

traittrait (e.g. RR, Rr, rr) (e.g. RR, Rr, rr) PhenotypePhenotype - - the physical feature the physical feature

resulting from a genotyperesulting from a genotype (e.g. red, (e.g. red, white) white)

The The Average Average

American American PhenotypePhenotype

Alleles

• T – is considered a dominant allele

• t – is considered a recessive allele

TT – is homozygous dominant

Tt or tT – is heterozygous dominant

tt - is Homozygous recessive recessive

Genotype & Phenotype in FlowersGenotype & Phenotype in Flowers

Genotype of alleles:Genotype of alleles:RR = red flower= red flowerrr = yellow flower= yellow flower

All genes occur in pairs, so All genes occur in pairs, so 22 allelesalleles affect a characteristic affect a characteristic

Possible combinations are:Possible combinations are:

GenotypesGenotypes RRRR RRrr rrrr

PhenotypesPhenotypesRED RED RED RED YELLOWYELLOW

The Law of Dominance• Law states that the dominant allele, if

present, will be expressed. DominantDominant - - stronger of two genes

expressed in the hybrid; represented by a capital letter (R)capital letter (R)

RecessiveRecessive - - gene that shows up less often in a cross; represented by a lowercase letter (r)lowercase letter (r)

Predicting traits• Probability is used to predict traits in offspring

• Punnett squares are diagrams used to predict outcomes from a cross

Types of Genetic CrossesTypes of Genetic Crosses

Monohybrid cross Monohybrid cross - - cross cross involving a single traitinvolving a single traite.g. flower color e.g. flower color

Dihybrid crossDihybrid cross - - cross involving cross involving two traits two traits e.g. flower color & plant heighte.g. flower color & plant height

How to do a monohybrid cross

Law of SegregationLaw of Segregation• During the During the formation of formation of

gametesgametes (eggs or sperm) (eggs or sperm) during meiosis, the during meiosis, the two allelestwo alleles responsible for a trait responsible for a trait separateseparate..

• Alleles for a trait are then Alleles for a trait are then "recombined" at fertilization"recombined" at fertilization.

Applying the Law of Applying the Law of SegregationSegregation

Make a Cross for the following:• Imagine you are crossing two vampire bats.

– The dominant trait for skin color is black (S).– The recessive trait for skin color is white (s).

• It you have one parent with the genotype Ss and one with the genotype ss, what kind of offspring would they have?

s

s

S s

Answer

S s s s

S s s s

S s

s

s

Group Assignment

• Let’s imagine we found a new species of dog called a Gir.– We are going to practice crossing this new species to get a

better knowledge of how Punnett Squares work.

A pure breed GREEN Gir has

the genotype GG

A pure breed RED Gir has

the genotype gg

A Gir with the genotype Gg will have a GREEN phenotype because green is dominant over red.

Breed the PBreed the P11 generation generation

• Green (GG) x Red (gg)Green (GG) x Red (gg)

G

G

g g

Solution:Solution:

G

G

g g

Gg

Gg

Gg

Gg All Gg = Green(heterozygous Green)

produces theFF11 generation generation

Green (GG) x Red (gg) dogsGreen (GG) x Red (gg) dogs

Breed the FBreed the F11 generation generation

• Green (Gg) x Green (Gg) Green (Gg) x Green (Gg)

G

g

G g

Solution:Solution:

GG

Gg

Gg

gg

G

g

G gproduces theFF22 generation generation

1/4 (25%) = GG1/2 (50%) = Gg1/4 (25%) = gg1:2:1 genotype1:2:1 genotype 3:1 phenotype3:1 phenotype

Green (Gg) x Green (Gg)Green (Gg) x Green (Gg)

Punnett Squares can also be used to determine the sex.

X

Y

X X

XX XX

XY XY

50% possibility of female XX

50% possibility of male XY

Dihybrid CrossDihybrid Cross

• A breeding experiment that tracks the A breeding experiment that tracks the inheritance of two traitsinheritance of two traits..

• Follows Mendel’s Follows Mendel’s “Law of Independent “Law of Independent Assortment”Assortment”– Each pair of alleles segregates Each pair of alleles segregates

independentlyindependently during gamete formation during gamete formation

Dihybrid CrossDihybrid Cross• Traits: Seed shape & Seed colorTraits: Seed shape & Seed color• Alleles:Alleles: R round

r wrinkled Y yellow y green

•

RrYy x RrYy

RY Ry rY ryRY Ry rY ry RY Ry rY ryRY Ry rY ry

All possible gamete combinationsAll possible gamete combinations

shapeshape

colorcolor

Law of Independent AssortmentLaw of Independent Assortment

• Alleles for Alleles for differentdifferent traits (like eye color and hair color) traits (like eye color and hair color) are distributed to sex cells (& offspring) independently are distributed to sex cells (& offspring) independently of one another.of one another.

Dihybrid CrossDihybrid CrossRYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Dihybrid CrossDihybrid Cross

Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1

9:3:3:1

Pedigrees• Pedigrees use symbols

to track a trait.• Trait is then tracked

through generations.

Example

Generation 1

Generation 2

Generation 3

Pedigree • Pedigree: is a diagram of family relationships

that uses symbols to represent people and lines to represent genetic relationships.

• These diagrams make it easier to visualize genetic relationships within families.

• Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases.

Incomplete DominanceIncomplete Dominanceandand

CodominanceCodominance

Incomplete DominanceIncomplete Dominance• F1 hybrids F1 hybrids have an appearance somewhat

in betweenin between the phenotypes phenotypes of the two parental varieties.

• Example:Example: snapdragons (flower) snapdragons (flower) – red (RR) x white (rr)

• RR = red flowerRR = red flower• rr = white flower R

R

r r

Incomplete Incomplete DominanceDominance

RrRr

RrRr

RrRr

RrRr

RR

RR

rr

All Rr =All Rr = pink pink(heterozygous pink)(heterozygous pink)

produces theproduces theFF11 generation generation

r

Incomplete DominanceIncomplete Dominance

CodominanceCodominance• Multiple allelesMultiple alleles are expressed in are expressed in heterozygous heterozygous

individualsindividuals..• Example:Example: blood type blood type

• 1.1. type Atype A = I= IAAIIAA or I or IAAii• 2.2. type Btype B = I= IBBIIBB or I or IBBii• 3.3. type ABtype AB = I= IAAIIBB

• 4.4. type Otype O = ii= ii A and B are types of

antigens. O type blood

does not have these antigens.

Codominance ProblemCodominance Problem• Example:

Type B (IBIB) x Type A (IAi)

What blood types are

possible in offspring?

IB

IA i

IB

Codominance ProblemCodominance Problem

• Example:

Type B (IBIB) x Type A (IAi)

IAIB IBi

IAIB IBi

1/2 = IAIB

1/2 = IBi

IB

IA i

IB

Another Codominance ProblemAnother Codominance Problem

• Example:Example: male Type O (ii) x female type AB (IAIB)

What are the possible blood types?

i

IA IB

i

Another Codominance Problem• Example:Example: male Type O (ii)

x female type AB (IAIB)

IAi IBi

IAi IBi

1/2 = IAi1/2 = IBi

i

IA IB

i

Sex-linked TraitsSex-linked Traits• Traits (genes) located on the sex

chromosomes• Sex chromosomes are X and Y• XX genotype for females• XY genotype for males• Many sex-linked traits carried on X

chromosome ONLY.– Color blindness, Hemophilia (can’t clot

blood), Kabuki syndrome, baldness• This means males get genes on X gene

from MOTHER.

Sex-linked TraitsSex-linked Traits

Sex ChromosomesSex Chromosomes

XX chromosome - female Xy chromosome - male

fruit flyeye color

Example: Example: Eye color in fruit Eye color in fruit fliesflies

Sex-linked Trait Problem• Example: Eye color in fruit flies• (red-eyed male) x (white-eyed female)

XRY x XrXr

• Remember: the Y chromosome in males does not carry traits.

• RR = red eyed• Rr = red eyed• rr = white eyed• XY = male• XX = female

XR

Xr Xr

Y

Sex-linked Trait Sex-linked Trait Solution:Solution:

XR Xr

Xr Y

XR Xr

Xr Y

50% red eyed female

50% white eyed male

XR

Xr Xr

Y

Alien Lab

• You will spend 2/3 class periods creating this booklet.

• DO NOT LOSE YOUR BOOKLET. – TURN IT IN TO ME after each class period so

you won’t lose it.– There are NO EXTRA COPIES.

You will create a booklet of an Alien you create and its FAMILY HISTORY in terms of genetics.

EVERYONE will have a DIFFERENT alien.

• Things to complete (look at rubric on page 11)– 1. Cover page (Day 1)– 2. Alien Trait Key (Day 1) – 3. Alien Personal Data (Day 1) – 4. Alien Personal Ad (Day 2)– 5. Alien Mate Data Sheet (Day 2).– 6 & 7 Alien Matchmaking Traits (Day 2)– 8. Alien Offspring Trait Key (Day2/3)– 9. Alien Offspring Drawings (Day 3)– 10. Discussion Questions (Day 3)

I will discuss each thing the DAY

we will do them. I will only cover items

1-3 today.

Alien Trait Key

• We will do this AS A CLASS.

• We will discuss what we want our ALIEN SPECIES TO LOOK LIKE.

# Trait HomozygousDominant

Heterozygous Dominant

HomozygousRecessive

Example

HH(heads/heads)

Hh(heads/tails)

hh(tails/tails)

1 Hair Color Blue Blue Yellow

2 Eye Color

3 # Heads

4 Tall? Short?

5 # Fingers

6 # Toes

7 Skin Color

8

9

10

11

12 Sex Female Male Circle one

Alien Personal Data

• Using a penny (Heads = H) (Tails = h) flip a coin to find out your personal genotype.

• Fill in column 1 with genotypes flipped.

• Using the information from the “alien trait key” fill in column 2 with your personal phenotype.

• Draw and color YOUR COVER PAGE based off this information on the cover of your Alien Lab Booklet.

# YOUR Alien’s Traits

(Genotype)

YOUR Alien’s Traits

(Phenotype)

Mate Information(Genotype)

Mate Information (Phenotype)

1 hh yellow2

3

4

5

6

7

8

9

10

11

12

Cover Page

• Have the students put their parent drawing here. They will get this information from the “alien personal data” sheet to be filled out on page 3.