• What is the difference between acquired and inherited traits?

• Austrian monk considered the “Father of Genetics”

• Did his experiments in 1866• He did plant experiments

using the garden pea plant• He discovered the pattern in

which organisms inherit traits

• Mendel chose to use the garden pea in his experiments for several reasons.

1. Availability

2. Easy to manipulate for breeding

3. Distinct traits

Mendel chose his subject carefully

What traits did Mendel study?

•Two different forms of the same gene =

•The factors that carry all traits =

• When he wanted to breed, or cross, one plant with another, Mendel opened the petals of a flower and removed the male organs.

Remove male parts

Mendel chose his subject carefully

• He then dusted the female organ with pollen from the plant he wished to cross it with.

Female part

Transfer pollen

Pollen grains

Maleparts

Cross-pollination

Mendel chose his subject carefully

PP pp

Pp Pp Pp PpHybrids

Purebred = Homozygous

Hybrid = Heterozygous

Pp Pp

PP Pp Pp pp

• Mendel called the observed trait dominant (represented by a CAPITAL letter) and the trait that disappeared recessive (represented by a lowercase letter).

The rule of dominance

P = purple, p = white

• Principle of Dominance: when there is a dominant allele and a recessive allele inherited together for a particular gene, the dominant allele will be expressed.

Mendel’s 1st Law of Inheritance

• Dominant

•Round

• Recessive

•wrinkled

• Express the dominant allele for

Round

• PHENOTYPE – physical characteristics that you SEE

• Ex. Round, wrinkled, green, yellow, purple flower, white flower

♦GENOTYPE – genetic

makeup represented

by letters

♦Ex. RR, rr, Rr, Yy,

PP, Ppyy

•Paternal •Maternal

wrinkledROUND

Pea Shape

You inherit two alleles for each gene (trait).

1 from MOM! 1 from DAD!

• The law of segregation states that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles.

The law of segregation

• During fertilization, these gametes randomly pair to produce four combinations of alleles.

RR rr

Rr Rr Rr Rr

Mendel’s 3Mendel’s 3rdrd Law of Inheritance Law of Inheritance Principle of Independent Assortment: the

alleles for different genes usually separate and inherited independently of one another. So, in

dihybrid crosses you will see more combinations of the two genes.

•BBbbTTtt

•diploid (2n)

•sperm

•haploid (n)

•meiosis II

•BBTT

•BBtt

•bbTT

•bbtt

The first generationDihybrid Cross round yellow x wrinkled green

Round yellow Wrinkled green

All round yellow

Round yellow Round green Wrinkled yellow Wrinkled green9 3 3 1

P1

F1

F2

Reginald Punnett

1.(1875-1967)

2.In 1902, created the

Punnett Square - a chart

which helped to determine

the probable results of a

genetic cross

•http://vector.cshl.org/dnaftb/concept_5/con5bio.html

Punnett Square

3.each parent can only contribute one allele per

gene4.these genes are found on the chromosomes carried

in the sex cells.5.offspring will inherit 2 alleles to express that

gene

•Male gametes

•Female gametes

Punnett SquaresPunnett Squares

•Steps to Solve Punnett SquaresSteps to Solve Punnett Squares

•Step 1Step 1: Assign letters for alleles.

•Step 2Step 2: Write down the cross you will make.

What are the genotypes of the parents?

•Step 3Step 3: Set up and solve the Punnett square.

How many squares will you need?

•Step 4Step 4: Answer questions, find ratios,

percentages or proportions.

MONOHYBRID CROSSESMONOHYBRID CROSSES - 1 trait crossed

Monohybrid CrossesMonohybrid Crosses

•CrossCross

•Bb x BbBb x Bb

•B •b•female gametes

•B

•b

•male gametes

•BB

•Bb

•Bb

•bb •Phenotypes

•%

•75% Brown eyed, 25% Blue eyed

•Ratio

•3 Brown eyed: 1 Blue eyed

•Genotypes

•%

•25% BB, 50% Bb, 25% bb

•Ratios

•1BB:2Bb:1bb

•STEP

•STEP

•STEP

•STEP

BB = brown eyes Bb = brown eyes bb = blue eyes

Cross two Alaskan huskies that are heterozygous for

brown eyes (Bb).

Your Turn

YY x Yy (Y-yellow, y-green)

Steps to Solve DIHYBRID Punnett Square word problem.

DIHYBRID CROSSES – 2 traits crossed

1. Assign letters to the different alleles for the trait.

2. Write the cross that you will be making.

3. Use the FOIL method to determine the combination of

alleles for each gamete.

4. Set up the Punnett Square by separating your female and

male gametes. Solve.

5. Answer the question and circle or square off the answer.

DIHYBRID CROSS•Problem: In pea plants round seeds are dominant to wrinkled

seeds and green pods are dominant to yellow. If 2 plants that

were heterozygous for both traits were crossed, what would be

the phenotypic and genotypic ratios?

•Cross: RrGg X RrGg

Gene Trait AppearanceR Roundr WrinkledG Greeng Yellow

•STEP

•STEP

DIHYBRID CROSSES

•

•Cross: RrGg X RrGg

•EXTRA STEP - Finding the possible gametes

•(R r) (Gg)•F.O.I.L

First

Outer

Inner

Last

•STEP

•

•PRACTICE F.O.I.L.

•Finding the possible gametes

•(r r) (Y y)

•F.O.I.L

First

Outer

Inner

Last•Try These:

TtBB

DDee

ffPp

•Phenotypic ratioPhenotypic ratio: 9 round, green: 3 round, yellow: 3 wrinkled, green: 1 wrinkled, yellow

(9:3:3:1)

•  •RG •Rg •rG •rg

•RRGg •RrGG •RrGg

•RRGg •RRgg •RrGg •Rrgg

•RrGG •RrGg •rrGG •rrGg

•RG

•Rg

•rG

•rg •RrGg •Rrgg •rrGg •rrgg

•STEP

•STEP

•RRGG

•Genotypic ratioGenotypic ratio: 1 RRGG: 2 RRGg: 2 RrGG: 4 RrGg: 1 RRgg: 2 Rrgg: 2 rrGg: 1 rrGG: 1

rrgg

PROBLEM: A pea plant that is heterozygous for round and yellow is crossed with one that is wrinkled and

green. What are the genotypic and phenotypic ratios for this cross?

R = round

r = wrinkledY = yellowy = green

Cross: RrYy X rryy

•Gametes: RrYy rryy

RY ry

Ry ry

rY ry

ry ry

•  •RY •Ry •rY •ry

•ry •RrYy •Rryy •rrYy •rryy

•Genotypic ratioGenotypic ratio - 1RrYy : 1 Rryy: 1 rrYy: 1 rryy (1:1:1:1)

•Phenotypic ratioPhenotypic ratio - 1 round, yellow: 1 round, green: 1 wrinkled,

yellow: 1 wrinkled, green (1:1:1:1)

Practice Problems1. TTyy x TtYY (T = tall, t = short, Y = yellow, y =

green)2. In llamas, floppy ears (F) are dominant to pointy

ears (f). Also, bowlegs are recessive (l). A bowlegged llama heterozygous for floppy ears is crossed with a llama that is heterzygous for both traits. Show the genotypes of these two parents.

3. In starfish, pink body color (P) is dominant to orange (p), and thick eyebrows (T) are dominant over thin (t). Patrick, who is heterozygous for body color but purebred for thick eyebrows, has met Patti, who is recessive for both traits. Is it possible for the new couple to have an offsprings that resembles their mother?

Punnett Square

Click image to view movie.