Write everything that is underlined

A. Dominant vs. RecessiveDominant traits: the ones you can see

Recessive traits: are hidden by dominant

Rule of Dominance: When a dominant trait is present the recessive trait is hidden

Phenotype:The way an organism looks.

No matter what genes are present, phenotype of a tall pea plant is tall and a short pea plant is short

Genotype:The gene combination of an organism

It consists of 2 allelesFor example:

Pure dominant, 2 dominant genesPure recessive, 2 recessive genesHybrid, 1 dominant and 1

recessive gene

Homozygous:When the 2 alleles are the same

2 dominant genes = Homozygous dominant

2 recessive genes = Homozygous recessive

Heterozygous:When the 2 alleles for a trait are different

It’s a hybrid1 dominant gene and 1 recessive gene

Punnett SquaresPunnett squares allow you to predict the ratios or percentages of offspring possible in a cross.

Punnett SquareLetteringDominant Genes

Always get capital letters.The letters will be the 1st letter of the trait.

Recessive GenesAlways get lower case letters.The letter used is the same as the one used for

the dominant gene.

Punnett Squares

All problems will consist of 5 steps:1. Labeling dominant and recessive

letters2. The Cross- Who are the parents3. The Square- draw and fill in the square4. Genotype ratios or percentages5. Phenotype ratios or percentages

Label the dominant Label the dominant and recessive traitsand recessive traits

R = Red flowerR = Red flowerr = Purple flowerr = Purple flower

Write the genotypes of each Write the genotypes of each parent to be crossedparent to be crossed

HybridHybrid Red Red (means heterozygous)(means heterozygous)

PurplePurple(since it is recessive (since it is recessive it has to be it has to be homozygous)homozygous) RrRr rrrr

RrRr x x rrrr

Set up the punnett square. Set up the punnett square. Each parent will give up one Each parent will give up one

gene or the other so there will gene or the other so there will be one gene per box be one gene per box for each for each

parentparent

RRr r rrrr

RRrr rrrr

R rrr

rr

2 of the 4 2 of the 4 (50%) (50%) offspring will offspring will be pure be pure recessiverecessive2 of the 4 2 of the 4 (50%) will be (50%) will be hybrids hybrids

RRrr rrrr

RRrr rrrr

R rrr

rr

50% of the 50% of the offspringoffspringwill be redwill be red

50% of the 50% of the offspringoffspringwill be purplewill be purple

RRrr rrrr

RRrr rrrr

R rrr

rr

Now try one on your ownTall plants are dominant over short plants in a tomato plant. What will the possible genotypes and phenotypes of the offspring of a Homozygous Tall plant and a Homozygous short plant?

Label the dominant Label the dominant and recessive traitsand recessive traits

T = Tall plantT = Tall plantt = short plantt = short plantRemember, it’s NOT T and SRemember, it’s NOT T and S

Write the genotypes of each Write the genotypes of each parent to be crossedparent to be crossed

HomozygousHomozygous Tall Tall (homo means same)(homo means same)

HomozygousHomozygous ShortShort(homo means same)(homo means same) TTTT tttt

TTTT x x tttt

Set up the punnett square. Set up the punnett square. Write the parents firstWrite the parents first

TTtt TTtt

TTtt TTtt

T Ttt

tt

4 of the 4 4 of the 4 (100%) (100%) offspring will offspring will be be heterozygous heterozygous (or hybrid) for (or hybrid) for plant heightplant height

TTtt TTtt

TTtt TTtt

T Ttt

tt

100% of the 100% of the offspringoffspringwill be Tallwill be Tallbecause having because having at least one T at least one T makes it tall makes it tall because T is because T is dominant over dominant over short (t)short (t)

TTtt TTtt

TTtt TTtt

T Ttt

tt