Patterns of Patterns of Inheritance Notes Inheritance Notes QOTD: Can we predict what the offspring of two individuals will look like? Explain why or why not.

For every trait you For every trait you receive one allele from receive one allele from

each parenteach parentPhenotype =Phenotype = Phenotype=Phenotype=

Straight-earsStraight-ears

SS or SsSS or SsGenotype=Genotype=

Floppy-earsFloppy-ears

Genotype=Genotype= ssss

Genotype and PhenotypeGenotype and Phenotype

Genotype – The Genotype – The gengenetic code of an etic code of an organismorganism

Phenotype – The Phenotype – The phphysical ysical characteristics that are created by characteristics that are created by that code.that code.

Crossing homozygous Crossing homozygous straight with straight with

homozygous floppyhomozygous floppySS x ssSS x ss

What will be the offspring’s genotype?What will be the offspring’s genotype?

What will be the What will be the offspring’s offspring’s phenotype?phenotype?

SsSs

Straight-earsStraight-ears

Cross a homozygous Cross a homozygous floppy with heterozygous floppy with heterozygous

straightstraightSs x ssSs x ss

Offspring of two types possible:Offspring of two types possible:

Ss or ssSs or ss

Heterozygous Heterozygous straightstraight

Homozygous floppyHomozygous floppy

But what if we cross two But what if we cross two heterozygous rabbits?heterozygous rabbits?

Ss x SsSs x Ss Now we need to think about sexual Now we need to think about sexual

reproduction again. How much DNA do you reproduction again. How much DNA do you get from each parent?get from each parent?

Meiosis divides the number of chromosomes Meiosis divides the number of chromosomes in half to make gametes. This process in half to make gametes. This process separates the two alleles of the parents.separates the two alleles of the parents.

Since genes are on chromosomes, we now Since genes are on chromosomes, we now have sperm with either S or s, and eggs have sperm with either S or s, and eggs with either S or s. We can put them in a with either S or s. We can put them in a Punnet square to see the possible outcomes.Punnet square to see the possible outcomes.

Recombining allelesRecombining alleles

Ss SsxParents:male female

SS s sGametes:sperm eggs

meiosis

SS ss

ss

SS

Genotypes Phenotypes

1 SS

2 Ss

1 ss

ss

SsSS

sSStraight

Straight

Floppy

Bikini Bottom Genetics!Bikini Bottom Genetics!