Introduction to Introduction to GeneticsGeneticsThe study of heredity: how genetic factors are The study of heredity: how genetic factors are passed down from one generation to the nextpassed down from one generation to the next

His experiments His experiments with with pea plants pea plants laid laid the foundations of the foundations of the science of the science of geneticsgenetics

Male part: produces pollenMale part: produces pollen

Female part: where fertilized egg will become a seedFemale part: where fertilized egg will become a seed

Mendel Mendel cross-pollinatedcross-pollinated a purple plant with a white a purple plant with a white

plantplant

He found all the offspring produced purple flowers.

What happened to the white flower trait?

P generationP generation: Parental generation; : Parental generation; always always True-breedingTrue-breeding, or , or “pure-bred”“pure-bred”

F1 generationF1 generation: First Filial : First Filial Generation; offspring of P gen, always Generation; offspring of P gen, always hybridshybrids

PP pppp

Ppp

PP PppPpp pppp

x

Ppp

Mendel made the Mendel made the F2 generation F2 generation by by crossing plants from F1 togethercrossing plants from F1 together. He . He

found found 3 purple flowers for every 1 3 purple flowers for every 1 white flowerwhite flower..

Mendel found the same pattern Mendel found the same pattern

with many other pea plant traitswith many other pea plant traits..

Mendel’s Mendel’s Law of Segregation Law of Segregation explains how genes are passed explains how genes are passed

to the next generation.to the next generation.

Alleles are segregated into separate Alleles are segregated into separate egg cells and sperm cells. Each egg cells and sperm cells. Each reproductive cell will pass on ONE of reproductive cell will pass on ONE of the alleles.the alleles.

New pairs of genes are created for New pairs of genes are created for the next generation during the next generation during fertilizationfertilization

Because of sexual reproduction, Because of sexual reproduction, you are a product of your mom’s you are a product of your mom’s

genes and your dad’s genesgenes and your dad’s genes

Each chromosome contains thousands Each chromosome contains thousands of of genesgenes. Each . Each genegene is the is the DNADNA code code

for making a specific proteinfor making a specific protein. The . The proteins give you your proteins give you your traittrait. .

The The alternate forms of genesalternate forms of genes are called are called allelesalleles. .

You You alwaysalways get two alleles for a get two alleles for a trait. trait.

The The combination of alleles for a combination of alleles for a specific traitspecific trait are called the are called the

genotypegenotype. This is . This is represented by two letters.represented by two letters.

PPpp

If both If both alleles are the samealleles are the same, then , then they are they are homozygoushomozygous. If . If they are they are

differentdifferent, they are called , they are called heterozygousheterozygous..

http://www.abpischools.org.uk/page/modules/genome/dna2.cfm

Sometimes, one Sometimes, one allele is expressed allele is expressed as a trait and the as a trait and the other isn’t. The other isn’t. The dominant allele is dominant allele is expressedexpressed and the and the recessive allele is recessive allele is notnot..

The The observable traitobservable trait is is called the called the phenotypephenotype. The . The phenotype is a result of the phenotype is a result of the

genotype.genotype.P P pp

P P

p

p

Off

sprin

g

Genoty

pes

If you know your genotype for a If you know your genotype for a specific trait, you can predict the traits specific trait, you can predict the traits

of your offspring! Use a Punnett of your offspring! Use a Punnett Square.Square.

How to Solve a genetics How to Solve a genetics problemproblem

1.1. Read the problemRead the problem

2.2. Take notes:Take notes: _____=Gray body_____=Gray body _____=black body_____=black body

3.3. Box the parent descriptions:Box the parent descriptions: Heterozygous gray bodyHeterozygous gray body Black bodyBlack body

4.4. Determine the genotypes of the parents (_, _)Determine the genotypes of the parents (_, _)

5.5. Fill in the Punnett square and solveFill in the Punnett square and solve

G g

g

g

Heterozygous X black Gray (Gg) (gg)

Genotype probabilities: Gg=50%, gg=50%

Phenotype probabilities: gray bodies=50%, black bodies=50%

Situation: A client wants to buy pure Situation: A client wants to buy pure bred black puppies from your dog. bred black puppies from your dog. This means your dog must be pure This means your dog must be pure black to make pure bred puppies.black to make pure bred puppies.

How can you tell if your black lab isBB or Bb?

Conduct a Conduct a test cross test cross and breed it with and breed it with a brown lab (a brown lab (homozygous recessivehomozygous recessive) to ) to find out and examine the traits of the find out and examine the traits of the

puppies.puppies.These puppies are not for sale, but give you important information about your dog.

Practice Makes PerfectPractice Makes Perfect

Now practice using the terminology Now practice using the terminology and Punnett Squares to determine and Punnett Squares to determine possible traitspossible traits