GeneticsGenetics

VocabularyVocabulary

TraitTrait - specific characteristic that varies from one - specific characteristic that varies from one individual to anotherindividual to another

GeneGene - sequence of DNA that codes for a protein and - sequence of DNA that codes for a protein and thus determines a traitthus determines a trait

AlleleAllele - one of a number of different forms of a gene- one of a number of different forms of a gene HybridHybrid - offspring of crosses between parents with - offspring of crosses between parents with

different traitsdifferent traits The The principle of dominanceprinciple of dominance states that some alleles states that some alleles

are dominant and others are recessive. are dominant and others are recessive.

Gregor Mendel –Gregor Mendel –Father of Modern GeneticsFather of Modern Genetics

True-breedingTrue-breeding - - term used to term used to describe describe organisms that organisms that produce offspring produce offspring identical to identical to themselves if themselves if allowed to self-allowed to self-pollinate.pollinate.

Mendel’s Mendel’s WorkWork

Mendel had true- Mendel had true- breeding pea plants.breeding pea plants.

He asked the question: He asked the question: What would happen if What would happen if he breed pea plants he breed pea plants with different traits?with different traits?

Dominant and Recessive Traits & Dominant and Recessive Traits & Gregor Mendel’s PeasGregor Mendel’s Peas

P – Parent generationP – Parent generation F1 – first generation of offspring (f – filial from F1 – first generation of offspring (f – filial from

latin filius “son”)latin filius “son”)

Punnett SquarePunnett Square

diagram showing the gene combinations that diagram showing the gene combinations that might result from a genetic crossmight result from a genetic cross

Cross Cross YY and YY and yyyy

YY YY

yy YyYy YyYy

yy YyYy YyYy

Crossing true-breeding parent Crossing true-breeding parent generationgeneration

Trait Trait Green peaGreen pea recessiverecessive

Genes (alleles)Genes (alleles) yyyy

Gametes Gametes formedformed y and yy and y

TraitTrait Yellow peaYellow pea dominantdominant

Genes (alleles)Genes (alleles) YYYY

Gametes formedGametes formed Y and YY and Y

Cross Cross YY and YY and yyyy

YY YY

yy YyYy YyYy

yy YyYy YyYy

P Generation

F1 Generation

Crossing the F1 generationCrossing the F1 generation

Trait Trait Yellow peaYellow pea

Genes (alleles)Genes (alleles) YyYy

Gametes formedGametes formed Y and yY and y

TraitTrait Yellow peaYellow pea

Genes (alleles)Genes (alleles) YyYy

Gametes formedGametes formed Y and yY and y

Cross Yy Cross Yy and Yyand Yy YY yy

YY YYYY YyYy

yy YyYy yyyy

F1 Gen.

F2 Generation

Probability and GeneticsProbability and Genetics

ProbabilityProbability - - likelihood that a likelihood that a particular event particular event will occurwill occur

Cross Cross YY YY and yyand yy

YY yy

YY YYYY YyYy

yy YyYy yyyy

Crossing the F1 Crossing the F1 generationgeneration

Segregation - separation of alleles during Segregation - separation of alleles during gamete formationgamete formation

When each F1 plant flowers, the two alleles are When each F1 plant flowers, the two alleles are segregated from each other so that each segregated from each other so that each gamete carries only a single copy of each gamete carries only a single copy of each gene. Therefore, each F1 plant produces two gene. Therefore, each F1 plant produces two types of gametes—those with the allele for types of gametes—those with the allele for tallness and those with the allele for shortness. tallness and those with the allele for shortness.

More vocabulary…More vocabulary…

HomozygousHomozygous - term used to refer to an - term used to refer to an organism that has two identical alleles for a organism that has two identical alleles for a particular traitparticular trait

HeterozygousHeterozygous - term used to refer to an - term used to refer to an organism that has two different alleles for the organism that has two different alleles for the same traitsame trait

PhenotypePhenotype - physical characteristics of an - physical characteristics of an organismorganism

GenotypeGenotype - genetic makeup of an organism - genetic makeup of an organism

Genotypes and Genotypes and PhenotypesPhenotypes

PhenotypesPhenotypes and and GenotypesGenotypes Although these Although these plants have different plants have different genotypes genotypes (TT(TT and and Tt)Tt), they have the , they have the same phenotype same phenotype (tall). (tall).

What are the ratios for What are the ratios for genotype and phenotype?genotype and phenotype?

Genotype ratio - 1:2:1Genotype ratio - 1:2:1 1 HoZ tall, 2 HeZ, 1 HoZ short 1 HoZ tall, 2 HeZ, 1 HoZ short

Phenotype ratio – 3:1Phenotype ratio – 3:1 3 tall pea plants, one short pea plant3 tall pea plants, one short pea plant

Cross Tt and TtCross Tt and Tt TT tt

TT TTTT TtTt

tt TtTt tttt

Using ratios from Punnett SquaresUsing ratios from Punnett Squares

Ratio of tall to short pea plants is 3:1Ratio of tall to short pea plants is 3:1 If we breed heterozygous tall pea plants If we breed heterozygous tall pea plants

with each other and in one generation we with each other and in one generation we made 1000plants, How many tall pea made 1000plants, How many tall pea plants and short pea plants should we plants and short pea plants should we have?have?

Law of Independent Law of Independent AssortmentAssortment

The principle of independent assortment states The principle of independent assortment states that genes for different traits can segregate that genes for different traits can segregate independently during the formation of gametes. independently during the formation of gametes.

In other words, genes (alleles) of different traits In other words, genes (alleles) of different traits separate independent of one another. Genes separate independent of one another. Genes (alleles) of one trait do not affect genes of (alleles) of one trait do not affect genes of another trait.another trait.

This allows us to cross genes for different traits This allows us to cross genes for different traits at the same time.at the same time.

Cross of heterozygous Cross of heterozygous

yellow and round peas.yellow and round peas. First, what is the First, what is the

genotype of the genotype of the parents?parents?

Second, how many Second, how many different gametes different gametes can be formed?can be formed?

Third, what are the Third, what are the different gametesdifferent gametes??

RYRY RyRy rYrY ryry

Parent:

RrYy

Cross of heterozygous Cross of heterozygous yellow and round peas.yellow and round peas.

How many different How many different phenotypes do we phenotypes do we have?have?

4

• What is the ratio What is the ratio for the for the phenotypes?phenotypes?

9:3:3:1

Summary of Summary of Mendel’s PrinciplesMendel’s Principles

The inheritance of biological characteristics is The inheritance of biological characteristics is determined by individual units known as genes. In determined by individual units known as genes. In organisms that reproduce sexually, genes are passed organisms that reproduce sexually, genes are passed from parents to their offspring.from parents to their offspring.

In cases in which two or more forms of the gene for a In cases in which two or more forms of the gene for a single trait exist, some forms of the gene may be single trait exist, some forms of the gene may be dominant and others may be recessive.dominant and others may be recessive.

In most sexually reproducing organisms, each adult has In most sexually reproducing organisms, each adult has two copies of each gene—one from each parent. These two copies of each gene—one from each parent. These genes are segregated from each other when gametes genes are segregated from each other when gametes are formed.are formed.

The alleles for different genes usually segregate The alleles for different genes usually segregate independently of one another.independently of one another.

1. List the four basic principles of genetics that Mendel discovered in his experiments. Briefly describe each of these principles.

2. What is probability? How does probability relate to genetics?

3. In pea plants, the allele for yellow seeds is dominant to the allele for green seeds. Predict the genotypic ratio of offspring produced by crossing two parents heterozygous for this trait. Draw a Punnett square to illustrate your prediction.

4. Designing Experiments In sheep, the allele for white wool (A) is dominant over the allele for black wool (a). How would you determine the genotype of a white ram, or male sheep?

5. Inferring Suppose Mendel crossed two pea plants and got both tall and short offspring. What could have been the genotypes of the two original plants? What genotype could not have been present?

6. Applying Concepts In guinea pigs, the allele for a rough coat (R) is dominant over the allele for a smooth coat (r). A heterozygous guinea pig (Rr) and a homozygous recessive guinea pig (rr) have a total of nine offspring. The Punnett square for this cross shows a 50 percent chance that any particular offspring will have smooth coats. Explain how all nine offspring can have smooth coats.

Beyond dominant Beyond dominant and recessive alleles.and recessive alleles.

Most genes do not follow the simple Most genes do not follow the simple patterns of dominant and recessive patterns of dominant and recessive alleles.alleles.

Some alleles are neither dominant nor Some alleles are neither dominant nor recessive, and many traits are controlled recessive, and many traits are controlled by multiple alleles or multiple genes. by multiple alleles or multiple genes.

Beyond dominant and Beyond dominant and recessive allelesrecessive alleles

incomplete incomplete dominancedominance - - situation in which situation in which one allele is not one allele is not completely completely dominant over dominant over anotheranother

There is no white no There is no white no red: red: new new phenotype pinkphenotype pink

Beyond dominant and Beyond dominant and recessive allelesrecessive alleles

Co dominanceCo dominance - - situation in which situation in which both alleles of a both alleles of a gene contribute gene contribute to the phenotype to the phenotype of the organismof the organism

Beyond dominant and Beyond dominant and recessive allelesrecessive alleles

multiple alleles - three or more alleles of the same genemultiple alleles - three or more alleles of the same gene

Beyond dominant and Beyond dominant and recessive allelesrecessive alleles

polygenic traitpolygenic trait - - trait controlled by trait controlled by two or more genestwo or more genes

Linkage and Gene MapsLinkage and Gene Maps

It’s easy to see how genes located on different It’s easy to see how genes located on different chromosomes assort independently, but what chromosomes assort independently, but what about genes located on the same about genes located on the same chromosome?chromosome?

Wouldn’t they generally be inherited together?Wouldn’t they generally be inherited together?

Thomas Hunt Morgan’s studies back in 1910 Thomas Hunt Morgan’s studies back in 1910 helped us to answer this question.helped us to answer this question.

Linkage and Gene MapsLinkage and Gene Maps

Just because two genes Just because two genes are located on the same are located on the same chromosome does not chromosome does not mean that they are linked mean that they are linked together forever.together forever.

Crossing-overCrossing-over

Also, the further apart Also, the further apart they are the more likely they are the more likely they are to separate. The they are to separate. The closer they are the less closer they are the less likely they are to separate.likely they are to separate.