GeneticsGenetics

Warm-UpWarm-Up

• If all of these puppies came from the If all of these puppies came from the same two parents and were born in same two parents and were born in the same litter…why don’t they look the same litter…why don’t they look identical?identical?

Mendel’s GeneticsMendel’s Genetics

• GeneticsGenetics•A branch of biology that A branch of biology that

studies heredity, or the studies heredity, or the passing of characteristics passing of characteristics from parents to offspringfrom parents to offspring

Gregor MendelGregor Mendel

• Austrian monk that first studied Austrian monk that first studied geneticsgenetics

• ““Father of Genetics”Father of Genetics”

• Experimented on pea plantsExperimented on pea plants

• Mendel used plants that had been bred Mendel used plants that had been bred for a specific trait (tallness, shortness) for a specific trait (tallness, shortness) to create hybrids (heterozygotes)to create hybrids (heterozygotes)

Generations are named as Generations are named as follows:follows:

• P = original parentsP = original parents

• F1 = first generation (children)F1 = first generation (children)

• F2 = second generation F2 = second generation (grandchildren)(grandchildren)

Mendel’s Conclusions (#1)Mendel’s Conclusions (#1)

• There are 2 forms of genes that There are 2 forms of genes that control each trait called allelescontrol each trait called alleles

• Example – 2 genes that control Example – 2 genes that control heightheight

• T = tallT = tall• t = shortt = short

Mendel’s Conclusions (#2)Mendel’s Conclusions (#2)

• The Rule of DominanceThe Rule of Dominance

• Dominant trait = the observed traitDominant trait = the observed trait

• Recessive trait = hidden by the Recessive trait = hidden by the dominant trait unless dominant is not dominant trait unless dominant is not presentpresent

Mendel’s Conclusions (#3)Mendel’s Conclusions (#3)

• Law of SegregationLaw of Segregation

• Because each plant has two alleles for Because each plant has two alleles for a trait, it can produce two types of a trait, it can produce two types of gametesgametes

• Pure tall (homozygous) = TTPure tall (homozygous) = TT• Pure short (homozygous) = ttPure short (homozygous) = tt• Hybrid (heterozygous) = TtHybrid (heterozygous) = Tt

Mendel’s 3 PrinciplesMendel’s 3 Principles

1.1. Principle of SegregationPrinciple of Segregation

1.1. Principle of DominancePrinciple of Dominance

2.2. Principle of Independent Principle of Independent AssortmentAssortment

Principle of SegregationPrinciple of Segregation

• During gamete formation, there is a During gamete formation, there is a random segregation (separation) of random segregation (separation) of alleles whereby each gamete alleles whereby each gamete receives only one allele from each receives only one allele from each pairpair

• Tt Tt • TT• tt

Principle of DominancePrinciple of Dominance

• The dominant allele (capital letter) The dominant allele (capital letter) are expressed whereas recessive are expressed whereas recessive alleles (lowercase letter) are not alleles (lowercase letter) are not because they are masked by the because they are masked by the dominant alleledominant allele

Principle of Independent Principle of Independent AssortmentAssortment

• Each characteristic is inherited Each characteristic is inherited independently of every other trait independently of every other trait

• Dihybrid crossesDihybrid crosses

STOPSTOP

Monohybrid CrossesMonohybrid Crosses

• Step 1Step 1• What are the genotypes of the parents?What are the genotypes of the parents?

• Step 2Step 2• Draw the Punnett SquareDraw the Punnett Square

• Step 3Step 3• Write in the alleles of the parentsWrite in the alleles of the parents

• Step 4Step 4• Fill in the squareFill in the square

• Step 5Step 5• Write the genotypes and phenotypes of potential Write the genotypes and phenotypes of potential

offspringoffspring

Concept 10.3Concept 10.3

• There are many variations of There are many variations of inheritance patterns.inheritance patterns.

• Key TermsKey Terms• Intermediate inheritanceIntermediate inheritance• CodominanceCodominance• Polygenic inheritancePolygenic inheritance

Intermediate InheritanceIntermediate Inheritance

• In a monohybrid cross where In a monohybrid cross where neither parent trait is dominant, neither parent trait is dominant, the hybrids have an intermediate the hybrids have an intermediate phenotypephenotype

• Andalusian ChickensAndalusian Chickens

CodominanceCodominance

• Both traits are Both traits are expressed – the expressed – the phenotype shows the phenotype shows the separate traits of both separate traits of both allelesalleles

Incomplete DominanceIncomplete Dominance

• A cross between a blue blahblah bird and a A cross between a blue blahblah bird and a white blahblah bird produces offspring that white blahblah bird produces offspring that are silver. are silver.

• What are the genotypes of the parent blahblah What are the genotypes of the parent blahblah birds in the original cross?birds in the original cross?

• What is/are the genotypes of the silver offspring?What is/are the genotypes of the silver offspring?

• What would be the phenotypic RATIO of offspring What would be the phenotypic RATIO of offspring produced by two silver blahblah birds?produced by two silver blahblah birds?

CodominanceCodominance

• Predict the phenotypic ratios of Predict the phenotypic ratios of offspring when a homozygous red offspring when a homozygous red cow is crossed with a roan bull.cow is crossed with a roan bull.

• What should the genotypes and What should the genotypes and phenotypes for parent cattle be if a phenotypes for parent cattle be if a farmer wanted only cattle with red farmer wanted only cattle with red fur?fur?

• A cross between a black cat and a tan A cross between a black cat and a tan cat produces a tabby pattern (black cat produces a tabby pattern (black and tan fur together).and tan fur together).

• What type of inheritance does this What type of inheritance does this illustrate?illustrate?

• What percent of kittens would have tan What percent of kittens would have tan fur if a tabby cat is cross with a black cat?fur if a tabby cat is cross with a black cat?

Polygenic InheritancePolygenic Inheritance

• 2 or more genes affect a single 2 or more genes affect a single charactercharacter

• In humans, height and skin color In humans, height and skin color have polygenic inheritance have polygenic inheritance

Dihybrid CrossDihybrid Cross

• In rats, black (B) fur is dominant to In rats, black (B) fur is dominant to white (b) fur and long (L) tails are white (b) fur and long (L) tails are dominant to short (l) tails.dominant to short (l) tails.

• Cross two heterozygous Cross two heterozygous individuals.individuals.

The Importance of The Importance of EnvironmentEnvironment

• Siamese catsSiamese cats • Enzyme Enzyme

responsible for responsible for black fur color is black fur color is only active at the only active at the cooler cooler temperaturestemperatures

Concept 10.4Concept 10.4

• Meiosis explains Mendel’s Meiosis explains Mendel’s principles.principles.

• Key TermsKey Terms• Chromosome theory of inheritanceChromosome theory of inheritance• Gene locusGene locus• Genetic linkageGenetic linkage

Chromosome Theory of Chromosome Theory of InheritanceInheritance

• Genes are Genes are located on located on chromosomes chromosomes and the behavior and the behavior of chromosomes of chromosomes during meiosis during meiosis and fertilization and fertilization accounts for accounts for inheritance inheritance patterns.patterns.

Genetic Linkage and Crossing Genetic Linkage and Crossing OverOver

Genetic linkage continues as Genetic linkage continues as homologoushomologous

chromosomes separate in the chromosomes separate in the formationformation

of sex cells of sex cells

                                                                                                                                                                  

                                                                                                                                                                  

                                                                                                                                                                  

Genetic Linkage and Crossing Genetic Linkage and Crossing OverOver

Crossing-over unlinks alleles of Crossing-over unlinks alleles of genes asgenes as

homologous chromosomes separate homologous chromosomes separate inin

the formation of sex cells    the formation of sex cells   

Concept 10.5Concept 10.5

• Sex-linked traits have unique Sex-linked traits have unique inheritance patterns.inheritance patterns.

• Key TermsKey Terms• Sex-linked genesSex-linked genes

Sex-DeterminationSex-Determination

There are 2 types of chromosomes

1. Autosomes : Body chromosomes = 22 pairs (44 total)

2. Sex Chromosomes: 23rd pair (X or Y)Female = XXMale = XY

Which parent determines the sex of the offspring?

Sex-Linked Inheritance

• Traits controlled by genes located on the sex chromosome are called sex-linked traits

• Thomas Hunt Morgan discovered sex linkage of traits using Drosophilia (fruit flies)

Sex-Linked TraitsSex-Linked Traits

White eyes in Drosophilia are a recessive trait.

Give the genotypes for the following individuals

• White-eyed male:• Red-eyed male:• White-eyed female:• Red-eyed female:

Cross a white-eyed male and a homozygous red-eyed

female.

• Offspring Genotype:

• Offspring Phenotype:

Sex-Linked Practice #1Sex-Linked Practice #1

• When crossing a white-eyed male and a heterozygous red-eyed female - what is the percentage of male children with white eyes?

Sex-Linked Practice #2Sex-Linked Practice #2

• Cross a red-eyed male and a white-eyed female.

• Give offspring genotypes and phenotypes.

Sex-Linked Practice #3Sex-Linked Practice #3

• Cross a homozygous red-eyed male and a heterozygous red-eyed female. What is the percentage that they will produce a red-eyed male?