Exploring Mendelian Exploring Mendelian GeneticsGenetics

Introduction to GeneticsIntroduction to Genetics

Chapter 11 Section 3Chapter 11 Section 3

Honors BiologyHonors Biology

Independent AssortmentIndependent Assortment

The two-factor crossThe two-factor crossF1: Mendel bred true bred round yellow (RRYY) F1: Mendel bred true bred round yellow (RRYY) with true bred wrinkled green (rryy)with true bred wrinkled green (rryy)All offspring were round yellow (RrYy)All offspring were round yellow (RrYy)

F2: Mendel self pollinated the F1 generation to F2: Mendel self pollinated the F1 generation to yield the F2 generationyield the F2 generationThe offspring produced a 9:3:3:1 ratioThe offspring produced a 9:3:3:1 ratio9 round yellow 3 round green 3 wrinkled 9 round yellow 3 round green 3 wrinkled yellow and 1 wrinkled greenyellow and 1 wrinkled green

The two factor F2 cross

Independent AssortmentIndependent Assortment Since the F2 generation contained combinations Since the F2 generation contained combinations

of alleles not found in P generation, this meant of alleles not found in P generation, this meant that the alleles separated independently of one that the alleles separated independently of one another. This principal is known as another. This principal is known as independent assortmentindependent assortment – chromosomes – chromosomes segregate independently of one another. Each segregate independently of one another. Each chromosome is a group of geneschromosome is a group of genes

The principal of independent assortment states The principal 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. Independent assortment helps account for the Independent assortment helps account for the many genetic variations observed in plants many genetic variations observed in plants animals and other organismsanimals and other organisms

Summary of Mendel's PrincipalsSummary of Mendel's Principals

Biological characteristics are determined by Biological characteristics are determined by genesgenes

In cases in which alleles for genes exist, one In cases in which alleles for genes exist, one allele is dominant and one is recessiveallele is dominant and one is recessive

In sexual reproducing organisms, there are 2 In sexual reproducing organisms, there are 2 copies for every gene, one from each parent. copies for every gene, one from each parent. The genes are segregated during formation of The genes are segregated during formation of gametesgametes

The allele for different genes usually segregate The allele for different genes usually segregate independently of one another independently of one another

Other Situations Beyond Dominant Other Situations Beyond Dominant and Recessiveand Recessive

Some alleles are neither dominant nor Some alleles are neither dominant nor recessive, and are controlled by multiple alleles recessive, and are controlled by multiple alleles or multiple genesor multiple genes

The case in which one allele is not completely The case in which one allele is not completely dominant over another is called dominant over another is called incomplete incomplete dominancedominance. The heterozygote phenotype is in . The heterozygote phenotype is in between the 2 homozygous phenotypesbetween the 2 homozygous phenotypes

Ex: A red flower (RR) crossed with a white flower Ex: A red flower (RR) crossed with a white flower (WW) creates pink offspring (RW)(WW) creates pink offspring (RW)

Other Situations Beyond Dominant and Recessive

Other Situations Beyond Dominant and Recessive

Other Situations Beyond Dominant Other Situations Beyond Dominant and Recessiveand Recessive

When both alleles contribute to the phenotype of the When both alleles contribute to the phenotype of the offspring this is called offspring this is called codominancecodominance

Ex: In certain chickens, the allele for black feathers is Ex: In certain chickens, the allele for black feathers is codominant with white feathers. Heterozygous chicken codominant with white feathers. Heterozygous chicken offspring are both black and white speckled (called offspring are both black and white speckled (called erminette)erminette)

Unlike the blending in incomplete dominance, both alleles Unlike the blending in incomplete dominance, both alleles appear separatelyappear separately

Ex: this can also been seen in humans with cholesterol Ex: this can also been seen in humans with cholesterol levels. People with the heterozygous form of the gene levels. People with the heterozygous form of the gene produce 2 different forms of the proteins, each with a produce 2 different forms of the proteins, each with a differnet effect on the cholesterol differnet effect on the cholesterol

Other Situations Beyond Dominant Other Situations Beyond Dominant and Recessiveand Recessive

Some genes are controlled by more than 2 Some genes are controlled by more than 2 alleles and are called alleles and are called multiple allelesmultiple alleles

This does not mean that a person can have This does not mean that a person can have more than 2 alleles, it means that more more than 2 alleles, it means that more than 2 alleles exist in the population for a than 2 alleles exist in the population for a single genesingle gene

Ex: rabbit fur color is controlled by 4 allelesEx: rabbit fur color is controlled by 4 allelesEx: human blood type (A B or O)Ex: human blood type (A B or O)

Multiple Alleles for Rabbit ColorMultiple Alleles for Rabbit Color Full Color: Brown CFull Color: Brown C

dominant to all other allelesdominant to all other alleles Chinchilla: Grey CChinchilla: Grey Cchch

partial defect in pigmentation. Dominant to Cpartial defect in pigmentation. Dominant to Chh and c and c allelesalleles

Himalayan: Color in Certain parts CHimalayan: Color in Certain parts Ch h Dominant to c Dominant to c alleleallele

Albino: No color cAlbino: No color crecessive to all other alleles recessive to all other alleles

Example: Blood Type is controlled by 3 allelesExample: Blood Type is controlled by 3 allelesA and B are codominant. Both are dominant over OA and B are codominant. Both are dominant over O

Other Situations Beyond Dominant Other Situations Beyond Dominant and Recessiveand Recessive

Some traits are controlled by more than one Some traits are controlled by more than one gene. These are called gene. These are called polygenic traitspolygenic traits, which , which means “having many genes”means “having many genes”

Polygenic traits often show a wide range of Polygenic traits often show a wide range of phenotypesphenotypes

Ex: at least 3 genes control the reddish-brown Ex: at least 3 genes control the reddish-brown pigment in the eye color of fruit fliespigment in the eye color of fruit flies

Ex: the wide range of skin color is because more Ex: the wide range of skin color is because more than four different genes control this traitthan four different genes control this trait

Genes and EnvironmentGenes and Environment Environment determines your phenotypes as Environment determines your phenotypes as

wellwell Characteristics are controlled by an interaction Characteristics are controlled by an interaction

between genes and environmentbetween genes and environment

Ex: a sunflower. Genes may control height and Ex: a sunflower. Genes may control height and color however some characteristics are also color however some characteristics are also controlled by soil type, water availability, amount controlled by soil type, water availability, amount of sunlight, and climateof sunlight, and climate

Genes provide a plan for development, but Genes provide a plan for development, but the environment depends on how that plan the environment depends on how that plan unfoldsunfolds

Class workClass work

Chapter 11 Section 3 AssessmentChapter 11 Section 3 Assessment