Bio.B.2- Genetics CHAPTER 11

B2: Genetics Describe and/ or predict observed patterns of inheritance i.e. dominant, recessive, co-dominant, incomplete dominance, sex- linked, polygenic and multiple alleles.

B2 Vocabulary genetics homozygous fertilization heterozygous trait hybrid gene allele Principle of dominance segregation Gamete probability homozygous heterozygous phenotype genotype punnett square incomplete dominance codominance multiple allele polygenic trai

Review… What are the four macromolecules? 1. Carbohydrates 2. Proteins 3. Lipids 4. Nucleic Acids Which of the four macromolecule is responsible for an individuals unique characteristics? Nucleic acids - DNA

Introduction Genetics = study of heredity Heredity = transfer of characteristics from parent to offspring

Gregor Mendel: Father of Modern Genetics Studied Pea Plants Observed recurring patterns Pea plants made good subjects to study because mendel could control breeding, the plants would produce many offspring plants in just one growing season and all of the traits he studies were “either-or” traits.

What Mendel Knew… A trait is a specific characteristic EX: pea color, pea shape, flower color

What Mendel Knew… Mendel could control fertilization Self-pollination – one plant fertilizes itself Cross-pollination – two different plants

What Mendel Knew… “true-breeding” plants always produced offspring plants that had the same trait as the parent EX: a true-breeding purple flower plant produces plants that also have purple flowers

What Mendel Knew… A “hybrid” = a cross between two different plants Offspring showed the characteristic of one parent

What Mendel Saw 1st generation parental trait disappears 2nd generation parental trait reappears in a 3:1 ratio

What Mendel saw P-generation True-breeding READ ONLY P-generation True-breeding When self pollinated, always produce offspring plants with identical traits Ex: a true-breeding purple plant ALWAYS produces plants with purple flowers

F1 generation (hybrids) READ ONLY F1 generation (hybrids) F1 Generation Produced by crossing pure-bred P plants Always saw the same results (parental trait disappears)

F2 generation Produced by self-pollination of F1 plants Mendel F2 generation READ ONLY Produced by self-pollination of F1 plants Always saw the same results (parental trait reappears) in a specific ratio 14 14 14 14 14 14 14

Mendel’s Conclusions: Traits are determined by “factors” that get passed from one generation to the next Factors = genes

Mendel’s Conclusions: There are different “forms” of a gene that account for variations in inherited characteristics Forms = alleles EX: purple allele or white allele

Mendel’s Conclusions: For each trait, an organism inherits two alleles (one from each parent) The alleles may be identical or they may be different Homozygous = two identical alleles Heterozygous = two different alleles

Mendel’s Conclusions: Physical appearance (phenotype) is influenced by the alleles inherited for the trait (genotype) some “alleles” are dominant and some are recessive One dominant allele will give the dominant trait Need two recessive alleles to have the recessive trait Letters used to differentiate alleles dominant = uppercase recessive = lowercase

Mendel’s Conclusions: Alleles segregate during gamete formation Gamete = reproductive cell that contributes to the new organism Each parent contributes only one allele to their offspring

Gene (A) or Allele (B) Hair color…….. Brown hair….... Purple flowers. Flower color…. Tall plant……… Plant height….. Tail length……. Long tail………. GENE ALLELE

Homozygous (A) or Heterozygous (B) AA ……. Bb ……. BB ……. bb ……. Rr ……. dd ……. Homozygous Dom. Heterozygous Homozygous Rec.

Genotype (A) or Phenotype (B) AA ……. Blue eyes heterozygous Bb Freckles Visible trait Genotype Phenotype

Dominant Trait (A) or Recessive (B) AA ……. Bb ……. BB ……. bb ……. Rr ……. dd ……. Dominant Recessive

Applying Mendel’s Principles 11.2

Probability Probability = the likelihood that a particular event will occur The way alleles separate during gamete formation is just as random as a coin toss Therefore, probability can be used to predict genetic outcomes.

Punnett Squares: mathematical tool used to predict genetic outcomes Axes of grid = possible gamete genotypes of parents Grid boxes = possible genotypes of offspring Reminders Genotype = genetic makeup (alleles) Phenotype = physical appearance When constructing Punnett Squares, ALWAYS Define the terms Define the genotypes of the parents Analyze the results

Punnett Squares can be used to explain Mendel’s results… F1 generation

Punnett Squares can be used to explain Mendel’s results… F1 generation

Punnett Squares can be used to explain Mendel’s results… F2 generation

Practice with Punnett squares For Simple Dominance Practice Problems, Click Here Practice with Punnett squares 11.2

Exceptions to Mendel Incomplete Dominance Codominance Multiple Alleles Sex-linked Traits Polygenic traits Epistasis Interaction of environment and genotype

Incomplete Dominance Neither allele is completely dominant Heterozygote has a blended phenotype

Codominance Both alleles get expressed Heterozygote has both traits

Multiple Alleles Trait with more than two alleles in a population Example – Blood Types 3 different alleles (A, B, O) A and B alleles are codominant O allele is recessive

Heterozygous for the A allele Homozygous for the A allele

Read Only

Sex-Linked Genes (X-linked) Carried on the sex chromosomes (female = XX; male = XY) More common in males XY = only need one allele for trait to be present Females need two copies of allele for trait to be present Can be carriers of the trait (heterozygous genotype) Passed from mother to son Examples include colorblindness and hemophilia

Polygenic Traits Traits that are determined by the interaction of 2 or more genes Ex: Skin color, eye color, height, etc

Practice with Punnett squares