BIO.B.2- GENETICS CHAPTER 11

B2: Genetics 1. 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  fertilization  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

What Mendel Knew… 1. A trait is a specific characteristic EEX: pea color, pea shape, flower color

What Mendel Knew… 2. Mendel could control fertilization SSelf-pollination – one plant fertilizes itself CCross-pollination – two different plants

What Mendel Knew… 3. “true-breeding” plants always produced offspring plants that had the same trait as the parent EEX: a true-breeding purple flower plant produces plants that also have purple flowers

What Mendel Knew… 4. A “hybrid” = a cross between two different plants OOffspring showed the characteristic of one parent

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

What Mendel saw  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 READ ONLY

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

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

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

2. There are different “forms” of a gene that account for variations in inherited characteristics  Forms = alleles  EX: purple allele or white allele

3. 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:

4. 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: 5. 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 GENE ALLELE GENE ALLELE

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

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

Dominant Trait (A) or Recessive (B) AA ……. Bb……. BB……. bb ……. Rr ……. dd ……. Dominant Recessive 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 11.2 For Simple Dominance Practice Problems, Click Here

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

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

PRACTICE WITH PUNNETT SQUARES