Unit 5 Mendelian Genetics

• Page 1: Introduction

• Unit Overview: AP Biology Unit Five covers Heredity, with Chapter 14 focusing on Mendelian Genetics.

Page 2: Introduction to Genetics

• Gregor Mendel: Conducted influential breeding experiments on garden peas.

  • Published findings in 1865 in "Experiments in Plant Hybridization."

• Principles of Inheritance: Tracked seven traits displaying either/or inheritance patterns.

• Generational Study: Explored multiple generations to establish genetic principles.

Page 3: Mendel's Procedure

1. Stamen Removal: Mendel removed one flower’s stamens to isolate the ovule.

2. Pollen Transfer: Transferred pollen from another variety to the isolated flower.

3. Seed Production: Resulted in hybrid seeds from the ovule of the first flower.

4. Maturation: Hybrid pea seeds matured in pods and were eventually planted.

5. Phenotypic Observation: The next generation displayed only purple flowers.

Page 4: Useful Genetic Vocabulary

• True-breeding Lineages: Created by repeated mating of a certain plant type, yielding offspring of the same variety.

• Self-pollinate: plants that produce offspring of the same variety

• Hybridization Process: Involves mating two true-breeding varieties:

  • Parental Generation (P generation) → Produces hybrid offspring (F1 generation).

  • Self-pollination or cross-pollination of F1 yields the F2 generation.

Page 5: Alleles and Genotypes

• Alleles: Different versions of a gene (represented as uppercase/lowercase letters).

  • Diploid Organisms: Carry two alleles for each trait a patircular locus on a homologous pair

• Phenotype vs Genotype: Appearance (phenotype) is shaped by genetic composition (genotype).

  • Dominant Alleles: Show in phenotype with one or more copies (uppercase).

  • Recessive Alleles: Display only when homozygous recessive (lowercase).

• Homozygous vs Heterozygous: Homozygous has identical alleles, heterozygous has different alleles.

Page 6: Dominant and Recessive Alleles

• Enzyme Relation: Illustrates the influence of alleles on traits.

• Example Alleles: Enzyme for purple flowers and the absence of enzyme for white flowers displayed.

Page 7: Laws of Inheritance

• Law of Segregation: Parent alleles segregate randomly into gametes during formation.

  

• Law of Independent Assortment: Alleles of different genes segregate independently of one another.

  

Page 8: Principles of Inheritance - Law of Segregation

• Hybrid Crossing: Alleles from hybrid individuals segregate during gamete formation.

• Phenotypic Ratio: Leads to a consistent 3:1 ratio in the F2 generation.

Page 9: Using a Testcross

• Purpose of Testcross: To deduce the unknown genotype of a dominant phenotype.

  • Breeding with a homozygous recessive individual reveals if the unknown parent is homozygous or heterozygous.

Page 10: Law of Independent Assortment

• Monohybrid Cross: Cross between heterozygotes affecting one character produces monohybrids.

• Dihybrid Cross: Involves two characters, resulting in the F1 generation of dihybrids to analyze inheritance patterns.

Page 11: Monohybrid Crosses Examples

• Steps for calculating offspring trait probabilities:

  • Designate allele letters: A for yellow, a for green.

  • Set parental genotypes, such as Aa and aa, and complete the Punnett square.

  • Results: Calculate traits based on inheritance patterns and ratios.

Page 12: Example - Sickle Cell Anemia

• Parental Genotypes: Both parents are carriers (Aa) for sickle cell anemia.

  • Utilize a Punnett square to predict offspring probabilities.

  • Ratio Outcomes: 1/4 chance of normal, 1/4 chance of sickle cell anemia.

Page 13: Analysis of Sickle Cell Anemia Example

• Repeat monohybrid cross analysis from the previous page for clarity.

Page 14: Rules of Probability

• Multiplication Rule: Combined probability of independent events.

• Addition Rule: Probability of at least one of multiple exclusive events occurring.

• Application: Useful for predicting phenotypes in Punnett Squares.

Page 15: Fertilization Dynamics

• Diploid Restoration: Fertilization combines haploid gametes (sperm and egg) restoring diploid numbers.

• Genetic Variation: Increases through random fertilization and diverse gametic contributions.

Page 16: Practical Example Case Study

• Experiment Setup: Cross of heterozygous and pure-breeding plants.

  • Steps for Analysis: Select allele representations, parental genotypes, and utilize Punnett squares to determine probabilities.

Page 17-18: Further Practical Example and Analysis

• Phenotypic Ratios: Calculation and interpretation through Punnett squares based on color and flower traits.

Page 19: Alternatives to Mendelian Inheritance

• Alternative Patterns: Include incomplete dominance, codominance, multiple alleles, polygenic inheritance, gene linkage, etc.

Page 20: Incomplete Dominance and Codominance

• Definitions: Distinct from traditional Mendelian inheritance, showcase examples.

• codominance

  • shows both traits

  • ex) black chicken + white chicken = speckled chicken

• incomplete dominance

  • neither allele is dominant, blend of both phenotypes

  • ex) red flower + white flower = pink flower

Page 21: Multi-Allelic Phenotypes

• Complex Traits: Discuss genetic interactions influencing phenotype expressions and instances of epistasis.

• multiple alleles: genes with more than 2 alleles can havem more than 2 phenotypes

• ex) The ABO blood group system is a classic example, where the presence of A, B, and O alleles results in four possible phenotypes: A, B, AB, and O.

  

• polygenic

  • many traits require groups of genes to be expressed concurrently; what phenotype the organism shows is based on the combination of genotypes and. the dominance relationship between each gene/allele involved in the process

  • ex) Skin color in humans is another example of a polygenic trait, where multiple genes contribute to the variation in pigmentation, resulting in a continuous range of phenotypes.

• epistasis

  • one gene impacts another genes expression

  • ex) The interaction between genes can lead to unexpected phenotypic outcomes, as seen in the example of coat color in Labrador retrievers, where one gene determines the pigment and another gene can modify its expression.

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Page 22: Observing Inheritance Over Generations

• Pedigree Charts: Visual representation of familial relationships and trait inheritance patterns.

  • squares represent males, circles represent females, shading represents affected

Page 23-24: Patterns of Inheritance

• Chromosomal Context: Mechanisms connected to autosomal and sex-linked traits.

• autosomal traits: first 22 pairs

Page 25: X-Linked Dominance and Inheritance Examples

• sex linked can be on either x or y chromosome

  • x-linkage describes an allele on the x chromosome

    • x linked recessive traits require two mutated x chromosomes in females or one mutated x chromosome in the male, to appear on the phenotype

    • x-linked dominant traits require at least one mutated x to appear in the phenotype

  • y linkage describes an allele on the y chromosome

    • a mutated y confers the affected phenotype

      

Page 26: Sex Linked Traits and Extranuclear Inheritance

• Inheritance: Mechanisms of mitochondrial inheritance and its effects on offspring.

• some genes are linked to x and y chromosomes

• sex linked instead of the autosome these genes are considered sex linked

• extranuclear- some traits are inherited from DNA found in the mitochondria and chloroplasts, these traits do not follow Mendelian inheritance rules. because organelles are randomly assorted to gametes and daughter cells during meiosis and mitosis

Page 27-29: Mendel Exceptions and Meiosis Application

• Chromosomal Behavior: How meiosis relates to Mendel's laws.

Page 30-31: Morgan's Contributions

• Fruit Fly Studies: Evidence linking chromosomes to inheritance.

• Sex-Linked Genes: Results from Morgan’s experiments determining gene locationsand their associations with specific chromosomes, particularly in the case of traits like eye color and body color in Drosophila. These findings established the foundation for understanding how traits are inherited and provided key evidence for the chromosomal theory of inheritance. \

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Page 32-34: Chromosomal Basis of Sex and Morgan's Findings

• Sex Determination: Male and female chromosomal differences

• in humans and other mammals, there are 2 varieties of sex chromosomes, a largr x chromosome and a smaller y chromosome

  • only the ends of the y chromosome have regions rhat are homologous wihr corresponding regions of the x chromosomes

• SRY gene- gene on y chromosome that codes for a protein that directs the development of male anatomical features

• other animals have different methods of sex determination

Page 35-39: Gene Mapping and Linkage Analysis

• linkage genes: genes on same chromosome that tend to be inherited

• gene linkage- an exception to Mendelian independent assortment

  • independent assortment asserts that different pairs of alleles are inherited independently of each other

• morgan crossed a dihybrid fruit fly with a double mutant

  • expected ratio was 1:1:1:1 or four phenotypes in equal priportion based on independent assortment

  • observed data didnt match predicted data

• Morgan found that body color and wing size are usually inherited together in specific combinations (parental phenotypes)

  • noted that these genes do not assort independently and reasoned that they were on the same chromosome

  • however non-parental or recombinant phenotype wer also produced

    • a 50% frequency of recombination is observed from any 2 genes on different chromosomes

  • morgan discovered that genes can be linked, but the linkage was incomplete because some recombinant phenotypes were observed

• he proposed that some process must occasionally break the physical connection between genes on the same chromosome

  • that mechanism was the crossing over of homologous chromosomes

  • recombinant chromsomes bring alleles together in new combination in gametes

    

Gene mapping

• the further apart 2 genes are, the higher the probability that a crossover/chiasma will occur between them and therefore the higher the recombination frequency

• linkage map is a genetic map of a chromosome based on recombination frequencies

• distances between genes an be express ed as map units

  • map inits indicate relative distance and order. not precise location of genes

• Genes that are fart apart on the same chromosome can have a recombination frequency

  • if you are above 50% map units, you’re too far to have recombinant

• phenotypic plasticity

  • ability of individual genotypes to produce different phenotypes when exposed to different environmental conditions

• gene penetrance

  • penetrance is likelihood that an organism will actually express its inherited genotype

  • mutations in the BRCA1 genes cause familial breast cancer, but only around 80% of individuals with he mutations develop breast cancer

• gene expressivity

  • expressivity is the degree to which the phenotype is expressed in an organism

  • can be influenced by allele combinations and/or environmental factors that affect gene expression

Summary

know mendellian crosses and their patterns

be able to work simple genetic problems

watch gentic vocab

be able to erad pedigree charts