1. Introduction to Genetics
Chapter 11 Lecture Notes

2. 11 – 1 The Work of Gregor Mendel
Austrian monk
“Father of Genetics"
Reported and published results in mid 1860’s
Did not get recognition for his work
Importance of his work was rediscovered in 1900

3. Experimented with pea plants to see how they passed on traits
Purple/white flower
Axial/Terminal flower
Yellow/green peas
Round/wrinkled peas
Green/Yellow pod
Inflated/Constricted pod
Tall/short

4. Crossed short stemmed with other short stemmed = short stemmed plants
Genetics - the study of how traits are passed from parents to offspring
Chose Pea plants
Had a lot of different traits
Reproduce rapidly
Cross plants with different traits
Crossed short stemmed with other short stemmed = short stemmed plants
True breeding short plants
Crossed tall stemmed with other tall stemmed plants = some tall, some short
Some tall stemmed plants that only produced other tall stemmed plants
True breeding tall plants

5. True breeding short x True breeding tall plant = all tall plants
F1 generation
Two factors for any one trait
Dominant and Recessive genes
Dominant trait - trait that is stronger
Recessive trait - weaker trait, masked by dominant
Hybrid - plant has one dominant and one recessive trait

6. Each parent had a gene pair
TT (true breeding tall plant)
tt (true breeding short plant)
Tt (hybrid)
Cross hybrid plants from F1 = some tall, some short in a ratio of 3:1, called the F2 generation

7. 11 – 2 Probability & Punnett Squares
Determines chance offspring have of inheriting certain traits.
Chance that an action will occur randomly
Results of chance events don’t effect results of the next
Each event happens independently
Punnett Squares
Crossing organisms showing one genetic trait

8. Homozygous Heterozygous Phenotype Genotype TT or tt
Has 2 identical alleles
True breeders
Heterozygous Tt
Alleles are different
Hybrid
Phenotype
Physical appearance
Tall or short
Genotype
Genetic makeup
TT, Tt, or tt

9. 11 – 3 Exploring Mendelian Genetics
Independent Assortment
Genes that segregate independently
Two-factor cross
Two genetic traits
R = round seeds
r = wrinkled seeds
Y = yellow seeds
y = green seeds
Cross homozygous parents
Parents RRYY x rryy
Offspring all RrYy heterozygous

10. Mendel’s Principles Inheritance of genes passed to offspring
Cross heterozygous parents
RrYy x RrYy
F2 Generation offspring
Round Yellow 9/16, Round Green 3/16, Wrinkled Yellow 3/16, Wrinkled Green 1/16
Mendel’s Principles
Inheritance of genes passed to offspring
For 2 or more alleles genes can have dominant or recessive traits
Sexual reproducers have 2 copies of each gene
Genes are segregated independently in gamete production

11. Beyond Dominant and Recessive Alleles
Incomplete Dominance
Heterozygous phenotype is in between homozygous phenotypes
Four O’clock pink flowers
Codominance
Both alleles contribute to phenotype
Type AB blood
Multiple Alleles
One gene with more than two alleles
Coat color in rabbits

12. Genetics and the environment
Polygenic traits
Traits controlled by two or more genes
Eye color, skin color, hair color
Genetics and the environment
Characteristic traits are coded for in genes
Environment can determine traits
Nutrition
Disease

13. 11 – 4 Meiosis Walther Flemming (1882) Chromosomes German biologist
Discovered chromosomes
Chromosomes
Protein composed of “Nucleic Acid"
Located in the nucleus of a cell
Provide the code to make proteins
Build
Repair
Reproduce

14. Meiosis
Division of sex cells
Produces egg or sperm cells
Each cell produced has 1/2 the regular genetic information (haploid (N))

15. 2 haploid daughter cells are formed Meiosis II
Interphase I
Chromosome replication
Each parent provides one chromosome
Each chromosome is replicated
4 copies of 1 type of chromosome
Meiosis I
Prophase I
Chromosome homologs pair up (tetrad)
Chromatids portions exchange (crossing over)
Metaphase I
Spindle fibers attach to chromosomes
Anaphase I
Homologs are pulled away from each other
Telophase I and Cytokinesis
2 haploid daughter cells are formed
Meiosis II
Prophase II (2 haploid daughter cells)
Metaphase II
Anaphase II
Sister chromatids are pulled apart
Telophase II and cytokinesis
4 haploid daughter cells are formed

16. Gamete Formation (in animals)
4 male gametes are formed (sperm)
4 female gametes formed (1 egg, 3 polar bodies)
Comparing mitosis and meiosis
Mitosis
1 cell division
2 Diploid (2N) daughter cells
Asexual reproduction
Meiosis
2 cell divisions
4 haploid (N) daughter cells
Gamete formation for sexual reproduction

17. 11 – 5 Linkage and Gene Maps Gene Linkage Gene Maps
Genes on the same chromosome
Genes do not show independent assortment
Gene Maps
Crossing over changes gene location on homologous chromosomes
Show locations of genes on chromosomes