Patterns of Inheritance

1. Patterns of Inheritance Mendelian Genetics

2. Mendel’s Principles Principle of Segregation Principle of Independent Assortment Punnett Squares and Pedigrees

3. Genetics is the science of heredity. • The science of heredity dates back to ancient attempts at selective breeding.

4. Some definitions and rules B B • Allele: an alternative form of a single gene passed from generation to generation • Dominant: typically overshadows recessive allele, phenotype is seen • Capital letter represents dominance and phenotype • Example: Black is dominant over white so B for black • Recessive: hidden trait, unless both alleles are recessive • Lower case letter, same as dominant allele • Again black dominant over white so b for white B b B = black fur B = white fur

5. Some definitions and rules B B • Homozygous: an organism with two of the same alleles for a particular trait • BB or bb • Heterozygous: an organism with two different alleles for a particular trait • Bb B b B = black fur B = white fur

6. Mendel’s Principles DiscoveredExperimental genetics began in an abbey garden • Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants • Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation • Mendel studied seven pea characteristics

7. White 1 • This illustration shows his technique for cross-fertilization Removed stamensfrom purple flower Stamens Carpel 2 Transferred pollen from stamens of white flower to carpel of purple flower PARENTS(P) Purple 3 Pollinated carpel matured into pod 4 Planted seeds from pod Stamen OFF-SPRING(F1) Carpel

8. FLOWER COLOR Seven pea characteristics Purple White FLOWER POSITION Axial Terminal SEED COLOR Yellow Green SEED SHAPE Round Wrinkled POD SHAPE Inflated Constricted POD COLOR Green Yellow STEM LENGTH Tall Dwarf

9. The parent generation is also known as the P generation.

10. Offspring of the P cross are the first filial (F1) generation. (Filial: having or assuming the relation of a child or offspring)

11. Principle of Segregation P GENERATION(true-breedingparents) Purple flowers White flowers • Mendel’s principle of segregation describes the inheritance of a single characteristic. • From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic. • One characteristic comes from each parent. All plants have purple flowers F1generation Fertilization among F1 plants(F1 x F1) F2generation 3/4 of plantshave purple flowers 1/4 of plantshave white flowers

12. A sperm or egg carries only one allele of each pair. • The pairs of alleles separate when gametes form. • This process describes Mendel’s principle of segregation. • Alleles can be dominant or recessive.

13. P GENERATION(true-breedingparents) GENETIC MAKEUP (ALLELES) PP pp Parent PLANTS Purple flowers White flowers Gametes: sperm or egg carry only ONE allele All P All p All plants have purple flowers F1generation All Pp F1generation F1 PLANTS(hybrids) Principle of Segregation Gametes: sperm or egg carry only ONE allele 1/2P 1/2p Fertilization among F1 plants(F1 x F1) P P Eggs Sperm PP p p F2 PLANTS Pp Pp Phenotypic ratio3 purple : 1 white F2generation 1/4 of plantshave white flowers 3/4 of plantshave purple flowers pp Genotypic ratio1 PP : 2 Pp : 1 pp

14. P GENERATION(true-breedingparents) Purple flowers White flowers All plants have purple flowers P Generation Cross Punnett Square Genotypic Ratio? Phenotypic Ratio? F1generation F1 PLANTS(hybrids) Fertilization among F1 plants(F1 x F1) F1 Generation Cross Punnett Square Genotypic Ratio? Phenotypic Ratio? 1/4 of plantshave white flowers 3/4 of plantshave purple flowers F2generation

15. Homologous chromosomes • Homologous chromosomes bear the two alleles for each characteristic. • Alternative forms of a gene (alleles) reside at the same locus (location) on homologous chromosomes. GENE LOCI DOMINANT allele P a B P a b RECESSIVE allele GENOTYPE: PP aa Bb HOMOZYGOUSfor thedominant allele HOMOZYGOUSfor therecessive allele HETEROZYGOUS

16. Principle of Independent Assortment • The principle of independent assortment is revealed by tracking two characteristics at once. • Example: pea color and seed shape • By looking at two characteristics, Mendel found that the alleles of a pair segregate independently of other allele pairs during gamete formation • This is known as the principle of independent assortment

17. Geneticists use the testcross to determine unknown genotypes. • The offspring of a testcross often reveal the genotype of an individual when it is unknown. TESTCROSS: GENOTYPES B_ bb Two possibilities for the black dog: BB or Bb If all of the offspring are black, then dad was homozygous. B B b GAMETES b Bb b Bb bb OFFSPRING All black 1 black : 1 chocolate

18. Mendel’s principles reflect the rules of probability. F1 GENOTYPES Bb female Bb male • Inheritance follows the rules of probability • The rule of multiplication and the rule of addition can be used to determine the probability of certain events occurring • Rule of Multiplication (F1s) • Rule of Addition (F2s) Formation of eggs Formation of sperm 1/2 B B 1/2 B B 1/2 b b 1/2 1/4 B b b B 1/4 1/4 b b F2 GENOTYPES 1/4

19. Punnett Squares • Use Punnett Squares to visualize the probabilities of offspring genotypes. • Monohybrid cross: a cross that involves hybrids for a single trait. • Dihybrid cross: the simultaneous inheritance of two or more traits in the same organism.

20. Monohybrid Cross F1 and F2 Generations for Pea Color

21. DihybridPunnett Square

22. Let’s Practice! • Punnett Squares Packet • Read Example One. Discuss: • Law of Segregation • Conventions • Genotypic Percents • Phenotypic Percents • Monohyrid Practice Problems (1-5) • ADVANCED: Turn to Example 3 and try the Dihybrid Crosses.