1. Single Gene Inheritance How Traits are Passed On

2. 2 Genetics Units Heredity/Classical Genetics Inheritance patterns Based on the work of Gregor Mendel in the mid 1800s Molecular Genetics DNA/Chromosomal explanations for inheritance patterns Defines our modern understandings of genetics

3. *Note We are covering the genetics of sexually reproducing eukaryotes like ourselves Bacteria/Archaea and asexual eukaryotes are a little different

4. Chromosomes Human DNA is split into 23 pairs of chromosomes (46 total) Each codes for hundreds to thousands of genes We have 2 versions of each chromosome, called homologous chromosomes

5. Human Chromosomes

6. Gene A gene is a segment of DNA that codes for one protein That protein can determine what trait we express E.g. a protein produces brown pigments in eyes

7. Inherited Traits Different versions of the gene are called alleles E.g. the brown allele is the DNA that codes for brown eyes We inherit one chromosome from each parent and thus 1 allele from each parent for every gene Homologous

8. Vocabulary Homozygous – to have 2 identical alleles for a particular gene Heterozygous – to have 2 different alleles HomozygousHeterozygous

9. So you have 2 alleles, which determines what you look like?? It depends. This is where genetics starts to get complicated Sometimes only 1 of the 2 alleles gets expressed Sometimes they both express themselves

10. Case 1 – Complete Dominance Only 1 trait is expressed The dominant trait OR the recessive trait is expressed

11. Human Examples You have dimples or you don’t You have freckles or you don’t You are a dwarf or you aren’t You have attached earlobes or you don’t You have cystic fibrosis or you don’t

12. Complete Dominance Dominant Allele Is expressed if it is present You can have 1 or 2 dominant alleles Represented by capital letters Recessive Allele Is expressed only if there is no dominant allele You must have 2 recessive alleles (usually) Represented by lower case letters

13. The Dominant Phenotype Phenotype = appearance Is shown by individuals who have 1 or 2 dominant alleles Called homozygous dominant (AA) or heterozygous (Aa) genotypes

14. The Recessive Phenotype Is only shown if the individual is homozygous recessive (aa)

15. “Genotypes” – Combinations of Alleles = homozygous dominant (shows dominant trait) =heterozygous (shows dominant trait) = homozygous recessive (shows recessive trait)

16. Punnett Square Show the possible alleles each parent could give. This example shows an Aa (heterozygous) person mating with an aa (homozygous recessive individual) Parent 1 Parent 2 Dad Mom Potential sperm Potential eggs Potential offspring

17. Say A codes for green eyes a codes for black eyes

18. Draw a Punnett Square for Two Heterozygotes Mating

19. Case 2 If 2 different alleles are both present, their affects are combined i.e. red allele + white allele  pink flowers Straight + curly hair  Wavy hair

20. “Genotypes” – Incomplete Dominance = AA (red flowers, or straight hair) =Aa (pink flowers, or wavy hair) = aa (white flowers, or curly hair)

21. Incomplete Dominance R= red allele, r= white allele RR = red flowers, Rr=pink flowers, rr= white flowers If red flowers are mated with white flowers, what will the offspring be? RR r Rr r

22. Draw a Punnett Square for 2 pink flowers being crossed

23. Case 3 Both alleles are expressed at the same and do not mix/form intermediate

24. Codominance I.e. blood types I A and I B alleles are both dominant There is a 3 rd, recessive allele called i (codes for blood type O)

25. Blood Types 4 possible types A (I A I A or I A i individuals) B (I B I B or I B i) individuals AB (I A I B individuals) O (ii individuals)

26. What parents could have children with type A or type B blood only

27. Summary You have 2 copies of every gene, one from your mom, one from your dad Which version you express depends on the gene, sometimes only 1 (complete dominance), sometimes a mixture (incomplete dominance) and sometimes both (co-dominant) The “traits” are due to which protein is produced