- Mendel's experiments helped formulate the particulate theory of inheritance and showed that inheritance involves reshuffling of genes from generation to generation. - The law of segregation states that each individual has two factors for each trait which segregate during gamete formation such that each gamete contains only one factor. - The law of independent assortment states that each pair of factors segregates independently of other pairs, resulting in all possible combinations of factors in gametes. Punnett squares can be used to determine possible offspring combinations.

1. Mendelian Patterns of Inheritance Chapter 11

2. Blending Inheritance At the time, most breeders believed parents of contrasting appearance always produce offspring of intermediate appearance. Mendel’s experiments helped him formulate the particulate theory of inheritance . Inheritance involves reshuffling of genes from generation to generation.

3. Law of Segregation Each individual has two factors for each trait. The factors segregate during gamete formation. Each gamete contains only one factor from each pair of factors. Fertilization gives each new individual two factors for each trait.

4. Law of Segregation Explained

5. Homologous Chromosomes Law of segregation applies to alleles on SEPARATE chromosomes. Alleles that tend to be inherited together are said to be linked .

6. Law of Independent Assortment Each pair of factors segregates independently of the other pairs. All possible combinations of factors can occur in the gametes. Possible combinations = 2 n where n = number of heterozygous chromosome pairs

7. Punnett Square Tool for determining all possible offspring combinations Every possible combination of alleles is placed within the squares. Single-Trait Cross means there will be two letters in each offspring’s square-one from mom and one from dad X

8. Dihybrid Cross: Two-trait Inheritance

9. Determining possible gametes… Identify parents’ gametes: Bbmm BbMm Bm BM Bm Bm bm bM bm bm

10. Building the Punnett Square bbmm bbmm Bbmm Bbmm bm bbMm bbMm BbMm BbMm bM Bbmm Bbmm BBmm BBmm Bm BbMm BbMm BBMm BBMm BM bm bm Bm Bm

11. Incomplete Dominance Exhibited when the heterozygote has an intermediate phenotype between that of either homozygote.

12. Multiple Allelic Traits When a trait is controlled by multiple alleles, the gene exists in several allelic forms. ABO blood types I A – A antigens on blood cells I B – B antigens on blood cells i - no antigens on blood cells Codominance - More than one allele is fully expressed. ABO blood type (multiple allelic traits)

13. Multiple Allelic Traits When a trait is controlled by multiple alleles, the gene exists in several allelic forms. ABO blood types Phenotype Genotype A I A I A ,I A i B I B I B ,I B i AB I A I B O ii

14. Inheritance of Blood Type

15. Hardy-Weinberg Principle ** Allele frequencies of gene pool will stay the same (equilibrium) IF No Mutations No Gene Flow Random Mating No Genetic Drift No Selection

16. Consider a trait with 2 possible alleles… p = frequency of dominant allele The probability that an allele chosen at random is dominant q = frequency of recessive allele The probability that an allele chosen at random is recessive p + q = 1; Why? Hardy Weinberg Math

17. Hardy-Weinberg Math What is the probability of an individual being homozygous dominant (AA) – the frequency of the AA genotype? f AA = p x p = p 2 What is the probability of an individual being homozygous recessive (aa)? f aa = q x q = q 2

18. Hardy-Weinberg Math What is the probability of an individual being heterozygous ( Aa ) – the frequency of the Aa genotype? f Aa = (p x q) + (q x p) = 2pq There are 2 possible combinations: allele 1 can be A and allele 2 can be a OR allele 1 can be a and allele 2 can be A

19. Human Genetic Disorders Autosome - Any chromosome other than a sex chromosome.

20. Human Genetic Disorders Autosome - Any chromosome other than a sex chromosome. When a genetic disorder is autosomal dominant, an individual with AA or Aa has the disorder. When a genetic disorder is autosomal recessive, only aa individuals have the disorder. Carriers - Individuals unaffected by a disorder but can have an affected child (carries the recessive allele)

21. Autosomal Recessive Pedigree

22. Autosomal Dominant Pedigree

23. Autosomal Recessive Disorders Tay-Sachs Disease Progressive deterioration of psychomotor functions. Cystic Fibrosis Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous. Phenylketonuria (PKU) Lack enzyme for normal metabolism of phenylalanine.

24. Autosomal Dominant Disorders Neurofibromatosis Tan or dark spots develop on skin and darken. Small, benign tumors may arise from fibrous nerve coverings. Huntington Disease Neurological disorder leading to progressive degeneration of brain cells, in turn causing severe muscle spasms and personality disorders.

25. Polygenic Inheritance Occurs when a trait is governed by two or more sets of alleles. Each dominant allele has a quantitative effect on the phenotype, and these effects are additive. Result in continuous variation of phenotypes.

26. Height in Human Beings

27. Terminology Pleiotropy - A gene that affects more than one characteristic of an individual. Sickle-cell (incomplete dominance) Codominance - More than one allele is fully expressed. ABO blood type (multiple allelic traits)

28. Terminology Epistasis - A gene at one locus interferes with the expression of a gene at a different locus. Human skin color (polygenic inheritance)

29. Epistasis and ABO Blood Group In order to produce A and B antigens, a person must have H antigen precursor. If both copies of H antigen are mutated, A and B antigens cannot be made.

30. Environment and Phenotype Himalayan Rabbits - Enzyme coding for black fur is active only at low temperatures. Black fur only occurs on extremities.