Patterns of Inheritance Complete Dominance Incomplete Dominance Co-dominance Co-dominance with Multiple Alleles Sex Linked

Impact of Mendel’s Work Mendel published his results in 1866 Mendel published his results in 1866 Paper received little notice Paper received little notice Mendel discontinued his experiments in 1871 Mendel discontinued his experiments in 1871 Paper rediscovered in 1900 Paper rediscovered in 1900

Mendel’s Law of Segregation Mendel’s Law of Segregation An individual inherits ONE “unit” of information (allele) about a trait from each parent An individual inherits ONE “unit” of information (allele) about a trait from each parent During gamete formation, the alleles separate from each other (Tt T or t ) During gamete formation, the alleles separate from each other (Tt T or t )page

Mendel’s Law of Independent Assortment Mendel concluded that one gene did not affect another gene Mendel concluded that one gene did not affect another gene Alleles for these genes separated random from each other Alleles for these genes separated random from each other TtRr T or t R or r so TR Tr tR tr so TR Tr tR trpage

Complete Dominance Inheritance True-breeding homozygous recessive parent plant True-breeding homozygous dominant parent plant An F 1 plant self-fertilizes and produces gametes: F 1 PHENOTYPE S F 2 PHENOTYPE S aa Aa AA aaAa AA aa A A A A aa a a AA 2 alleles; one dominant or the other 2 alleles; one dominant or the other if dominant allele present, it will be expressed if dominant allele present, it will be expressed 2 distinct phenotypes; 3:1 ratio 2 distinct phenotypes; 3:1 ratio

Genetics After Mendel 1. Incomplete Dominance 2. Co-dominance 3. Co-dominance with Multiple Alleles 4. Sex Linked

Incomplete Dominance Incomplete Dominance X Homozygous parent Homozygous parent All F 1 are heterozygous X F 2 shows three phenotypes in 1 : 2 : 1 ratio 1. Incomplete Dominance neither allele is completely dominant over the other neither allele is completely dominant over the other 3 phenotypes 3 phenotypes heterozygous is a “intermediate or “blend” heterozygous is a “intermediate or “blend”page R r R r R R r r R r

both alleles are expressed at the same time in the heterozygous (roan) both alleles are expressed at the same time in the heterozygous (roan) 3 phenotypes; 3 phenotypes; 1 : 2 : 1 ratio page 2. Co-dominance

3. Co-dominance with Multiple Alleles: ABO Blood types 3 alleles; two that are co-dominant and one recessive 3 alleles; two that are co-dominant and one recessive I A, I B, i page GenotypePhenotype I A I A or I A i Type A I B I B or I B i Type B IAIBIAIB Type AB ii Type O

ABO Blood Types type of blood determined by antigen on surface (flag) type of blood determined by antigen on surface (flag) type of blood make antibodies against other antigens type of blood make antibodies against other antigens

Blood Transfusions During transfusions recipient’s antibodies in plasma will attack blood cells that have an unfamiliar surface antigen (agglutination – clumping of blood) During transfusions recipient’s antibodies in plasma will attack blood cells that have an unfamiliar surface antigen (agglutination – clumping of blood) Type AB is universal recipient since it does not have any antibodies because it has both antigens – any blood can be donated to them! Type AB is universal recipient since it does not have any antibodies because it has both antigens – any blood can be donated to them! Type O is universal donor since it has neither type A nor type B antigen for antibodies to attack – give to anyone Type O is universal donor since it has neither type A nor type B antigen for antibodies to attack – give to anyone

Transfusions Antibodies Antibodies Can Receive Can Receive Blood From Blood From Type A B A or O A or O Type B A B or O B or O Type AB none none A, B, AB, O A, B, AB, O Type O A and B A and B only O only O

Rh Factor another protein marker on red blood cells another protein marker on red blood cells independent of type of blood independent of type of blood inheritance works according to complete dominance inheritance works according to complete dominance either Rh+ or Rh- ; Rh+ is dominant either Rh+ or Rh- ; Rh+ is dominant special problem during pregnancy of second child if mom is Rh- and first was baby Rh+ special problem during pregnancy of second child if mom is Rh- and first was baby Rh+

4. Sex Linked genes on the sex chromosomes genes on the sex chromosomes have different probabilities in females and males have different probabilities in females and males examples of recessive X linked traits examples of recessive X linked traits – hemophilia – red/green colour blindness page page

Other types of Inheritance 5. Multifactorial/Multiple Genes/Polygenic 6. Sex Limited 7. Sex Influenced 8. Gene Linkage

5. Multifactorial/Multiple Genes/Polygenic Traits show wide range of phenotypic expression; continuous distribution Traits show wide range of phenotypic expression; continuous distribution Controlled by more than one gene Controlled by more than one gene Traits maybe influenced by other factors Traits maybe influenced by other factors Examples human hair colour, height, eye colour, skin colour Examples human hair colour, height, eye colour, skin colour

Describing Continuous Distribution Range of values for the trait Number of individuals with some value of the trait (line of bell-shaped curve indicates continuous variation in population)

6. Sex Limited Traits Expression of the trait is limited by sex of the individual Expression of the trait is limited by sex of the individual Traits NOT on sex chromosome Traits NOT on sex chromosome Thought to be influenced by hormones Thought to be influenced by hormones Example: heavy beards – phenotype in males only but females inherit but don’t express it but can pass trait to sons Example: heavy beards – phenotype in males only but females inherit but don’t express it but can pass trait to sons

7. Sex Influenced Traits Idea of how genes are influenced by internal environments Idea of how genes are influenced by internal environments Genes may be dominant in one sex but recessive in other; genotype interpreted differently Genes may be dominant in one sex but recessive in other; genotype interpreted differently Baldness – dominant trait in males; in females recessive trait and don’t see “bald” but rather thin Baldness – dominant trait in males; in females recessive trait and don’t see “bald” but rather thin

Nature verse Nurture Expression of traits are not fully under control of just what your genotype is (NATURE) Expression of traits are not fully under control of just what your genotype is (NATURE) An organism’s internal environment and external environmental factors influence how genes may be expressed (NURTURE) An organism’s internal environment and external environmental factors influence how genes may be expressed (NURTURE) Example – height – may have genetics to be tall but if there is hormonal imbalance or nutritional deficiency than won’t reach genetic potential Example – height – may have genetics to be tall but if there is hormonal imbalance or nutritional deficiency than won’t reach genetic potential

Temperature Effects on Phenotype Rabbit is homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin- producing pathway Rabbit is homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin- producing pathway Melanin is produced in cooler areas of body Melanin is produced in cooler areas of body

Environmental Effects on Plant Phenotype Environmental Effects on Plant Phenotype Hydrangea macrophylla Hydrangea macrophylla Action of gene responsible for floral color is influenced by soil acidity Action of gene responsible for floral color is influenced by soil acidity Flower color ranges from pink to blue Flower color ranges from pink to blue