Mendelian Genetics Chapter 6.3 & 6.4

Gregor Mendel Gregor Mendel: Father of genetics, Gregor Mendel: Father of genetics, studied pea plants. Genetics: study of heredity Genetics: study of heredity Heredity: transmission of genetic characteristics from parents to offspring Heredity: transmission of genetic characteristics from parents to offspring Trait: a characteristic controlled by genes Trait: a characteristic controlled by genes Ex) tongue roller, hair color, eye color, etc. Ex) tongue roller, hair color, eye color, etc

Recessive and Dominant Traits Dominant: A trait that covers or masks another trait. Dominant: A trait that covers or masks another trait. Recessive: A trait that is covered or masked when paired with a dominant trait. Recessive: A trait that is covered or masked when paired with a dominant trait.

Chromosomes and Genes Gene: A segment of DNA Gene: A segment of DNA on a chromosome that controls a particular trait. Allele: alternative form Allele: alternative form of a gene, one is dominant and one is recessive. An individual An individual inherits 2 alleles for inherits 2 alleles for every gene – 1 from every gene – 1 from mom and 1 from dad mom and 1 from dad

In genetics, alleles are represented by letters. In genetics, alleles are represented by letters. Dominant alleles: represented with a capital letter Dominant alleles: represented with a capital letter Example: F = dominant allele Example: F = dominant allele for purple flowers Recessive alleles: represented with a lower case letter Recessive alleles: represented with a lower case letter Example: f = recessive allele that will yield white flowers Example: f = recessive allele that will yield white flowers Ff Homologous chromosomes Different alleles for the same gene

Mendel’s Laws Law of Segregation: during gamete formation (MEIOSIS) pairs of alleles separate and are randomly united during fertilization Law of Segregation: during gamete formation (MEIOSIS) pairs of alleles separate and are randomly united during fertilization Offspring receives 1 allele from each parent Offspring receives 1 allele from each parent Segregation happens here during Anaphase 1

Mendel’s Laws Cont’d Law of Independent Assortment: allele pairs separate independently of one another during gamete formation. Law of Independent Assortment: allele pairs separate independently of one another during gamete formation. This law would be violated, for example, if the “G" allele was always associated with the “Y" allele (and thus eliminating the possibility of Gy and gY gametes). OROR

Chapter 6.4 & 6.5

Genotype and Phenotype Genotype: the genetic makeup of an organism Genotype: the genetic makeup of an organism Consists of 2 alleles inherited from parents Consists of 2 alleles inherited from parents Phenotype: the physical appearance of an organism resulting from genotype Phenotype: the physical appearance of an organism resulting from genotype

Genotype and Phenotype Genotype: FF FF Ff Ff ff ffPhenotype: Purple flowers White flowers F = allele for purple flowers (dominant) f = allele for white flowers (recessive)

Homozygous: both alleles are alike Homozygous: both alleles are alike Homozygous Dominant: has 2 dominant alleles (FF) Homozygous Dominant: has 2 dominant alleles (FF) Homozygous Recessive: has 2 recessive alleles (ff) Homozygous Recessive: has 2 recessive alleles (ff) Heterozygous: each allele differs (Ff) Heterozygous: each allele differs (Ff) Heterozygous organisms usually display the dominant phenotype Heterozygous organisms usually display the dominant phenotype Always write capital letter first! Always write capital letter first!

Monohybrid Crosses Monohybrid Cross: a cross that involves 1 pair of contrasting traits Monohybrid Cross: a cross that involves 1 pair of contrasting traits We use diagrams called Punnett square to predict offspring traits. We use diagrams called Punnett square to predict offspring traits.

Create a box & add parent genotypes

Fill in potential offspring genotypes. Offspring

Genotypic and Phenotypic Ratios Genotypic Ratio: ratio of genotypes that will appear in the offspring Genotypic Ratio: ratio of genotypes that will appear in the offspring Expressed in order from Most Dominant to Most Recessive Expressed in order from Most Dominant to Most Recessive 1 RR : 2 Rr : 1 rr 1 RR : 2 Rr : 1 rr Phenotypic Ratio: ratio of phenotypes that will appear in the offspring Phenotypic Ratio: ratio of phenotypes that will appear in the offspring Also expressed in order from Most Dominant to Most Recessive Also expressed in order from Most Dominant to Most Recessive 3 Red : 1 white 3 Red : 1 white