Genetics

Dominant versus Recessive Traits Dominant traits can mask or cover up others. Dominant traits can mask or cover up others. Dominant traits are represented by capital letters. Dominant traits are represented by capital letters. Recessive traits are masked or covered up. Recessive traits are masked or covered up. Recessive traits are represented by lower- case letters. Recessive traits are represented by lower- case letters.

Mendel’s Principles Heredity is not blending- there are discrete dominant and recessive traits. Heredity is not blending- there are discrete dominant and recessive traits. There are units or particles of heredity- we know now that these are genes. There are units or particles of heredity- we know now that these are genes. Every individual has a pair of these units for every trait- we have 2 alleles for every trait. Every individual has a pair of these units for every trait- we have 2 alleles for every trait. These pairs separate in gametes- this happens during meiosis where one homologue goes to each daughter cell. These pairs separate in gametes- this happens during meiosis where one homologue goes to each daughter cell. Each gamete receives only one unit from each pair- they are haploid and combine to become diploid. Each gamete receives only one unit from each pair- they are haploid and combine to become diploid.

Alleles

Homozygous versus Heterozygous Homozygous means that both alleles are the same thus both letters are the same. Homozygous means that both alleles are the same thus both letters are the same. The letters may be either both capital or both lower-case. The letters may be either both capital or both lower-case. Heterozygous means that the alleles are different meaning that the letters are different. Heterozygous means that the alleles are different meaning that the letters are different. One letter is capital and the other letter is lower-case. One letter is capital and the other letter is lower-case.

Genotype versus Phenotype Heterozygous and homozygous refer to your genotype. Heterozygous and homozygous refer to your genotype. Your genotype is what alleles you have. Your genotype is what alleles you have. Phenotype only refers to what you look like. Phenotype only refers to what you look like. Thus, if you show a dominant phenotype you can be heterozygous or homozygous dominant. Thus, if you show a dominant phenotype you can be heterozygous or homozygous dominant. If you show the recessive phenotype, you must be homozygous recessive. If you show the recessive phenotype, you must be homozygous recessive.

To determine the phenotypes and genotypes of offspring, You make a Punnett Square!

Unattached Earlobe Dominant Phenotype Attached Earlobe Recessive Phenotype Earlobe Attachment

Genotypic and Phenotypic Ratios Genotypic ratios express the results of the genotypes of the offspring resulting from a Punnett Square. Genotypic ratios express the results of the genotypes of the offspring resulting from a Punnett Square. Therefore, they would state how many offspring would be homozygous and heterozygous. Therefore, they would state how many offspring would be homozygous and heterozygous. Phenotypic ratios express the results of the phenotypes of the offspring resulting from a Punnett Square. Phenotypic ratios express the results of the phenotypes of the offspring resulting from a Punnett Square. Therefore, they would state how many of the offspring would show a certain trait. Therefore, they would state how many of the offspring would show a certain trait.

Punnett Squares Show Theoretical Ratios and Percentages

Recessive Traits Tay-Sachs Disease Tay-Sachs Disease Cystic Fibrosis Cystic Fibrosis PKU PKU

Dominant Traits Huntington Disease Huntington Disease Hypercholesterolemia Hypercholesterolemia Marfan Syndrome Marfan Syndrome Achrondroplasia Achrondroplasia

Non-Mendelian Inheritance

Polygenic Inheritance

X Yellow Lab Black Lab Chocolate Lab

Multiple Alleles

Co-Dominance

Blood Type Alleles

Blood Types and Paternity Testing This used to be all there was and only allows you to exclude someone as the father, not to prove he is the father. Now we have DNA fingerprinting!

Sickle Cell Genotypes and Phenotypes Hb A Hb A Normal Hb A Hb S Sickle Cell Trait Hb S Hb S Sickle Cell Anemia

Females Have 2 Copies of the X Chromosome, Males Only Have 1. The Male’s X Chromosome Comes From His Mother.

Since Males Have Only 1 X Chromosome, They Will Show the Traits on that Chromosome.

Sex Linked Traits Men Cannot Be Carriers of a Sex-Linked Trait Men Cannot Be Carriers of a Sex-Linked Trait

Sex Influenced Traits

Environmental Influence