Genetics

What is Genetics Genetics is the scientific study of heredity. Heredity is what makes each species unique. Heredity is the passing on of genes from one generation to the next.

Basic Genetics Terminology Section of DNA on a chromosome that determines I trait Allele Different forms of a gene Dominant – allele masks other alleles; represented by capital letter Recessive – allele is only shown (epressed) when a dominant gene is not presentIndividuals with identical alleles are called homozygous

Genetics Terminology Cont… Homozygous When both alleles for a trait are identical Heterozygous When the alleles for a trait are different Genotype Actual genetic make-up for a trait Homozygous dominant = DD Homozygous recessive = dd Heterozygous = Dd Phenotype The expression of the gene; physical characteristic Descriptive such as tall for TT or Tt

Genetics Terminology Cont… F1 Generation The first generation of offspring from two parents F2 Generation The offspring from the breeding of two F1 generation offspring Test Cross an experimental cross of an individual organism of dominant phenotype but unknown genotype to an organism with a  homozygous recessive genotype to determine if the dominant parent is homozygous or heterozygous

Probability & Genetics Probability is the likelihood that an event will happen. The principle of probability can be used to predict the outcomes of genetic crosses.

Punnett Squares Diagram used to predict genetic crosses.

How to use Punnett Squares Choose a letter to represent the alleles. Write the genotypes of the parents. Determine the possible gametes (reproductive cells) of each parent. Enter the possible gamete at the top and side of the Punnett square. Complete the Punnett square by writing the alleles from the gametes in the appropriate boxes. Determine the phenotypes of the offspring. Using the results of step E and F write down the genotypic and phenotypic ratios.

More Punnett Squares Note: Always put The dominant Alleles first In the squares

Punnett Squares Monohybrid & Dihybrid Crosses

Gregor Mendel Austrian Monk Famous for his work with pea plants He is known as the father of genetics

Mendel

Mendel’s Work Mendel used true-breeding plants which means if they were left to breed with themselves they would produce offspring identical to themselves. Mendel studied 7 different traits in pea plants. A trait is a specific characteristic that varies from one individual to another.

The Principle of Dominance The principle of dominance states that some alleles are dominant and others are recessive. Dominant alleles are always expressed. Recessive alleles are only expressed if both alleles are recessive.

Segregation & Independent Assortment The separation of alleles during meiosis to form gamates (sex cells). The Law of Independent Assortment states that genes for different traits can segregate independently during the formation of gamates.

Law of Segregation

Laws of Inheritance

Mendel’s Principles The inheritance of biological characteristics are determined by genes. For two or more forms of a gene, dominance and recessive forms may exist. Most sexually reproductive organisms have two sets of genes that separate during gamete formation. Alleles segregate independently.

Genetics Practice Monohybrid In summer squash, white colored fruit is dominant over yellow. If you place pollen from a yellow–fruited plant on the pistil of a hybrid white–fruited ( heterozygous ) plant, what type of seeds would you expect from the seed which come from this cross?

Problems Continued… In cats the gene for short hair is dominant over the gene for long hair (angora). A short– haired tom is mated with an Angora female. What are the expected genotypic and phenotypic ratios?

Beyond Dominant and Recessive Incomplete Dominance – One allele is not completely dominant over the other. White flower crosses with a red = pink flower. Phenotype of a heterozygous individual is a blend

Beyond Dominant and Recessive Codominance – Both alleles contribute to the phenotype. Red cow X White Cow = Roan Cow. Two capital letters are usually used in Punnett square

Beyond Dominant and Recessive Multiple Alleles – More than two alleles control the phenotype. Coat color of rabbits.

Multiple Alleles – Blood Type Blood Type is the phenotype A and B are codominant Both A and B are dominant to O I stands for immunoglobulin

Beyond Dominant and Recessive Polygenic traits – Several genes control the trait. Human skin and eye color; dark colors are usually dominant to lighter colors

Evolution of Polygenic Traits