Genetics

What is Genetics Genetics is the scientific study of heredity. Heredity is what makes each species unique.

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

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. (Pure) Mendel studied 7 different traits in pea plants. A trait is a specific characteristic that varies from one individual to another.

More on Mendel’s Work Hybrids are offspring from parents with different traits. It is a cross between two pure-breds. (HH x hh = Hh). Genes are the chemical factors that determine a trait. The different forms of a gene are called alleles.

The Principle of Dominance The principle of dominance states that some alleles are dominant and others are recessive. Dominant alleles are always expressed (We use capital letters to represent dominant alleles). Recessive alleles are only expressed if both alleles are recessive (We use lower case letters to represent recessive alleles).

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

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

Punnett Squares Diagram used to predict genetic crosses. Individuals with identical (same) alleles are called homozygous (HH or hh) Individuals with different alleles are called heterozygous (Hh) Phenotype – physical characteristic Genotype – genetic makeup (genes/alleles/letters)

How to use Punnett Squares Choose a letter to represent the alleles in the cross. Write the genotypes of the parents. Determine the possible gametes (reproductive cells) that the parent can produce. Enter the possible gamete at the top and side of the Punnett square.

More Punnett Squares 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.

Naked Punnett Square

Punnett Squares Monohybrid & Dihybrid Crosses

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.

Beyond Dominant and Recessive Incomplete Dominance – One allele is not completely dominant over the other. White flower crosses with a red = pink flower. Codominance – Both alleles contribute to the phenotype. Red cow X White Cow = Roan Cow. Multiple Alleles – More than two alleles control the phenotype. Coat color of rabbits. Polygenic traits – Several genes control the trait. Skin color in humans.

Examples

Karyotypes

Karyotypes Are an organized profile (micrograph) of a person’s chromosomes arranged by size and shape and banding pattern. This arrangement allows scientists to quickly identify chromosomal abnormalities/disorders. Ex: Down’s Syndrome (Trisomy 21).

Sex-Linked Traits Traits/Genes located on the sex chromosomes (XX or XY). Ex: Color blindness and Hemophilia.