Genetics

DNA (Deoxyribonucleic Acid) DNA: stores and passes on genetic information from one generation to the next James Watson and Francis crick discovered the structure of DNA

Chromosomes (made up of) ↓ DNA (contains) ↓ Genes

Structure of DNA DNA looks like a twisted ladder, or spiral staircase called a double helix The “steps” are formed by pairs of substances called nitrogen bases Nitrogen bases contain the element nitrogen

Structure of DNA The four types of nitrogen bases 1. Adenine (A) 2. Thymine (T) 3. Cytosine (C) 4. Guanine (G) In the DNA ladder, A always pairs with T C always pairs with G

Structure of DNA The genetic code is actually the sequence of nitrogen bases on the DNA molecule Any change in the order of bases can result in a new gene that determines a completely different trait.

DNA Replication Cells divide into two identical cells in the process called mitosis Before the cell can divide, the DNA must be replicated so that each cell gets the same amount of DNA as the parent cell.

Replication= the process in which DNA molecules form exact duplicates. The Steps of Replication: 1.The DNA ladder separates, along the bases 2.Free nitrogen bases that are floating in the cytoplasm begin to pair up with the bases on each half of the DNA. 3.Two new DNA molecules form

GENETICS

Genetics = The study of how traits are inherited through interactions of alleles Heredity = the passing of traits from parents to offspring Traits = characteristic of an organism controlled by genes

Question: What are some examples of traits?

Purebred = an organism that always produces offspring with the same form of the trait as the parent Hybrid = an organism that has two different alleles for a trait

GREGOR MENDEL’S PEA EXPERIMENT

Mendel’s Results of Experiment 1.Factors that control each trait exist in pairs. One parent contributes one factor, while the other parent contributes the other factor. 2.One factor can hide or masked by the other factor Examples:

Dominant trait = a trait that always shows up in the organism when the allele is present. Recessive Trait = a trait that is masked or hidden, whenever the dominant allele is present. (A recessive allele will only show up if the organism does not have the dominant allele.)

Gene = a piece of hereditary information on a chromosome Example Alleles = different forms of a trait that a gene may have Example

USING SYMBOLS IN GENETICS

A dominant allele is represented by a capital letter Example: Tall plants = T A recessive allele is represented by a lowercase letter Example: Short plants = t

Homozygous Dominant = when a plant inherits two dominant alleles = TT Homozygous Recessive = when a plant inherits two recessive alleles = tt Heterozygous = when a plant inherits one dominant allele and one recessive allele = Tt

Genotype = an organism’s genetic make-up or allele combinations Example: Genotype for plant height = Tt Phenotype = an organism’s physical appearance, or visible traits Example: Phenotype for Tt = tall plant

PUNNETT SQUARES

Probability = the likelihood that a particular event will happen Gregor Mendel was the first scientists to realize that the principles of probability can be used to predict the results of genetic crosses

Punnett Square = a chart that shows the possible combinations of genotypes that can result from a genetic cross Scientists use a punnett square to figure out all possible genotypes that can result when crossing to organisms.

Types of Crosses Monohybrid Cross compares only one trait Dihybrid cross compares two traits B= Brown Feathers b= Yellow Feathers Results =

Ratio of Genotypes: How often would expect to see brown chicks? Convert this fraction to a percentage:

Lemmings: Crossing Aa x Aa

Pedigree Charts Pedigree charts trace a genetic trait in a family tree. It shows the presence or absence of a particular trait in each generation.

GENETICS ODDS AND ENDS

2 Important Laws of Genetics Organisms inherit genes in pairs, one gene from each parent 1.Meiosis= gene pairs separate during the sex cell formation (egg or sperm cell) 2.Independent Assortment = each gene pair for a trait is inherited independently of the gene pairs for all other traits

Incomplete Dominance Incomplete dominance = neither gene pairs mask the other Each gene is co-dominant with the other

Mutations (a change in a gene or chromosome) can be… Harmful For example: sickle cell anemia Beneficial For example: Naval oranges Single mutation occurred in 1820 Seedless and bigger than regular oranges

Sex-Linked Traits XX = femaleXY = male X chromosomes: carry genes for traits other than sex Y chromosomes: carry little to no traits, other than those for maleness Therefore any gene- even a recessive gene- carried on the X chromosome will produce a trait in a male who inherits the gene. This is because there is one gene to express it Question: Are sex-linked traits carried on the X or Y chromosome?

Examples of Sex-Linked Traits Colorblindness- cannot see the difference between certain colors, such as red and green Loss of function of cone system