Heredity and Genetics

A Punnett Square is a tool to predict the probability that an offspring will express a certain trait.

Homozygous is an organism that has the SAME two alleles. EXAMPLE: $RR$ or $rr$.

Heterozygous is an organism that has different alleles. EXAMPLE: $Rr$.

This is a Punnett Square for two heterozygous round pea plants, $Rr \times Rr$.

This cross would predict that:

• 25% $RR$ = Homozygous Dominant Round

• 50% $Rr$ = Heterozygous Round

• 25% $rr$ = Homozygous Recessive

Try the following Punnett Squares

1. Brown eyes are dominant over blue eyes. If two hybrid brown-eyed people have children, what are the chances they will have a blue-eyed child?

2. In pea plants, purple is the dominant flower color over white. A pea plant with purple flowers is crossed with a white one. Both are taken from a homozygous plants. What genotype and phenotype percentages will there be?

3. In garden peas, round seed coats ($R$) are dominant over wrinkled seed coats ($r$). What will the results be of a cross between a homozygous dominant and a purebred recessive?

Natural Selection

The theory of natural selection describes how species change over time and adapt to their environment based on environmental pressures that select for specific genetics.

Jean Baptiste de Lamarck

The first scientist in the early 1800s to propose a model of how life evolves. He thought an individual organism can acquire a new trait during its lifetime and then pass that trait on to its offspring. This theory was eventually disproved.

Charles Darwin

Charles Darwin observed organisms in many places around the world, including the Galapagos Islands. He found that organisms with traits that were best suited to their environment were most likely to survive to reproduce and pass their traits on to their offspring. He called this process natural selection.

Steps of Natural Selection

Examples of how species will adapt in their environments.

Genetic Mutation and Drug Resistance

Genetic mutations can create variations. When drugs are present, bacteria with mutations that confer resistance are more likely to survive and reproduce, leading to populations of drug-resistant bacteria.

Theory of Evolution

Many of the species of fungi, plants, animals and bacteria we know on Earth today existed in a very different form millions of years ago. The change and development of a species over the course of many generations is called the theory of evolution.

Theory: A widely accepted statement based on scientific evidence that helps explain a group of facts.

Evolution: Change over time. In Biology we are talking about how life has changed over time.

Evidence of the Theory of Evolution

1. Fossil Record: history of life as documented by fossils, the remains or imprints of organisms from earlier geological periods preserved in sedimentary rock.

   

2. Genetic Evidence: Every organism on earth has a form of genetic information. We can get an idea of how closely related two species are by comparing how similar their DNA is to each other.

3. Radiometric Dating: Measures the rate of decay of a type of radioactive matter. This is used to date fossils and rocks.

   

4. Homologous Structures = Skeletal parts or organs that have the same structure, but have a different job. Demonstrates how organisms that look completely different can still share a common ancestor by reusing the same body plan for a different role.

   

5. Embryological Evidence = Similarities in development. Shows how different species develop in similar ways.

   

6. Gradualism vs Punctuated Equilibrium =

   Punctuated equilibrium describes a process of evolution that suggests very short, rapid periods of change followed by long periods of stability.

   Gradualism describes a process of evolution that suggests that changes occur slowly and constantly over time.