Traits and Inheritance EQ: how do genes and chromosomes work together to determine an organism’s traits?

A great idea Mendel figured out that when his garden pea plants were crossed, for every three pea plants that showed a dominant trait, such as purple flowers, yellow seeds, green pods, tall plants, there was one plant that exhibited recessive traits, such as white flowers, green seeds, yellow pods and short plants. This is a 3:1 ratio What did this tell him about how traits are passed from parents to their offspring?

Alleles Mendel knew from his experiments that there must be two sets of instructions for each characteristic . The first-generation plants carried these instructions for both the dominant and recessive traits. Scientists call these instructions for an inherited trait genes.

Alleles Each parent gives one set of genes to their offspring. The offspring then has two forms of the same gene for each characteristic. One from each parent. The different forms of a gene are called alleles.

Alleles Alleles are a different form of a gene. They occupy specific places on a chromosome. http://web.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/index.shtml Dominant alleles are shown with a capital letter Recessive alleles are shown with a lowercase letter

Phenotypes and Genotypes Genes affect the traits of an offspring. An organism’s appearance is know as its phenotype. EX: brown hair

Phenotypes and Genotypes Genotypes are a little more complicated… Both inherited alleles together form an organism’s genotype. The genotype of an organism represents its exact genetic makeup, that is, the particular set of genes it possesses. Because the allele for purple flowers (P) is dominant, only one P allele is needed for the plant to have purple plants. It’s genotype may be either PP or Pp If a plant has white flowers, we know that it’s genotype will be pp, because the allele for white flower is recessive. The organism must have two p alleles for the recessive trait to be expressed. EX: BB or Bb for brown hair

Homozygous vs. heterozygous A gene with either two dominant or two recessive alleles EX: PP or pp Root “homo” means “same” A gene with two different alleles EX: Pp Root “hetero” means “different”. The dominant trait will be expressed.

Punnett squares A Punnett Square is used to organize all the possible combinations of offspring from their parents.

Punnett squares Each parent has two alleles for each gene. When these alleles are different, the offspring are equally likely to receive either allele. When they are the same, the offspring will definitely receive either the dominant or recessive allele being passed

Genotype Probability The mathematical chance that something will happen is called probability. Probability is most often written as a fraction or percentage. If you toss a coin, the probability of tossing tails is ½, or 50%. To find the probability of that you will toss two heads in a row, multiply the probability of tossing the first head (1/2) , by the probability of tossing the second head (1/2). The probability of tossing two heads in a row is ¼, or 25%

The same holds true when figuring out genetic probabilities!!! Genetic probability The same holds true when figuring out genetic probabilities!!!

Genotype Probability For example, to have white flowers, a pea plant must receive a p allele from each parent. Each offspring from a Pp X Pp cross has a 50% (1/2) chance of receiving either allele from either parent.

Genotype Probability The probability of inheriting two p alleles is ½ X ½ This equals ¼ or 25%

More about traits As you may have already figured out, things are usually more complicated than they first appear to be! Mendel uncovered the basic principles of how genes are passed from one generation to the next. But as scientists learned more about heredity, they began to find exceptions to Mendel’s principles

One gene, many traits Sometimes one gene influences more than one trait. An example of this phenomenon is shown by the white tiger. The while fur is determined by a single gene. However, this gene will also determine the tiger’s eye color, which is blue. The gene that controls fur color also influences eye color

Incomplete dominance Sometimes one trait is not completely dominant over another. These traits do not blend together, but each allele has its own degree of influence. This is called incomplete dominance. An example is when you cross red snapdragons with while snapdragons, you will end up with pink snapdragons

Many genes, one trait Some traits, such as the color of your skin, eyes, and hair are the result of several genes working together. That’s why many shades of a single color are possible. http://glencoe.mcgraw-hill.com/sites/007874184x/student_view0/brainpop_movies.html#

Probability EQ: How do Genes and chromosomes work together to determine an organism’s traits?

Probability Probability is the mathematical chance that an event will occur When you flip a coin, there is a 50% chance that you’ll land on tails. The way a coin lands is completely random

Probability Like flipping a coin, the chance of inheriting a certain allele from a parent is random In today’s activity, you will have a chance to experience the effect of probability on genetics as you flip coins for different traits.

The Scenario NASA has found a first generation of Crazy Creatures on Geneticus that all have the same combination of alleles, one dominant and one recessive (heterozygous) – for all of their traits. Since all parents have the same alleles, many have incorrectly assumed that generations will look exactly like their parents. You know this isn’t the case! It’s true that in sexual reproduction, you get at least one allele from your mother and one from your father.

The Scenario However, you know that the alleles you inherit are determined by two factors: The alleles that your parents have The alleles that you inherit from each parent. The alleles you inherit from each parent are determined by chance, or probability. In this investigation, you will do an activity that demonstrates how probability can help predict the appearance of Crazy Creature offspring

Procedures overview As a table, you are expected to read and follow the detailed directions on your activity sheets! Determining the genotype: Use the appropriate coins to determine the sex of your Crazy Creature and the alleles it will inherit, record the alleles and genotype and phenotypes in the appropriate places Stop and Think: complete as a group Building your creature: Using the information in your table and the materials in the kit, build your Crazy Creature (see me for box at the time) Analyzing the results: Complete questions a-e (HW if not complete)

Predicting traits EQ: How do genes and chromosomes work together to determine an organism’s traits?

Predicting traits You can predict the genotypes and phenotypes of offspring if you know the genotypes of the parents. A Punnett Square shows all of the possible combinations of alleles from two parents. Each of the four boxes represents one possible genotype that the offspring might have

The Scenario NASA is setting up an educational exhibit to teach people about Crazy Creatures and their planet, Geneticus. NASA has asked you to help them select the initial breeding pair to include in their exhibit. They want to be sure that the parents that they pick and their offspring will represent a variety of all the traits that Crazy Creatures can have.

The Scenario You know that you can predict the genotypes and phenotypes of offspring if you know their genotypes of the parents. A Punnett Square will show all the possible combinations of alleles from the parents. In this investigation, you will use Punnett Squares to help NASA select the best creatures for their new display

The Procedures As a table, you are expected to read and follow the detailed directions on your activity sheets! Using a model to make predictions: Read the info about probability as a group. See me to find out which team you will be paired with today. Bring your group’s paperwork from yesterday with you when you meet with your expanded group. Using your info from yesterday, fill in the genotype and phenotype for the mother and father (purple paper) Create Punnett Squares using the genotypes of the mother and father on the blank sheet of paper Predict the offspring’s phenotype from the info Figure out the probability of the offspring inheriting this trait Stop and Think: Complete questions a&b as a group (green paper) Checking the predictions: Using the appropriate coins, flips to determine the sex of the offspring as well as for the genotypes for each trait. Record your results in actual genotype column on the purple paper See me for your box to build your new creature Analyzing data : Answer questions a-d (HW if unfinished)