Pima Medical Institute Online Education Classic Genetics Classic Genetics Pima Medical Institute Online Education

Plants and animals are bred to have certain characteristics How can one predict the outcome of a particular breeding? More pest-resistant More milk production Plants are strategically bred to have certain characteristics, such as being more pest-resistant or stronger than usual. Animals are also selectively bred to encourage desirable traits in offspring, such as cows that give more milk or horses that are more muscular. The question is, how can you predict the outcome of a particular breeding? Plants and animals are bred to have certain characteristics

Lab results for a genetic code Father Sperm Mother Egg Lab results for a genetic code Offspring are also inclined toward the same illnesses are their parents Chromosomes Genes are the part of an organism’s DNA that hold the instructions for building and maintaining that organism's cells. Since you possess your parents’ DNA, you will also possess their genes. In turn, your cells will be built and maintained like theirs. This explains why offspring tend to look like their parents and may be inclined towards the same illnesses as their parents. Genes hold the instructions for building and maintaining cells

mathematical probability? What is the mathematical probability? You have a different genotype from your siblings Some genes make you tall while some genes make you short What are the odds that I will grow up to be tall? Some genes make you tall, some genes make you short. Some genes give you brown hair while others give you black. These observable characteristics are called phenotypes. Your phenotype is determined by the genes in your DNA, and there are many versions of genes. These versions are referred to as alleles.   There are various combinations of alleles that can determine your phenotype—how you actually look. This combination is referred to as genotype. Genotype explains why you look different from your brother or sister even if you have the same parents. Is there a way to calculate the mathematical probability of inheriting a specific trait? Word Bank Phenotypes: Observable characteristics Alleles: Different versions of genes Genotype: Combinations of genes

University of Cambridge The Punnett Square G g Gg Yes, this technique is called the Punnett square. It was invented in the early 20th century by an English geneticist named Reginald Punnett. The Punnett square is a diagram used to predict the outcome of a particular breeding and the probability that the offspring will have a specific genotype. Let’s look at how a Punnett square is used to determine eye color. Reginald Punnett University of Cambridge Word Bank Punnett square: A diagram used to calculate the probability of specific genotypes

b b Bb B B The Punnett Square Word Bank Parent 2 Genotype Parent 1 Dominant allele Recessive allele Parent 1 B Each gene has two forms, or alleles. One variation is dominant and symbolized by a capital letter, the other variation is recessive and symbolized by a lowercase letter. In this example, the letter B represents eye color. B is dominant and b is recessive. To create a Punnett square, begin by drawing a grid that contains 9 squares.   The next step is to write the alleles for Parent 1 (Bb) on the left column of the Punnett square. Next, write the alleles from Parent 2 (Bb) in the first row of the Punnett square.   Now, fill each square with the allele from Parent 1 that lines up with the corresponding row. Word Bank Punnett square: A diagram used to calculate the probability of specific genotypes

b b Bb B B The Punnett Square Word Bank Parent 2 Genotype Parent 1 Dominant allele Recessive allele Parent 1 B Now, fill each square with the allele from Parent 2 that lines up with the corresponding column.   You should have two letters in each square. Each pair of letters represents one potential outcome for an offspring’s genotype.   Word Bank Punnett square: A diagram used to calculate the probability of specific genotypes

The Punnett Square Word Bank Possibilities 2/4 = 50% Bb 1/4 = 25% BB Heterozygous Possibilities 2/4 = 50% Bb 1/4 = 25% BB 1/4 = 25% bb Homozygous dominant Homozygous recessive This square contains BB. When both alleles are the same, it is referred to as a homozygous genotype. Because both alleles are dominant, the genotype is described as homozygous dominant. This square contains bb. Since the alleles are the same, it is also described as homozygous. Specifically, this genotype is homozygous recessive. These two squares contain Bb. Genotypes that have two different alleles are described as heterozygous. This square gives us four possibilities. Two of these four possibilities yield capital B lowercase b. This means that there is a 50% chance that an offspring will have a heterozygous genotype. One of these four possibilities is capital B capital B. This means there is a 25% chance that an offspring will have a homozygous dominant genotype. And respectively, there is a 25% chance that an offspring will have a homozygous recessive genotype. Word Bank Homozygous: Two of the same alleles Heterozygous: Two different alleles

What does the Punnett square tell us about phenotypes? B = Brown b = Blue Now that we know the possibilities for genotype, what about does the Punnett square tell us about phenotype?   For homozygous genotypes, it’s easy to tell what the phenotype will be. If capital B specifies brown, offspring with a BB genotype will have brown eyes. If lowercase b specifies blue, offspring with a bb genotype will have blue eyes. But for a heterozygous genotype, you must know which allele is dominant and which one is recessive. A dominant allele will determine the phenotype in a heterozygous genotype, and conversely, a recessive allele will only affect an offspring’s phenotype if the genotype is homozygous. In our example, the B allele is dominant. Therefore, in the heterozygous genotypes, the offsprings’ eyes will be brown. Now, if you saw an offspring with one blue eye and one brown eye, this would be referred to as incomplete dominance. Word Bank Dominant: Always determines phenotype Recessive: Only determines phenotype in a homozygous genotype Incomplete Dominance: Phenotype is a mixture

Knowledge Check: Terms and Definitions

Knowledge Check: Punnett Square

Knowledge Check: Probability

Resources: End of presentation Nchpeg.org Contexto.info Code.ca anthro.palomar.edu biology.arizona.edu