Table of Contents
How are allele combinations represented?
Alleles are often represented by upper and lower case letters. The upper case letters represent the dominant form while the lower case letters represent the recessive form. The expression of a genotype is called the phenotype.
What are the possible combinations of alleles?
The total possible combination of alleles for those genes in humans is approximately 70,368,744,177,664. This is trillions of times more combinations than the number of people who have ever lived. This accounts for the fact that nearly everyone, except monozygotic twins, is genetically unique.
What is a chart that shows all the possible combinations for an allele from a cross?
Chap. 3 Genetics: The Science of Heredity
| A | B |
|---|---|
| Punnett square | a chart that shows all the possible combinations of alleles that can result from a genetic cross |
| phenotype | an organism’s physical appearance or visible traits |
| genotype | an organsim’s genetic makeup, or allele combination |
| homozygous | having 2 identical alleles for a trait |
What is a Punnett square used for?
A Punnett Square is a helpful tool that helps to predict the variations and probabilities that can come from cross breeding. This includes predicting crossing plants, animals, even humans with each other.
Why do genotypes have 2 letters?
The two letters in a genotype represent the pair of alleles. The uppercase letter represents the dominant allele and the lowercase letter represents recessive allele.
What are the three possible combinations of alleles?
When the gene for one trait exists as only two alleles & the alleles play according to Mendel’s Law of Dominance, there are 3 possible genotypes (combination of alleles) & 2 possible phenotypes (the dominant one or the recessive one).
When both alleles are expressed this is called?
Codominance is a relationship between two versions of a gene. Individuals receive one version of a gene, called an allele, from each parent. In codominance, however, neither allele is recessive and the phenotypes of both alleles are expressed.
When two alleles are the same they are?
If the two alleles are the same, the individual is homozygous for that gene. If the alleles are different, the individual is heterozygous. Though the term allele was originally used to describe variation among genes, it now also refers to variation among non-coding DNA sequences.
How do you calculate a Punnett square?
Count the total number of boxes in your Punnett Square. This gives you the total number of predicted offspring. Divide the (number of occurrences of the phenotype) by (the total number of offspring). Multiply the number from step 4 by 100 to get your percent.