Punnett Squares: Codominance and Incomplete Dominance

Quick Review Which organelle carries the information needed for making proteins in a eukaryotic cell? ________ nucleus nucleus The nucleus has one job, and that is to store the ______. DNA 2

Quick Review Image by Richard Wheeler DNA is packaged into a very long molecule called a _____________. When you talk about chromosomes you need to realize that you are talking about ______. chromosome DNA Human Chromosomes 3

sequence nitrogen bases The instructions or __________ for making proteins are found in the ______. The information is carried in the ______________________. The sequences of DNA that helps to create and regulate proteins are known as a ______. The different versions of a gene are known as _______. blueprint DNA sequence nitrogen bases genes alleles Madeleine Price Ball

Phenotype for Eye Color The combinations of alleles in an organism make up the organism’s _____________. If a gene affects the physical appearance of an organism, we say that it has been ____________. If a gene does not affect the physical appearance of an organism, we say that it is ______________. genotype expressed unexpressed Subject A Subject B Subject C Genotype for Eye Color BB Bb bb Phenotype for Eye Color

Phenotype for Eye Color The physical appearance of an organism that results from the expression of genes is known as the organism’s ____________. phenotype Subject A Subject B Subject C Genotype for Eye Color BB Bb bb Phenotype for Eye Color Brown Eyes Blue Eyes Brown eyed photo by Erin Silversmith Blue eyed photo by J Drewes

Define the following words using a vocabulary reference sheet if available. Define homozygous: ____________________________________________________________________________________ Define heterozygous: ____________________________________________________________________________________ Homozygous gametes form when the same genes join together. (GG, gg, TT, ss, etc.) Heterozygous gametes form different genes join together. (Gg, Ss, Tt, Bb, etc.)

FF Solid gray fur Tt Long tails bb Blue eyes Ff Solid gray fur TT Long tails ff Spotted fur BB Brown eyes Bb Brown eyes

Codominant genes are BOTH expressed in the phenotype! What you have been taught so far is a very simplified version of how genes interact. It is often more complicated than just one gene being __________ over another. Sometimes, genes are considered ______________. This means that they are both __________ (made into proteins). Blood types are a perfect example of this. dominant codominant expressed Codominant genes are BOTH expressed in the phenotype!

If a person has genotype IAIA, their blood type (phenotype) will be ______ If a person has genotype IAi, their blood type (phenotype) will be ______ If a person has genotype IBIB, their blood type (phenotype) will be ______ If a person has genotype IBi, their blood type (phenotype) will be ______ If a person has genotype ii, their blood type (phenotype) will be ______ If a person has genotype IAIB, their blood type (phenotype) will be ______ A A B B O AB

red A B do NOT both expressed Red blood cell Your blood type results from a protein that is found in the membrane of your _____ blood cells. If you have gene IA, then you make protein ___. If you have gene IB, then you make protein ___. If you have gene i, then you _________ make a protein. If you have both gene IA and gene IB, then you make ______ proteins. They don’t prevent each other from being ___________ (made into proteins), so they are codominant over gene i. red A B do NOT both expressed

% A = _____ % O = _____ 100% % A = _____ % B = _____ % O = _____ IA i IA i IA IA IA i IA IB i IA IB IB IAIA IAi IAIB IBi IAIA IAIA IAIB IBi IAIA IAi IAi ii IAIB IAIB IAIB IBi % A = _____ % O = _____ 100% % A = _____ % B = _____ % O = _____ % AB = _____ 25% % A = _____ % B = _____ % AB = _____ 50% % A = _____ % B = _____ % O = _____ % AB = _____ 0% 0% 25% 0% 50% 25% 50% 0% 25% 50%

% B = _____ % O = _____ 75% % A = _____ % B = _____ % O = _____ IB i i i IA IA IA i IB i IA IB IBIB IBi IAi IAi i IA IB IAi IAi IAIA IAi IBi ii IBi IBi IAi IAi IAIB IBi % B = _____ % O = _____ 75% % A = _____ % B = _____ % O = _____ % AB = _____ 50% % A = _____ % O = _____ 100% % A = _____ % B = _____ % O = _____ % AB = _____ 50% 25% 0% 50% 25% 0% 0% 0% 25%

As we have seen, not all gene combinations are as simple as having one dominant gene and one recessive gene. Below is an example of another exception known as ___________ dominance. Based on the diagram, how would you define incomplete dominance? incomplete R R r R r → X RR rr Rr

Incomplete dominance occurs when a combination of genes produces an _____________ trait. One trait is not completely dominant, and a diluted phenotype appears that is in between the homozygous dominant and recessive phenotypes. R r R r R R R r intermediate R r r r

Examining Incomplete Dominance 1. A species of flowers exhibits incomplete dominance between the allele for red flowers and the allele for white flowers. If a plant homozygous for red flowers is crossed with a plant that is homozygous for white flowers, what percentage of offspring will have pink flowers? R R r R r R r R r R r 100% pink flowers

Examining Incomplete Dominance You get 3 different phenotypes! 2. A species of flowers exhibits incomplete dominance between the allele for red flowers and the allele for white flowers. If two heterozygous, pink plants are crossed, what percentage of each color of flower will appear in the offspring? R r R r R R R r R r r r 25% red flowers 50% pink flowers 25% white flowers You get 3 different phenotypes!

Genotype for Flower Color Phenotype for Flower Color Complete the following Punnett squares about incomplete dominance and answer the questions go with each cross. Subject A Subject B Subject C Genotype for Flower Color RR Rr rr Phenotype for Flower Color Red Pink White r r R r R r R R R r Rr Rr R r RR Rr r Rr rr R r RR RR rr rr Rr rr Rr rr Rr Rr 50% 3 50% 50%

Codominance vs. Incomplete Dominance Two different types of chickens are shown below. Assume each the chicken below is the results of a cross between a parent with black feathers and a parent with white feathers. Based on the definitions we have learned, which breed shows co-dominance between feather color and which shows incomplete dominance. Chicken with Black & White Feathers Chicken with Gray Feathers Incomplete Dominance An intermediate trait appears in the offspring. Codominance Both traits appear in the offspring.

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