2Remember…Genes are sections of a chromosome that have coded instructions for making proteins.Alleles are different forms of a gene.
3Simple Inheritance 2 alleles 2 phenotypes One allele is dominant The other allele is recessiveThe DOMINANT allele completely masks the recessive allele
4Mendel Got LuckyIn many ways Gregor Mendel was quite lucky in discovering his 4 genetic laws. He happened to use pea plants. Things in nature aren’t always so simple.
5Not-so-Simple Inheritance 4 Main TypesCodominanceIncomplete DominanceMultiple AllelesPolygenic Traits
6Red Cow x White Cow Roan Cow Codominance“Co” means together!Codominance = two alleles are dominant together.This produces a third heterozygous phenotype where BOTH traits are expressed TOGETHEREx: Human Blood TypeABOABRed Cow x White Cow Roan CowRoan cattle have both red and white hairs mixed in together!
7red x white red & white spotted Codominancered x white red & white spotted
8copyright cmassengale Mendelian Genetics4/1/2017CodominanceTwo alleles are expressed (multiple alleles) in heterozygous individuals.Example: blood type1. type A = IAIA or IAi2. type B = IBIB or IBi3. type AB = IAIB4. type O = iicopyright cmassengale88
9copyright cmassengale Mendelian Genetics4/1/2017Codominance ProblemExample: homozygous male Type B (IBIB)x heterozygous female Type A (IAi)IBIAiIAIBIBi1/2 = IAIB1/2 = IBicopyright cmassengale99
10Another Codominance Problem Mendelian Genetics4/1/2017Another Codominance ProblemExample: male Type O (ii) x female type AB (IAIB)iIAIBIAiIBi1/2 = IAi1/2 = IBicopyright cmassengale1010
11copyright cmassengale Mendelian Genetics4/1/2017CodominanceQuestion: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents?boy - type O (ii) X girl - type AB (IAIB)copyright cmassengale1111
12copyright cmassengale Mendelian Genetics4/1/2017CodominanceAnswer:IBIAiIAIBiiParents:genotypes = IAi and IBiphenotypes = A and Bcopyright cmassengale1212
13Amel & Ultra are incompletely dominant to each other. Incomplete DominanceIncomplete Dominance = neither of the two alleles is completely dominantThis produces a third heterozygous phenotype where the traits are BLENDED.Amel & Ultra are incompletely dominant to each other.Amel x Ultra Ultramel
14red flower x white flower PINK flower Incomplete Dominancered flower x white flower PINK flower
15Multiple Alleles Any of a set of three or more alleles. Only two of alleles can be present in a diploid organism.Examples:Human Blood TypeHuman skin, hair, and eye colors
17Polygenic Traits Result of the interaction of several genes Human skin, hair, and eye colorInfluenced by more than one gene at different locations on the chromosomesHuman Blood PressureNot just 1 “blood pressure” gene with several allelesCaused by several genes that control other traits such as weight, cholesterol level, kidney function, etc…Human HeightThe combined size of all of the body parts from head to foot determines the height of an individual.
18Role of EnvironmentOur environment also plays a key role in how traits are expressed.Genes can be turned on/off due to external environmental factors.Examples:StressNutritionChemical exposureLightTemperature
19Example of Environmental Influence Human Height is heavily influenced by hormones produced in the pituitary gland and our diet during childhood and puberty.Usually, about 10% of an individual's height is due to the environment.
20Sample Questions1. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull.2. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?
21Sample Questions3. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). a) What pattern of inheritance does this illustrate? b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?
22Sample Questions1. A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver. The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross? b) What is/are the genotype(s) of the silver offspring? c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?
23Sample Questions2. The color of fruit for plant "X" is determined by two alleles. When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants?