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Transcript
Mendel and Genetics, Continued… Bell Question: Explain the difference between a phenotype and a genotype. Answer: The phenotype is what a trait looks like. The genotype is the specific alleles that code for the phenotype. Mendel and Genetics, Continued… Last time we learned … … that Gregor Mendel is the Father of Genetics. … he looked at pea plants and studied various, discrete traits. … that there were ratios that seemed to consistently describe what happened in the plants. … how different alleles affect the phenotype. … the difference between genotypes and phenotypes. … how to use Punnett Squares to predict the ratios of phenotypes. We’re not done! Onward and upward! Mendel and Genetics, Continued… • We can continue to further describe genotypes. Dominant and recessive are helpful, but they help us more with phenotypes. • GG and gg are homozygous. The alleles are the SAME. GG is for green, while gg is for yellow. • For this, we say that GG is homozygous dominant. • How could we describe gg? homozygous recessive Mendel and Genetics, Continued… Word Definition having two of the same Homozygous alleles for a gene Picture GG gg Mendel and Genetics, Continued… • What about Gg? Its phenotype is for green peas. • It has one allele for green peas and one allele for yellow peas. • We call this genotype heterozygous. • Heterozygous is one of each allele. We KNOW that one of the alleles is dominant, so the plant would grow green peas. Mendel and Genetics, Continued… Word Definition having two different Heterozygous alleles of a gene Picture Gg Mendel and Genetics, Continued… • This is a German family tree from the 1500s. • We can study the tree and learn about the relationships between members. • We can also create a genetic tree to learn about the phenotypes and genotypes of families. Mendel and Genetics, Continued… Looks a little different, doesn’t it? • This special tree is called a pedigree. • In a pedigree, we look at specific phenotypes which can lead to figuring out an individual’s genotype. Mendel and Genetics, Continued… • The squares are males. • The circles are females. • The red individuals are affected (have a specific phenotype). The blue individuals are not. • Let’s take a closer look. Mendel and Genetics, Continued… Each row is a new generation first generation second generation third generation horizontal lines mean marriage vertical lines mean offspring Mendel and Genetics, Continued… your grandfather If someone has the Ooga Booga disease, then he or she is considered affected (red). If you are in the third generation, who has Ooga Booga your grandfather or your grandmother? Mendel and Genetics, Continued… Do you remember that when Mendel started his experiments, he began with mice but soon switched to pea plants? It was a great decision since pea plants reproduce quickly, have distinct traits, and the phenotypes are easily recognized. Mendel and His Pea Plants Not all phenotypes are expressed so easily or clearly. • Sometimes, the phenotypes are a mixture. • Sometimes, more than one trait is expressed. • Sometimes, it takes more than 2 alleles to express a trait. With Mendel, if the dominant allele was in the genotype, the dominant trait was the phenotype. Not so with these… Mendel and Genetics, Continued… Some phenotypes are a blend of alleles. Camellia flowers are like this: White flower r Red flower r R • If you cross a red flower camellia with a white flower camellia, you get… PINK flowers! R • This is incomplete dominance. Mendel and Genetics, Continued… Word Definition offspring’s phenotype is Incomplete a BLEND of dominance the parents’ Picture + Mendel and Genetics, Continued… Codominance can also be expressed in offspring. Codominance is when the phenotypes of BOTH parents are seen in the offspring. When the red bull mates with the white cow, the offspring have BOTH red and white hair. Mendel and Genetics, Continued… Word Definition the phenotypes of BOTH Codominance parents are seen in the offspring Picture Mendel and Genetics, Continued… Sometimes there are more than two alleles. Blood types are like this. • The four blood types are A, B, O, and AB. • The three alleles to code for blood types are IA, IB, and i. • The i allele is actually missing the markers that IA and IB have. • IA and IB are both dominant over i. The i allele is recessive. • IA and IB are codominant. What does that mean if a person is IAIB? The person will show the phenotypes of BOTH alleles. Mendel and Genetics, Continued… Can you figure out the phenotypes for these genotypes? Remember, IA and IB are codominant, and both these alleles are dominant to i. Genotype IAIA or IAi IBIB or IBi ii IAIB Phenotype Type A blood Type B blood Type O blood Type AB blood Mendel and Genetics, Continued… • Mendel thought that only one gene determines each trait. We now know that isn’t the case. • Certain characteristics like height, eye color, and skin color are determined by more than one gene. • Polygenic inheritance occurs when more than one gene determines the phenotype of a trait. Mendel and Genetics, Continued… Word Definition Polygenic inheritance when multiple genes determine a trait Picture example: height Mendel and Genetics, Continued… Genes are not the only thing that impact you. Your environment also affects your phenotype. Just because you may come from a long line of healthy hearts, doesn’t mean that you shouldn’t eat healthy foods and exercise. Your environment is an influence, too! Mendel and Genetics, Continued… Exit question: When an offspring has a BLEND of its parents’ phenotypes, that is _______________ dominance.