5-9-18 Understanding Inheritance

Do Now: Take out your homework Do Now: Take out your homework. Read the provided text (both sides) and answer the following questions in your notebook. What symbols are used to identify dominant alleles? Recessive alleles? Uppercase letters identify dominant alleles; lowercase letters indicate recessive alleles. How do alleles determine the expression of traits? If at least one of the two alleles is dominant, then the dominant trait will be expressed. If both alleles are recessive, the recessive trait will be expressed. Assume black fur color is dominant over brown fur color in an organism. What fur color will an organism with a heterozygous genotype have? Explain. The fur would be black, because black is the dominant allele and brown is recessive.

HW Review: Key Concept Builder – What determines trait expression HW Review: Key Concept Builder – What determines trait expression? (Fill-in-the-blank) Genes, chromosomes Genes, alleles Phenotype Genotype Alleles, genotype, homozygous Alleles, genotype, heterozygous Heterozygous, dominant Recessive, homozygous

HW Review: Key Concept Builder – What determines trait expression HW Review: Key Concept Builder – What determines trait expression? (Phenotypes) Shaggy Green Long Pointed Straight Blue Big Ozmox alleles: Hair—shaggy (S); short-haired (s) Nose—orange (O); green (o) Tail—long (L); stubby (l) Teeth—pointed (P); rounded (p) Claws—curved (C); straight (c) Eyes—red (R); blue (r) Ears—big (B); small (b) Glork’s genotypes: Ss, oo, LL, Pp, cc, rr, BB

EQ: How can inheritance be modeled?

Modeling Inheritance Imagine flipping a coin and guessing heads or tails. Because a coin has two sides, there are only two possible outcomes – heads or tails. You have a 50% chance of heads and a 50% chance of tails. The chance of getting an outcome can be represented by a ratio. The ratio of heads to tail is 50:50 or 1:1.

Modeling Inheritance Plant & animal breeders use a method for predicting how often traits will appear in offspring that does not require performing the crosses thousands of times (like Mendel). Two tools – a Punnett square and a pedigree – can be used to predict and identify traits among genetically related individuals. If the genotypes of the parents are known, then the different genotypes and phenotypes of the offspring can be predicted.

Modeling Inheritance Punnett square: a model used to show the probability of all possible genotypes and phenotypes of offspring. Cuadro de Punnett: modelo que se utiliza para demostrar la probabilidad de que todos los genotipos y fenotipos posibles de cria.

Analyzing a Punnett Square Ex: cross between two pea plants that are heterozygous for pea seed color – Yy and Yy. Yellow is the dominant allele – Y Green is the recessive allele – y The offspring can have one of three genotypes – YY, Yy, or yy. The ratio of genotypes is written as 1:2:1. Because YY and Yy represent the same phenotype – yellow – the offspring can have one of only two phenotypes – yellow or green. The ratio of phenotypes is written 3:1. Therefore, the probability that a cross between two heterozygous pea plants will produce yellow seeds is 75% The probability that it will produce green seeds is 25%

Using Ratios to Predict Given a 3:1 ratio, you can expect that an offspring from heterozygous parents has a 3:1 chance of having yellow seeds. But you cannot expect that a group of four seeds will have 3 yellow and 1 green seed. This is because one offspring does not affect the phenotype of another offspring. However, if you counted large numbers of offspring from a particular cross, the overall ratio would be close to the ratio predicted by a Punnett square.

Skill Practice: Punnett Squares Purpose: To model the possible genotypes and phenotypes of offspring. In science, models are not just physical representations like plastic models. Instead, scientists use models to explain how something in nature works. In genetics, models are used to help predict the chances that a trait will appear in an offspring. Follow the directions on your handout to complete the assignment. Work with your shoulder partner.

Skill Practice: Review T T 1. 2. Tt 3. 1:0 (curly wings:straight wings) 4. All offspring will have curly wings. None of the offspring will have straight wings. 5. No; the results of the Punnett square will be the same, no matter where the parent genotypes are located. 6. The phenotypic ratios of the offspring will be 3:1 (curly wings:straight wings). t Tt T t T t TT Tt tt

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