Guided Notes: Simple Genetics

Transcription

1 Punnett Squares Guided Notes: Simple Genetics In order to determine the a person might inherit, we use a simple diagram called a o Give us of an offspring having particular traits Pieces of the Punnett Square Allele: A form of a o Humans inherit allele from each parent that determines a o Ex. Curly/straight hair, tall/short, etc. Dominant Allele: A allele shows their effect even if there is only copy of the allele (think strong!) o Dominant alleles are denoted by a capital letter (Ex. ) Recessive Allele: A allele will only show up if no dominant alleles are in place. (think weak!) o Recessive alleles are denoted by a lower case letter (Ex. ) Dominant and recessive alleles pair together to determine a! (Ex. ) Homozygous: If both letters are (both dominant (capital) or both recessive (lowercase)), the alleles are o Homo means o Ex. Let s say A represents the allele for a widow s peak, and a represents the allele for a straight hairline A person with AA would be called homozygous A person with Aa would be called homozygous Heterozygous: If both letters are (one dominant (capital) and one recessive (lowercase)), the alleles are o Hetero means o Ex. A person with Aa would be heterozygous Would they have a widow s peak or a straight hairline?

2 Genotype: The, information of an organism o Example: A person s genotype is Aa (heterozygous); they can pass on either a dominant allele or a recessive one Phenotype: The, appearance of an organism o Example: A person has a widow s peak Dominant or Recessive? Heterozygous or Homozygous Phenotype or Genotype? A AA She s homozygous recessive b Bb She has blue eyes B cc Building a Punnett Square Consider the following alleles for color of a pea plant: AA (Yellow-homozygous dominant) Aa (Yellow-heterozygous) aa (Green-homozygous recessive) Problem: Let s say you had two pea plants, both heterozygous yellow (Aa), and you wanted to know what color plants would be produced. How would you find out? 1. Setting up the square a. What we know: b. So, cross will be carried out in the Punnett Square 2. Carrying out the square a. Father s letters cross to the b. Mother s letters cross c. Notice each combination has one allele from dad and one from mom 3. Interpreting the final square a. Once the square is finished, determine the and ratios of the possible offspring i. Genotype: ii. Phenotype:

3 Tt x tt What is the probability of producing offspring that have short whiskers from a cross of two long whiskered seals, one homozygous dominant and one heterozygous? Genotype: Phenotype: Genotype: Phenotype: A Few Notes on Genetics: Some traits are controlled by pair of genes, and so present a wide range of phenotypes (ex. Skin, hair, eye color) All traits depend on both and factors o Heredity determines your traits, but the environment may play a role in how they act Guided Notes: Genetic Diseases Dominant or Recessive? If a disease is, both parents have to pass on a mutated allele to the offspring o Those who are heterozygous (Aa) are, meaning they have the mutated allele and can pass it on, but are themselves If a disease is, only one parent has to pass on the mutated allele for offspring to have it o Can a person with a dominant disease be a carrier?

4 Genetic Diseases Disease Dominant or Recessive? Characteristics Cystic Fibrosis Causes buildup in lungs and digestive system Those affected have and Common in those with ancestry Life expectancy up to years thanks to Sickle Cell Anemia Affects a person s cells The sickle or bent shape causes the cells to get stuck in Common in those with ancestry Carriers associated with resistance PKU Stands for Missing the to break down phenylalanine, an amino acid Results in deterioration People affected must keep low diet + inject enzyme Huntington s Disease Affects the of the body Affected will have decline Often does not show signs until a person reaches mid

5 A woman who is a carrier for Cystic Fibrosis marries a man who is also a carrier. What is the probability that they will have a child with Cystic Fibrosis? A woman is concerned that she may develop Huntington s Disease because her father has it. What is the probability that she has Huntington s?