Bell Ringer Which features do you have that match your mother? Your father? Which of the following features do you have? Widow s Peak? Ability to roll your tongue? Attached earlobes?
Simple Genetics Exploring How Traits are Passed On
Punnett Squares In order to determine the traits that a person might inherit, we use a simple diagram called a Punnett Square! Punnett Squares give us the probability of an offspring having particular traits
Pieces of the Puzzle Before completing a square, you must know the components Allele-An allele is a variant form of a gene Humans inherit one allele from each parent that determines a trait For example, alleles might determine if you have curly or straight hair, are tall or short, etc. Dominant-A dominant allele show their effect even if there is only one copy of the allele (think of them as being strong!) Dominate alleles are denoted by a capital letter (ex. A) Recessive- A recessive allele will only show up if no dominant alleles are in place (think of them as being weak!) Recessive alleles are denoted by a lowercase letter (ex. a) Dominant and Recessive alleles pair together to determine a trait (ex. AA, Aa, aa)
Homozygous vs. Heterozygous So alleles pair together (AA, aa, Aa) Homozygous-if both letters are identical (both dominant (capital) or both recessive (lowercase)), the alleles are homozygous Homo means same 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 dominant A person with aa would be called homozygous recessive Heterozygous-if both letters are different (one dominant (capital) and one recessive (lowercase)), the alleles are heterozygous Hetero means different A person with Aa would be heterozygous Would they have a widow s peak or a straight hairline?
Phenotype and Genotype All of these allele combinations tell us the phenotype and genotype of a person Genotype-The genetic, inheritable information of an organism Example: A person s genotype is Aa (heterozygous); they can pass on either a dominant allele or a recessive one to their children. Phenotype-The outward, physical appearance of an organism Example: A person has a widow s peak
Let s Practice Dominant or Recessive? A b B Heterozygous or Homozygous? AA Bb cc Phenotype or Genotype? She is homozygous recessive (rr) She has blue eyes
Building a Punnett Square Consider the following alleles for pea plant color: AA (Yellow-homozygous dominant) Aa (Yellow-heterozygous) aa (Green-homozygous recessive) 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? Set up and Punnett Square
Building a Punnett Square What we know: Both parent plants are Aa So, cross Aa x Aa will be carried out in the Punnett Square below: Mother Father *Note: It doesn t matter where you set up the mother/father, the results will be the same!
Building a Punnett Square So, how do you carry out a Punnett Square? Father s letters cross to the right Mother s alleles cross down, filling in the squares to complete the allele Mother Father AA Aa Aa aa *Notice each potential combination has one allele from mom and one from dad
Interpreting the Final Square Once the square is finished, always determine the genotype and phenotype ratios of the possible offspring Genotype: 1:2:1-1 AA, 2 Aa, and 1aa Phenotype: 3:1-3 Yellow, 1 Green Note: These ratios are equally probable for each offspring, meaning each offspring has the same chance of inheriting the traits!!
Practice Complete the Cross: Tt x tt Genotype: Phenotype:
Practice W= long whiskers (dominant) w=short whiskers (recessive) 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:
A Few Notes on Genetics Some traits are controlled by more than one pair of genes, and so present a wide range of phenotypes (ex. Skin, hair, eye color) All traits depend on both genetic and environmental factors Heredity determines your traits, but the environment may play a role in how they act
Bell Ringer W= long whiskers (dominant) w=short whiskers (recessive) What is the probability of producing offspring that have short whiskers from a cross of two seals, one homozygous recessive and one heterozygous? Draw the Punnett Square Determine the Genotype ratios Determine the Phenotype ratios Answer the above question
Bell Ringer W= long whiskers (dominant) w=short whiskers (recessive) What is the probability of producing offspring that have short whiskers from a cross of two seals, one homozygous dominant and one heterozygous? Draw the Punnett Square Determine the Genotype ratios Determine the Phenotype ratios Answer the above question
Genetic Diseases How Diseases are Carried Through Generations
Dominant and Recessive If a disease is recessive, both parents have to pass on a mutated allele to the offspring Those who are heterozygous (Aa) are carriers, meaning they have the mutated allele and can pass it on, but are healthy themselves If a disease is dominant, only one parent has to pass on the mutated allele for offspring to have it Can a person with a dominant disease be a carrier?
Let s take a look at some specific genetic diseases
Cystic Fibrosis (cf)-recessive This disease causes a mucus buildup in the lungs and digestive system Those affected have difficulty breathing and poor growth Common in those with European Ancestry Live expectancy up to 35 years thanks to gene therapy
Sickle Cell Anemia-Recessive This disease affects a person s red blood cells A mutation causes the cells to be long and bent ( sickle shaped) The odd shape causes the cells to get stuck in blood vessels Cuts off blood flow and circulation Common in those with African ancestry Carriers are associated with malaria resistance-we ll discuss why later!
PKU-Recessive PKU- Phenylketonuria A condition in which the body is missing the enzyme that breaks down phenylalanine, an amino acid This means it builds up in the body, which results in mental deterioration Memory loss/identity loss! People affected have to keep a low protein diet and have the enzyme injected regularly This must be done for life!
Genetic Disease Punnett Squares 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? Note: The mother does not have Huntington s Disease.
Huntington s-dominant This disease affects the muscles of the body Those affected will slowly have muscle function decline Painful, like a muscle cramp that won t go away Unfortunately, it often does not show signs until the person reaches mid 30s-can take up to 20 years to kill! Shows up after the person has already had children, meaning that they have already passed the allele Affects all people!
Genetic Disease Punnett Squares 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?
Bellringer-4/23/15 Complete the Genetic Diseases Review Worksheet on your desk. We will work on this for 30 minutes.
Bellringer-4/24/15 We have a quiz today. You have 10 minutes to study for your quiz. Be sure to review: Definitions How to complete Punnett Squares Genetic Disease patterns and symptoms
Bellringer-4/27/15 Complete the Punnett Square review sheet on your desk!
Complex Genetics Codominance, Incomplete Dominance, Sex-Linked Traits, and Blood Typing
Incomplete Dominance Sometimes, one allele is not completely dominant over another allele In this case, the offspring are blends of both parents! The heterozygote has a unique phenotype because one gene does not dominate the other Example: Red Flower (RR) + White Flower (WW)= Pink Flowers (RW)
Incomplete Dominance During incomplete dominance, organisms who are heterozygous for a trait have the opportunity to pass either gene to the offspring Therefore, a cross between two heterozygous organisms have the following results: 1 RR: 2 Rr: 1 rr 1 Red: 2 Pink: 1 White
Incomplete Dominance Example A red carnation is crossed with a white carnation and the resulting offspring are all pink (indicating incomplete dominance). What would be the result of a cross between a pink and a white carnation?
Codominance Sometimes, both alleles are equally dominant Therefore, both alleles will be expressed in phenotype In this case, the offspring display the traits of both parents! Example: White Cow (WW) + Brown Cow (BB)= White and Brown Cow (BW)
Case Study: Sickle Cell Anemia Although we discussed Sickle-Cell Anemia s recessive inheritance pattern, the disease does display a certain codominance Those homozygous affected (aa) have misshapen cells Those homozygous unaffected (AA) have normal cells Those heterozygous (Aa) are unaffected carriers, but can have some misshapen cells mixed in This unique feature means heterozygous individuals are resistant to severe malaria!
Codominance Example A bird with white and blue feathers mates with another white and blue bird (BW). What are the phenotypic ratios of the offspring?
Bellringer-4/28/15 Complete the bellringer sheet on your desk!
Blood-Typing Human blood types include a codominance pattern Humans can have type A, B, AB, or O blood The alleles involved are two codominant alleles (I A and I B ), and one recessive allele (i) Genotype Blood Type I A I A or I A i I B I B or I B i I A I B ii A B AB O
Blood Type Practice Problem The father is type A homozygous, and the mother is type O. What are the possible blood types of their children?
Is Parentage Possible? Ralph has type B blood and his wife Rachel has type A blood. They are very shocked to hear that their baby has type O blood, and think that a switch might have been made at the hospital. Can this baby be theirs? Explain.
Bellringer-4/29/15 Write the possible genotypes for the following blood types: Type A: or Type B: or Type AB: Type O: Solve: There is a mixup between babies at the hospital. The baby has type O blood. On set of parents have the genotypes I A I A and I A i. The other set of parents are a heterozygous Type A mother and a heterozygous Type B father. Make the crosses of both sets of parents. Which set does the baby belong to?
Sex-Linked Traits Genes located on the sex chromosomes are called sex-linked genes Usually found on the X Chromosome Because of this, males are much more likely to express a trait than females, because males only have one X chromosome!
Sex-Linked Traits Let s take a look at the possible alleles in a recessive sexlinked disease: Female: X A X A, X A X a, X a X a Notice that the female must inherit 2 recessive copies to display the trait. It is also possible for females to be carriers of sex-linked traits. Male: X A Y, X a Y Notice the male does not have a second X to help mask the trait. This means that if he inherits the recessive copy, he will display the trait! Because of this, males are much more likely to inherit a sex-linked trait!!!
Common Sex-Linked Traits Hemophilia-A bleeding disorder that slows the blood clotting process Color-Blindness-The inability to see color, or perceive color differences Because of its X-linked inheritance, both of these conditions are more common in men
Sex Linked Problems Cross a woman carrier for hemophilia to a hemophiliac man. What percentage of the females could inherit the trait? Males?
Pedigrees Inheritance Patterns Through Generations
What is a Pedigree? A pedigree is the recorded ancestry of a family Pedigrees allow us to see the genotypes and inheritance patterns through the generations of a family
What Does a Pedigree Tell Us? Pedigrees can give us insight into how traits are passed through families. You can tell a lot through a pedigree. For example: The phenotypes and genotypes of individuals The inheritance pattern. If more males are affected, it is likely sex linked If there are no carriers and one of the parents must have it, the disorder is dominant If carrier parents produce some affected children, the disease must be recessive
Pedigree Example Problems What type of inheritance pattern is shown below? What would be the genotype of individual I-1?
Pedigree Example Problems What type of inheritance pattern is shown below? What would the genotypes be of individuals II-1 and III-5?
Bellringer-4/30/15