3.2 probability and heredity 2
- 1. Chapter 3 Genetics: The science of heredity Miss Luzma Fabre
- 2. Introduction Toss a coin and describe the probability 2 possibilities: heads or tails Each of these events is equally likely to occur (50%)
- 3. Section 2: Probability and heredity Probability is a number that describes how likely it is that an event will occur It can be described as a fraction or percentage Example: ½ or 50%
- 4. Independence of events Suppose you toss a coin 5 times and it lands with heads up each time. What is the probability that it will land with heads up on the next toss? 1 in 2, or 50% Each event occurs independently
- 5. Probability and genetics Mendel recognized that the principles of probability can be used to predict the results of genetic crosses A Punnett square is a chart that shows all the possible combinations of alleles that can result from a genetic cross
- 6. How to make a Punnett square Male parent´s alleles Female parent´s alleles
- 7. Using a Punnett square You can use a Punnett square to calculate the probability that offspring with a certain combination of alleles will result In a genetic cross, the allele that each parent will pass on to its offspring is based on probability
- 8. What tool can be used to predict the results of a cross?
- 9. Phenotypes and genotypes An organism´s phenotype is its physical appearance, or visible traits. Ex: blue eyes An organism´s genotype is its genetic makeup, or allele combinations. Ex: bb
- 10. An organism that has 2 identical alleles for a trait is said to be homozygous. Ex: SS, ss An organism that has 2 different alleles for a trait is heterozygous (hybrid). Ex: Ss
- 11. Describe the genotypes given as: Homozygous recessive, homozygous dominant or heterozygous Dd dd DD
- 12. In humans, brown eyes (B) are dominant over blue (b)*. A brown-eyed man marries a blue- eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. Draw the Punnett square that illustrates this marriage. What is the man’s genotype? What are the genotypes of the children?
- 13. Bb bb b Bb Genotype of male parent: Bb Phenotype: brown eyes Genotype of children: Bb and bb Phenotype of children: brown and blue
- 14. What are the phenotypes of the following genotypes? In other words, what eye color will they have? BB Bb bb
- 15. Codominance For some alleles, an inheritance pattern called codominance exists In codominance, the alleles are neither dominant nor recessive. As a result, both alleles are expressed in the offspring.
- 16. Codominance