Presentation on theme: "Probability and Heredity"— Presentation transcript:
1Probability and Heredity Key ConceptsWhat is probability and how does it helpexplain the results of genetic crosses?What is meant by genotype and phenotype?What is codominance?
2Key Terms Probability Punnett square Phenotype Genotype Homozygous Heterozygouscodominance
3Principles of Probability Probability – a number that describes how likely it is that an event will occurMathematics of probability – In a coin toss there are 2 possible outcomes. The coin can land heads up or tails up. Each result has an equal chance of occurring – 1 out of 2.Probability can be expressed as a ratio, fraction orpercent – 1:2, ½, or 50%
4Percentage Percentage – a number compared to 100 If 3 out of 5 coins land with heads up. The percentage is calculated as follows:3 out of 5 = 3/53/5 x 100% = 60%Practice:Suppose 3 out of 12 coins landed with tails up. How can you express this as a percentage?
6Independence of Events The results of one coin toss do not affect the results of subsequent coin tossesEach event occurs independentlyEx. If you toss a coin 5 times and it lands heads up each time. What is the probability that it will land heads up on the next toss?
7Independence of Events The probability is still 1 out of 2 or 50%
8Probability and Genetics Mendel was the first to recognize that the principles of probability could be used to predict the results of genetic crossesWhen he crossed the two plants that were hybrids for stem height, ¾ had tall stems and ¼ had short stemsThe probability of such a cross producing tall stems was 3 in 4. The probability of producing short stems was 1 in 4
9Punnett SquaresA chart that shows all the possible combinations of alleles that can result from a genetic cross
10To make a Punnett square 1. draw a box and divide it into 4 boxes2. Write male parent’s alleles along the top and female parent’s alleles along the sideR rRr
11Punnett Square3. Copy the female parent’s alleles into the boxes to their right R r R R r 4. Copy the male parent’s alleles into the boxes beneath them R r RRRrrRRRrRrrr
12Using a Punnett SquareThe Punnett square show all the possible allele combinations in the offspringIn a genetic cross theallele that a parentpasses on to anoffspring is based onprobability
13Predicting Probabilities Punnett squares can be used to predict probabilities.If a purebred pink flamingo is crossed with a purebred blue flamingo. There is a 100% probability that the offspring will be pink
14Phenotypes and Genotypes Phenotype – an organism’s physical appearance, or visible traits (what you see)Genotype – genetic makeup, or allele combinationThe genotypes Tt and TT have the same phenotype – tallThe genotype tt has the phenotype short
15Phenotypes and Genotypes Homozygous- an organism that has two identical alleles for a traitEx. TT or ttHeterozygous – an organism that has two different alleles for a trait. Also called hybridEx.Tt
16CodominanceNot all traits have alleles that are dominant or recessive.Codominance – both alleles are expressed in the offspring
17Examples of codominance ABO blood typesFur color in mammalsSpotted flowers