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Heredity and Genetics. Just think…. “My parents have brown eyes, why are mine blue?” “My brother is tall. Why am I short?” “Why does my sister have blonde hair while mine is brown?”. Science can answer some of these questions…. Heredity - the passing of characters from parents to offspring
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Just think… “My parents have brown eyes, why are mine blue?” “My brother is tall. Why am I short?” “Why does my sister have blonde hair while mine is brown?”
Science can answer some of these questions… Heredity- the passing of characters from parents to offspring Genetics- the branch of biology that focuses on heredity
Gregor Mendel Father of Genetics
During his early years at the monastery, Mendel began studying and breeding mice. The bishop was not pleased.
Why Peas? • The garden pea is a good subject for several reasons. Peas… • Have traits that are inherited by simple dominance, one trait is dominant to another, ie. Tall is dominant to short in peas • Have male and female reproductive parts enclosed on the same structure - mating can be controlled and done with the bristles of a brush • Are small, grow easily, mature quickly, and produce many offspring (results can be quickly obtained and there are plenty of subjects to count)
Mendelian Theory of Heredity(the foundation of genetics) • For each inherited character, an individual has two copies - one from mom and one from dad • There are different • versions of genes = alleles For example, the gene for pea seed color can be green or yellow. What are different alleles for eye color?
Mendelian Theory of Heredity(the foundation of genetics) 3. When two different alleles (versions) occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance. Dominant- the expressed form of the trait Ex. E Recessive- the trait that is not expressed if a dominant allele is present Ex. e
Mendelian Theory of Heredity(the foundation of genetics) • When gametes are formed (in what process?) alleles for each gene separate - gametes only carry one allele for each characteristic During fertilization, gametes unite - each gamete contributes one allele to the offspring.
Modern Terms Genotype- the genetic makeup of an organism (the set of alleles an individual has) Ex. EE, Ee, ee Phenotype- the physical appearance of an organism Ex. Purple, tall, round
Modern Terms • Homozygous- the two alleles present for a character are the same ex. EE or ee • Heterozygous- the two alleles present for a character are different ex. Ee
Labeling the Generations • P generation – parent generation • F1 Generation – first filial, offspring of the P generation • F2 generation – second filial, offspring of the F1 generation
Probability The likelihood that a specific event will occur First Law: Each trial of a chance event is independent of all other trials of the same change event. Application: What is the chance that you will roll a 1 the first time you roll a dice? What is the chance that you will roll a 1 the second time you roll a dice?
Second Law (also called Law of Muliplication): The chance of independent events occurring together is the product of the chances for each independent event occurring separately. Application: Two people have a coin. They are tossing the coins at the same time. What is the chance that both will come up heads? • What is the chance that both will come up tails?
Probability What is the probability that a couple will have four boys in a row? 1/2 1/2 1/2 1/2 ½ x ½ x ½ x ½ = 1/16
Problem: If one out of two students is female and one out of eight students is left handed and one out of 12 is red haired, what is the probability that the next person you will see will be left-handed, red-haired girl?
Third Law (also called Law of Addition): The probability of an event that can occur in two or more different ways is the sum of the separate possibilities of those ways. Application: Two people have a coin. They are tossing the coins at the same time. What is chance that one will come up heads and the other come up tails?
Now, let’s see if this works in the real world… • Each student will flip a penny 10 times and record the results. Based on probability, how many heads should there be? Tails? • Your results: • Heads_______ • Tails ________ • Class results: • Heads _______ • Tails ________ • Which results are closest to your prediction based on probability? Yours or the classes?
Each student needs a penny and a partner! • Each student with their partner each flip their penny. Record the results whether it be 2 heads, 2 tails or 1 heads and 1 tails. Do this 20 times. • What is the predicted result based on probability? • Your results: HH_____ HT _____ TT_____ • Class results: HH _____ HT _____ TT______ • Which are closer to the predicted results? Yours or the classes? Why?
a. Miguel has just received an IPOD as a gift. He has downloaded 3 country music songs,1 rhythm and blues song, 5 rap songs, and 1 song that is the theme song to his favorite movie. If the IPOD is set on playing these songs at random, what is the probability that he will hear a country music song?
b. Sherri has a pocket full of colored candy jelly beans. She has 6 pink jelly beans, 3 yellow jelly beans, 10 green jelly beans, and 1 orange jelly bean. What is the probability that Sherri will select a green jelly bean and then, without replacing it, randomly select an orange jelly bean from her pocket?
A a AA A Aa a Aa aa Monohybrid Cross:a cross that shows the possible offspring for one trait Example: Cross two heterozygote individuals: Aa x Aa A: White fur a: Brown fur Genotypic Ratio: 1:2:1 Phenotype: 3 white:1 brown
A A a a Practice! Cross a HOMOZYGOUS dominant with a HOMOZYGOUS recessive using the same trait. What is the genotypic ratio? Aa Aa 4/4 which gives 1 What is the phenotypic ratio? Aa Aa 4/4 which is 1 or 100% white fur
A A A a Practice! Cross a HOMOZYGOUS dominant with a HETEROZYGOUS using the same trait. What is the genotypic ratio? AA AA 2:2 which reduces to 1:1 What is the phenotypic ratio? Aa Aa 4/4 white fur, which reduces to 1 or 100%
Test Cross Animal breeders and horticulturists often need to know if an organism is homozygous dominant or heterozygous for a character. However, it is impossible to tell simply by looking at an organism. They can use a test cross…
Test Cross An individual whose phenotype is dominant, but whose genotype is not know, is crossed with a homozygous recessive individual. (Based on the outcome of the cross, you can tell if the individual in question is homozygous dominant (TT) or heterozygous (Tt).)
p p p p Test Cross Is this purple flowering pea plant PP or Pp? Cross the unknown with a homozygous recessive individual. P? X pp Set up a Punnett squares: P p P P Pp pp Pp Pp Pp pp Pp Pp Based on the actual outcome of the cross, determine the genotype of the unknown. (If all offspring are purple, the unknown must have been PP)
Test Cross • Consider that tallness in pea plants is dominant to dwarfism. A horticulturalist has a tall plant, however is unaware of its genotype. She has a contract to produce all tall plants. Show the test cross she will have to make in order to be sure that the tall plant she uses to make offspring is a purebreeding tall plant. What are the possibilities with a tall plant? • The tall plant could be either TT or Tt. So you cross it will a tt.
