Genetics
Interest Grabber Look at your classmates. Note how they vary in the shape of the front hairline, the space between the two upper front teeth, and the way in which the ear lobes are attached. Make a list of the different forms of these traits you have observed in the class or among other people you know. Could these traits be inherited? From whom could they be inherited? How is it possible that these traits could be found in a person and his or her biological grandparents but not in the biological parents?
Inheritance What is inheritance? l The genetic characters transmitted from parent to offspring, taken collectively What are genetics? l The scientific study of heredity
Peas for Everyone! Gregor Mendel l Austrian Monk Worked with garden peas Had several different types of pea plant stock l The type from which a group of animals or plants has been derived
True-Breeding These peas were true-breeding l This means, if bred to a pea plant just like themselves, they would produce pea plants identical to themselves For example: + =
True-Breeding Peas One stock would only produce tall plants l The other would only produce short plants One stock would only produce green seeds l The other would only produce yellow seeds These true-breeding plants were the basis of Mendel s experiments.
Self Pollination vs. Cross Pollination Usually, peas that are true-breeding have reproduced via self pollination l The pollen from a plant has fertilized the egg on the same plant l The result is offspring from one parent Cross pollination occurs when the pollen from one plant, fertilizes the egg on another l The result is offspring from two parents
Cross Pollination Mendel had to select the pea plants that he would mate with each other How did he manage to do this? l He removed the male part of the flower (stamen) l He then dusted the flower with pollen from another plant l The resulting seeds were crosses between two plants
Genes and Dominance Mendel studied seven different pea plant traits l Traits-a specific characteristic, such as seed color or plant height, that varies from one individual to another He called the original pair of plants (stocks) the P for parental generation
Genes and Dominance He called the offspring the F 1 or first filial l Filial is the Latin word for son What are some examples of F 1 generations?
Examples + = + = + =
Hybrids Another name for the cross between two different plants. What did the hybrid pea plants look like? l Were they a blend of their parents traits? Would a cross between a tall plant and a short plant yield a medium height plant?
Hybrids All of the offspring had the characteristic of only one of the parents The other parent s trait seemed to have disappeared
Conclusions Mendel confirmed two conclusions: l Inheritance is determined by factors that are passed from one generation to the next Today these factors are called genes Different forms of these genes were called alleles l The principle of dominance states that some alleles are dominant and the others are recessive Mendel s experiments showed that the allele for tall plants was dominant and the allele for short plants was recessive
Dominance An organism with a dominant allele for a trait will always have that form An organism with a recessive allele for a trait will have that form only when the dominant allele is not present
Dominance For example: The allele for black hair coat is dominant (B) The allele for red hair coat is recessive (b) An animal with a gene of Bb or BB is going to be black Only an animal with the alleles bb would be red
Segregation Has the recessive gene disappeared all together? No: It is still there and will reveal itself if the proper cross is made The alleles are separated from one another during the formation of the gametes l Gametes-sex cells
Handout 11-1 l Exploring Mendel
11-2 Interest Grabber In your lab groups: l Designate a reporter l Designate a flipper Obtain a coin (quarter preferably) Flip the coin 100 times Record, in a table, how many times the coin lands heads and how many times the coin lands tails
When done, answer these questions l What is the probability of the flips landing heads up? l What is the probability of the flips landing tails up? Abuse of this activity will result in extreme book work!
Probability The likelihood that a particular event will occur For example: The likelihood of flipping a coin tails up is 1 out of 2 or ½ or 50% The principles of probability can be used to predict the outcomes of genetic crosses
Funtivities with Phone Numbers!!! Take the last four digits of your phone number 6623 Even numbers are dominant and will be represented now by a capital D Odd numbers are now recessive and will be represented by a lowercase d The number 6623 will now be represented by DDDd
Funtivities with Phone Numbers!!! DDDd needs to be split into two parents alleles DD will be the father and Dd will be the mother Make a punnett square using your alleles D D D d
Funtivities with Phone Numbers!!! Remembering that dominant genes (D) beat out recessive genes (d) show the outcomes of your cross D D D DD DD d Dd Dd
Funtivities with Phone Numbers!!! If the D allele is for dimples and the d allele is for no dimples, how many of the offspring have dimples from your phone number? Mine: l All of them will have dimples! l They all had a dominant D!
Punnett Squares A diagram used to determine the outcome of a genetic cross The letters represent alleles Capital letters represent dominant alleles Lowercase letters represent recessive alleles
Punnett Squares Organisms that have two identical alleles for a particular trait (TT or tt) are said to be homozygous Organisms that have two different alleles (Tt) are said to be heterozygous What percentage of your phone number cross were homozygous? What percentage were heterozygous? l Mine was 50% homozygous and 50% heterozygous!
Handout 11-2
11-3 Mendelian Genetics Does the segregation of one pair of alleles affect the segregation of another pair? l Does the gene that determines whether a seed is smooth or wrinkly have anything to do with the gene for seed color? To determine this, Mendel performed an experiment known as a two-factor cross.
Two-Factor Crosses F1 First Mendel crossed Yellow smooth seeds (RRYY) with green wrinkled seeds (rryy) RRYY RY RY RY ry RrYy RrYy RrYy rryy ry RrYy RrYy RrYy ry RrYy RrYy RrYy ry RrYy RrYy RrYy RY RrYy RrYy RrYy RrYy
Two-Factor Crosses F1 This resulted in an F1 cross of RrYy l 100% Heterozygous yellow, smooth seeds What would happen if he crossed the F1 s together to form an F2 cross? Try it yourself!
Two-Factor Crosses F1 RrYy RY Ry ry ry RY RRYY RRYy RrYY RrYy RrYy Ry RRYy RRyy RrYy Rryy ry RrYY RrYy rryy rryy ry RrYy Rryy rryy rryy
Results What percent are yellow and round? l 9/16 or 56% What percent are yellow and wrinkly? l 3/16 or 19% What percent are green and round? l 3/16 or 19% What percent are green and wrinkly? l 1/16 or 6% Does one segregation of one allele affect the outcome of another allele?
Independent Assortment The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes?
Summary of Mendel s Principles The inheritance of biological characteristics is determined by individual units known as genes. In organisms that reproduce sexually, genes are passed from parents to their offspring. In cases in which two or more forms of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.
Summary of Mendel s Principles In most sexually reproducing organisms, each adult has two copies of each gene-one from each parent. These genes are segregated from each other when gametes are formed. The alleles for different genes usually segregate independently of one another.
Laws or Guidelines? It would be wrong to determine Mendel s work as laws While they are important guidelines, there are important exceptions to each.
Incomplete Dominance When one allele does not dominate the other Results in a mixed offspring
Codominance Both alleles contribute to the phenotype Both alleles are expressed + =
Multiple Alleles Some genes have more than two alleles This does not mean that an individual can have more than two alleles, it only means that there are more than two possible alleles existing in a population
Polygenic Traits Traits that are controlled by two or more alleles. Fruit flies have reddish-brown eyes l This eye color is controlled by 3 different genes!
Beyond Mendel Geneticist Thomas Hunt Morgan did his own experiments on fruit flies l Why fruit flies? They produce large numbers of offspring in a short period of time making it easier to see genetic patterns faster
Handout 11-3