CHAPTER 9 Fundamentals of Genetics I Gregor Mendel

CHAPTER 9: Fundamentals of Genetics: -

I. Gregor Mendel (1822 -1884) A. History • Austrian Monk • Taught high school, worked in the garden • 1851 -Entered University of Vienna to study science, math & statistics. • • Mendel formulated 2 fundamental laws of heredity in the early 1860's.

The “Father of Modern Genetics” • Mendel’s experiments established the basic ideas & _____that _______the pattern of inheritance from generation to generation. Photo from: http: //www. savoirs. essonne. fr/dossiers/le-patrimoine/histoire-des-sciences/johann-gregor-mendel-la-foi-en-la-science /

Mendel • Did his work from 1856 to 1865, with out a microscope, without ever having heard of a “chromosome”. • His results were published in one paper in 1866. • With the lack of communication at those times, his work went unnoticed until 1900 scientists repeated the experiments and then found that Mendel had already developed the ideas some 40 years previous! http: //www. exploringnature. org/db/detail. php? db. ID=22&det. ID=54 http: //kentsimmons. uwinnipeg. ca/cm 1504/mendel. htm

Vocabulary: Heredity • the transmission of characteristics from parents to offspring. ________ • An inheritable feature (flower color, height) ________ • A genetically determined variant of a characteristic. (white or red flower)

B. Work with Peas: Mendel used statistics to study 7 Characteristics, each occurred in 2 Contrasting Traits: 1. Flower Color – 2. Flower Position along Stem – axial or terminal 3. Seed or Pea Color 4. Seed Texture or Shape – round (smooth) or wrinkled 5. Pod Color – green or yellow 6. Pod Appearance or Shape – inflated or constricted 7. Plant Height -

Seven pea plant characteristics studied:

http www. exploringnature. org/db/detail. php? db. ID=22&det. ID=54 : //

• _____: when pollen grains (from anther- male) are transferred to stigma(female). • _____- occurs when pollen is transferred from flower anthers to stigma of either same flower or flowers on the ______plant. • ______- occurs between flowers of 2 plants. Pea plants usually Reproduce through self-pollination.

2. Pollination Methods • Mendel first collected seeds that were true breeding (always produce offspring with that trait) for many generations, (collected 14 traits) • Then he interrupted ____& performed _______ • Did this by removing all the Anthers from flowers on a plant, • Then manually pollinating the Stigma of this plant with pollen from another plant.

Cross section of a flower

3. Three Steps of Mendel’s Experiments 1. Produce a true-breeding or - By self-pollination for several generations “P” is for parent saw: 2 pure traits- 1 for each parent 2. Produce an - By cross-pollination of parents pure for different traits. Example- yellow pods w/ green “F 1” is for first filial generation saw: only 1 trait (dominant - the recessive 1 disappeared) 3. Produce an - By allowing F 1 generation to self-pollinate “F 2” is for second filial generation saw reappearance of recessive trait in 3: 1 ratio

http: //www. anselm. edu/homepage/jpitocch/genbio/geneticsnot. html

4. Mendel’s results & conclusions Experiments were repeated carefully for hundreds of crosses • See table 9 -1 page 176 in textbook • Results of F 1 generation- showed all offspring of crossed true-breeding plants were of one trait. – Example: purple flowers vs white parents – Offspring all purple • Results of F 2 generation- showed a 3: 1 ratio – Example: 705 purple and 224 white flowers

Results of Mendel’s Experiments: __ – 2 different pure traits __- all offspring show same trait. F 2 Generation -3 out of 4 offspring (3: 1 ratio) Show the trait hidden in F 1

a. Dominant & Recessive • When strains of plants pure for a trait were crossed, one trait always failed to appear in the F 1 generation. The absent trait reappeared in ¼ of the F 2 generation. • Mendel concluded that each trait was inherited by means of a separate factor, so a pair of factors controlled each trait. • _____- Term for a factor (we now call these alleles) that masks the presence of another factor. • _____ - Term for a factor (allele) that is masked by the presence of another allele.

Law of Segregation Basic Principle of genetic inheritance stating that: • for any particular trait, the pair of factors of each parent separate (during the formation of sex cells) and only one gene from each parent passes on to an offspring.

Law of Independent Assortment Basic principle of genetic inheritance stating that: • different pairs of factors are passed to offspring independently • so that new combinations of genes, present in neither parent, are possible. – Example: • In other words, the distribution of one pair of alleles does not influence the distribution of another pair-the genes controlling different traits are inherited independently of one another.

Karyotype • A picture (photomicrograph) of chromosomes. • Notice that – 22 homologous pairs of autosomes – Plus 2 sex chromosomes. (Is this person male or female? ) Karyotype Copied from: http: //homepages. uel. ac. uk/V. K. Sieber/human. htm

Mendel succeeded due to a combination of good work & luck • • He kept detailed records of crosses for several years • Collected numerical data- it was the ratios of the crosses that clinched the arguments for his theories • The chosen characters all showed dominant/recessive traits- this made his analysis much easier • He was lucky- some of his characters were on the same chromosome, but were so far apart that crossing-over made them sort nearly independently

C. Modern Support of Mendel • Much of his work was not understood until well into the 1900 s. • Modern genetics verified what he discovered. • Biologist Walter Sutton read Mendel’s papers and proposed the chromosome theory, linked meiosis with Mendel’s work. • Molecular Genetics- the study of the structure & function of chromosomes & genes.

Factors now called “alleles” & now represented by letters. • • • Example 1: Brown eyes dominant: Blue recessive – “B” for brown & “b” for blue • Example 2: Red flower dominant-White recessive – “R” for red and “r” for white – REMEMBER- USE ONLY 1 LETTER PAIR: Bb or Rr for example - don’t mix!!! Never: Rw!!!

II. Genetic Crosses • How do we predict the likely outcome of a genetic cross? • ___ WHAT IS ON THE GENES – the genetic make- up of an organism for a trait – the alleles that the organism inherits from its parents – Not always observable. • _____ WHAT YOU SEE – An organism’s appearance or other observable characteristic – the detectable expression that results from the organism’s genotype

Genotype & Phenotype: http: //kentsimmons. uwinnipeg. ca/cm 1504/mendel. htm

Homozygous & Heterozygous • - (2 OF THE SAME) -When both alleles of a pair are alike. – Example: RR (Both alleles red color) rr (both white color) • -(2 DIFFERENT) – When the alleles in the pair are different. – Examples: Rr (one Red & one white) – Or Tt (one tall & 1 short) ( REMEMBER not to use Ts or Rw !!!!)

Note: there are 2 different genotypes that produce the dominant Phenotype; but only 1 genotype produces the recessive phenotype http: //cikgurozaini. blogspot. com/2010_06_01_archive. html

Probability: • The likelihood that something will happen. • Predicted results more likely for more trials. • Example: flipping a coin. Q 1 - What is the chance that it will be head or tails? Q 2 - Discuss what happens if you flip it 10 times? 100? Q 3 - If you flip 2 coins- Does that result have anything to do with the other- why or why not? • REVIEW: Relate this back to the law of independent assortment.

Practice Problem: • Tongue Rolling is Dominant (R) You can roll your tongue but your spouse cannot. Your first child also cannot roll his tongue. Q 1 What is your genotype for this trait? Q 2 What is the probability of having a tongue roller child next time?

Predicting Monohybrid Cross Results • ____-A cross in which only 1 trait is tracked. • ____– A graphic or diagram used to predict the results of a genetic cross. Draw a Punnett square - 4 small squares in the shape of a window. Write the possible gene(s) of one parent across the top and the gene(s) of the other parent along the side of the Punnett square.

Example • Fill in each box of the Punnett square by transferring the letter above and in front of each box into each appropriate box. • As a general rule, the capital letter goes first and a lowercase letter follows. • The letters inside the boxes indicate probable _______. Predict the phenotype of these offspring:

Homozygous X Homozygous • Black- BB homozygous dominant • White- bb homozygous recessive • -

Homozygous recessive bb X Heterozygous Bb Bb (Heterozygous genotype, Black phenotype) Bb (homozygous recessive genotype white phenotype) Offspring: Genotype 50% Bb, 50% bb Phenotype 50% Black 50% White

Heterozygous X Heterozygous • Can cross 2 heterozygous parents (Bb) x (Bb) such as 2 black rabbits. B b • Offspring: BB Bb • Genotypic ratio: B – 1 BB: 2 Bb: 1 bb • Phenotypic ratio– 3 black: 1 white b Bb bb

Remember that: • AN ORGANISM WITH A RECESSIVE TRAIT ALWAYS HAS A HOMOZYGOUS RECESSIVE GENOTYPE (two lowercase letters). • BUT -a DOMINANT TRAIT MAY HAVE EITHER BB OR Bb GENOTYPE!

Testcross • Since you don’t know if a black rabbit might have a genotype of BB or Bb, you perform a test cross. • A test cross is an individual of unknown genotype crossed with a homozygous recessive (bb). • Try this on your white boards to see what happens with BB, then Bb crosses.

You always know that bb is recessive… Is the black phenotype BB or Bb? Use a test cross to find out.

"Key Points" to remember about a TEST CROSS. 1. the organism with the dominant trait is always crossed with an organism with the recessive trait 2. if ANY offspring show the recessive trait, the unknown genotype is heterozygous 3. if ALL the offspring have the dominant trait, the unknown genotype is homozygous dominant 4. large numbers of offspring are needed for reliable results List reasons why would you Never use a test cross on humans. http: //www. hobart. k 12. in. us/jkousen/Biology/testcrss. htm

Incomplete Dominance • Mendel was lucky to pick traits with complete dominance. (one trait masks the other, shows dominate OR recessive) • Incomplete Dominance occurs when a heterozygous trait is intermediate between phenotypes of the parents. • The dominant allele is unable to express itself fully. • Example: Japanese four o’clock flowers RR is Red Rr is pink Rr is white

Codominance • When ___for a gene are ___ in heterozygous offspring. • Neither allele is dominant • Alleles do not blend. • If a red & a white allele are present in a flower- BOTH will be expressed! Human blood types M, N & MN also show codominance. MN, M, N is different than the better known ABO blood type which actually a type of trait expressed by _______ http: //blog. savcds. org/swanson/2010/01/08/codominance-and-incomplete-dominance-upcoming-assessments/

Dihybrid Crosses • A cross in which 2 characters are tracked. • More complicated ry ry ry RY Rr. Y y RY y Rr. Y y • On the white boards, practice rryy x RRYY RY y. Rr. Y Homozygous vs Homozygous Rr. Yy Rr. Y y Rr Yy Rr. Y y y ry Rr. Yy

Heterozygous vs Heterozygous Rr. Yy x Rr. Yy