Heredity and Genetic Analysis

Heredity and Genetic Analysis When you look at the seeds below you see the results of gametogenesis and fertilization. They represent a fraction of this plants potential progeny. In this chapter we will learn how Gregor Mendel experimented with pea plants to develop one of the key principles of Biology.

Unit 8: Key learnings • The heredity of genes follows mathematical laws and can be predicted using Punnett square analysis. • Contributions from both parents contribute equally to the probability of inheriting any given trait.

Unit 8: Essential question How can the probability of a given trait's inheritance be predicted using Punnett square analysis?

4 Launch activity: • Find individuals in the classroom who demonstrate the following characteristics. • Complete the reading and class demonstration utilizing PTC testing paper _____ _____ _____ _____ _____ _____

Unit 8: Concepts • Probability (C) • Mendel's work (I) • Monohybrid crosses (E) • Dihybrid crosses (C) • Special patterns of inheritance (I) • Environmental considerations (C)

Essential question 1.1: How do sample size, the product rule and the sum rule affect the probabilities of calculated events? LAB TIME!

LEQ 1 summary: • Using a large sample size reduces the effect of random chance on the results. • PRODUCT RULE: To determine the probability of two events occurring simultaneously(this AND that), multiply their individual results. • SUM RULE: To determine the probability of two events occurring interchangeably(this OR that), add their individual results.

Essential question 2.1: How did Mendel prove that each parent contributes one copy of each gene to their offspring?

I. The passing of genes from one generation to the next is called heredity. • In 1866, a monk named Gregor Mendel began experimenting on hereditable patterns in pea plants. • Mendel followed the work of a British farmer who noticed some strange patterns in the reproduction of peas. • Mendel varied his approach from his predecessors by counting every single plant and noting its result (quantitative analysis).

II. Peas have several useful features that make their study very effective. • Contrasting traits. • Tall versus short plants. • Round peas versus wrinkled peas. • Male and female parts can be easily separated to control matings. • New generations of peas are easy to produce and yield lots of easily interpreted results. • Each mating produces hundreds of offspring. • Many physical characteristics are available for study.

Manual transferof pollen

Mendel’s Experimental design Parental generation (P) Purebred for contrasting traits F1 Generation – All Purple F2 Generation – 3:1 – Purple : White Click the flower to watch the video –Mendelian Inheritance: The Big Picture

III. Mendel began with monohybridcrosses. (one trait at a time) • All of the plants he used were purebred. • When self pollination occurs, only one trait appears in the offspring. (example: Offspring always have purple flowers) • These purebred plants were used for the Parental generation (P). • Mendel cross pollinated two parental plants that had contrasting traits (white flowers with purple flowers) and produced an F1 generation.

III. Continued… • Each of Mendel’s F1 plants showed only one form of the trait (the dominant trait). • He allowed each F1 plant to self pollinate and produce an F2 generation. • Each of Mendel’s F2 generations showed a 3:1 ratio of dominant to recessive traits (recessive is the trait that hides in the F1).

7 traits observed by Mendel

Trait Studied Dominant Form Recessive Form F2 Dominant-to- Recessive Ratio SEED SHAPE 5,474 round 1,850 wrinkled 2.96:1 SEED COLOR 6,022 yellow 2,001 green 3.01:1 2.95:1 POD SHAPE 882 inflated 299 wrinkled 428 green 152 yellow 2.82:1 POD COLOR FLOWER COLOR 705 purple 224 white 3.15:1 FLOWER POSITION 651 long stem 207 at tip 3.14:1 STEM LENGTH 787 tall 277 dwarf 2.84:1

Question: What is a purebred plant? • When self pollination occurs, the results are 100% predictable. • Example: Self pollinated white flowered plants yield only white flowered offspring.

Question: What aspect of Mendel’s experiment allowed him to discover the pattern? (Hint: think probability lab.) • He used massive repetition to minimize the effect of random chance (a principle of probability). • He accurately counted and analyzed his numerical data to discover the trend (quantitative).

Essential question 2.2: How do modern scientists explain the patterns of inheritance that Mendel observed?

IV. Mendel’s work became a theory on inheritance. • Before Mendel, people thought that offspring were just a blend of their parents characteristics. • Mendel made four hypothesis about inheritance: • For each inherited trait, an individual has two copies of the gene - (homologous pair). • There are alternative versions of each gene (alleles). • When two different versions are expressed together, one will dominate the other and prevent it from being expressed (dominant and recessive versions). • When gametes form, the two alleles separate so that each gamete receives only one copy (meiotic division). • These hypothesis have since been proven and modern vocabulary added (in parenthesis).

V. Mendel’s findings have been put in modern terms. • Each trait is given a letter to represent both of its different versions (‘F’ and ‘f’ for the freckle gene). (Typically the capital letter corresponds with the first letter of the dominant description) • If an individual has two of the same letter, they are said to be homozygous(FF or ff). • If an individual has two different letters, they are said to be heterozygous(Ff).

V. continued… • The set of alleles that an organism has is known as its genotype (FF, Ff, or ff). • The result (physical manifestation) of that genotype is called the phenotype(Freckles or no freckles). • The dominant phenotype may be coded for by 2 genotypes (FF and Ff). • The recessive phenotype can only be reached by one genotype (ff).

VI. Mendel’s ideas have been condensed into two laws of heredity. • The law of segregation states that alleles will separate during gamete formation. • The law of independent assortment states that the alleles for different traits will segregate(separate) without influencing each other. (Show video from folder) • Example: The alleles for pea height, will segregate without affecting the alleles for pea color. A plant is just as likely to be tall with green peas as it is tall with yellow peas.

Click to watch the video - the law of segregation

Essential question 3.1: What information can be learned from a Punnett square analysis of a parental cross?

Example: If tallness is the dominant trait, how would we show the cross for a purebred tall pea plant with a purebred short pea plant? Mendel’s P cross (P x P) Click to watch video Mendelian Inheritance Punnett square: Beginning – 1:16

I. A Punnettsquare is a diagram that predicts the outcome of a genetic cross. • There are 3 types that we’ll consider: • Monohybrid: one characteristic(4 blocks) • Dihybrid: two characteristics(16 blocks) • Trihybrid: three characteristics (64 blocks)

I. Continued… • There are a few simple rules when using a Punnett square: • The cross must be written above the square (HH x Hh). • All possible parental gametes must be predicted (along the left and top of the Punnett square). • The results are EXPECTED outcomes for each genotype, NOT the actual number and type of offspring that WILL be born. • Answers must be written in the proper form: genotypesor phenotypes as requested.

Mendel’s F1 cross (F1 x F1) F2 generation

F1 X F1 example 2 Note that while neither parent exhibited the albino phenotype they both carried a masked gene for albinism that they transmitted to a portion of their offspring.

Standard Mendelian Cross #1:If purple flower color is dominant, what phenotypes are expected if a purebred purple flowered plant is crossed with a purebred white flowered plant. WW x ww 100% Purple or 4/4 Purple

Standard Mendelian Cross #2:If purple flower color is dominant, what genotypes are expected if a heterozygote is crossed with another heterozygote. Ww x Ww 1 WW: 2 Ww: 1 ww or ¼ WW: 2/4 Ww: ¼ ww or 1 homozygous dominant: 2 heterozygous: 1 homozygous recessive

Sample quiz question:What genotypes and phenotypes are possible in the F1 and F2 when a homozygous dominant yellow plant is crossed with a green one? YY x yy F1 = 100% Yy, 100% yellow F2 = 1 YY: 2 Yy: 1 yy, 3 yellow: 1 green

Essential question 3.2: How can the unknown genotypes of organisms be determined using a test cross?

II. It is possible to determine the genotype of a dominant phenotype by performing a test cross with that individual. • A dominant phenotype may be eitherXX or Xx. • When this unknown genotype is crossed with a homozygous recessive individual (xx), the results will reflect the presence or absence of a recessive allele. • If the unknown individual produces any recessive phenotype offspring, it must havebeen a heterozygote (Xx). • If the unknown individual produces all dominant phenotype offspring, it is probably homozygous dominant (XX).

7.7If a normally pigmented alligator crossed with a white alligator produces some normally pigmented offspring and some white offspring, what can you conclude regarding this normally pigmented alligator? Since the white coloration is a recessive trait, offspring would have to receive a recessive white allele from both parents. Therefore, the normally pigmented alligator in question must be a heterozygote, possessing one allele for normal pigmentation and one allele for white pigmentation.

Question: How would you show the test cross (show both possibilities)if a yellow pea plant was test crossed with a green one. Click to watch video – Mendelian Inheritance: Punnett square 1:16 – 2:43

Essential question 3.3: How do the phenotypes of polygenic traits differ from those affected by only one gene?

III. Most traits are not controlled by simple dominant-recessive single gene alleles. • Polygenic traits are influenced by many genotypes affecting the same phenotype. • The phenotypes of these traits demonstrate continuous variation. • Examples: height, weight, skin color, intelligence.

Continuous variation in skin color

Essential question 4.1: Why does the number of predicted possibilities increase when conducting a dihybrid cross?

I. Dihybridcrosses involve two pairs of contrasting traits. • First consider how the four alleles from each parent can combine to form different gamete combinations. • XxYy can produce gametes with XY, Xy, xY, or xy • Set up a Punnett square with spaces for 16 offspring. • Be sure that each gamete combination has only one allele from each trait (2 total - one of each). • Be sure that each offspring predicted has two copies of each allele for both traits (4 total- two of each). • A standard Mendelian cross of parents holding contrasting homozygous genotypes will result in a 9:3:3:1 ratio of phenotypes in the F2 generation.

Dihybridexample #1

Example #2: List the gamete combinations possible for each of the genotypes listed below: AB, AB, aB and aB AaBB aB, aB, aB, and aB aaBB AB, Ab, aB, and ab AaBb

Example #3 Concept IV - Summarizing - page 11 in your guided study: In horses, black color dominates chestnut color. The trotting gait dominates the pacing gait. A cross is made between a horse homozygous for black color and pacing gait, and a horse homozygous for chestnut color and the trotting gait. List the probable phenotypes of offspring in the F1 and F2 generations.

Example #3: answer F1: 100% black color and trotting gait F2: 9 black/trotting:3 black/pacing: 3 chestnut/ trotting:1 chestnut/pacing

Example 4:Concept IV – Reviewing #3 – Guided study page 12. 0% In certain breeds of dogs, black color is dominant and red color is recessive. Solid color is dominant and white spotting is recessive. A homozygous black and white spotted male is crossed with a red and white spotted female. What percent of the offspring will be solid black puppies? All offspring will be Bbcc Black and white spotted pups.

Heredity and Genetic Analysis