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 (E) • Environmental considerations (C)

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

Genetics Lab – Part 1 • Complete “Part 1 - Probability and the Effect of Sample Size” in your Genetics Lab

Genetics Lab – Part 2 Step 1: Determine face shape – Square Face (rr) Round Face (RR or Rr)

LEQ 1 summary: • PRODUCT RULE: To determine the probability of two events occurringsimultaneously(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. • Using a large sample size reduces the effect of random chance on the results.

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

Launch • How Mendel’s Pea Plants Helped Us Understand Genetics

The passing of genes from one generation to the next is called heredity. • People have always noticed that children share traits with their parents. Nobody was able to predict which traits would be passed down to the next generation until… • In 1866, a monk named Gregor Mendelbegan experimenting on hereditablepatterns in pea plants. • Mendel varied his approach from his predecessors by counting every single plant and recording its result (quantitative analysis).

Why Peas? 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. • Easier to control the variables in the experiment. • Pea plants grow very quickly and produce many offspring when they reproduce. • Allows for creating large sample sizes when using quantitative analysis to look for patterns.

7 contrasting traits observed by Mendel

Controlled Mating…

Mendel Studied Large Numbers of Pea Plants Round vs. Wrinkled: 7,324 plants Yellow vs. Green: 8,023 plants Round vs. Wrinkled: 1,181 plants Green vs. Yellow: 580 plants Purple vs. White: 929 plants Axial vs. Terminal: 858 plants Tall vs. Short: 1,064 plants

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

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.

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

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?

Review from previous Units: • Chromosomes are made of DNA wrapped around proteins • Homologous chromosomes = maternal & paternal chromosome • Gene: A distinct sequence of nucleotides forming part of a chromosome, the order of which determines the order of amino acids in a protein.

Seed shape Flower color Seed color Flower position Pod shape Stem length Pod color

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 andrecessiveversions). • When gametes form, the two alleles separate so that each gamete receives only one copy (meiotic division). • These hypotheses have since been proven and modern vocabulary added (in parenthesis).

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).

Who are we?

continued… • The set of alleles that an organism has is known as its genotype(FF, Ff, or ff). • The result (physicalmanifestation) 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).

Mendel’s ideas have been condensed into two laws of heredity. • Thelaw of segregation states that alleles will separate during gamete formation. • Thelaw 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.

Watch the video - the law of segregation

Concepts to Know… • Law of segregation • Law of independent assortment • Homozygous vs. Heterozygous • Dominant vs. Recessive • Genotype vs. Phenotype • Probability • Sum Rule • Product Rule • Quantitative analysis • Allele • Purebred • P generation • F1 generation • F2 generation

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

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)

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

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 EXPECTEDoutcomes for each genotype,NOTthe actual number and type of offspring that WILLbe born. • Answers must be written in the proper form: genotypes orphenotypes 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 3.3: How do the phenotypes of polygenic traits differ from those affected by only one gene?

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

Genetics Lab – Eye Color & Hair Color * Due to linkage, the presence of Red Hair will trigger the appearance of freckles AND the lightening of the skin by two shades. Use colored pencils

Genetics Lab – Skin Tone Sienna Tawny Terra Cotta Golden Beige Tan Bronze Beige 1 6 15 20 15 6 1 Make the lips beige in all cases

Essential questions 5.1-5.2: 1. How does sex linkage affect the heredity of genes located on the X chromosome? 2. What trends on pedigrees help us to determine the pattern of inheritance of genetic disorders?

Heredity and Genetic Analysis