FUNDAMENTALS OF GENETICS

This is a Ms. Brown educational production

Introduction



The Audience:

 This project is intended for the 9 th school biology student. and/or 10 th grade high 

The Objective:

By the end of this tutorial you will be able to:  Determine the genotype and phenotype of monohybrid crosses using a punnett square  Explain how offspring inherit traits from their parents

New Vocabulary

           Genetics Heredity Trait Gene Allele Dominant Recessive Genotype Phenotype Probability Gametes          Parental (P) Generation 1 st 2 nd Filial (F 1 ) Generations Filial (F 2 ) Generations Cross Pollinate Self Fertilization Monohybrid Dihybrid Heterozygous Homozygous

Genetic Terminology

 Genetics-The scientific study of heredity  Heredity- Passing of traits from parents to offspring  Trait- any characteristic that can be passed on from parent to offspring (ex. Pea plant color, shape, length, etc.)

Genetic Terminology

 Gene- Segment of DNA for trait expression  Allele- Each of the alternative forms of a gene (ex. dominant or recessive)

Genetic Terminology

 Dominant- Masks the other allele, represented by Capital Letter (ex. Y)  Recessive- The masked allele, represented by lowercase letter (ex. y)  Genotype- Genetic make up of the organism (ex. YY, Yy, or yy)  Phenotype- Appearance of an organism due to genotype (ex. Yellow or green seed color)

Genetic Terminology

 Monohybrid Cross- The crossing of one characteristic (ex. YY x yy)  Dihybrid Cross- The crossing of two characteristics (ex. YYRR x yyrr)  Heterozygous genotype- Two different alleles (ex. Yy)  Homozygous genotype- Two alleles that are the same (ex. YY or yy)  Probability-The likelihood of an event to occur

Genetic Terminology

 P Generation- The original parental cross 

1 st

Filial Generation- The offspring of the parent generation 

2 nd

Filial Generation- The offspring of the F 1 generation  Cross Pollination- reproduction occurs between two flowers (sexual)  Self-Fertilization- reproduction occurs in the same flower (asexual)

Genetics & Probability

Genetics & Probability

 The likelihood that a particular event will occur is called Probability.  The principles of probability can be used to predict the outcomes of genetic crosses.

Genetics & Probability

 Probabilities predict the average outcome of a large number of events.



Probability cannot predict the precise outcome of an individual event.

 In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.

POP Quiz!

1. Probability can be used to predict A.

B.

C.

D.

average outcome of many events.

precise outcome of any event.

how many offspring a cross will produce.

which organisms will mate with each other.

That is Incorrect!

 Please go back and choose the correct answer.

 Think About This: If I say it will “probably” rain, does that guarantee rain? Probability cannot predict the precise outcome of an individual event.

That’s Correct!

 GOOD JOB!

 That’s right, probability can only give you an estimated answer.

Pop Quiz

2. Compared to 4 flips of a coin, 400 flips of the coin is A.

B.

more likely to produce about 50% heads and 50% tails.

less likely to produce about 50% heads and 50% tails.

C.

D.

guaranteed to produce exactly 50% heads and 50% tails.

equally likely to produce about 50% heads and 50% tails.

That is Incorrect!

 Please go back and choose the correct answer.

 In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.

That’s Correct!

 GOOD JOB!

 Predictions based on probability are accurate only if a large number of events are involved.

Punnett Squares

Punnett Squares

 The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett Square.

 Punnett Squares can be used to predict and compare the genetic variations that will result from a cross

Punnett Squares

 Named for Reginald Punnett (British geneticist)  Used to help solve genetics problems  Visual representation of all probable results of a genetic cross

POP Quiz!

3. The Punnett Square allows you to predict A.

B.

C.

D.

only the phenotypes of the offspring from a cross.

only the genotypes of the offspring from a cross.

both the genotypes and the phenotypes from a cross.

neither the genotypes nor the phenotypes from a cross.

That is incorrect!

 Please go back and choose the correct answer.

 Hint: A Punnett Square is a visual representation of all probable results of a genetic cross.

That’s Correct!

 GOOD JOB!

 Geneticists use probability to predict the phenotypes and genotypes that MAY result from a genetic cross

Dominant & Recessive

 A capital letter represents the Dominant allele for tall.

 A lowercase letter represents the recessive allele for short.

 In this example, T = tall t = short

Homozygous vs. Heterozygous

 Organisms that have two identical alleles for a particular trait are said to be homozygous.  Organisms that have two different alleles for the same trait are heterozygous.

 Homozygous organisms are true-breeding or purebred for a particular trait.  Heterozygous organisms are hybrid for a particular trait.

Genotypes & Phenotypes

 All of the tall plants have the same phenotype, or physical characteristics.  The tall plants do not have the same genotype, or genetic makeup.

 One third of the tall plants are TT, while two thirds of the tall plants are Tt

Genotypes & Phenotypes

 The plants have different genotypes (TT and Tt), but they have the same phenotype (tall).

Genotypic & Phenotypic Ratios

     One fourth (1/4) of the F tallness (TT).

2 plants have two alleles for 2/4 or 1/2 have one allele for tall (T), and one for short (t). One fourth (1/4) of the F 2 have two alleles for short (tt). Genotypic Ratio is 1:2:1 Phenotypic Ratio is 3:1

Genotypes & Phenotypes in Flowers 

Genotype of alleles: Y y = yellow seed = green seed



All genes occur in pairs, so 2 alleles characteristic affect a



Possible combinations are:



Genotypes YY



Phenotypes YELLOW Y y YELLOW yy GREEN

Possible Combinations

Genotype vs. Phenotype?

4. The physical appearance of the organism is considered the…?



Genotype



Phenotype

That is incorrect!

 Please go back and choose the correct answer.

 Hint: PHysical appearance not GENetic make-up.

That’s Correct!

 The PHysical appearance is the PHenotype!

 GOOD JOB!!

Punnett Square Procedure

1.

2.

3.

4.

5.

6.

Determine the genotypes of the parents Write down the cross (mating) Draw the Punnett Square Split the letters of the genotype for each parent & put them outside the square (gametes) Determine the possible genotypes of the offspring by filling in the Punnett Square Summarize results (genotypes, phenotypes & ratios)

Let’s Try One!!

 Tall stem length is dominant in garden pea plants. A heterozygous tall stem length garden pea plant’s eggs are pollinated by a heterozygous tall stem length pea plant.

 You must go through all the steps in the correct order…

Step 1: Determine Genotype

 Designate letters which will represent the genes/traits. Capital letters represent dominant traits, and lowercase letters represent recessive traits.  T = tall  t = short

Step 2: Write Down the Cross

 Write down the genotypes (genes) of each parent.

 These are often given to you or are possible to determine.  Tt x Tt

Step 3: Draw Punnett Square

 Draw a Punnett square - 4 small squares in the shape of a window.

Tt x Tt

Step 4: Determine Gametes

 Gametes produced by each parent are shown along the top and left side of the grid/chart.

 List the genes that each parent can contribute.

 Females eggs across the top  Males sperm along the left side  Tt = T or t

Step 5: Fill in Punnett Square

 Fill in each box of the Punnett Square by transferring the letter above and in front of each box into each appropriate box.  Offspring possibilities abound within the grid/chart  As a general rule, the capital letter goes first and a lowercase letter follows.

Steps 4 & 5

Step 6: Give Results

 List the possible genotypes and phenotypes of the offspring for this cross.  The letters inside the boxes indicate probable genotypes (genetic makeup) of offspring resulting from the cross of these particular parents.  There are 4 boxes, and the genotypic & phenotypic results can be written either as fractions or percents.

Step 6: Give Results

 Genotypes- TT, Tt, or tt  Phenotypes- Tall or short  Genotypic Ratio- 1:2:1  Phenotypic Ratio- 3:1

Quick Review

POP Quiz!

5. Gametes are also known as A. Genes.

B. Sex Cells.

C. Alleles.

D. Hybrids.

That is Incorrect!

 Please go back and choose the correct answer.

 Hint: The process of meiosis produces these.

That’s Correct!

 GOOD JOB!!

 The scientific term for sex cells is Gametes.

POP Quiz!

6. Two F 1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall? A.

B.

100% 50% C.

D.

0% 25%

That is incorrect!

 Please go back and choose the correct answer.

 Hint: Organisms that have two identical alleles for a particular trait are said to be homozygous.

That’s Correct!

 GOOD JOB!

 When you cross two recessive parents the only possible outcome you can have is that recessive trait.

POP Quiz!

Tall stem length is dominant in garden pea plants. A homozygous tall stem length garden pea plant’s eggs are pollinated by a homozygous short stem length pea plant.

7. What is the genotype of the female plant?

A. TT B. Tt C. tt D. tT

That is Incorrect!

 Please go back and choose the correct answer.

 Hint: A females eggs get pollinated by a male.

That’s Correct!

 GOOD JOB!!

 Genotype is the genetic make-up of an organism which is represented by letters.

POP Quiz!

8. What step comes after determining gametes?

A.

Write down the cross B.

C.

D.

Draw the Punnett Square Give the results Fill in the Punnett Square

That is Incorrect!

 Please go back and choose the correct answer.

 Hint: As a general rule, the capital letter goes first and a lowercase letter follows.

That’s Correct!

 GOOD JOB!

 After you line the gametes outside of the Punnett Square you must fill in the possible offspring.

Congratulations!!

 You have just completed the Fundamentals of Genetics Tutorial successfully!

 By now you should know what probability is, how it relates to genetics, and how to use a Punnett Square to predict possible offspring variations.  If you think this was fun just wait until we are looking at more than one trait at a time! Dihybrids, Trihybrids, Multiple Alleles, Oh My!!