After Completing This Work Package, You Will Be Able To

After Completing This Work Package, You Will Be Able To

Mendelian Genetics

Around the mid 1800’s, an Australian monk experimented and worked out the fundamental laws that govern the inheritance of traits. Although Gregor Mendel had no concern of the gene or chromosome, his meticulous data collection and analytical skills led him to make conclusions that are supported by modern day discoveries. He is often referred to as the father of modern day genetic theory.

After completing this work package, you will be able to:

-state the three laws that Mendel developed

-Use Punnett squares to illustrate Mendel’s laws.

-Use the following terms as they apply to genetic theory

Define:

Dominant genePhenotypeMonohybrid cross

Recessive geneGenotypeDihybrid cross

HomozygousAlleleF1 generation

HeterozygousHybrid

Log on to Lubey’s Biology Help Pages. Click on Lubey’s Brain. Go to the Genetics Topic and click on “Mendel’s Genetic Laws”.

Please read through the text screens – THOUROUGHLY and complete the following as indicated.

  1. Important Vocabulary (need to know and be able to use)

On a sheet of loose leaf, write down and define the following terms:

GenotypeHomozygousHeterozygousPhenotype

Allele

  1. Vocabulary Review Quiz

Check your understanding of the important vocabulary by answering the quiz that follows. You can check your answers AFTER you finish the quiz. You must be able to use and understand this terminology.

Vocabulary Review Quiz

  1. Which of the following is a possible abbreviation for a genotype?
  2. BC
  3. Pp
  4. Ty
  5. fg
  1. What is the best way to determine the phenotype of the feathers on a bird?
  2. Analyze the bird’s DNA (genes)
  3. Look at the bird’s feathers
  4. Look at the bird’s beak
  5. Examine the bird’s droppings
  1. Which of the following pairs is not correct?
  2. kk = hybrid
  3. hybrid = heterozygous
  4. heterozygous = Hh
  5. homozygous = RR
  1. The genes present in an organism represent the organism’s ______.
  2. Genotype
  3. Phenotype
  4. Physical traits
  1. Which choice represents a possible pair of alleles?
  2. k & t
  3. K & T
  4. K & k
  5. K & t
  1. How many alleles for one trait are normally found in the genotype of an organism?
  2. 1
  3. 2
  4. 3
  5. 4
  1. Which statement is not true?
  2. Genotype determines phenotype
  3. Phenotype determines genotype
  4. A phenotype is the physical appearance of a trait in an organism
  5. Alleles are different forms of the same gene
  1. Mendel’s Laws

Write outMendel’s 1st Law. Read how Mendel came to this conclusion.

  1. Name the two alleles that control height in pea plants.
  2. Which of these two alleles is dominant? Recessive?
  3. Which two symbols are used to designate these alleles?
  4. Name other dominant alleles in pea plants
  5. List the possible phenotypes for height in pea plants.
  6. List the possible genotypes for height in pea plants. *Use genotype symbols and genotype vocabulary

Mendel’s Laws can be illustrated using PUNNETT SQUARES. Punnett squares are often used to solve genetic problems, so you must learn how to use them. Copy down the example that illustrates Mendel’s 1st Law. A few jot notes on the side explaining details may be helpful.

Write outMendel’s 2nd Law. Read how Mendel came to this conclusion.

Copy down the Punnett Square that illustrates Mendel’s 2nd Law.

List the genotypic probabilities (%) and the phenotypic probabilities for the F2 generation

This cross is often called a monohybrid cross. The MONO means ONE trait is being traced and the HYBRID means both parents are heterozygous for the trait.

Write outMendel’s 3rd Law. Read how Mendel came to this conclusion.

a)What does it mean when Mendel stated that different traits were inherited independently of one another? Use the example of pea plants.

b)What is meant by a dihybrid cross?

c)Write the genotypes of two parent pea plants that are hybrid for the two traits of seed shape and pod colour.

d)What are the possible gametes these two parents can produce? Write them out.

Hint: Check for the number of letters – there should only be two because gametes should have half the number of chromosomes as the starting cell.

Check which letters are used – there should be two different letters because you are dealing with two different traits.

Check for all the possible combinations of the two letters.

Copy out the Punnett Square that illustrates Mendel’s 3rd Law. This is a dihybrid cross.

* Dihybrid crosses always have the same results.

Of the 16 possible genotypes in the dihybrid cross you copied, how many would produce:

-A homozygous recessive plant (wrinkled see/yellow pod)?

-A plant with round seeds/green pods?

-A homozygous round seeds/green pod plant?

What is the phenotype ratio of the trait for seed texture only? What law does this ratio remind you of?

There! Now you have learned about Mendel’s great contribution to modern day genetic theory.

Try the review questions below. Check your answers AFTER you have finished.

Review Questions:

  1. Which cross would best illustrate Mendel’s Law of Segregation?
  2. TT x tt
  3. Hh x hh
  4. Bb x Bb
  5. rr x rr
  1. In the cross Yy x Yy, what percent of offspring would have the same phenotype as the parents?
  2. 25%
  3. 50%
  4. 75%
  5. 100%
  1. In a certain plant, purple flowers are dominant to red flowers. If the cross of two purple-flowered plants produces some purple-flowered and some red-flowered plants, what is the genotype of the parent plants?
  2. PP x Pp
  3. Pp x Pp
  4. pp x PP
  5. pp x pp

Base questions #4-8 on the following information.

-A white-flowered plant is crossed with a pink-flowered plant. All of the F1 offspring from the cross are white.

  1. Which phenotype is dominant?
  1. What are the genotypes of the original parent plants?
  1. What is the genotype of all the F1 offspring?
  1. What would be the percentages of genotypes and phenotypes if one of the white F1 plants is crossed with a pink-flowered plant?
  1. Which of Mendel’s Laws is/are illustrated in this question?
  1. Crossing two dihybrid organisms results in which phenotypic ratio?
  2. 1:2:1
  3. 9:3:3:1
  4. 3:1
  5. 1:1
  1. The outward appearance (gene expression) of a trait in an organism is referred to as:
  2. Genotype
  3. Phenotype
  4. An Allele
  5. Independent assortment
  1. In the homologous chromosomes shown in the diagram, which is a possible allelic pair?
  2. cD
  3. Ee aBcdeF
  4. AB
  5. ee ABcDef
  1. The phenotype of a pea plant can best be determined by:
  2. Analyzing its genes
  3. Looking at it
  4. Crossing it with a recessive plant
  5. Eating it
  1. Mendel formulated his Law of Segregation after he had:
  2. Studied F1 offspring
  3. Studied F2 offspring
  4. Produced mutations
  5. Produced hybrids
  1. Which cross would produce phenotypic ratios that would illustrate the Law of Dominance?
  2. TT x tt
  3. TT x Tt
  4. Tt x Tt
  5. tt x tt
  1. The mating of two curly-haired brown guinea pigs results in some offspring with brown curly hair, some with brown straight hair, some with white curly hair, and even some with white straight hair. This mating illustrates which of Mendel’s Laws?
  2. Dominance
  3. Segregation
  4. Independent Assortment
  5. Sex-Linkage

Try the Punnett Square Practice Page. You can refer to the topic called, “The Punnett Square (In Baby Steps)”, if you need help in doing Punnett squares. The Punnett Square practice problems should be done showing all the work and handled in.

Top View