Name: ______Date: ______Class: ______Page 1/39

2009-2010 CP2 GENETICS UNIT PACKET FOR COMPLETE DOMINANCE

MA STATE Frameworks: (This is what the state of MA says you need to be able to do on your MCAS test)

Broad Concept: Genes allow for the storage and transmission of genetic information. They are a set of instructions encoded in the nucleotide sequence of each organism. Genes code for the specific sequences of amino acids that comprise the proteins that are characteristic of that organism.

3.3Explain how mutations in the DNA sequence of a gene may or may not result in phenotypic change in an organism. Explain how mutations in gametes may result in phenotypic changes in offspring.

3.4Distinguish among observed inheritance patterns caused by several types of genetic traits (dominant, recessive, incomplete dominance, codominant, sex-linked, polygenic, and multiple alleles).

3.5Describe how Mendel’s laws of segregation and independent assortment can be observed through patterns of inheritance (such as dihybrid crosses).

3.6Use a Punnett Square to determine the probabilities for genotype and phenotype combinations in monohybrid crosses.


GENETICS: COMPLETE DOMINANCE (10.1-10.2)

Exploring Life concept 10.1: Genetics developed from curiosity about inheritance

Exploring Life concept 10.2: Mendel discovered that inheritance follows rules of chance

Exploring Life concept 10.4: Meiosis Explains Mendel’s Laws

TOPICS:

  • Mendel
  • Monohybrid cross
  • Test Cross
  • Dihybrid cross

OBJECTIVES:

Date:

______1. Describe the methods Mendel used in his plant-breeding experiments

______2. Tell what the F in F1 and F2 stand for and what the P in “P generation” stands for.

______3. Describe Mendel’s 3 laws

______4. Predict the possible offspring of a monohybrid cross by using a Punnett Square and calculate the probability of each type (genotype and phenotype) being born.

______5. Model a test cross to prove the genotype of a dominant individual.

______6. Contrast genotype and phenotype

______7. Predict the possible offspring of a dihybrid cross by using a Punnett Square.

______8. Explain how genetic linkage provides exceptions to Mendel’s principle of independent assortment

KEY TERMS:

Allele: alternative form of a gene

Complete Dominance: inheritance pattern in which a heterozygote expresses the dominant phenotype

Dominant: description of an allele in a heterozygous individual that appears to affect the trait.

Dihybrid Cross: crossing organisms differing in two characters

F1 generation: first generation of offspring from P generation

F2 generation: second generation of offspring from P generation

Genetic linkage: the tendency for the alleles on one chromosome to be inherited together.

Name: ______Date: ______Class: ______Page 1/39

Genetics: the study of heredity

Genotype: an organism’s combination of alleles

Heterozygous: having different alleles for a gene

Homozygous: having the same alleles for a gene

Hybrid: offspring of two different true-breeding varieties

Law of Dominance: in every pair of contrasting traits, one trait is dominant

Monohybrid cross: mating of two organisms that differ in only one character

P generation: true-breeding parents

Phenotype: observable traits of an organism

Punnett Square: diagram showing the probabilities of the possible outcomes of a genetic cross

Recessive: description of an allele in a heterozygous individual that does not affect a trait.

Test cross: mating of an individual of unknown genotype (but dominant phenotype) with an homozygous recessive individual

NOTES: Mendel and Rules of Inheritance (10.1, 10.2)

Traits: A trait is a variation of a particular character

  • Example: one plant might have the trait of red flowers, while another might have the trait of yellow flowers.

Mendel’s Plant Breeding Experiments

  • In the 1800’s, a scientist named Gregor Mendel applied an experimental approach to study inheritance
  • His work eventually gave rise to genetics: the study of heredity.
  • For seven years, Mendel bred pea plants and recorded inheritance patterns in the offspring. He found that parents pass on to their offspring packages of traits (today called genes) that are responsible for inherited traits.
  • Mendel used garden pea plants because they….
  • are small
  • are easy to grow
  • produce large numbers of offspring
  • mature quickly
  • can be cross or self-fertilized
  • have many varieties available
  • Mendel studied seven traits:

Name: ______Date: ______Class: ______Page 1/39

  • flower color (purple or white)
  • seed color (yellow or green)
  • seed shape (round or wrinkled)
  • pod color (green or yellow)
  • pod shape (inflated or constricted)
  • flower position on stem (terminal or axial)
  • plant height (tall or short)

Name: ______Date: ______Class: ______Page 1/39

  • Before he started…
  • He allowed plants to self fertilize for many generations to ensure true-breeding plants. (offspring produced only one form of a trait – like, only green pods, or only yellow pods)
  • Mendel called the true-breeding plants the parental generation (P)
  • Parental generation were true breeding yellow and true breeding green
  • First Experiment:
  • Cross-fertilize the P (parent) generation (cross the pure yellow with the pure green)
  • Mendel called the offspring of the P generation the first filial generation (F1)
  • (filial comes from the Latin word for “son”)
  • F1 generation were all yellow
  • Second Experiment:
  • Allow the F1 generation to self-fertilize.
  • Mendel called the offspring of the F1 generation the second filial generation (F2)
  • F2 generation were yellow and green in about a 3:1 ratio.

Rules of Inheritance

  • Parents transmit traits to their offspring.
  • Forms of a trait are called alleles.
  • Individuals have 2 alleles for each trait; one from each parent.
  • The presence of an allele does not guarantee the expression of that trait.

Mendel’s 3 Laws of Heredity:

  • Law of Dominance: In every pair of contrasting traits, one trait is dominant.
  • Law of Segregation: The two alleles an organism has for a trait separate randomly when gametes are formed. (during meiosis)Remember, an organism gets one allele from Mom, and one from Dad!
  • Law of Independent Assortment: Alleles for different traits are inherited independently of each other (…Which means that inheriting one does not affect the chance of inheriting the other…unless they are on the same chromosome)
  • Example: Just because you inherit blond hair does not mean that you will inherit blue eyes.

THE LAW OF DOMINANCE:

In every pair of contrasting traits, one trait is dominant.

THE LAW OF SEGREGATION:

The two alleles an organism has for a trait separate randomly when gametes are formed.

THE LAW OF INDEPENDENT ASSORTMENT:

Alleles for different traits are inherited independently of each other (…Which means that inheriting one does not affect the chance of inheriting the other…unless they are on the same chromosome)

  • Example: Just because you inherit blond hair does not mean that you will inherit blue eyes.


NOTES: Inheritance of Traits - Complete Dominance

(Concept 10.1, 10.2)

Homozygous / Heterozygous

  • For each inherited character, an organism has two alleles for the gene controlling that character (one from mom and one from dad)
  • If the two alleles are the same, the individual is homozygous (or pure)
  • If the two alleles are different, the individual is heterozygous.

Dominant / Recessive

  • Dominant alleles are those that keep recessive alleles from showing up in the phenotype.
  • Dominant traits are represented by UPPER CASE LETTERS (BB)
  • Recessive traits are represented by lower case letters (bb)
  • Only ONE dominant allele needs to be present for the organism to show that Trait (Bb) or (BB)
  • If an individual has the phenotype BB, he is called homozygous dominant, or pure dominant for the trait
  • If an individual has the phenotype Bb, he is called heterozygous dominant.
  • To show the recessive phenotype, BOTH alleles present must be recessive (bb)
  • This individual is called homozygous recessive.
  • Example
  • Mom: Brown hair (BB)
  • Dad: Blond hair (bb)
  • They can only have children that have BROWN hair (Bb)

WS: Punnett Square – Widow’s peak


Punnett Square 26: Offspring From Two Heterozygous Parents


MONOHYBRID CROSS COMPLETE DOMINANCE

PRACTICE PROBLEMS #1

  1. In fruit flies, long wings are dominant over short wings. (Use W and w)
  1. What letter(s) is/are used for long wings?______
  1. What letter(s) is/are used for short wings?______
  1. What genotype and phenotype will each of the following have:

Genotypephenotype

Pure dominant______

Pure recessive ______

Heterozygous______

  1. What are the gametes of the pure dominant fly? ______
  1. What are the gametes of the pure recessive fly? ______
  1. What are the gametes of the heterozygous fly? ______
  1. Complete the Punnett square below for a cross between the pure dominant and the pure recessive fly.
  1. In pea plants, purple flowers are dominant over white flowers. (Use P and p)
  1. What letter(s) is/are used for purple flowers?______
  1. What letter(s) is/are used for white flowers?______
  1. What genotype and phenotype will each of the following have:

Genotypephenotype

Pure dominant______

Pure recessive ______

Heterozygous______

  1. What are the gametes of the pure dominant plant? ______
  1. What are the gametes of the pure recessive plant? ______
  1. What are the gametes of the heterozygous plant? ______
  1. Complete the Punnett square below for a cross between the pure dominant and the heterozygous plant.

Should This Dog Be Called Spot???

A sperm cell from a male dog fuses with an egg cell from a female dog. Each dog’s gamete carries 39 chromosomes. The zygote that results from the fusion of the gametes contains 78 chromosomes – one set of 39 chromosomes from each parent.

One homologous pair of the zygote’s 78 chromosomes are shown below:

Each chromosome of the homologous pair contains alleles for the same traits. But

one chromosome may have a dominant allele and the other a recessive allele. Use the drawings and the table to answer the questions.

1. Will the puppy have a spotted coat?

2. Does the female dog have a spotted coat? Explain.

3. Does the male dog have a spotted coat? Explain.

4. What will the texture of the puppy’s coat?

5. Will the texture of the puppy’s coat resemble that of either of its parents? Explain.

6. Will the puppy have curly hair or straight hair?

7. Does the female dog have curly hair?

8. Does the male dog have curly hair?

9. Define the term heterozygous.

10. For which traits is the puppy heterozygous?

11. Define the term homozygous.

12. For which traits is the puppy homozygous?

13. Explain why you cannot completely describe the puppy’s parents even though you can accurately describe the puppy.
NOTES: Probability (10.1, 10.2 -??)

PROBABILITY

•Probability is the likelihood of a specific event occurring

•An event is a possible outcome

•For example: When a coin is flipped, one possible event (outcome) is “heads” and another possible event (outcome) is “tails.”

PROBABILITY FORMULA

•Probability = # of one kind of event

# of all possible events

•For Example: What is the probability of a single coin landing on heads?

Probability = _____ Heads (1)____

Tails or Heads (2) = 1 out of 2 = ½ = 0.5 = 50%

INFLUENCE

•If two coins are flipped, the outcome of one coin does NOT predict or influence the outcome of the other coin.

PRODUCT RULE

•The probability of two or more events occurring simultaneously is the product of their individual probabilities.

•For example: What is the probability of getting heads on both coins when two coins are flipped together?

–We calculated the probability of flipping heads once as 50% (or ½).

–To calculate the probability of flipping heads twice, we multiply each probability together:

•Probability of getting heads on coin 1 x coin 2 = % chance

•½ x ½ = ¼ = 25%

WHY THIS IS IMPORTANT

•The parents’ alleles are like two sides of a coin, and a child receives one allele from mom and one allele from dad.

•In meiosis, these alleles are segregated (separated) independent of one another, like flipping a coin.

WS: PROBABILITY PROBLEMS #1

  1. A man and a woman are heterozygous for freckles. Freckles (F) are dominant over no freckles (f). What are the chances that their children will have freckles? Draw a Punnett square below to prove your answer.
  1. A man heterozygous for a widow's peak (W) marries a woman with a straight hairline (w). A widow's peak is dominant over a continuous hairline. What is the chance their children will have a Widow’s peak? Draw a Punnett square below to prove your answer.
  1. Look at problems 1 and 2 above. Assume the two people in both problems are the same couple. What is the probability that this man and woman will have…
  1. A child with freckles and a widow’s peak?
  1. A child with freckles and no widow’s peak?
  1. A child with no freckles and a widow’s peak?
  1. A child with no freckles and no widow’s peak?
  1. Suppose a pea plant has two alleles for flower-color, purple (F) and white (f). Purple is dominant to white. If a plant with one purple allele and one white allele is mated to a plant with two white alleles, what percentage of the offspring will have purple flowers? Draw a Punnett square below to prove your answer.
  1. The chance for the pea plants above also having yellow peas vs. green peas is 50%. What is the chance of the above plants producing offspring that have yellow peas AND purple flowers?

WS: PROBABILITY PROBLEMS #2

Using the traits for dog fur listed below, answer the following questions.

  1. If dogs with these two genotypes (Male: HH and Aa, Female: Hh and Aa) mate, what are their chances of having puppies who have… (you will need to do TWO crosses… one for HHx Hh and one for Aa x Aa)
  1. Spotted, curly fur
  1. Spotted, straight fur
  1. Solid, curly fur
  1. Solid, straight fur
  1. If a male dog who is heterozygous for short hair and has straight hair and a female dog who has long hair and is pure for curly hair breed, what are their chances of having a puppy who has….
  1. Short, curly fur
  1. Long, curly fur
  1. Short, straight fur
  1. Long, straight fur

NOTES: TEST CROSS

A test cross is used to determine the GENOTYPE of a PHENOTYPICALLY DOMINANT individual by looking at the offspring it has already had with a RECESSIVE individual.

A test cross is two pretend matings on paper that look at the types of offspring an individual has already had and compares it to the two possible outcomes of a mating between a phenotypically dominant individual and a recessive individual.

There are ALWAYS two test crosses:

  • One between the homozygous dominant individual with a recessive individual
  • One between the heterozygous dominant individual with a recessive individual

One of the test crosses will show the genotype of the individual.

Sample Problem

A male mouse with black fur is mated with a female mouse with white fur. Seven offspring result, three black and four white. Black fur (B) is dominant to white fur (b). What is the genotype of the father?

Sample Test Cross:

Genotypes %Genotypes %

Phenotypes %Phenotypes %

Using Punnett Squares: Practicing Skills (Some Test Cross)

Show the results of the following crosses using Punnett squares and the information in the accompanying figure above.

  1. Heterozygous short hair x heterozygous short hair
  1. Heterozygous tabby x stripeless
  1. Colorpoint x homozygous normal
  1. Homozygous tabby x homozygous tabby
  1. In order to determine the genes of a tabby cat, you could perform a test cross by crossing it with a homozygous recessive cat. Show what the expected kittens would be if the tabby is heterozygous and if the tabby is homozygous.

Heterozygous tabby x recessive stripeless: Genotype and Phenotype of offspring:

Homozygous tabby x recessive stripeless: Genotype and Phenotype of offspring:

  1. If the above tabby cat had 12 kittens, 3 of whom were stripeless, could you determine what its genotype is? If yes, what is it? If not, tell why.
  1. If the above tabby cat had 12 kittens, none of whom were stripeless, could you determine what its genotype is? If yes, what is it? If not, tell why.

Test Cross Problems #1

  1. Brown eyes (B) is dominant to blue (b). A mother with blue eyes and a father with brown eyes have four children. Three with brown eyes, on with blue. What is the genotype of each parent? Show your work.
  1. In pea plants, purple flowers (P) are dominant to white (p). A purple-flowered plant is crossed with a white-flowered plant and 37 offspring result, all with purple flowers. Show your work and answer the questions below.
  1. What is the genotype of the white flower?
  1. What is the genotype of the purple flower?
  1. In guinea pigs, black fur is dominant to brown. A male guinea pig with black fur is mated with a female with brown fur. They have 26 baby guinea pigs, 10 with brown fur and 16 with black. What is the genotype of each parent? Show your work.
  1. In dogs, having erect ears (E) is dominant to having droopy ears (e). A droopy-eared male dog fathers a litter of puppies with an erect-eared mother. Eight puppies result, seven erect eared dogs and one droopy-eared. What is the genotype of each parent? Show your work.
  1. In dogs, having a short coat (L) is dominant to having a long coat (l). A breeder is looking for a dog that has a homozygous genotype for short coat. She has four dogs with short coats but does not know their genotypes. What could she do to know for sure what the genotype of each dog is? FULLY EXPLAIN your answer and include Punnett squares as part of the explanation.

WS: TEST CROSS #2 – Pea Plants and Cucumbers