Link to Genetics Student Learning Guide

1. Introducing some key genetics concepts

Start by viewing this slideshow about sickle cell anemia, and inherited genetic disease.

Note that if you can’t view the slideshow below, don’t worry: it’s all covered below. It’s something in your District’s network settings that’s blocking your view (and as much as I’d like to share this with you, I can’t). Sorry!

2. An interactive reading: Cystic Fibrosis

To review some basic genetics concepts, let’s look at the most common genetic disease to affect North Americans of European descent. The disease is cystic fibrosis. It’s primarily a lung disease. The key symptom is the buildup of a sticky mucus that leads to chronic infections in the lungs. In addition, this same mucus causes problems throughout the body. Even with the best medical care, people with cystic fibrosis have much shorter lifespans than people without the disease. As you read about this disease, fill in the blanks as needed.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Cystic Fibrosis I.R. (Genetics)”]

[h]Cystic Fibrosis, Interactive Reading

[i]

Symptoms of cystic fibrosis

[q labels=”top”]

Cystic fibrosis is caused by a defect in a protein found in cell membranes. The ______ for this protein is found on chromosome 7. That makes the gene an ___________ gene (because it’s not on the X or Y chromosome).

If you inherit a working ______ (version) of this gene, you’ll be fine, even if you inherit one defective allele. That’s because the disease allele is __________. If you inherit the working, __________ allele, then this allele will be translated into the working membrane protein. Your cells will function as they should, and there’ll be no build-up of the sticky mucus that underlies the disease.

You can only have the disease if you inherit two defective alleles. Another way to say this is that you have to be ____________ for the cystic fibrosis allele in order to have cystic fibrosis. Being homozygous means that you’ll have two copies of the allele. People who are _____________, with one dominant allele and one recessive allele, don’t get the disease. They have a normal __________ (no sticky mucus).

Typically, we represent alleles with symbols. If we use C to represent the normal allele and c to represent the cystic fibrosis allele, then we have three __________:

  • ____________ dominant: CC
  • _____________: Cc
  • homozygous __________: cc

[l]allele

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]autosomal

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]dominant

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]gene

[fx] No. Please try again.

[f*] Great!

[l]genotypes

[fx] No. Please try again.

[f*] Great!

[l]homozygous

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]heterozygous

[fx] No. Please try again.

[f*] Good!

[l]phenotype

[fx] No. Please try again.

[f*] Excellent!

[l]recessive

[fx] No. Please try again.

[f*] Excellent!

[q]Just to check your understanding. Cystic fibrosis is an autosomal [hangman] condition. That means you’ll only have the phenotype if you inherit [hangman] copies of the allele.

[c]recessive

[c]two

[/qwiz]

3. Extending your learning

Follow this link (it’ll open in a new tab) to the Genetics Home Reference about Cystic Fibrosis. Spend about five minutes reading the first three sections. Record what you’ve learned on your student learning guide.

4. Genetics vocabulary flashcards

To make sure you’re on top of the terms used above, study these flashcards.

[qdeck qrecord_id=”sciencemusicvideosMeister1961-Genetics Vocabulary Flashcards” style=”min-height: 400px !important; width: 550px !important;”]

[h] Genetics Vocabulary Flashcards

[!!!!]Question 1 [/!!!]

[q] If both of an organism’s alleles for a particular trait are the same, then the organism is _________.

[textentry]

[a] If both of an organism’s alleles for a particular trait are the same, then the organism is homozygous.

[!!!!]Question 2 [/!!!]

[q] If both of an organism’s alleles for a particular trait are different, then the organism is _________.

[textentry]

[a] If both of an organism’s alleles for a particular trait are the same, then the organism is heterozygous.

[!!!!]Question 3 [/!!!]

[q] An alternative version of a gene is known as an  _________.

[textentry]

[a] An alternative version of a gene is known as an allele.

[!!!!]Question 4 [/!!!]

[q] An organism’s appearance is its __________.

[textentry]

[a] An organism’s appearance is its phenotype.

[!!!!]Question 5 [/!!!]

[q] The underlying genes that an organism has for a trait is its ___________.

[textentry]

[a] The underlying genes that an organism has for a trait is its genotype.

[!!!!]Question 6 [/!!!]

[q] The underlying genes that an organism has for a trait is its ___________.

[textentry]

[a] The underlying genes that an organism has for a trait is its genotype.

[!!!!]Question 7 [/!!!]

[q] The type of allele that always shows up in an organism’s phenotype is a _______ allele.

[textentry]

[a] The type of allele that always shows up in an organism’s phenotype is a dominant allele.

[!!!!]Question 8 [/!!!]

[q] The type of allele that can be masked or hidden by another allele is called a ________ allele

[textentry]

[a] The type of allele that can be masked or hidden by another allele is called a recessive allele.

[!!!!]Question 9 [/!!!]

[q] The ______ is the basic unit of heredity..

[textentry]

[a] The gene is the basic unit of heredity.

[!!!!]Question 10 [/!!!]

[q] A gene that’s located on any chromosome except the X or Y chromosome is a(n) _________ gene. .

[textentry]

[a] A gene that’s located on any chromosome except the X or Y chromosome is an autosomal gene. .

[x]

[restart]

[/qdeck]

5. Guided Punnett Square 1: Autosomal Inheritance

Gregor Mendel, By Iltis, Hugo via Wikimedia Commons

The most basic type of genetics problems involve dominant and recessive autosomal alleles. The principles behind these problems were discovered by Gregor Mendel in work that he did with garden peas in the 1860s.

I’ll use a sample problem to demonstrate how you can go about finding a solution.

Sample Problem: In one of the varieties that Mendel experimented with, the allele for purple flower color (P) is dominant to the allele for white flower color (p). What genotypes and phenotypes will be produced if a heterozygous purple-flowered pea plant is crossed with a white-flowered pea plant?

STEP 1: Figure out the alleles of the parents
Heterozygous means that the alleles are different. Therefore the first parent has to be Pp. The second parent is showing the recessive phenotype, and has to be homozygous recessive, or pp.
STEP 2: Draw a punnett square.

 A  A
 A  AA AA
 A  AA  AA

STEP 3: Place the alleles of the parents to the left and to the top of the Punnett square. Remember that these alleles represent the possible alleles in the gametes (sex cells) that this parent could create.

P p
p
p

STEP 4: Bring the alleles in the parents’ gametes over and down to fill in the four inner squares. Each of those squares represents a potential zygote.

P p
p Pp pp
p Pp pp

STEP 5: Represent the possible genotypes as a ratio.
50% of the offspring will have the genotype Pp. 50% will have the genotype pp. You can also state this as
1 Pp: 1pp. Or 1/2 Pp and 1/2 pp.
STEP 6: Represent the possible phenotypes as a ratio
50% purple flowers: 50% white flowers (or 1 purple-flowered: 1 white flowered)

Got it? Try the problems in the quiz below. On some you’ll be guided, and on some you’ll need paper and pencil to find the solution.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Guided Punnett Square, Autosomal Inheritance (Genetics)”]

[h]Guided Punnett Square 1: Autosomal inheritance

[q] In peas, the tall allele (T) is dominant to the short allele (t). Cross a plant that is homozygous tall with a plant that is heterozygous tall.

Step 1: Determine the genotypes of the parents

Parent 1) Homozygous tall: ___ ___

Parent 2) Heterozygous tall: ___ ___

Steps 2 through 4: Complete your Punnett square. Note that for this quiz, you have to place the alleles of the gametes of the 1st parent to the left of the Punnett square, and put the alleles of the second parent’s gametes on top. On paper, you could do it in either order.

 

Parent 2
       __    __
 Parent 1 __ ___ ___ ___ ___
__ ___ ___ ___ ___

 

Step 5: Genotype ratio: _____ TT: ____Tt: ____tt

Step 6: Phenotype ratio: _____ Tall: ______Short

 

[l]T

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]t

[fx] No. Please try again.

[f*] Great!

[l]0%

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]25%

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]50%

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]75%

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]100%

[fx] No. Please try again.

[f*] Great!

 

[!!!!] Question 2 [/!!!!!]

[q]In carnations, the gene for red flowers (R) is dominant to the gene for white flowers (r). What will happen if a plant homozygous for red flowers is crossed with a plant homozygous for white flowers?

Step 1: determine the genotypes of the parents

Parent 1) homozygous red flowers: ___ ___
Parent 2) Homozygous white flowers: ___ ___

Step 2: Draw the Punnett square (already done below)

Step 3: Place the alleles of the gametes that the 1st parent can make to the left of the Punnett square. Put the alleles that the 2nd parent can make on top. (note: these required positions (left and top) are solely so that this quiz program will work. On paper, you can put them in either position.

Step 4: Move the gametes to the right or downward into the square, simulating fertilization and zygote formation.

Parent 2
 __  __
 Parent 1   __ ___ ___ ___ ___
__ ___ ___ ___ ___

Step 5: Genotype ratio: _____ RR: ____Rr: ____rr

Step 6: Phenotype ratio: _____ Red-flowered, ____white flowered

[l]R

[fx] No. Please try again.

[f*] Excellent!

[l]r

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]0%

[fx] No. Please try again.

[f*] Correct!

[l]25%

[fx] No. Please try again.

[f*] Good!

[l]75%

[fx] No. Please try again.

[f*] Great!

[l]100%

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[!!!!]Question 3 [/!!!!]

[q]In peas, the gene for tall (T) is dominant to the gene for short (t). What genotypes and phenotypes will result in the offspring if two heterozygous plants are crossed with each other?

Step 1: determine the genotypes of the parents

Parent 1) Heterozygous tall: ___ ___
Parent 2) Heterozygous tall: ___ ___

Step 2: Draw the Punnett square (I did that one for you)

Step 3: Place the alleles of the gametes that the 1st parent can make to the left of the Punnett square. Put the alleles that the 2nd parent can make on top. (note: these required positions (left and top) are solely so that this quiz program will work. On paper, you can put them in either position).

Step 4: Move the gametes to the right or downward into the square, simulating fertilization and zygote formation.

Parent 2
     __  __
 Parent 1  __ ___ ___ ___ ___
__ ___ ___ ___ ___

Step 5: Genotype ratio: _____ TT: ____Tt: ____tt

Step 6: Phenotype ratio:

_____ Tall, _____medium, _____ short

[l]T

[fx] No. Please try again.

[f*] Great!

[l]t

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]0%

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]25%

[fx] No. Please try again.

[f*] Excellent!

[l]50%

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]75%

[fx] No. Please try again.

[f*] Correct!

[l]100%

[fx] No. Please try again.

[f*] Great!

[/qwiz]

Links

  1. Solving ABO blood type problems (the next tutorial)
  2. Genetics Main Menu