[qwiz style=”width: 550px !important; min-height: 400px !important;” qrecord_id=”sciencemusicvideosmeister1961-Introducing Genetics (v2.0)”]

[h] Introducing Genetics: The story of Hunter Haymore

[i]

Hunter Haymore (center) with her parents. Hunter was born with sickle cell anemia.

[q]Genetics is the study of how genetic information gets passed from parents to offspring. The basic principles of genetics were figured out by an Austrian monk named Gregor Mendel, who carried out a series of genetic experiments in the 1860s. In his honor, these principles are called Mendelian Genetics.

 

[q]We’ll look at Mendel’s experiments later in this unit. In this tutorial, as a way of introducing genetics concepts, we’re going to look at the inheritance of a disease called sickle cell anemia, which we discussed in the context of protein structure in Unit 1.

As we do, we’re going to focus on Hunter Haymore, a person who was born with sickle cell anemia.

 

[q]In sickle cell anemia, an inherited mutation changes a single amino acid in hemoglobin, the protein that transports oxygen in red blood cells. As a result, hemoglobin molecules cluster together (see the lower part of the diagram), causing red blood cells to deform into a sickled shape. These sickled blood cells get stuck in blood vessels, causing tissue damage and debilitating pain.

Over the past decades, treatment options have vastly increased the lifespan and quality of life of people born with sickle cell anemia. In addition, recent advances involving gene therapy and stem cells have put a cure for the disease on the horizon.

[q]Sickle cell anemia is the most common inherited genetic disease among Americans of African descent, occurring in 1 in 365 African-American births. About 1 in 13 African Americans (7%) carry the gene.

In some parts of Africa, the prevalence of people who carry the gene is much higher (above 14%).

Note that later in this tutorial we’ll address

1. The difference between being born with the condition and carrying the gene, and
2. Why this gene is in such high frequency in Africa.

[q multiple_choice=”true”] Let’s return to Hunter. The image on the right is a pedigree chart. It shows the inheritance of a trait. Here’s how to read it.

• Squares represent males.
• Circles represent females.
• An empty square or circle means the trait is absent.
• A filled-in square or circle means the trait is present.

True or false: Hunter’s mother and father suffer from sickle cell anemia.

[c]IFRydWU=[Qq]

[f]IE5vLiBUaGUgY2lyY2xlIGZvciBIdW50ZXImIzgyMTc7cyBtb3RoZXIgYW5kIHRoZSBzcXVhcmUgZm9yIEh1bnRlciYjODIxNztzIGZhdGhlciBhcmUgYm90aCBlbXB0eS4gVGhhdCBtZWFucyB0aGF0IHRoZXkgZG9uJiM4MjE3O3Q=IGhhdmUgdGhlIHRyYWl0LiBJZiBuZWl0aGVyIG9mIHRoZW0gaGFzIHRoZSBkaXNlYXNlLCB0aGVuIGhvdyBkaWQgSHVudGVyIGluaGVyaXQgaXQ/[Qq]

[c]IEZh bHNl[Qq]

[f]IENvcnJlY3QuIFRoZSBjaXJjbGUgZm9yIEh1bnRlciYjODIxNztzIG1vdGhlciBhbmQgdGhlIHNxdWFyZSBmb3IgSHVudGVyJiM4MjE3O3MgZmF0aGVyIGFyZSBib3RoIGVtcHR5LiBUaGF0IG1lYW5zIHRoYXQgdGhleSA=ZG9uJiM4MjE3O3Q=IGhhdmUgdGhlIHRyYWl0LiBJZiBuZWl0aGVyIG9mIHRoZW0gaGFzIHRoZSBkaXNlYXNlLCB0aGVuIGhvdyBkaWQgSHVudGVyIGluaGVyaXQgaXQ/[Qq]

[q] The hemoglobin gene is found on human chromosome 11. A gene is a unit of heredity that is transferred from parent to offspring and determines some trait.

[q] The hemoglobin gene comes in two forms. As we discussed in relation to meiosis, an alternative form of a gene is known as an allele.

In the case of sickle cell anemia, the two alleles are HB^A, which codes for normal hemoglobin, and HB^S, which codes for the mutated form of hemoglobin that causes sickle cell anemia.

[q] Let’s make sure the distinction between the two terms we just discussed is clear. A [hangman] is a unit of heredity that determines some trait.

[c]IGdlbmU=[Qq]

[f]IENvcnJlY3Qh[Qq]

[q] Alternative versions of genes are called [hangman].

[c]IGFsbGVsZXM=[Qq]

[f]IEdyZWF0IQ==[Qq]

[q] Hunter inherited two copies of the mutant HB^S allele. That makes Hunter, for this particular allele, a homozygote: an organism that has two identical alleles for the same trait.

[q] Hunter’s parents are heterozygotes. That means that they have two different alleles. One is the normal version, HB^A, and the second is the mutated version, HB^S.

 

 

 

[q] But if Hunter’s parents both have the HB^S allele, why don’t they have sickle cell anemia?

[q] HB^S, the sickle cell allele, is recessive. It only has an effect on an individual who inherits two copies. In other words, a recessive allele like HB^S will only cause sickle cell anemia in an individual who (like Hunter) is a [hangman].

[c]IGhvbW96eWdvdGU=[Qq]

[f]IEdyZWF0IQ==[Qq]

[q]

HB^A, the normal allele, is dominant. If you inherit a dominant allele, you’ll express the dominant trait (even if you also inherit the recessive allele). In the case of sickle cell anemia, the normal allele is normal hemoglobin and normal blood cells.

[q] A few additional terms are going to be useful in our study of genetics:

• Phenotype: an organism’s appearance.
• Genotype: an organism’s underlying genes.

For example, Mr. W’s eye-color phenotype is brown-eyed. And while the genetic basis of eye color inheritance is complex (involving up to three genes), Mr. W knows (based on his children’s and father’s blue-eyed phenotype) that he has to be a heterozygote.

[q]

Neither of Hunter’s parents has sickle cell anemia. That’s a description of their [hangman]. At the same time, we know that they’re heterozygotes, and have the sickle cell gene. That’s a description of their [hangman]

[c]cGhlbm90eXBl[Qq]

[c]Z2Vub3R5cGU=[Qq]

[q]

And here’s another term. Heterozygotes like Hunter’s parents possess the recessive HBS allele but don’t have sickle cell disease. That makes them carriers. Note that this term is only used to refer to heterozygotes, who are carrying a recessive allele (in each of their cells) but not expressing it. Homozygous recessive individuals like Hunter, even though they obviously have the HBS allele (two copies, in each of their cells) are referred to as homozygotes or homozygous recessive.

[q] When Hunter’s parents created the gametes that led to Hunter, each had a 1 in 2 chance of creating a gamete with a copy of chromosome 11 that carried the HB^S allele. So what was the chance that Hunter would inherit two mutant alleles, leading her to have sickle cell anemia?

Fill in your answer below: it’s a 1 in ____ chance?

[textentry single_char=”true”]

[c]ID Q=[Qq]

[f]IEV4Y2VsbGVudC4gVGhlIGNoYW5jZSBvZiBIdW50ZXIgaW5oZXJpdGluZyB0d28gSEI=^Uw==IGFsbGVsZXMgd2FzIGEgMSBpbiAyIGNoYW5jZSBvZiByZWNlaXZpbmcgSEI=^Uw==IGluIGhlciBtb3RoZXImIzgyMTc7cyBlZ2csIG11bHRpcGxpZWQgYnkgYSAxIGluIDIgY2hhbmNlIG9mIHJlY2VpdmluZyBIQg==^[Qq]S in her father’s sperm. That makes for a 1/4 chance.

[c]Kg==[Qq]

[f]Tm86IGhlcmUmIzgyMTc7cyBob3cgdG8gdGhpbmsgYWJvdXQgaXQuIFRoZSBjaGFuY2Ugb2YgSHVudGVyIGluaGVyaXRpbmcgdHdvIEhC^Uw==IGFsbGVsZXMgd2FzIGEgMSBpbiAyIGNoYW5jZSBvZiByZWNlaXZpbmcgSEI=^Uw==IGluIGhlciBtb3RoZXImIzgyMTc7cyBlZ2csIG11bHRpcGxpZWQgYnkgYSAxIGluIDIgY2hhbmNlIG9mIHJlY2VpdmluZyBIQg==^[Qq]S in her father’s sperm. That makes for a 1/4 chance.

[q] Here’s a more elaborate representation that might make this 1 in 4 chance clearer. This diagram uses the capital letter S to represent the dominant allele (HB^A) for normal hemoglobin and the lowercase letter s to represent the recessive (HB^S) allele for sickle cell hemoglobin. Study the diagram for a moment, and then go on to the next card.

[q]

When a heterozygote (such as Hunter’s mother and father) creates gametes, there’s a 1:2 chance that they’ll pass on their recessive allele. To figure out the chance that two heterozygotes will have a child with two recessive alleles, you multiply 1/2 X 1/2 = 1/4. Hunter had the misfortune to be on the receiving end of that 1 in [hangman] chance.

[c]Zm91cg==[Qq]

[q]There’s the happy ending to this story. Hunter had a bone marrow transplant that cured her of sickle cell anemia.

And there’s more good news on the horizon: diseases like sickle cell anemia are current targets for genetic therapies that might provide other ways to cure people of the disease (at lower cost and less risk than a bone marrow transplant).

[q]Here’s a final point. Why is the sickle cell allele so frequent among African Americans (and Africans)? It’s for an evolutionary reason. When looking from the outside, there’s no phenotypic difference between people who are homozygous dominant (SS) and heterozygotes (Ss). But carrying a single copy of the allele causes a difference in the protein chemistry of their red blood cells. This difference provides heterozygotes with protection against a mosquito-borne disease called malaria. As a result, in areas with a lot of malaria, there’s been natural selection to increase the number of heterozygotes, despite the harm caused to individuals who are homozygous recessive.

We’ll talk more about this phenomenon, called heterozygote advantage, in AP Bio Unit 7 (evolution).

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[qwiz qrecord_id=”sciencemusicvideosmeister1961-Genetics Vocabulary (v2.0)”]

[h]Genetics Vocabulary Check

[q]The founder of genetics was an Austrian monk named Gregor [hangman]. In his honor, the basic principles of genetics are referred to as [hangman] genetics.

[c]TWVuZGVs[Qq]

[c]TWVuZGVsaWFu[Qq]

[q] An allele that always shows up in the offspring is a(n) [hangman] allele.

[c]ZG9taW5hbnQ=[Qq]

[q] An alternative form of a gene is called a(n) [hangman].

[c]YWxsZWxl[Qq]

[q]A(n) [hangman] allele will only show up in the offspring if the offspring inherits two copies of that allele.

[c]cmVjZXNzaXZl[Qq]

[q] An organism that has two identical alleles for a particular gene is known as a(n) [hangman].

[c]aG9tb3p5Z290ZQ==[Qq]

[q] An organism that has two different alleles for a particular gene is known as a(n) [hangman].

[c]aGV0ZXJvenlnb3Rl[Qq]

[q]Another term for a heterozygote refers to the fact that they possess the allele, don’t display the trait, and can pass it on to the next generation. That term is [hangman].

[c]Y2Fycmllcg==[Qq]

[q] A unit of heredity that is passed from parent to offspring is known as a(n) [hangman].

[c]Z2VuZQ==[Qq]

[q] The chance that a heterozygote parent will pass on a recessive or a dominant allele is one in [hangman] (write out the number).

[c]dHdv[Qq]

[q] The chance that the offspring of two heterozygotes will inherit two recessive alleles is one in [hangman](write out the number).

[c]Zm91cg==[Qq]

[q] Your underlying genes make up your [hangman]. Your appearance is your [hangman].

[c]Z2Vub3R5cGU=[Qq]

[c]cGhlbm90eXBl[Qq]

[q]A chart (like the one below) used to show the inheritance of a trait is a(n) [hangman] chart.

[c]cGVkaWdyZWU=[Qq]

[q]A person with a genotype that would be symbolized as Aa or Cc is

[c]aG9tb3p5Z291cyBkb21pbmFudA==[Qq]

[f]Tm8uIEhvbW96eWdvdXMgbWVhbnMgdGhlIHR3byBhbGxlbGVzIGFyZSB0aGUgc2FtZS4gSW4gdGhpcyBjYXNlLCB0aGUgdHdvIGFsbGVsZXMgYXJlIGRpZmZlcmVudC4gQSBob21venlnb3VzIGRvbWluYW50IGdlbm90eXBlIGxvb2tzIGxpa2UgdGhpczogU1MsIEFBLCBHRywgZXRjLiBBbHdheXMgdHdvIHVwcGVyY2FzZSBsZXR0ZXJzLg==[Qq]

[c]aGV0ZXJvenlnb3VzIC hhbmQgZG9taW5hbnQp[Qq]

[f]TmljZS4gQ2Mgb3IgQWEgZ2Vub3R5cGVzIGFyZSBoZXRlcm96eWdvdXMgKGFuZCBoZXRlcm96eWdvdGVzIGFsd2F5cyBkaXNwbGF5IHRoZSBkb21pbmFudCB0cmFpdCwgd2hpY2ggaXMgd2h5ICYjODIyMDtkb21pbmFudCYjODIyMTsgaXMgaW4gcGFyZW50aGVzaXMu[Qq]

[c]aGV0ZXJvenlnb3VzIChhbmQgcmVjZXNzaXZlKQ==[Qq]

[f]Tm8uIElmIHlvdSYjODIxNztyZSBoZXRlcm96eWdvdXMsIHlvdSYjODIxNztsbCBkaXNwbGF5IHRoZSBkb21pbmFudCB0cmFpdC4gWW91IGNhbiYjODIxNzt0IGJlICYjODIyMDtoZXRlcm96eWdvdXMgcmVjZXNzaXZlLiYjODIyMTs=[Qq]

[c]aG9tb3p5Z291cyByZWNlc3NpdmU=[Qq]

[f]Tm8uIEhvbW96eWdvdXMgcmVjZXNzaXZlIHBoZW5vdHlwZXMgbG9vayBsaWtlIHRoaXM6IGNjLCBzcywgYWEsIGV0Yy4gQWx3YXlzIHR3byBsb3dlcmNhc2UgbGV0dGVycy4=[Qq]

[q]A person with a genotype that would be symbolized as aa or cc is

[c]aG9tb3p5Z291cyBkb21pbmFudA==[Qq]

[f]Tm8uIEEgZG9taW5hbnQgZ2Vub3R5cGUgYWx3YXlzIGhhcyBhbiB1cHBlcmNhc2UgbGV0dGVyLiBBIGhvbW96eWdvdXMgZG9taW5hbnQgZ2Vub3R5cGUgbG9va3MgbGlrZSB0aGlzOiBTUywgQUEsIEdHLCBldGMu[Qq]

[c]aGV0ZXJvenlnb3VzIChhbmQgZG9taW5hbnQp[Qq]

[f]Tm8uwqAgSGV0ZXJvenlnb3VzIG1lYW5zIHRoYXQgdGhlIHR3byBhbGxlbGVzIGFyZSBkaWZmZXJlbnQuIEZvciBleGFtcGxlLCAmIzgyMjA7QWEmIzgyMjE7IGlzIGEgaGV0ZXJvenlnb3VzIGdlbm90eXBlLg==[Qq]

[c]aGV0ZXJvenlnb3VzIChhbmQgcmVjZXNzaXZlKQ==[Qq]

[f]Tm8uIEhldGVyb3p5Z291cyBtZWFucyB0aGF0IHRoZSB0d28gYWxsZWxlcyBhcmUgZGlmZmVyZW50LiBGb3IgZXhhbXBsZSwgJiM4MjIwO0FhJiM4MjIxOyBpcyBhIGhldGVyb3p5Z291cyBnZW5vdHlwZS4gQWxzbywgeW91IGNhbiYjODIxNzt0IGJlIGhldGVyb3p5Z291cyBhbmQgcmVjZXNzaXZlLiBIZXRlcm96eWdvdGVzIGFsd2F5cyBkaXNwbGF5IHRoZSBkb21pbmFudCB0cmFpdC4=[Qq]

[c]aG9tb3p5Z291cy ByZWNlc3NpdmU=[Qq]

[f]V2F5IHRvIGdvLiBIb21venlnb3VzIHJlY2Vzc2l2ZSBwaGVub3R5cGVzIGFsd2F5cyBoYXZlIHR3byBsb3dlcmNhc2UgbGV0dGVycy4=[Qq]

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[qwiz qrecord_id=”sciencemusicvideosmeister1961-Cystic Fibrosis Interactive Reading (v2.0)”]

[h]Cystic Fibrosis, Interactive Reading

[i]

[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]cmVjZXNzaXZl[Qq]

[c]dHdv[Qq]

[/qwiz]

[qwiz qrecord_id=”sciencemusicvideosmeister1961-Guided Punnett Square, Autosomal (v2.0)”]

[h]Guided Punnett Square 1: Autosomal inheritance

 

[/qwiz]