AY Honors/Heredity/Answer Key

Heredity

1. What is meant by the term "heredity"?

Heredity refers to the transfer of biological characteristics from a parent organism to offspring, and is practically a synonym for genetics, as genes are now recognized as the carriers of biological information.

2. Draw a picture of an animal cell and label the following parts: Cell membrane, cytoplasm, nucleus, nuclear membrane, ribosomes.

3A. What is a chromosome and where are they located?

A chromosome is a very long, continuous piece of DNA which contains many genes. Chromosomes are located within the nucleus of a cell.

3B. What is a gene and where is it found?

Genes are the units of heredity in living organisms. They are encoded in the organism's genetic material (usually DNA or RNA), and control the physical development and behavior of the organism. They are located on the chromosomes.

4A. What is meant by the term "allele"?

An allele is any one of a number of viable DNA codings of the same gene occupying a given position on a chromosome. Humans have paired chromosomes in their somatic cells, and these contain two copies of each gene. In some cases the two copies of the gene are identical — that is, have the same allele. In other cases, the two copies are different. Humans inherit two copies of every gene, one copy comes from the mother, and the other comes from the father.

4B. How does a dominant allele differ from a recessive allele?

Characteristics associated with a certain allele can sometimes be dominant or recessive, but often they are neither. A dominant trait will be expressed when at least one allele of its associated type is present, whereas a recessive trait will be expressed only when both alleles are of its associated type.

4C. Determine which allele you have of the following genetic traits:

• 

  Widow's Peak

• 

  Free earlobe(left) and attached earlobe (right)

• Dimples.jpg

  Dimpled cheeks

Widow's Peak

A widow's peak is a descending V-shaped point in the middle of the hairline (above the forehead). The trait is inherited genetically and dominant. The term comes from English folklore, where it was believed that this hair formation was a sign of a woman who would outlive her husband.

Free earlobe

The free earlobe is a dominant trait, and its counterpart is the attached earlobe. Geneticists are unsure if it is the result of a single gene or if multiple genes are involved.

Dimples

Dimples are small indentations in the cheeks most evident when a person possessing this trait smiles.

Curved thumb

Bent pinky

Digit hair

Rolling tongue

Second toe longer

4D. Using a punnet square, predict the ratio of offspring produced from these monohybrid crosses: TT (tall) crossed with tt (short), Tt (tall) crossed with Tt (tall), Tt (tall) crossed with tt (short).

A punnet square is a genetic diagram used to determine the probability of an offspring expressing a particular genotype. An allele can be dominant or recessive. If a dominant allele (represented as a capital letter) is present, the trait will be expressed. The recessive trait will be expressed only of both alleles are recessive (represented as a lower case letter).

In our example, tallness is the dominant allele and it is represented by the capital 'T'. Shortness is the recessive allele, and it is represented as a lowercase 't' (not by an S). First we construct a table showing the alleles of the parents. The mother (with alleles TT) is generally shown across the top, and the father (with alleles tt) is shown down the left column:

	T	T
t
t

Next we copy the alleles from the mother's row and the father's column, placing the dominant allele ahead of the recessive one (so we would always show Tt rather than tT). In this case, all four outcomes are identical: Tt.

	T	T
t	Tt	Tt
t	Tt	Tt

Next we show a Tt mother and a Tt father. In this case, the pair has produced one TT, two Tt's, and one tt.

	T	t
T	TT	Tt
t	Tt	tt

Finally, we show the cross between a Tt and a tt. In this case, we get two Tt's, and one tt.

	T	t
t	Tt	Tt
t	tt	tt

So what does all this mean? A TT individual has two dominant alleles for tallness. All of that individual's offspring will be tall, but all will not necessarily be TT. A Tt individual will also be tall, but can have short offspring if crossed with either another Tt (75% tall, 25% short), or if crossed with a tt (50%-50%). Only individuals with tt alleles will be short, but if crossed with a TT or a Tt, can still have tall offspring (though all offspring will be carriers for shortness).

9. Know at least five genetic disorders and tell a story about a famous person or someone that you know who has had one of these disorders.

• Color-blindness
  • Former U.S. President Bill Clinton
  • Former Majority Leader, Senator Bob Dole.
• Cystic fibrosis
• Down syndrome
  • Stephane Ginnsz, actor (Duo (film)) First actor with Down syndrome in the lead part of a motion picture.
  • Chris Burke, actor (Life Goes On) and autobiographer
  • Andrea Friedman, actor (Life Goes On), guest appearances on many other shows
  • Pascal Duquenne, actor (Le Huitième Jour aka The Eighth Day, Toto le héros aka Toto the Hero)
  • Anne de Gaulle (1928-1948), daughter of Charles de Gaulle
• Hemophilia
• Huntington's Disease
  • Woody Guthrie
• Sickle Cell Anemia
• Spina bifida
  • Olympian and eight-time Boston Marathon winner Jean Driscoll[1]
  • 1980s rock star, John Mellencamp
  • Welsh Paralympian, Tanni Grey-Thompson
  • U.S. country music singer, Hank Williams
• Tay-Sachs disease

References

• K12science.org - Genetic traits