Download Heredity

Name ______________________________________________________
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Heredity
Inquiry / Discovery Lab
From previous lab, keep in mind the following:
• How do we conduct good science? (… develop concept of Scientific Method)
• How do we design an appropriate experiment?
Why do you possess your specific physical traits or characteristics? Are these traits really
determined by your genes, or can you control some of them? Where, or more correctly, from
whom did you get these traits? Did you get all of them from you mother? …from your father?
Or did one or more traits seem to skip your parents and come from your grandparents? If your
siblings have the same parents as you, do you look just like them? Why not? Why didn’t you
get one or more traits that one of your parents has?
IN CLASS DISCUSSION:
All of these questions deal with the study of heredity. Heredity is the study of how traits (and the
genetic information that encodes them) are passed on. You already have, or will, be studying
genetics in class. Genetics is often the broader science, dealing more in structure of genes, and
the processes that lead to gene expression. This heredity lab will give a human application to
concepts discussed in lecture. You will be taking an inventory of traits that you, your relatives,
and you classmates have (or have not!). You will summarize class data, and from them calculate
the relative frequencies of each trait. You will learn about the genetic basis for particular traits.
Finally, you will make predictions/deduce (when possible) your own genotype for a particular
trait that you possess.
Terms:
Allele – one form of a specific gene. There may be (and often are) two or more alleles for a
given gene. Each allele expresses the information encoded in the gene somewhat differently.
For example, there is one gene that determines flower color in peas, but two alleles of that
gene. One allele codes for purple flowers; plants with the purple allele have purple flowers.
Another allele codes for white flowers; white flowered plants have “white” alleles. Alleles
occur in pairs in adult organisms; therefore, the flowering plants of our example might have
two of the same allele (either purple or white), or one of each allele, depending on what they
inherited from their parents.
Dominant allele – this is an allele that is always expressed when it is present. For example,
purple is a dominant allele in peas. Therefore, whether a plant inherits a P allele from both
parents, or only from one, the offspring will be purple. This is called a “dominant” allele
because whatever other allele it is paired with, it will always “dominate”, or be expressed.
Recessive allele – an allele that may or may not be expressed, depending on what other allele
it is paired with. When paired with another like itself, they trait will be expressed. When
paired with a dominant allele, the recessive will not be expressed. For example, the white
flower allele, p, is recessive in peas. Therefore, for a plant to express white flowers, it must
have a genotype of pp. What will be the phenotype of a plant with the genotype Pp?
Character(istic) – the same as a trait.
Name ______________________________________________________
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Genetics – the study of the genes; how they are put together, how they function, how they
are passed on.
Genotype – the specific allele combination for a particular trait. If we designate purple
alleles as “P” and white alleles as “p”, then we might see three possible genotypes: PP, Pp,
pp.
Phenotype – the physical expression of the genotype; what we might call a “trait”. For
example, blood types O, A, B, AB are all different phenotypes that are genetically based.
Heredity – the study of how traits are passed from generation to generation.
Pedigree analysis – the keeping of records among family members of specific traits.
Trait – a condition that is genetically determined and inherited; a character.
________________________________________________________________________
Lab Assignment: working in groups of 3-4, you will examine yourself or each other for the
following traits (see diagrams and discussion, below). Each group will record the number of
individuals within their group that has specific traits. When all groups are finished we will
combine that data for the entire class, calculating class frequencies.
Traits:
PTC: Each person will taste a piece of untreated paper. Next, each person will chew a piece
of paper that was soaked in PTC (phenythiocarbamide), a harmless chemical. Being able to
taste the PTC is genetically determined by a dominant allele, T; the recessive (not being able
to taste it) is t.
Hairline: The dominant hairline is the widow’s peak, W. The recessive allele for straight
hairline is w.
Name ______________________________________________________
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Eye color: although total eye appearance is controlled by several genes, blue eyes is
recessive (e) to non-blue (brown, hazel, green, etc.) (E).
Tongue Rolling: The ability of rolling the tongue (R) into a tube is dominant to the inability
to roll the tongue (r).
Earlobe attachment: Earlobes that dangle below where the ear attaches to the side of the
head are said to be “free”; this condition is dominant, F. Attached earlobes have the recessive
allele, f.
Name ______________________________________________________
4/7
Hitchhiker’s Thumb: If the distal portion of the thumb can be flexed 60-85° from vertical,
that person has the recessive n allele. The dominant allele (normal, straight thumb) is N.
Thumb crossing: Bring your hands together and interlace your fingers. Left thumb on top
of right thumb (L) is dominant to right thumb on top of left (l).
Bent Pinky Finger: If the distal joint of your pinky finger is bent sharply toward your other
fingers, you have the dominant allele, B. The recessive allele for straight fingers is b.
Name ______________________________________________________
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Mid-Digit Hair: Look at the middle segment of your ring finger. If hairs are present (even
one!) you have the dominant allele, H. Lacking hairs indicates the recessive allele, h.
Blood type: Three alleles (A, B, O) can give rise to four blood types: A, B, AB, O. Both the
A and B alleles are dominant to the recessive O allele. A and B alleles are codominant to
each other. Fill in the following chart for possible genotypes of each phenotype.
Phenotype Possible Genotype(s)
A
B
O
AB
Fill in the following table for your group. When we have discussed data from all the
groups, you will complete the last two columns of the table:
Trait
Class Phenotypic Pedigree Chart
Your
Your
Number in
Number in
Phenotype Genotype Your Group Class w/ Trait
Dom Rec. Dom. Rec.
% of Class
with Trait
Dom. Rec.
PTC Taste
Hairline
Eye
Color
Tongue
Rolling
Earlobe
Attachment
Hitchhiker
Thumb
Thumb
Crossing
Bent
Pinky
Mid-digit
Hair
Blood
Type
A:
AB:
B:
O:
A:
AB:
B:
O:
A:
AB:
B:
O:
Name ______________________________________________________
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1. Which phenotypes do you have that are dominant? List them.
2. Which phenotypes do you have that are recessive? List them.
3. If you and a particular classmate shared all the same traits examined in this lab, what
other traits do you have that you could use to describe your uniqueness?
4. PTC can be tasted by those people that have a certain allele. Those people that have a
different allele are unable to taste PTC. Why was it important that the paper not have a
taste?
5. Is it possible to determine the genotype of a person showing a dominant phenotype?
Why, or why not? A recessive phenotype? Why, or why not?
6. Are dominant alleles more common than recessive alleles? Why or why not? Are
dominant phenotypes more common than recessive phenotypes? Why or why not?
Name ______________________________________________________
Trait
PTC Taste:
Taster (T) /
non-taster (t)
Hairline:
Widows peak (W)
vs. straight (w)
Eye color:
Non-blue (E)
vs. Blue (e)
Tongue
Rolling:
Rolling (R) vs.
Flat tongue (r)
Earlobes:
Free lobes (F)
vs. Attached (f)
Hitchhiker
Thumb:
Normal thumb (N)
vs. Hitchhiker (n)
Thumb Crossing:
Left over right (L)
vs. right over left (l)
Bent Pinky:
Bent pinky (B) vs.
Normal pinky (b)
Mid-digit
Hair:
Hair present (H)
or Absent (h)
Blood Type:
A, B, AB (all dom)
O (rec)
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Phenotypic Pedigree Chart
-You- -Sibl- -Sibl- Moth. Fath. Mat. Mat. Pat. Pat.
1
2
Gr-m Gr-f Gr-m Gr-f