Phenotype and genotype...

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BSC 1020 Homework
Unit E
Meiosis, Mendel, Oh My!
This homework is worth 25 points. Please use the textbook, the PPT lecture handouts of
Chapter 8 and 9, and the internet, to answer the following five questions
Question 1 (8 points)
You are unique, just like everyone else! In this activity, you will be using
several recognizable traits to demonstrate the diversity in humans. These traits are
controlled by a single gene with two alleles. Remember that alleles are alternative forms
of the same gene.
Dimpled chin A cleft in the chin is a dominant trait (D), while the absence of a cleft is
recessive (d).
Free earlobes The E allele for a free earlobe is dominant over the recessive e allele for
attached earlobes.
Freckles The presence of freckles is a dominant trait (F), while their absence is
recessive (f).
Mid-digit hair Hair on the middle segment of fingers (between two joint knuckles) is a
dominant trait (M), while the absence of hair is recessive (m).
Hitchhikers thumb The S allele for a straight thumb is dominant over the recessive s
allele for a bent thumb (i.e.: the tip of the thumb can bend backwards more than 45o)
Widows peak The W allele for widows peak is dominant over the recessive w allele
for a straight hairline. (Note: The hairline in widows peak forms a distinct point in the
middle of the forehead)
You can see pictures of all of these traits in Figure 9.12 (p 153) of your textbook, and
in the PDF file that is posted alongside the homework handout.
i)
For each of these traits, record your phenotype and genotype in Table 1. For the
phenotypes, use one of the following terms: Dimpled chin or Normal chin, Free earlobes
or Attached earlobes, Freckles or No freckles, Mid-digit hair or No hair, Hitchhikers
thumb or No hitchhikers thumb, Widows peak or Straight hairline.
For the genotypes, do the following: If your phenotype is recessive, indicate this with two
lower case letters (Example: dd), and if it is a dominant phenotype, use a single
uppercase letter followed by a big dash (Example: D).
TABLE 1
Trait
Dimpled chin
Free earlobes
Freckles
Mid-digit hair
Hitchhikers thumb
Widows peak
Your Phenotype
Your Genotype
ii)
Determine your overall genotype by tracing your probable genotypes from trait 1
through trait 5 until you reach the genotype number. Indicate that number in the box below.
TABLE 2
Earlobes
Freckles
Mid-digit
hair
Hitchhikers
Thumb
S
M
ss
F
S
mm
ss
E
S
M
ss
ff
S
mm
ss
S
M
ss
F
S
mm
ss
ee
S
M
ss
ff
S
mm
ss
My genotype number is =
Widows
Peak
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
W
ww
GENOTYPE
NUMBER
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Question 2 (6 points)
Use the media available to you to research and describe the following diseases.
Disease
Cystic
fibrosis
Duchenne
Muscular
Dystrophy
Hemophilia
Huntington
Chorea
Sickle Cell
Anemia
Tay-Sachs
Disease
Brief description of
underlying problem
Is the disease
Dominant
Recessive or
Sex-linked?
Is the disease
common in a
particular group?
Which ones?
Question 3 (4 points)
The ability of humans to taste the bitter chemical phenylthiocarbamide (PTC) is
an inherited trait, under the control of the two alleles of a single gene. The T allele for
tasting is dominant to the recessive t allele for non-tasting.
i)
Could two non-taster parents have a child able to taste PTC? Explain your answer.
ii)
Could two parents able to taste PTC have a non-taster child? Explain your answer.
iii)
Minnie and Mickey are married and both can taste PTC. Minnies mom and
Mickies dad are non-tasters. The couple is expecting their first child. What is the chance
that the child will be able to taste PTC? Show your work.
Question 4 (3 points)
As discussed on p. 165, red-green colorblindness results from a sex-linked recessive
allele. The dominant allele, N, produces normal color vision, and the recessive n allele is the
colorblind allele. A man with normal color vision marries a color-blind woman.
i)
What is the probability of their having a color-blind son? Explain your answer.
ii)
The woman gives birth to a color-blind daughter (who has no other chromosomal
abnormality). The husband sues for a divorce on the grounds of adultery. Will his case stand
up in court? Explain your answer.
Question 5 (4 points)
A mule is the offspring of a male donkey and a female horse. A donkey sperm
contains 31 chromosomes and a horse egg 32 chromosomes, so the zygote contains a total
of 63 chromosomes. The zygote develops normally. The combined set of chromosomes is
not a problem in mitosis, and the mule combines some of the best characteristics of horses
and donkeys. However, a mule is sterile, meiosis cannot occur normally in its testes and
ovaries. Explain why mitosis is normal in cells containing both horse and donkey
chromosomes, but the mixed set of chromosomes interferes with meiosis.

 

Solution ID:350938 | This paper was updated on 26-Nov-2015

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