Download Chapter 15 Assignment - kyoussef-mci

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Date: _________________________
In-Class Assignment
Chapter 15 – Chromosomes and Heredity
Section A: Linked and Sex-linked Genes – Text pgs. 175-177
1. Who were the scientists in 1902 that discovered that the behavior of chromosomes during
meiosis was related to the behavior of “factors” or alleles in Mendel’s experiments?
2. Linked Genes are those genes that are located on the same chromosome. As a result, they
tend to be inherited together in genetic crosses. For example, genes A, b and C on the
chromosome on the right are considered to be linked because they are on the same
chromosome.
A
a. Would you expect the results of breeding experiments to follow those expected
from Mendel’s laws? Explain why or why not.
b. Based upon what you know about genetics so far, what event or process during
meiosis might occasionally “break” the physical connection between genes on
the same chromosome?
b
C
c. In reality, the genes for seed colour and seed shape in peas are said to be
linked (i.e. on the same chromosome). Why do the alleles for seed colour and
seed shape always segregate and assort independently? Hint: look at the
picture of the chromosome on the right. Why are b and C genes almost always
inherited together, while A is almost always inherited separately from b and C?
3. Define: sex-linked inheritance. Why are very few Y-linked traits known?
4. “Many times in the history of biology, important discoveries have come to those insightful
enough or lucky enough to choose an experimental organism suitable for the research problem
being tackled” (Campbell & Reece, 2005). An example is Mendel and the “Humble Pea”.
Explain two reasons why fruit flies are excellent experimental organisms for Morgan?
5. In Drosophila flies, describe the genotype and phenotypes of the mutant and wild-type flies for
eye colour only. Note: your textbook does not write the genotypes correctly. Read the
description below which shows you the correct notation. It may be a little confusing at
first, but it is imperative that you understand it because you will be using this notation
for a lab later this week.
Trait(s)
G/T
Phenotype
Wild-Type (Dominant)
Mutant (Recessive)
Phenotype
Normal colour and wings
Black, vestigial wings
Genotype
bl+ bl+ vg+ vg+
bl bl vg vg
Eye Colour
Genotype
Body Colour and
Wing Type
In fruit fly genetics, the normal fly is called a "wild type" and any fly exhibiting a phenotypic mutation is
called a "mutant". Mutant flies are given names that generally denote the type of mutation the fly
exhibits. For example, the mutant "ebony" has a much darker body than the wild type fly. Each mutation
is also given a letter code. Thus, in the case of ebony, the code is a lower case e. The wild type fly is
denoted by a superscript + over the mutant letter code. For example, e+ denotes a wild type fly for the
ebony body trait - meaning it has normal body color (not ebony).
The above description is for a gene located on an autosome (a non-sex chromosome). Of course, fruit
flies also have sex chromosomes and they contain a subset of genes as well. If the gene is located on
a sex chromosome, we use a slightly different notation. Under normal diploid conditions a female fruit
fly has two X chromosomes, a male has an X and a Y chromosome. Sex-linked genes are located on
one of the sex chromosomes (usually the X chromosome). Thus, the genotypic notation for a mutant
gene for white eye color on the X chromosome would look like:
Xw Xw = white-eyed female
Xw+Xw = wild type heterozygote female
Xw Y = white-eyed male
Xw+ Y = wild type male
6. Explain the full experiment and results that Morgan used which proved that some genes are
sex-linked. Use Punnett Squares to demonstrate the crosses. Use appropriate genotype
notation.
7. If females have two X chromosomes and males only have one, why is it that both males and
females produce the same amounts of proteins coded by genes on X chromosomes?
Section B – Patterns of Inheritance and Nondisjunction - Pg. 211, 214, 175-177, 226
1. Based upon the readings, hypothesize the genotypes of individuals with genetic diseases for
each type of inheritance pattern. Assume allele A is dominant over allele a.
a. Autosomal Dominant
i. You have the disorder if you have the following genotype(s):
ii. You do not have the disorder if you have the following genotype(s):
b. Autosomal Recessive
i. You have the disorder if you have the following genotype(s):
ii. You do not have the disorder if you have the following genotype(s):
iii. You are a carrier if you have the following genotype(s):
c. Sex-Linked Dominant (X-Linked) – Distinguish between male and female genotypes
i. You have the disorder if you have the following genotype(s):
ii. You do not have the disorder if you have the following genotype(s):
d. Sex-Linked Recessive (X-Linked) – Distinguish between male and female genotypes
i. You have the disorder if you have the following genotype(s):
ii. You do not have the disorder if you have the following genotype(s):
iii. You are a carrier if you have the following genotype(s):
2. Complete the accompanying worksheets entitled, Developing Conclusions about Different
Modes of Inheritance and Pedigree Analysis.
3. Some genetic diseases are caused by nondisjunction.
a. Define nondisjunction. When can non-disjunction occur during meiosis?
b. Hypothesize the meaning of: trisomy and monosomy.
c. The following are karyotypes of different individuals. For each answer the following
questions:
i. What problem is shown?
ii. What is the resulting disorder?
iii. Would this be labeled as monosomy, trisomy or neither?
iv. What is the gender of the individual?
Condition
Syndrome
Trisomy 21
Down
Trisomy 18
Edward
Trisomy 13
Patau
XXY
Klinefelter
XYY
Jacobs
XXX
XO (1 X
chromosome
only)
Triple X
Turner
Characteristics
Autosome
Intellectual disabilities, abnormal patterns of palm creases,
almond-shaped eyes, flattened face, short stature
Intellectual and physical disabilities, facial abnormalities,
extreme muscle tone, early death
Intellectual and physical disabilities, wide variety of defects in
organs, large triangular nose, early death
Sex Chromosome
Sexual immaturity (inability to produce sperm), breast
swelling
Typically no unusual symptoms; some individuals may be
taller than average
Tall and thin, menstrual irregularities
Short stature, webbed neck, sexually underdeveloped