BI30-GB2 Investigate the storage, transmission, and expression of genetic information at the chromosomal level. a. Describe the structure and organization of chromosomes, including supercoiling of DNA. (K) b. Investigate the importance of meiosis, including crossing-over and homologous chromosomes, creates genetic variation in gametes. (K) c. Explore chromosomal recombination and mutation and their implications on evolution by natural selection. (K) https://docs.google.com/presentation/d/19GDM6VHuQlF8XAqDNLtee-AZciFv0CHpXMeRhSqZ78/present?slide=id.i0
Please complete the Meiosis Internet Tutorial d. Recognize various types of chromosomal abnormalities (e.g., deletion, insertion, non-disjunction, inversion, and translocation) and how they may lead to chromosomal disorders within a variety of plants and animals. (K)
Human Genetic Disorders
You will be given a specific genetic disorder found in humans. You will be responsible for giving a short
(1-2 minute) presentation that explains each of the following points about your disorder.
1. A description of the symptoms of the disorder (*make sure that you can pronounce it!)
2. How is it caused? What kind of chromosomal abnormality is the cause? Please include a sketch or image of the chromosome or karyotype. If it is not a chromosomal abnormality, how does it happen?
Disorder List
Cystic Fibrosis
Charcot –Marie–Tooth disease (CMT)
Hemophilia
Tay-Sachs
Achondroplasia
Huntington's Disease
Fragile X

Duchenne Muscular Dystrophy
Red-Green Colorblindness
Phenylketonuria (PKU)
Sickle Cell Disease
Usher Syndrome
Polydactyly
Marfan Syndrome
Maple Syrup Urine Disease
Cri du Chat Syndrome
Neurofibromatosis (NF)
Williams Syndrome e. Represent organisms’ genomes using karyotypes. (K, S)
Please complete a chromosome study. f. Identify the haploid, diploid and polyploid conditions of organisms, including those conditions’ advantages and disadvantages. (K) http://study.com/academy/lesson/polyploidy-definition-types-quiz.html
Why would it be advantageous to have more chromosones? g. Investigate applications of and limitations to gene mapping as it pertains to single-gene and polygenic traits. (K, STSE)
Gene Linkage & Chromosome Maps http://www.biologycorner.com/APbiology/inheritance/12-2_gene_linkage.html
Thomas Hunt Morgan studied fruit flies and found that in some crosses, expected outcomes weren't happening. Further experiments confirmed that alleles located on the same chromosome are inherited together.

*Mendel's dihybrid cross AaBb x AaBb would not have yielded a 9:3:3:1 ratio if he had chosen alleles located on the same chromosomes.
A common cross used to demonstrate linkage groups is the cross of a heterozygote wild type vestigial wings/ black body with a recessive mutant.
The cross would look like this
It may be easier at this point to use the older notation for letters, where the cross would look like AaBb x aabb
There are two possible arrangements for the heterozygote (AaBb) in the above cross.
If the dominant alleles are on different chromosomes (Ab) then it is called TRANS
If the dominant alleles AB are on the same chromosome, it is called a CIS arrangement
Cross produces: 50% wild type / 50 % mutant
If no crossing over has occurred, the outcome will always be 1:1, however this is not what Thomas Hunt
Morgan observed.
Wild Type
Expected
50
Observed
33

Mutant
Vestigial Wings, Wild
Wild, Black Body
50
0
0
33
17
17
Question: How would you explain these results? The two offspring that did not look like either parent are called recombinants. They are a result of CROSS-OVER which occurred during meiosis, the alleles switch position.
Using this methodology, the chromosomes of the fruit fly were mapped. Each MAP UNIT represents how far apart the alleles are on the chromosome, the number is based on how often crossing over occurs.
How to Create a Chromosome Map from Crossover Frequencies
Recombination: During crossing-over (prophase I of Meiosis), genes on chromosomes switch places.
Crossover is random, but the likelihood that 2 genes crossover will increase if those genes are farther apart. Genes closer together are more likely to "stick together" and not switch places.
Gene Linkage Maps: Using the crossover frequencies, you can construct a map to represent the distances between genes.
This map shows chromosome #2 of Drosophila melanogaster . The distance between the genes can be written as a percentage or as a MAP UNIT. The gene for body color and and wing size are 17 map units apart.

Sample Problem:
Given the crossover frequency of each of the genes on the chart, construct a chromosome map.
Gene
A-C
B-C
B-D
A-D
Frequency of Crossover
30%
45%
40%
25%
Step 1: Start with the genes that are the farthest apart first: B and C are 45 map units apart and would be placed far apart.
B ----------------------------------------- 45% ------------------------------------------C
Step 2: Solve it like a puzzle, using a pencil to determine the positions of the other genes.
Step 3: Subtraction will be necessary to determine the final distances between each gene.

Practice Problems
1. In Drosophila, bar shaped eyes (B), scalloped wings (S), Crossveinless wings (W), and Eye Color (C) are located on the X chromosome. The recombination frequency of each gene is indicated on the table.
Construct a chromosome map.
Gene
W-B
W-C
B-C
B-S
W-S
C-S
Frequency of Crossover
2.5%
3.0%
5.5%
5.5%
8.0%
11.0%
2. The following chart shows the crossover frequencies for genes on an autosome of the Armor Plated Squirtlesaur. Construct a chromosome map.
Gene
P-Q
P-R
P-S
Q-R
Q-S
Frequency of Crossover
5%
8%
12%
13%
17%
Mapping works well in these examples with multiple genes. What if there was a single gene? Or multiple genes over multiple chromosones?