Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 16: Chromosomes and Genes - Coggle Diagram
Chapter 16: Chromosomes and Genes
Linkage: genes are linked because they're on the same chromosome
Example
Red, long x white, short -->
F1: all red, long -->
F2: red, long; red, short; white, long; white, short (parental genotypes were more common than recombinant)
Alleles of different genes on the SAME CHROMOSOME can recombine as a result of crossing over
Nonsister chromatids of homologous chromosomes form a tetrad at the chiasma (site of crossing over) --> metaphase I --> metaphase II: the homologous chromosomes separate --> sister chromatids separate and daughter cells get either parental or recombinant chromosomes
Frequency of crossing over can be measured using a test cross (cross between heterozygous x homozygous recessive)
must use homozygous recessive parent because it allows us to determine genotype of fly (if another heterozygous parent was used or homozygous dominant parent was used, then the homozygozity of the gene would dominate the other allele)
measure frequency of crossing over = (recombinants/all offspring) x100
If 2 genes are close to each other on the same chromosome, they tend to be inherited together during meiosis
ex. determine specific sequence of disease gene using SNP --> how frequently do people with this SNP have the disease?
In people with the SNP, if there is an equal ratio of sick people as there are healthy people --> no association of this particular SNP and the disease gene --> CANNOT determine location of disease gene
ex. Association between mutant allele of a gene and G-C SNP (lots of sick people have the G-C SNP) --> the mutant allele is located near the SNP
Sex chromosomes
The X and Y chromosome are mostly different (X a lot bigger than Y) but can pair with each other at a smmall region of homology
XX: female, XY: male
Many X-linked traits in humans are more common in males than in females (i.e. red-green color blindness, hemophilia, duchenne muscular dystrophy, glucose-6-phosphate deficiency)
Why? Because the Y chromosome lacks most of the genes for these traits
Mutant mom
Males that inherit a recessive X linked mutation from their mother WILL express mutation
Females that inherit a recessive X-linked mutation from their mother will NOT express this mutation
Mutant dad: no offspring will be affected
BUT daughters WILL INHERIT the trait
males WILL NOT inherit the trait because they get normal X from mom, Y from dad)
In mammals, gene dosage in males and females is equalized by inactivating the X chromosome in females
ex. callico cats: different cells inactivate different X chromosomes
Variation in chromosomes number and structure
Aneuploidy: variation in the number of a single member of a chromosome set
Non-disjunction can occur in meiosis I or II --> can cause miscarriagee, more common in older women
meiosis I: nondisjunction causes homologous chromosomes to not unpair
meiosis II: nondisjunction that causes sister chromatids to not unpair
Polyploidy: increase in the number of haploid chromosome sets beyond the diploid number (3N, 4N, 6N, etc.)
ex. wheat, kiwi, potato
polyploidy has desirable agronomic trait: bigger
polyploidy can be engineered
triploid watermelon (3n): 4n x 2n
Types of chromosomal rearrangements
deletion: removes a chromosomal segment
duplication: repeats a segment
inversion: reverses a segment within a chromosome
translocation: moves a segment from one chromosome to another, nonhomologous one