BIOL 2500 - Topic 6 (part 1)

Why is it important to know where genes are located on chromosomes

1.) It allows us to understand complex genotypes and their interactions (i.e. genetic interactions)

2.) It allows us to understand gene structure and function, and how mutations changes both the structure and function

3.) It helps us infer evolutionary relationships between related organisms, based on how many bp have changed

Chromosome map

Refers to the arrangement of genes on the chromosome

Loci

Term used for the location of genes

Two kinds of chromosome maps

1.) Recombination maps (i.e. relative maps)

2.) Physical maps

Recombination maps

1.) It maps the loci of genes that have been identified by mutant phenotypes that show single-gene inheritance patterns

2.) The distance between them are measured relative to one another, using recombination frequency or map units

What can we use to build recombination maps

Linkage analysis

Physical maps

Maps that show the specific gene locations on a chromosome, by measuring the distances between them using kbp (i.e. the number of nucleotides)

Independent assortment

It is when different genes on different chromosomes assort independently, since chromosomes assort independently

Homologous recombination

Refers to the crossing over that occurs during prophase I, which results in recombinant chromosomes (i.e. non-parental chromosomes)

Four possible gametes from independent assortment, with homologous recombination

It results in 4 possible gametes, two parental and two recombinant, but all of which have a 1:1:1:1 ratio

Parental/non-recombinant chromosomes

Refers to chromosomes that do not cross over and therefore retain the same alleles as the parent chromosome

Syntenic genes

Refers to genes that are located on the same chromosome

Consequences of syntenic genes

Genes that are very close to one another may not be able to independently assort, therefore resulting in genetic linkage

Genetic linkage

1.) It produces a distinctive pattern of gamete genotypes, since they recombine less during meiosis, such that the 1:1:1:1 ratio is not seen

2.) Instead, you see a higher frequency in parental chromosomes and a lower frequency for recombinant chromosomes (since not a lot of crossing over is occurring)

Syntenic genes that are far apart from one another

They do assort following Mendel’s law of independent assortment

Parental and recombinant are ________ to what the parents are

Relative

Parental and recombinant are relative to what the parents are

1.) This means that the parental is not always homozygous, sometimes it is heterozygous

2.) Parental just means it is the same as the parent, not that it is homozygous

2.) Recombinant means it is different from the parent, not that it is heterozygous

Frequency of gamete genotypes/progeny phenotypes when unlinked

1.) Independent assortment occurs, therefore the parental gametes will be produced the same amount as recombinant gametes

2.) Such that in a test cross, 4 genetically different gamete combnations are produced, with a 1:1:1:1 ratio

Frequency of gamete genotypes/progeny phenotypes when linked

Independent assortment does not occur, therefore the parental gametes will be produced more by chance (>50%) and the recombinant gametes will be produced less by chance (<50%)