Molecular Genetics Lecture 7 - Linkage and Genetic Mapping

What plays a huge role in discovering the functions of human genes?

linkage mapping

Alleles of two different genes do not always assort independently. True or false.

true

What is Mendel’s law of independent assortment?

alleles at one locus assort independently of alleles at another locus

What is genetic linkage?

tendency of genes that are closer to each other on a same chromosome to assort and inherit together

What are some examples of linked genes?

hair and eye colors

Allele do not assort independently if genes are

located next to each other or closer on a same chromosome (linked genes)

what is genetic linkage?

the exchange of chromosomal segments during cross over (recombination) takes place between large segments of chromosomes

What does genetic linkage lead to?

a generation of gametes with more parental alleles than recombinant alleles

crossing over is ____ likely to occur between closely linked genes than between those farther apart on a chromosome

less

recombination ______ significantly if the genes are closer to each other

decreases

what is crossing over in simple terms?

two non-sister chromatids exchange chromosomal segments

what are recombinants?

reshuffling of allele combinations between non-sister chromatids of homologous chromosomes

what are parentals?

alleles stay the same as parents because of no crossover

what is the phenotypic ratio that occurs when there is independent assortment?

1:1:1:1

what is the phenotypic ratio that occurs when there is complete linkage (no cross over at all)?

1:1

what is the results of incomplete linkage (limited cross over)?

parental gametes are 80% and recombinant gametes are 20% of these genes

what can incomplete linkage be used to measure?

the relative genetic distance between 2 genes (genetic mapping) based on recombination frequency

what is genetic distance?

relative distance between 2 linked genes on a chromosome can be estimated using recombination frequencies

what is genetic distance measured in?

map units or centiMorgans

how do you know if two genes are linked?

recombination frequency is less than 50%

what is two-point mapping?

estimation of genetic distance between 2 linked genes

what are some cross overs that are involved with three-point mapping?

single cross over, double cross over

what is single cross over (SCO)?

single exchange of chromosomes between two loci

what is double cross over (DCO)?

double exchange of chromosomes between three loci

how can you identify parental offspring?

highest frequency

how can you identify SCO offspring?

intermediate frequency

how can you identify DCO offspring?

lowest frequency

what is interference?

inhibition of further crossover by crossover events in nearby region of a chromosome

if there is complete linkage, there is

no cross over at all

if there is incomplete linkage, there is

reduced cross over

what do you use to construct a genetic map?

recombination frequencies

what is a locus?

location of a gene on a chromosome

what is a cytogenetic map?

based on the visual appearance of chromosomes after staining reveals distinctive features of different chromosomes

what is a genetic map?

relative distance and positions of genes on a chromosome estimated using recombination frequencies

what is a physical map?

relative distance and positions of genes on chromosomes expressed in nucleotide base pairs

what does physical distance mean in terms of linkage and genetic mapping?

distance between 2 genes on a chromosome expressed in nucleotide base pairs (DNA sequencing)

what are some applications of genetic/linkage mapping?

linkage mapping, forward genetics, genome sequencing

what is an application of linkage mapping?

linking a phenotype to a locus (gene) on a chromosome by estimating recombination frequencies

what is an application of forward genetics

start with a defective phenotype (breast cancer) and link the phenotype to a locus (BRCA1 gene) on a chromosome

what are forward genetic screens combined with and used for?

combined with linkage mapping to identify many genes in various biological processes in various organisms

how was the breast cancer suppressor gene BRCA1 discovered by?

genetic mapping