genetic map
a diagram that describes the order of genes along a chromosome
synteny
two or more genes are located on the same chromosome. (genes that are syntenic are physically linked)
genetic linkage
genes that are close together on the same chromosome tend to be transmitted as a unit
*linkage can be altered during meiosis (crossing over occurs during prophase of meiosis I)
linkage groups
a term used for chromosomes because a group of genes are physically linked together
*# of linkage groups = # chromosome types; humans have 22 autosomal linkage groups and an X chromosome linkage group (males have a Y chromosome linkage group)
*human mitoc
dihybrid cross
geneticists follow two or more characters in a cross (trihybrid cross = 3 characters)
genetic recombination
crossing over occurs in which two homologous chromosomes exchange pieces resulting in a combination of alleles different from the original chromosomes
*the grouping of linked alleles has changed
--> now haploid cells are called "nonparental cells" or "rec
parental offspring (nonrecombinant offspring)
offspring that have inherited the same combination of alleles that are found in the chromosomes of their parents
Bateson and Punnett
found that some traits may not assort independently
*studied flower color and pollen shape in a cross with a sweet pea
*refuted mendel's law of independent assortment saying a dihybrid cross between two heterozygous individuals should yield a 9:3:3:1 phen
Bateson and Punnett's experiment
1. cross true breeding strain with purple flower (PP) and long pollen (LL) X with red flower (pp) and round pollen (ll)
2. F1 had all PpLl
3. F2 had 4 different phenotypic categories but NOT in 9:3:3:1 ratio! (greater proportion of the two phenotypes foun
Morgan
studied three characters in drosophila;
*crossed wild-type male fruit flies with grey body (y+), red eyes (w+), and long wings (m+) mated to females with yellow bodies (yy) white eyes (ww) and mini wings (mm)
*F1 produced wild-type females, and males with
explanation for nonparental combinations
homologous X chromosomes (in the female) can exchange pieces of chromosomes and produce new, nonparental combinations of alleles and nonparental combinations of traits in F2 generation
*there are fewer nonparental offspring if the genes are located close
double crossover
two homologous chromosomes to crossover twice (very unlikely)
*grey body, white eyes, and long wings
chi square analysis
used to determine if the outcome of a dihybrid cross is consistent with linkage or independent assortment
*standard hypothesis: two genes are not linked and assort independently (allows us to calculate the expected number of offspring based on the genotyp
null hypothesis
assumes there is no real difference between the observed and expected values
if chi square value is low
we cannot reject the null hypothesis and infer that the genes assort independently
*if chi square value is high we can reject our hypothesis and accept the alternative hypothesis (genes are linked)
Creighton and McClintock
*hypothesis: offspring with nonparental phenotypes are the product of a crossover
*proved that crossing over produced new combinations of alleles and resulted in the exchange of segments between homologous chromosomes
*microscopically distinguished two ho
corn
used in creighton and mcClintock's experiments
*has 10 chromosomes per set
*some strains were found to have an unusual chromosome 9 with a darkly staining knob at one end
*abnormal 9s could also have an extra piece of chromosome 8 attached at the other en
knobbed end of chromosome 9
gene located near the knobbed end of chromosome 9 provided color to corn kernels (C or c)
translocated piece of chromosome 8
second gene located near the translocated piece of chromosome 8 affected the texture of the kernel endosperm
*Wx = starchy endosperm
*wx = waxy endosperm (recessive)
crossover with a normal 9 and a knobbed/translocated 9
produces a chromosome with either a knob or translocation but not both
*distinctly different than either of the parental chromosomes
parts of the corn plant
*tassel: pollen-bearing structure
*silk (equivalent to the stigma and style): connected to the ovary
*ovary: develops into an ear of corn after fertilization
*each kernel is a separate seed that has inherited a set of chromosomes from each parent
Colored, waxy (Cc wxwx) and colorless waxy (cc wxwx)
unambiguous phenotypic categories (can only be produced if recombination occurred in parent A)
*colored, waxy could only happen if recombination did NOT occur in parent A (must pass the knobbed, translocated chromosome to offspring)
*colorless and waxy co