get nerdy with judy scher bee sex...it’s just plain fascinating to nerds like me!!! this is a big...
TRANSCRIPT
Get Nerdy with Judy Scher
It’s just plain fascinating to nerds like me!!!
This is a BIG area of research now
See articles in magazines like “American Bee Journal” on bee genetics
and may hear future speakers talk about this in conventions.
Helps to appreciate the challenges in breeding bees for selective traits
Fast review of chromosomes and genes
Epigenetics: What makes a queen and not a worker
Haplodiploidy in Hymenoptera
Mixing of the honey bee gene pool
Recombination of genes
Promiscuity of queen
Sex alleles: What makes “femaleness/maleness” in honey bees?
DNA structure (nucleotide pairs)
Mitosis (cell division)
Genes involved in hygienic traits
Selective breeding for certain traits
Cape bees (thelytoky)
(hey!...we only have 40 minutes!!!)
Genes located on Chromosomes in the cells
Each chromosome is composed of loooong strand of DNA
DNA contains all the genetic information of an organism
e.g.. the gene that codes for producing the protein insulin
Location of the gene on the chromosome is a Locus (plural is Loci)
Different expressions of the same gene are alleles (e.g.. brunette or blonde or red hair)
Dominant vs Recessive Traits
Heterozygous alleles Same gene with small differences in DNA
One may be Dominant and the other Recessive.
Example: Gene for brown eyes is dominant to gene for blue eyes
Homozygous alleles Same gene with identical DNA
2 recessive genes will be expressed in this case because there
is no dominant gene.
Diploid vs Haploid
All FEMALE hymenoptera are Diploid
Chromosomes are paired: 1 mother + 1 father
Queen and Worker
Have complete genetic material 50% from their mother, 50% from father.
Homologous Chromosomes
Haploid # A. mellifera =16 16 pairs of chromosomes in female
Diploid # A. mellifera = 32
Cells of DRONES (all hymenoptera males) are Haploid
Chromosomes are NOT paired.
Drones receive ONE set of chromosomes from the unfertilized egg
Cells have the haploid # of 16 chromosomes
The Drone:
Does not have father, but has a grandfather
Does not have sons, but has grandsons
I lied! There is one type of cell in all females that must be haploid
– THE EGG
Gametes are the egg and sperm
produced in the ovaries and testis by MEIOSIS – 2 special divisions of the cell
1’st results in 2 haploid cells (females)
2’nd like mitosis – results in 4 cells (females), 2 cells (drones)
Reduction of chromosomes by half from diploid to haploid
So the union of egg and sperm results in an organism with a diploid set of
chromosomes - not multiples!!!
Very important to maintain a good gene pool
Mixing the genes results in “hybrid vigor”
Less mixing results in poor genetic variability (inbreeding) and more lethal genes
In North America the A. mellifera gene pool is limited
A. mellifera has very few queen breeding operations
We can’t import bees from other countries
A gene pool is the collection of all the genes of a population within a species.
e.g.. The population of A. mellifera in Canada and the US.
The sum of all the alleles at all the loci.
In the first phase of meiosis CROSSING OVER of chromosome pairs
- resulting in even more mixing of genes.
In A. Mellifera meiotic cross-over areas are greater than any other animal studied.
40x more than in humans!! Kudos to the female bee!!!!!
Meiosis (in female hymenoptera) results in mixing of genes
half from father, half from mother
keeps variability in the gene pool
Interphase DNA
replicates
Prophase I Crossing Over
(Recombination)
Tetrads of homologous
chromosomes
X-over at non gene areas
Metaphase I: Pairs line up
Spindles attached
Anaphase I Homologous pairs
separated
Telophase I nuclear membrane forms
Cytokinesis takes place
Formation of 2 haploid
cells
Prophase II
Metaphase II
Anaphase II
Telophase II
4 haploid cells all genetically different
(poor drones getting ANOTHER bad rap)
Meiosis in the honey bee drone is incomplete. “Meiosis Interruptus”
The sperm are identical.
No mixing of the gene pool in the drone!!!
In the first division the process is confused!
But still goes on to a second division to produce germ cells which will divide
and become sperm.
Meiosis I
Meiotic apparatus “blebbed” off cell
No spindles attach to chromosomes
Incomplete division
Cell divides as in Meiosis II
2 identical cells will develop into sperm
Promiscuity of the virgin queen leads to more genetic variability
Queens may mate with up to 20 drones
A well mated queen is recognized by the workers:
Queen puts out more queen pheromone
Better retinue
Less chance of supercedure.
CAVEAT: if breeding to select a certain trait, drones need to all have that trait.
Leads to less variability
There are no sex chromosomes in honey bees like there are in animals.
Mammals have one unmatched pair of chromosomes XX = female Xy = male
In bee there is a key gene governs sex determination
csd “complementary sex determiner
gene is on one locus on one chromosome
csd has around 19 different alleles: Expression of the same gene
.......................
This csd gene is expressed in the embryo in the egg at 12 hours
It has been mapped to chromosome # 8 and the DNA has been sequenced
The paired chromosomes MUST be heterozygous to result in a FEMALE The queen fertilizes an egg with sperm of a different allele
These pairs, for example will result in a female bee
The unfertilized egg only has one chromosome # 8 and ALWAYS results in a
drone
This HOMOZYGOUS pair will result in a DIPLOID
DRONE (2 genetically identical csd genes)
Source: Glenn Apiaries http://www.glenn-apiaries.com/genetics.html#anchor1561346
Diploid drone eggs hatch, produce a pheromone which
tells workers to destroy the larva
This is what results from inbreeding
Breeding for a certain trait can produce this
Since queens are fertilized by an assortment of drones in a big DCA
this is uncommon
Also queens go to a different DCA than their brothers!
Epigenetics
Something from the environment that causes a direct change
in the DNA which affects gene expression.
Until recently thought to be the substance
which caused the queen to become a queen!
Royal jelly (nope)
Fed to Queen entire life
Fed to worker larvae up to 96 hours (worker jelly very similar to royal jelly)
Produced by nurse bees in hypopharyngeal glands
Extremely nutritional, high protein, etc.
Researchers studying the immune response bees obtain by consuming
certain chemicals in pollen and honey.
p-coumeric acid (and other phenolics)
Help plants discourage plant-eating insects
Found in pollen and honey
Helps workers detox pesticides faster
**Bee bread (fermented pollen and honey) contains
p-coumeric acid and fed to workers starting at 96 hours!
Increases immune response in adult bees
Serendipity In Research!!
Researchers found that :
Workers developed increased growth in ovaries at 96 hours!
This is irreversible!
When workers fed p-coumeric acid
When p-coumeric acid was NOT fed to workers
Workers had ovaries <<<< in size than queens
(which is normal)
But there may be many other chemicals which regulate her development
In bees NOT fed p-coumeric acid
Researchers found 14 genes involved in queen/worker differentiation
were “upregulated” or “expression” increased
When fed p-coumeric acid
In nature Queen NEVER fed pollen or honey therefore NEVER receives
p-coumeric acid in her life
50% of genes involved in organ size were significantly changed in
gene expression.
At 96 hours workers get their first taste of bee bread and p-coumeric acid
This is the point of no return!!
The End
Photo by Judy Scher