the human genome and heredity nutrition and gene expression jan 22, 2015
TRANSCRIPT
This graphic is a simple cartoonthe genome (46 chromosomes).Most of your cells contain thiscomplete set of chromosomes.(note FEMALE/MALE difference).
If your progeny got exactlythese genes, Then your progeny wouldbe essentially your twin(except of course, muchyounger than you!).
But that’s NOT what happens.
Your children will have46 chromosomes, but 23 of thosechromosomes will be fromthe maternal set, and 23 of thosewill be from the paternal set.
23 are selectedfor the ovum
23 are selectedfor the sperm
The new embryo has a full setof 46 chromosomes
MATERNAL SET PATERNAL SET
SIMPLE MITOSIS: Duplicationof Chromosome 2.
This happens as a regular partof each cell division, since eachcell needs a complete copyof all the DNA in the cell.
For a homework assignment, you willneed to fill in the missing steps. SEVERAL STEPS
DNA REPLICATION: If every gene was copied perfectly, the genes in the gametes would be identical to the parental genes.
This is what is supposed to happen
ATGCTAATGTGCCTAT ATACG
TACGATTACACGGATATATGC
ATGCTAATGTGCCTAT ATACG
TACGATTACACGGATATATGC
ATGCTAATGTGCCTAT ATACG
TACGATTACACGGATATATGC
TWO EXACT COPIESOF ORIGINAL DNA
BUT ONE COPY CAN HAVE THEWRONG DNA BASE!
ATGCTAATGTGCCTAT ATACG
TACGATTACACGGATATATGC
ATGCTAATGTGCCTAT ATACG
TACGATTACACGGATATATGC
ATGCTAATGTGTCTAT ATACG
TACGATTACACAGATATATGC
DEFECTIVE COPY
A WHOLE REGION CAN BE DELETED
ATGCTAATGTGCCTAT ATACG
TACGATTACACGGATATATGC
ATGCTAATGTGCCTAT ATACG
TACGATTACACGGATATATGC
ATGCTAATGTGCTATACG
TACGATTACACGATATGC
This copy has lost 3 bases from each strand
The duplication of the chromosomes during
formation of gametes (eggs and sperm) is
called MEIOSIS.
This is different in fundamental ways from
mitosis. The mechanism of meiosis explains
major features of the way genes are passed
on to the offspring.
Mutations that occur here can be very significant
as will be drawn on the board.
MEIOSIS
THESE SLIDES HAVE COMPLEX NOTATION.
FURTHER EXLANATION WILL BE PROVIDED
DURING LECTURE.
We use different codes, for example:
#1 = chromosome 1 (forms a pair, in most cells)
M = maternal chromosomes, P = paternal
a,b = each of the two maternal chromosomes
that can be provided to the gamete
DURING MEIOSIS, GAMETES ARE FORMED THAT
ONLY HAVE ONE COPY OF EACH CHROMOSOME.
THE EMBRYO OF COURSE HAS TWO COPIES.
THE PROCESS IS VERY COMPLEX, AND IS OFTEN MISUNDERSTOOD.I WILL SHOW YOU GRAPHICALLY, IN THE FOLLOWING SLIDES, THE STEPS THAT ACTUALLY OCCUR IN THE FORMATION OF GAMETES.
OvumDNA
SpermDNA
BOTH ARE HAPLOID
DIPLOID EMBRYO
Several steps
The following slides expand on the steps of
meiosis. It is of interesting because it
allows the MIXING of genetic material.
1CHROMOSOMES, SET 1 MEIOSIS:The process is shown onlyfor the process in the ovum,it’s in the same in the sperm.
We will illustrate this only forchromosome 1.
When the DNA is duplicatedfor the ova, the female hasa chromosome from her mother (a) and her father (b) that can be used.
NOTICE THE COLOR DIFFERENCE BETWEENMATERNA AND PATERNAL.
a b ba
ba
STEP 1: Each copy ofchromosome 1is duplicated.
a b ba
The chromosomeshave been duplicated.Two of them MOVEwithin the cell, so theare directly adjacent.
a b ba
STEP 2:One of the copiesfrom maternal, andone from paternal,pair up!
STEP 3Part of the DNA sequenceis exchanged betweenthe two that are paired.(this is called: CROSSING OVER).
a b ba
RESULT: For 2 of the4 chromosomes, therehas been PARTIALDNA exchange.
This shows one exchange,there may be 2-3 crossoversror each meiotic pair.
a b/a ba/b
a ba/b b/a
POSSIBLE DNA STRUCTURES FOR CHROMOSOME 1 IN THE OVUM
From mother: no changes
From father: no changes
IN THIS DIAGRAM, MOTHER and FATHER REFER TO THECHROMOSOME YOU GOT FROM EACH PARENT.
NOTE: THE OVA AND SPERM ARE HAPLOID, ANDHAVE ONLY 1 COPY OF EACH CHROMOSOME.
Mixture/maternaland paternal
Mixture/paternaland maternal
WHAT DOES THIS MEAN? It means that
50% of the time, the chromosome #1 that
you provide your child has been
REARRANGED so it has a mixture
of your PATERNAL #1 DNA and your
MATERNAL#1 DNA.
You could also provide a chromosome #1
that is identical, to what you got from your
father or from your mother.