Transcript Blue Atom Template

NICE GENES!
UNIT 3 INTRODUCTION
Homunculus (late 17th century)
Think about this…
• We share 99% of our
DNA with this
chimpanzee…
• And 60% of the DNA in
the banana he is
eating!!
HOW DID
YOU…
BECOME
YOU?!?!
Nature Theory
• Scientists have known for years that traits
such as eye color and hair color are
determined by specific genes encoded in
each human cell.
• The Nature Theory takes things a step
further to say that more abstract traits such
as intelligence, personality, aggression, and
sexual orientation are also encoded in an
individual's DNA.
Nature Theory
• The search for "behavioral"
genes is the source of
constant debate. Many fear
that genetic arguments
might be used to excuse
criminal acts or justify
divorce.
• Twin studies have (to some
extent) supported this
theory…twins raised apart
have shown same interests
and behaviour.
• Savants
Nurture Theory
• While not discounting
that genetic tendencies
may exist, supporters
of the nurture theory
believe they ultimately
don't matter - that our
behavioral aspects
originate only from the
environmental factors
of our upbringing
Nurture Theory
“Give me a dozen healthy infants, well-formed,
and my own specified world to bring them up
in and I'll guarantee to take any one at
random and train him to become any type of
specialist I might select...regardless of his
talents, penchants, tendencies, abilities,
vocations and race of his ancestors.”
-Behavioural Psychologist John Watson-
Nature Vs. Nurture
• Researchers on all sides of the Nature Vs Nurture debate
agree that the link between a gene and a behavior is not the
same as cause and effect.
• While a gene may increase the likelihood that you'll behave
in a particular way, it does not make people do things.
Which means that we still get to choose who we'll be when
we grow up.
What is a Chromosome?
• A human somatic
(body) cell contains 46
chromosomes which
are paired up to make
23 Homologous Pairs.
• These cells are Diploid.
• 1 of each pair comes
from mom, 1 from dad!
What is a Gene?
• Each chromosome is one
molecule of DNA.
• The smaller sections of
DNA, which code for
certain features, are called
Genes.
• Each gene is responsible
for the production of
mRNA, which makes a
protien
• Eg. Blue eye pigment,
hemoglobin etc.
Homologous Chromosomes
• Both chromosomes contain the same genes, BUT they are
not identical.
• For example: EYE COLOUR
The mother’s chromosome could have the coding for blue
pigment and the father’s could have coding for brown.
Homologous Chromosomes
B
MITOSIS
The Role of Mitosis
• Two Stages
-Divide nucleus & DNA
-Divide cell
(cytokinesis)
• Purpose: to produce 2
identical cells for…
-Growth
-Repair of tissue
-Replace dead cells
-Asexual Reproduction
Terms to know!
• DIPLOID (2n):
Full complement of
chromosomes.
• In humans 2n = 46
• HAPLOID (n):
Number of unique
chromosomes
• In humans n = 23
Diploid or Haploid?
In a cabbage cell the Diploid number is
2n = 18
What is the Haploid number?
n=9
How many homologous pairs?
9
Centrioles
Uncondensed DNA –
“Plate of Spagetti”
Spindle Fibres
Sister Chromatids
• A condensed molecule of
DNA (chromosome) is
called a Chromatid.
• A sister Chromatid is an
exact replica of the original!
• The pair is called a DYAD
• Chromatids are held
together by a centromere
The Cell Cycle
• See page 122
• Most of the cell’s time
is spent in Interphase!
Stages of Mitosis - Interphase
•
•
•
•
This is the parent cell
Rapid growth
Cell doing its job
DNA replication
(chromatin)
• Prepares for division
Stages of Mitosis - Prophase
• DNA condenses into
chromatids – Dyads
form.
• Nuclear membrane
disappears
• Spindle fibers form
from centrioles and
attach to centromeres.
Stages of Mitosis - Metaphase
• Dyads line up down the
middle.
• Pulled into place by
spindle fibres.
Stages of Mitosis - Anaphase
• Dyads are pulled apart
(by s.f.’s) to form
monads
Stages of Mitosis - Telophase
• Nuclear membrane
reforms
• Cytokinesis occurs
(cell divides)
• 2 identical daughter
cells (DIPLOID – 2n)
Mitosis in Plant Cells
• No centrioles
• A cell plate forms,
then cell wall.
Meiosis and Variation
• Recall…Variation is key
for species survival,
allows organisms to
adapt!
• During Meiosis, two
events occur which
increase variation…
Independent (Random)
Assortment
• When tetrads line up at
Metaphase I, the
paternal and maternal
chromosomes line up
randomly on the left
and right.
• 223 = 8 388 608
different combinations!
Crossing Over
• While the dyads are in the
tetrad, pieces of
homologous chromatids
can change places,
creating different
chromosomes.
• This is desirable and
occurs frequently
• If one piece gets
misplaced, a mutation
occurs (genes are missing)
Errors during Meiosis
• Errors usually occur during Anaphase I, due to
NONDISJUNCTION.
• The homologous dyads in a tetrad do not separate.
• The resulting gametes can have too many or too
few chromosomes.
Chromosomal Abnormalities
Down Syndrome-Trisomy 21
-1 in 700 births
-An extra chromosome
#21
-Abnormal facial features,
development
-Probability increases
with age of mother
Chromosomal Abnormalities
Klinefelter Syndrome XXY
-1 in 800
-Extra ‘X’ from mother
-Sterile ‘male’, long arms
Chromosomal Abnormalities
Super male XYY
-Extra ‘Y’ from father
-Tends to produce
violent males
Chromosomal Abnormalities
Turner’s Syndrome XO
-1 in 10 000
-One missing sex
chromosome
-Girl is usually short
and sterile
Things to do!
1.
2.
3.
4.
5.
Mitosis & Meiosis Colour Code
Page 139 – Chromosome Numbers Activity
Page 151 - #13
Page 142 – Study Mitosis Vs. Meiosis Chart
P.142 (#5,6), P. 146 (#2), P.150 (#2-4, 8, 9,
16)
Some Interesting Facts…
• The human genome contains 3164.7 million chemical
nucleotide bases (A, C, T, and G).
• The average gene consists of 3000 bases, but sizes vary
greatly, with the largest known human gene being
dystrophin at 2.4 million bases.
• The total number of genes is estimated at 30,000 —much
lower than previous estimates of 80,000 to 140,000 that had
been based on extrapolations from gene-rich areas as
opposed to a composite of gene-rich and gene-poor areas.
• Almost all (99.9%) nucleotide bases are exactly the same in
all people.
• The functions are unknown for over 50% of discovered
genes.
Junk DNA
The Wheat from the Chaff
• Less than 2% of the genome codes for proteins.
• Repeated sequences that do not code for proteins
("junk DNA") make up at least 50% of the human
genome.
• Repetitive sequences are thought to have no direct
functions, but they shed light on chromosome
structure and dynamics. Over time, these repeats
reshape the genome by rearranging it, creating
entirely new genes, and modifying and reshuffling
existing genes.
How is DNA Arranged?
• Genes appear to be concentrated in random areas
along the genome, with vast expanses of noncoding DNA between.
• Stretches of up to 30,000 C and G bases repeating
over and over often occur adjacent to gene-rich
areas, forming a barrier between the genes and the
"junk DNA." These C-G islands are believed to help
regulate gene activity.
• Chromosome 1 has the most genes (2968), and the
Y chromosome has the fewest (231).
Variations and Mutations
• Scientists have identified about 1.4 million locations
where single-base DNA differences (SNPs) occur in
humans. This information promises to revolutionize the
processes of finding chromosomal locations for
disease-associated sequences and tracing human
history.
• The ratio of sperm to egg cell mutations is 2:1 in males
vs females. Researchers point to several reasons for
the higher mutation rate in the male, including the
greater number of cell divisions required for sperm
formation than for eggs.
http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml
Genetics…A Historical Survey
• Let’s take up the
History Sheets!
HOMUNCULUS!
Probability and Genetics
ANYONE FOR A GAME OF PLINKO?
Predicting Probability
• The Punnet Square is used to predict the
genotypes and phenotypes of possible offspring!
• Expressed as a ratio, % or a fraction
• This is not an outcome…just the likelihood of the
outcome!
• You need a large sample size in order to come
close to the predicted outcome.
(Eg. In one family – rarely ½ boys and ½ girls, but
in all of Canada it is!)
Probability and Genetics
~Mendel’s Two Laws~
1. Law of Segregation
-A pair of alleles for a given trait are
separated randomly into gametes.
(Flip coins)
2. Law of Independent Assortment
-When two or more pairs of alleles are
considered at one time, each pair shows
dominance and segregation independently of
the other.
Monohybrid Cross
• In Review…
• In a monohybrid cross we
observe 1 pair of alleles for
1 gene.
• Example: Colour of flower
• Alleles:
– B = purple
– b = white
Monohybrid Cross
Dihybrid Cross
• We observe 2 pair of alleles for 2 different genes.
• Note: The 2 genes are not linked…they must be on
2 separate chromosomes!
• Example…Mendel’s Peas
• Gene 1 (on chromosome A): Colour of seed
Alleles: Y = Yellow, y = Green
• Gene 2 (on chromosome B): Shape of seed
Alleles: R = Round, r = wrinkled
Parental Generation
RRYY
Plant with round,
Yellow seeds
Gametes:
RY
X
rryy
Plant with
wrinkled, green
seeds
ry
F1 Generation
• All plants produce
round, yellow seeds
RY
ry
RrYy
100%
Cross the F1 Generation
• RrYy
• Gametes:
• RY, Ry, ry, rY
X
RrYy
RY, Ry, ry, rY
The Results!
•
•
•
•
9
3
3
1
Yellow Round
Yellow Wrinkled
Green Round
Green Wrinkled
• Try These: P 166 a-c
The Test Cross
• Also called a “back cross”
• Purpose: To determine the genotype of an
individual showing the dominant phenotype!
• Question: Is the genotype Tt or TT?
• Answer: Cross the individual with a
homozygous recessive individual
Possible Outcomes of the Test
Cross
• If the genotype of the
parent in question is
TT…
• Then 100% of the
offspring from the test
cross will show the
dominant trait!
T
T
t
Tt
Tt
t
Tt
Tt
Possible Outcomes of the Test
Cross
• If the genotype is of the
parent in question is Tt…
• Then 50% of the offspring
from the test cross will be
recessive for the trait!
• The appearance of only
one recessive individual
means the parent must be
heterozygous for the trait!
T
t
t
Tt
tt
t
Tt
tt
Try These!
• P.167 #2 (a-e),8
• P. 233 #22
• P. 184 #2,3,4,11