Transcript Differentiation of Cells

Genetics
God’s Provision for the Community
of Life
Heredity – The
transmission of
characteristics from
parents to offspring by
means of genes in the
chromosomes of the cells
Differentiation of Cells
When certain cells in a
growing organism are
called out to do a specific
task it is called
differentiation.
This happens in asexual
reproduction when
organisms grow into new
organisms and in sexual
reproduction when the
embryo first begins to
grow
Sexual Reproduction – A
type of reproduction that
requires the joining
together of sex cells.
There needs to be two
different (male and
female) sex cells for
reproduction
These cells are called
haploid cells because
they contain half the
normal amount of
chromosomes
Haploid cells are made
through the process of
meiosis (NOT MITOSIS!)
Fertilization occurs in
sexual reproduction
when an egg and a
sperm unite
This makes a zygote
and the cell is called a
diploid cell because it
contains a normal
amount of chromosomes
Meiosis – A special type
of cell division that
makes sex cells
(haploid).
Also called reduction
division because the
number of chromosomes
is reduced. (Not the
same as Mitosis)
Spermatogenesis is
meiosis that forms sperm
cells
Oogenesis is meiosis
that forms an egg cell
First Meiotic Division
Interphase – Cell
replicates DNA
(Chromosomes)
Prophase I
–Chromosomes coil tightly
–Nucleolus and nuclear
envelope is dismantled
–Additional sets of
Centrioles are produced
Metaphase I
–Spindle apparatus is
formed
–Homologous
chromosomes (pair of
Chromatids) line up on
the “equator” of the cell
Anaphase I
–Homologous
chromosomes become
separated. Complete
replicated chromosomes
are dragged to opposite
ends of the cell
Telophase I
–Nucleolus and Nuclear
envelope forms in each new
daughter cell.
–Each daughter cell has half
the original amount of
chromosomes and their
copies
Second Meiotic Division
Prophase II
–Nucleolus and nuclear
envelope are dismantled
–Additional sets of
Centrioles are produced
Metaphase II
–Spindle apparatus is
formed
–Chromatids (Copies of
chromosomes) line up on
the “equator” of the cell
Anaphase II
–Chromatids are dragged
to opposite ends of the
cell
Telophase II
–Nucleolus and Nuclear
envelope forms in each new
daughter cell.
–Each daughter cell has half
the original amount of
chromosomes
Differentiation
–Daughter cells become
Gametes
Classical Genetics
Gregor Mendel (18221884) – Austrian monk who
conducted experiments
dealing with the heredity of
pea plants. Known as the
father of genetics.
Genetics – The scientific
study of heredity.
He used pea plants
which normally selfpollinate, which made
the patterns easier to
recognize.
Pea Flower
Genotype – The genes
that are present in the
chromosomes
(examples: Aa, AA, aa)
Phenotype – The
physical characteristic
the gene gives
Homozygous – A
genotype where both
genes have the same
trait
Heterozygous – A
genotype where one
gene is different from the
other
Dominant Traits – The
trait that shows up in
when the offspring is
heterozygous (Capital
letters)
Recessive Trait – The trait
that does not show up
when the dominant trait is
present.
For this trait to show up,
both genes have to be
recessive. (Lower case
letters)
AA–Homozygous Dominant
Aa-Heterozygous/Hybrid
aa-Homozygous Recessive
Alleles – Different forms
of a gene for a particular
trait. (Examples: R =
round, r = wrinkle) It
takes 2 alleles to make a
gene.
Hybrid – An organism
that has two different
alleles for a particular
trait (Heterozygous)
Liger
Dihybrid – An organism
that is a hybrid for two
different traits.
These traits are inherited
independently because
they are on different
chromosomes.
Linkage groups – Traits
that are inherited
together because they
are on the same
chromosome.
The Law of Dominance
– Dominant traits show
up in the offspring even if
a gene of a different trait
is present.
Incomplete Dominance –
When the dominant and
recessive traits are
mixed or blended in the
offspring
Law of Segregation –
When hybrids are crossed
with each other, the
recessive trait segregates,
or separates, again for
some of the offspring.
Law of Independent
Assortment – Different
traits in an organism are
inherited independently
from each other.
Classical Genetics (Cont.)
Seeds
Law of Dominance
–Pure yellow (YY) crossed
with pure green (yy)
Y
y
y
Y
y
y
Y
Y
Yy
Yellow
Hybrid
Yy
Yellow
Hybrid
Yy
Yellow
Hybrid
Yy
Yellow
Hybrid
Law of Segregation
–Yellow Hybrids (Yy)
crossed
Y
Y
y
y
Y
y
Y
y
YY
Pure
Yellow
Yy
Yellow
Hybrid
Yy
Yellow
Hybrid
yy
Pure
Green
Flowers
Incomplete Dominance
–Red flowers (RR) crossed
with White flowers (WW)
R
W
W
R
W
W
R
R
RW
Pink
Hybrid
RW
Pink
Hybrid
RW
Pink
Hybrid
RW
Pink
Hybrid
Incomplete Dominance
and Law of Segregation
–Pink Hybrids (RW)
Crossed
R
R
W
W
R
W
R
W
RR
Pure
Red
RW
Pink
Hybrid
RW
Pink
Hybrid
WW
Pure
White
Genetic Research in the 20th
Century
Sutton’s Hypothesis –
1902 Sutton wrote a
paper which
hypothesized the
following things
–An organism’s heredity
is determined by its
parents sex cells
–“Heredity factors” were
tiny particles on
chromosomes (later
called genes)
–Different “factors” were
found on different
chromosomes
Morgan’s Research –
Researched the genetic
traits of the fruit fly,
which gave us proof that
Mendel and Sutton were
correct in their thinking
Sex Chromosomes – All
Chromosomes in male
and female flies were the
same except one pair.
The pair of
chromosomes that are
different are the sex
chromosomes because
they determine the sex of
the organism.
–Morgan named the two
chromosomes in the
female X (female = XX)
–He named the similar
one in the male X, but
the different one Y
(male = XY)
–Most organisms
function this way with
the male determining
the sex of the offspring.
–However there are
some organisms where
the sex chromosome in
the female is different.
Sex-linked Traits – Traits
that are carried on the X
chromosomes and
appear in relation to the
sex of the organism
–Examples: Eye color in
fruit flies, Hemophilia,
Color blindness, faulty
enamel etc.
Sex-linked traits
Male (XY) crossed with
Female (XX)
X
X
X
Y
X
X
XX
Female
X
XX
Female
Y
XY
Male
XY
Male
Eyes
r
Male w/white eyes (X Y)
crossed with Female w/
R
R
pure red eyes (X X )
Xr
R
X
XR
Y
R
X
XR
Xr
Y
XRXr
Female
Red
R
r
X X
Female
Red
XRY
Male
Red
R
X Y
Male
Red
R
(X Y)
Male w/red eyes
crossed with Female w/
R
r
hybrid red eyes (X X )
XR
R
X
Xr
Y
R
X
Xw
XR
Y
XRXR
Female
Red
R
r
X X
Female
Red
XRY
Male
Red
r
XY
Male
White
r
(X Y)
Male w/white eyes
crossed with Female w/
R
r
hybrid red eyes (X X )
Xr
R
X
Xr
Y
R
X
Xr
Xr
Y
XRXr
Female
Red
r
r
XX
Female
White
XRY
Male
Red
r
XY
Male
White
Variety
Crossing over – There is
an exchange of genetic
material when the
homologous pairs are
together during synapsis.
… (Homologous pair = 1
from mom, 1 from dad:
All four chromatids =
Tetrad)
Assortment of
chromosomes – During
meiosis the homologous
pairs line up we have
number
of
homologous
pairs
2
different combinations
23
2 =8,388,608
You can make
8,388,608 different
gametes.
These factors are used
to breed certain
characteristics from
plants and animals
–Examples Wheat, corn,
cows, hogs, chickens,
dogs, etc.
Human Genetics
Dominant Gene
Inheritance:
Dominant/Recessive
Free/Attached Ear Lobes
Full/Thin Lips
Curly/Straight Hair
Polydactyly/Normal
Freckles/No Freckles
Roll Tongue/ Not
Dimples/No Dimples
Normal Arches/Flat Feet
Gene Frequency – The
extent, which a certain
gene exists in a
population
This does not mean it is
dominant or recessive.
Polydactyly – (Having
more than 5 fingers or
toes on a limb) A
dominant trait that is very
rare
Cystic Fibrosis– (Having
a thickened mucus in the
lungs which may cause
life threatening
infections)
A recessive trait that
occurs in 1 out of every
25 Americans (Fairly
common)
Incomplete Dominance
Sickle-Cell Anemia Recessive trait that
causes a formation of
abnormal hemoglobin.
When oxygen is low,
long chains of
hemoglobin molecules
form and cause the red
blood cells to become
sickle shaped.
1
H
If
represents the
2
normal trait and H
represents the sickle trait,
then because of
incomplete dominance we
have the following:
1
1
–H H
Normal hemoglobin
is produced. Round Cells
1
2
–H H
(Heterozygous)
Some normal and some
abnormal hemoglobin is
produced. Some Sickle,
some Round.
2
2
–H H
Abnormal
hemoglobin is produced.
Sickle Cells
Multiple Gene Inheritance
– When there are more
than two alleles for a
particular trait
–Blood Type – The alleles
for blood type are A, B,
and O, and are denoted
A
B
O
I , I , and I
–A – Sugar added to the ID
tag on a Red Blood Cell
–B – Different sugar added
to the ID tag on a Red
Blood Cell
–O– Add neither sugar to
the ID tag on a Red Blood
Cell
This gives us 4 different
blood types
–Type A
–Type B
–Type AB
–Type O
A
A
I I
A
O
I I
or
B
B
B
O
I I or I I
A
B
I I
O
O
I I
Pleiotropy and Polygenic
Inheritance
Pleiotropy Inheritance –
Where a gene may
influence several traits
Polygenic Inheritance –
Where many genes
influence one trait (skin
color and height)
The more genes you
have influencing the trait
the more variety you
have.
Sex-linked Traits
Hemophilia – (A condition
where a persons blood
does not clot) A recessive
trait found on the X
chromosome.
The following are
phenotypes and
genotypes that exist.
–Normal
XHXH
–Carrier
XHXh
–Hemophilia
XhXh
XHY
XhY
Carrier – A person who
has the trait present in
their genotype, but the
trait does not show in the
phenotype
Colorblindness – (A
condition where a person
is not able to see all the
colors) A recessive trait
found on the X
chromosome.
The following are
phenotypes and
genotypes that exist.
–Normal
XBXB
–Carrier
XBXb
–Colorblind XbXb
XBY
XbY
Genetic Advances –
Through these advances
we have been able to
detect different genetic
diseases present in
fetuses.
Spina Bifida Corrective Surgical
Procedure
Positive – We can treat
these diseases sooner
and better than before.
Negative – Many babies
are aborted as a result of
these tests even though
there could be false
positives.
Eugenics – The attempt
to improve the human
race by controlling
breeding and sterilizing
those that are
“genetically inferior.”