Transcript Unit 6: Genetics and Reproduction

Unit 6: Genetics and
Reproduction
Cell Growth and Reproduction
• The bigger a cell gets, the smaller its
surface area to volume ratio becomes.
Volume vs. Surface Area
• 6cm2 : 1 cm3 = 6
• 24cm2 : 8cm3 = 3
• 96cm2 : 64 cm3 = 1.5
Cell Growth and Reproduction
• If a cell became too big it would take too
long for wastes from the middle to make it
all the way out through the membrane.
• Also it would take way too long for
nutrients to reach from the surface all the
way to the middle.
Chromosome
• Two identical
chromatids
(sisters) are
held together
by a
centromere.
• The tips are
called
telomeres.
The Cell Cycle
• is the
sequence
of growth
and division
of a cell.
Interphase
• The majority of a
cell’s life is spent in
the growth period
known as
interphase.
• DNA gets
duplicated (copied)
during this time.
Mitosis
• is the process by
which two daughter
cells are formed,
each containing a
complete set of
chromosomes.
Step 1. Prophase
• It is the longest
step.
• The long stringy
chromatin coils up
into chromosomes.
Step 1. Prophase (cont’d)
• The nucleus
disappears; the
nuclear envelope
and nucleolus
dissolve.
• The centrioles
migrate to opposite
poles and the
spindle forms.
Step 2. Metaphase
• The doubled
chromosomes
become attached
to the spindle
fibers by their
centromeres.
Step 2. Metaphase (cont’d)
• The chromosomes
are pulled by the
spindle fibers to
the middle
(equator).
Step 3. Anaphase
• The centromeres
split apart.
• The microtubules
of the spindle
fibers shorten.
• The sister
chromatids
separate.
Step 4. Telophase
• Chromatids reach
the opposite sides
(poles) of the cell.
• Chromosomes
unwind into
chromatin.
• Spindle breaks
down.
Step 4. Telophase (cont’d)
• The nuclear
envelope and
nucleolus reform.
• A new double
membrane begins
to form between
the two nuclei.
Cytokinesis
• After mitosis, the
cell’s cytoplasm
divides during this
stage.
• In animals, the
cells simply pinch
off.
Cytokinesis
• In plant cells a cell
plate is laid down
and the plasma
membrane and cell
wall form on either
side of it.
Meiosis
• is the process via which sex cells are
made.
• gametogenesis = spermatogenesis =
ovagenesis
• Sex cells = gametes
Meiosis (cont’d)
• Diploid = regular number of chromosomes
(2 copies)
• Haploid = 1 copy of each chromosome
The history
• Gregor Mendel
(1822- 1884) was an
Austrian Monk whose
studies earned him
the title of Father of
Genetics.
What is Genetics?
• Genetics is the branch of biology that
studies heredity.
• Heredity is the passing of characteristics
from parents to offspring.
What is Genetics? (2)
• Characteristics that are inherited are
called traits.
• Sex cells, eggs and sperm are called
gametes.
• When the two unite through fertilization, a
zygote is formed.
Mendel and the Peas
• Mendel did research
using pea plants.
• Normally these plants
fertilize themselves:
self-pollination.
Mendel and the Peas (cont’d)
• If he wanted to,
Mendel could take
pollen from one
plant and fertilize
another: crosspollination.
Mendel was a careful
researcher…
• He only studied one
trait at a time,
• analyzed his data
mathematically,
Mendel as a researcher (cont’d)
• worked with true
breeding pea plant
populations,
• and this set him
apart from all
others who had
done heredity
research before.
Mendel’s Monohybrid Crosses
• A hybrid is the
offspring of parents
that have different
forms of a trait.
• The crossing of a
female tiger and
male lion results in
the hybrid animal:
the lyger.
• The opposite
crossing results in
tions.
The nomenclature
• P stand for parent.
• F stand for filial (son or
daughter).
• P1 = grandparents
• F1 = parents
• F2 = kids
Mendel’s experiments
1. Mendel crossed true
breeding tall and short
pea plants.
2. All the F1 came out tall.
They were allowed to
self-pollinate.
3. The F2 came out tall
75% of the time and
short 25% of the time
(3:1 ratio).
4. No matter what trait
Mendel studied the
numbers came out the
same.
3. The F2 came out
tall 75% of the
time and short
25% of the time
(3:1 ratio).
4. No matter what
trait Mendel
studied the
numbers came
out the same.
The rule of dominance:
• One trait is dominant
over another. In the
case of pea plants,
tall is dominant over
short.
or…
• Short is recessive to
tall.
The rule of unit factors:
• Mendel concluded
that each organism
has two factors that
control each trait.
• We now know these
as genes found on
chromosomes.
The law of segregation
1. Every individual has
two alleles of each
gene.
2. Their gametes get
only one.
3. During fertilization
these randomly pair
producing four
combinations.
The law of independent assortment
• Genes for
different traits
are inherited
independently of
each other.
Alleles
• Alleles are
alternative forms of
a gene for each
variation of a trait
of an organism.
• For example height
has two alleles in
pea plants: short
and tall.
Phenotype vs. Genotype
• Phenotype is the
way an organism
looks and behaves.
• Genotype is the
allele combination
the organism
contains.
There are 3 main genotypes:
• AA
homozygous dominant
• Aa
heterozygous
• aa
homozygous recessive
It was time for a joke.
Punnett Squares
• In 1905 Reginald
Punnett created a
simple way to
determine phenotype
ratios.
• This is now known as
the Punnett Square.
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Sometimes there’s more
• Occasionally a
geneticist wants to
study two traits at
once.
• A dihybrid cross is
done for just that
purpose.
When weird stuff happens
• So far we’ve learned
about completely
dominant alleles.
• For example free
earlobes being
dominant to attached
earlobes.
Incomplete Dominance
• Sometimes traits mix together to create a new
allele.
• In the picture above the red and white flower
were crossed and a pink flower was created.
Codominance
• In codominance
both traits are
expressed (can be
seen).
• The flower on the
right shows
codominance
because it is the
offspring of red and
a white flowering
plants.
Multiple Alleles
• Sometimes there are many different alleles
(variations) for a trait.
• Human hair color, for example, varies greatly.
• There are way more than just two alleles.
Polygenic Inheritance
• Some characteristics,
such as eye color, are
controlled by several
genes.
• Sometimes the genes
are on the same
chromosome.
• Sometimes they are
found on different
chromosomes.
Polyploidy
• Sometimes
organisms have extra
chromosomes.
• In animals this is rare
and usually results in
death or serious
defect.
• In plants this usually
makes them stronger
and bigger.
Determining Sex
Reading a Pedigree
Reading a Karyotype: a picture of
an organism’s chromosomes
Genetic Disorders
• Sickle cell anemia
• Turner’s Syndrome
• red-green color
• Testicular
blindness
Feminization
Syndrome
• Hemophelia
• Klinefelter’s
• Down syndrome
Syndrome
• Huntington’s diesease
• Jacob’s Synrome
• and many more…
Remember…
• In humans…
• XX = female
• XY = male
So what’s up with
•
•
•
•
XO?
and XXY?
and XYY?
and XY but with AS?
Turner’s Syndrome 45XO
• Turner’s syndrome
affects females only.
• Symptoms:
• short
• webbed necks
• small breasts
Klinefelter’s Syndrome 47 XXY
• Klinefelter’s syndrome
affects males only.
• Symptoms
• tall
• small genitals
• small breasts
Jacob’s Syndrome 47 XYY
• Tall
• Acne (body and face)
• Predisposition to
criminal
insanity/behavior
Androgen Insensitivity Syndrome
46XY
•
•
•
•
•
Externally female
Blind vaginas
Testes located inside
Infertile
Cannot produce nor
ingest male hormones
•
Formerly known as
Testicular Feminization
Syndrome