Transcript Patterns of Heredity

Introduction to genetics
Ch. 11
Meiosis….Some terms to know
• Haploid (1n)- a cell
with only one
complete set of
chromosomes
(gametes or sex cells).
Diploid (2n)- a cell
that contains two
complete sets of
chromosomes. (all
other cells)
Which are diploid and which are haploid?
How do you know sex cells (eggs and sperm) are only haploid?
Homologous Chromosomes
come from a Tetrad
• Homologous
chromosomes are
pairs of chromosomes
where each one is
identical to the other.
• A tetrad is a structure
containing 4 strands of
DNA tightly paired
together.
Meiosis
• There is a meiosis I and
II. Each are the same
steps as mitosis.
• You begin with one
diploid cell and
produce 4 haploid.
• This gives you many
different combinations
of genes to be passed
on. It’s all chance on
the ones you get.
Crossing Over
• Occurs during
prophase 1 when
homologous
chromosomes pair up
and form tetrads and
exchange portions of
chromatids.
Meiosis Provides for Genetic
Recombination
• 1.28a Sorting and
recombination of
genes in sexual
reproduction, allows
for a great variety of
possible gene
combinations.
• That is why no two
people are alike.
(Besides identical
twins- why?)
1.46 A great diversity of species increases the chance
that at least some living things will survive in the
face of large changes in the environment.
• Why is this?
• So, is diversity good?
Give an example.
The Steps…Let’s review.
•
•
•
•
•
•
•
•
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
TelophaseII
• What occurs during
each step?
1.8c Mitosis vs. Meiosis
• Mitosis
– Somatic cells
– One cell division
– Two daughter cells
with same number of
chromosomes as
parent.
– Daughter cells are
identical to parent.
– Asexual
• Meiosis
– Sex Cells
– Two cell divisions
– Four daughter cells
with half chromosomes
as parent
– Daughter cells not
identical to parents.
– Sexual
Genetics
• Genetics is the study of
heredity.
• What is heredity?
• Genetics involve traits
being passed from one
parent to offspring.
• What are some traits you
got from your parents?
Fertilization
• Gametes- Sex Cells
– Sperm and Egg
Fertilization- process of sperm fertilizing the egg.
Zygote- fertilized egg
Embryo- zygote- 8 weeks.
Fetus- 9 weeks - delivery
Gregor Mendel..The Father of
Genetics
•
Mendel studied peas
for 3 reasons:
1. Structure of pea
2. Presence of
distinctive traits.
3. Rapid reproduction
cycle. 90 days
• What are the male and
female parts of a
flower?
• How do you think he
cross fertilized them?
Purebred vs. Hybrids
• Since flowers have both
male and female (anther in • A hybrid is an
organism that receives
stamen and ovary in pistol),
different forms of a
they are able to self-fertilize.
genetic trait from each
• True-breeding- if org. were
parent.
allowed to self fertilize, they
would have offspring
identical to self.
• (pure-bred, same genetic
traits from each parent)
Generations
• P is the Parental
Generation.
• F1- what you get when
the parents reproduce.
YOU.
• F2- The offspring of
F1. YOUR KIDS.
What are P, F1 and F2 in these pictures,
assuming everyone is from the same
family?
Mendel’s Experiments
•
He tested 7 traits of
the pea pod:
1.
2.
3.
4.
5.
6.
7.
Flower Color
Flower position
Pea color
Pea shape
Pod color
Pod shape
Height
Mendel’s Peas
Mendel’s Study
• Cross pollinated pea plants,
taking a stamen and putting
that into the pisil of another
flower using two pure-bred
plants. All of them had
yellow peas.
• Allowed them to selffertilize. He got 75%
yellow and 25% green.
• He thought they would
blend to form a
chartreuse color? Why?
• He ended up crossing all
7 traits. See Figure 11-3.
Mendel’s Results
P-
Green X yellow
F1-
Yellow
F2-
Green and Yellow
Principles of Inheritance
• Chromosome Theory
of Heredity states that
genes in chromosomes
carry the material of
inheritance.
1.21 Genes are coded in DNA molecules and pass
information from parents to offspring.
• Genes are sections of
a chromosome that
code for a traits.
• Alleles are one form
of a gene.
• Alleles can be
dominate or recessive.
• Dominate- always
expressed.
• Recessive- only
– Ie. Eye color can be
expressed if no
blue, green, brown, etc.
dominate is present.
– You receive one allele
• Let me explain.
from your mom and
• BB, Bb, bb
one from your dad.
Allele Expression
• Homozygous dominant- HH
(pure)
• Heterozygous dominant- Hh
(hybrid)
• Homozygous recessive- hh
(pure)
• If H is long hair and h is short
hair, which will have long and
which short? (on a cat)
Genotype and Phenotype
• Genotype represents
the genetic make up.
HH 
Hh
hh
• Phenotype represents
the outward
expression.
Long Hair
Long Hair
Short Hair
Review of Terms
Mendel’s laws
• 1.22b Law of Independent
• 1.22a Law of
Assortment states that genes for
Segregation states
different traits can segregate into
that allele pairs
gametes randomly and
segregate during
independently of each other.
meiosis.
Chromosomes not genes assort
• What does segregate
independently.
mean?
• Law of Dominance states that
A a
A a
the dominant allele is expressed
Mom
Dad and the recessive allele can be
hidden.
Genetics and Predictions
• Punnett Squares are used to
determine probabilities of
outcomes for offspring.
• Let’s make one.
• What do you get in each
box?
A
• What are the genotypes and
phenotypes?
a
• What are their probabilities?
A
a
Monohybrid and Dihybrid
Crosses
• Monohybrid crosses
deal with one trait.
• Dihybrid crosses deal
with 2 traits.
• Let’s do one of each.
• If R is dominant and is
round, and Y is
dominant and is
yellow and you cross
RrYy x RrYy, what do
you get?
Test Crosses
Test Crosses are used to
distinguish between
homozygous dominant and
heterozygous organisms.
You breed an organisms
unknown genotype with a
homozygous recessive
organism.What are the
outcomes?
Show how this is helpful and
works!
Y=Yellow, y=green
Y
Y
Y
y
y
y
y
y
Difficult Predictions
• Incomplete
Dominance is when
two different alleles
for the same trait
combine.
R=red, W=white
RW= Pink
• Codominance is when
both alleles express
themselves fully.
Blood type.
A, B or AB
Polygenic Traits
• Polygenic traits are
controlled by two or
more genes.
• Eye color- many genes
control the pigment
(tone, amount, and
position).
• Skin tone, hair color,
height
Multiple alleles and Pleitropy
• Multiple alleles are
when three or more
alleles are found in the
population.
• Ie. Rabbits have 4
different alleles for hair
color, but each rabbit
only has 2 of them.
• Blood types
• Pleitropy occurs when
a single gene affects
more than one trait.
• Sickle Cell anemia.
Environmental Effects
• 1.1b Different parts of
the genetic
instructions are used
in the different kinds
of cells and are
influenced by the
cell’s environment and
past history.
.
• Himalayan rabbits fur color
is affected by temperature.
• Western white butterfly
wing coloration is affected
by temp.
• Japanese goby fish can
change its sex back and
forth in response to
changes in its social
environment.
Linked Genes
• Genes that are located on the
same chromosome, which
are inherited together.
– Ie. Fruit fly’s red eyes and
miniature wings inherited
together.
– Those closer together, more
likely to be inherited together.
• It is the chromosomes that
assort independently, not the
genes.
Genetic Mapping
• Researchers have made gene
maps that show what
traits(alleles) are on what
chromosomes and where.
• The farther apart the 2 genes
are located, the more likely
they are to be separated by a
crossover. (Cross over more
frequently)
Genetics Review
• Go to the following link and click on your
book. Take the self-test and review the
Active Art.
• Ch. 11 Review