Download Heredity and Genetics - Olympic High School Home Page

Heredity (Inheritance)
and Genetics
Heredity
1. Is it possible for two parents with blue
eyes to have a brown eyed child?
Heredity
2. Is it possible for two parents with brown
eyes to have a blue-eyed child?
Heredity
3. Rebecca and Leah look so much alike
that everyone says they must be sisters.
What kind of test should we do to
determine if they are sisters?
Review
What do you know about each of the
following:
• DNA
• Genes
• Chromosomes
Chromosomes have genetic
information and are passed to offspring
Dividing onion cells
chromosomes
chromosomes
cell wall
nucelus
Chromosomes have genetic
information and are passed to offspring
Human chromosomes
stained with a special
chemical and viewed
under a high-powered
microscope
What exactly are chromosomes?
How do chromosomes contain
genetic information?
Chromosome structure- DNA
• Chromosomes = long pieces of DNA
Chromosome structure- genes
• Parts of chromosomes are called genes
• Genes help determine your characteristics
– what are some example characteristics?
Human chromosome # 7
• Contains about
1,800 genes
• Contains over 150
million nucleotides
Link to view genes and DNA sequence
Trait – a characteristic of an organism
– Example: “flower color”
Gene – part of a chromosome that helps
determine a specific trait
– Example: “flower color gene”
Allele – a form of a gene
– Example:
• One allele is the “blue” form of the gene
• One allele is the “red” form of the gene
Review
How do the terms trait, chromosome,
gene, and allele relate to each other?
Chromosomes come in pairs
Cut out from picture and
match each in pairs. This is called a KARYOTYPE
Homologous chromosomes?
• Humans = 23 chromosome pairs, or 46 total. We
think we have about 20,000 genes.
• Pea flower = 7 chromosome pairs (14 total)
• Fruit fly = 4 chromosome pairs (8 total) 13,601
genes identified so far!
– What part of a chromosome do you think is
homologous or identical?
– What effect do these differences have on
characteristics?
Chromosomes come in pairs
• You get one copy of a chromosome from
one parent and one copy of a
chromosome from the other parent.
• This pair of chromosomes is called a
“homologous pair” because they have the
same genes on them flower color gene
Flower chromosome 3
From
Dad
From
Mom
Chromosomes come in pairs
IMPORTANT: homologous pairs have the
same genes, but they are NOT IDENTICAL
– Alleles can be different
flower color gene
“Blue” allele
of flower color
gene
“Red” allele
of flower color
gene
From
Dad
From
Mom
Chromosomes are shuffled
When homologous chromosomes are
reunited following meiosis and sex, the
combination of Alleles can be different
flower color gene
“Blue” allele
of flower color
gene
“Red” allele
of flower color
gene
From
Dad
From
Mom
The combination of alleles determines
the observed characteristics
RED
Chromosome
combination
Allele
combination
RED
allele
allele
red, red
RED
BLUE
allele
allele
red, blue
(or blue, red)
BLUE
allele
BLUE
allele
blue, blue
Observed
characteristic
RED
?
BLUE
Dominant and recessive alleles
Only one red allele is needed for the flower
to look red.
• Scientists call this a DOMINANT allele
Two blue alleles are needed for the flower to
look blue.
• Scientists call this a RECESSIVE allele
Symbols used for alleles
• The traditional symbols used for alleles
are big and small letters
• The letter chosen usually refers to the
dominant allele
Example: R = Red allele
r = Blue allele
The combination of alleles determines
the observed characteristics
RED
Chromosome
combination
Allele
combination
RED
allele
allele
red, red
RED
BLUE
allele
allele
red, blue
(or blue, red)
BLUE
allele
BLUE
allele
blue, blue
Observed
characteristic
RED
RED
BLUE
The combination of alleles determines
the observed characteristics
Chromosome
combination
Allele
combination
R
R
R
r
RR
Rr
RED
RED
r
r
rr
Observed
characteristic
BLUE
Phenotype – the observed (or measurable)
trait of an organism that relates to one
gene
Genotype – the two alleles that an organism
has for a trait
Example: Trait
=
Phenotype =
Genotype =
“flower color”
“RED” or “BLUE”
“RR” or “Rr” or “rr”
The combination of alleles determines
the observed characteristics
Chromosome
combination
Allele
combination
R
R
R
r
RR
Rr
RED
RED
r
r
rr
Observed
characteristic
BLUE
The combination of alleles determines
the observed characteristics
Chromosome
combination
GENOTYPE
R
R
R
r
RR
Rr
RED
RED
r
r
rr
PHENOTYPE
BLUE
Homozygous – the two alleles are the same
• RR and rr are homozygous genotypes
Heterozygous – the two alleles are different
• Rr is a heterozygous genotype
Review
• What are homologous chromosomes?
• What part of a chromosome do you
think is homologous or identical.
• What is a dominant allele?
• What is a recessive allele?
• What is homozygous?
• What is heterozygous?
• What is phenotype?
• What is genotype?
Modeling Genetic crosses
• Documents and Models how genetic
information is passed along.
• Accounts for patterns seen in a pedigree
• Makes predictions about the phenotypes
and genotypes seen in the next generation
Possible combinations of inherited
chromosomes/genes
Dad
Parents
Rr
Mom
Rr
X
RR
Possible
Offspring
Order doesn’t matter,
these two are the same (Rr)
Rr
r R
r r
What are all possible genotypes produced from the parents?
RR,
Rr,
rr
Punnett squares organize all
possible offspring combinations
Dad
Rr
Mom
X
Rr
Your turn:
R
r
R
RR
Rr
r
Rr
rr
What are all
possible genotypes
produced by
crossing Rr with rr?
Punnett squares predict ratios of all
genotypes and phenotypes produced
R
r
R
RR Rr
r
Rr
rr
Genotypic ratio = 1RR: 2Rr:1rr or 25%RR:50%Rr:25%rr
Phenotypic ratio = 3 Red:1 blue or 75% Red:25% Blue
Predicted ratios determine the
probability of each genotype/phenotype
R
r
R
RR Rr
r
Rr
rr
Genotypic ratio = 1RR: 2Rr:1rr
Phenotypic ratio = 3 Red:1 blue
1 out of 4 possibilities is rr = 25% chance of rr
• What is probability of Rr?
• How many out of 4 are red?
• What is the probability of red?
• What is the probability of blue?
Punnett square practice
Calculate the predicted genotypic and
phenotypic ratios
Calculate the probability of each genotype
and phenotype
1) Hh X HH – H(hairy) is dominant over
h(not hairy)
2) Gg X gg – G(green sepals) is dominant
over g(yellow sepals)
Review
• What is the relationship between genotype and
phenotype?
• What is the relationship between Homozygous
and Heterozygous
• Give an example of a heterozygous genotype
for height (T = tall; t = short):
• Give an example of a homozygous genotype
for height (T = tall; t = short):
• What is the phenotype of a plant heterozygous
for the height gene?
Dihybrid cross
• Used to predict the combinations of 2 traits
contained on two separate chromosomes.
• For example for the traits of stripes and
tails on a cat:
– Two double-heterozygous striped, with tail
cats are crossed.
– How many offspring will be striped and have a
tail, how many will be striped with no tail, how
many will be plain with a tail…
Practice
•
•
•
Construct a Punnett Square for each of the
following crosses.
Remember: the two traits are on two different
chromosomes.
Write the Genotypic and Phenotypic Ratio
below the Punnett Squares.
1. SsTt X SsTt
2. SSTt X SsTt
3. SSTT X SsTt
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
St
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
St
sT
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
St
sT
st
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
ST
St
sT
st
St
sT
st
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
St
sT
st
ST
SSTT SSTt SsTT SsTt
St
SSTt SStt
SsTt
sT
SsTT SsTt
ssTT ssTt
st
SsTt
ssTt
Sstt
S = striped
s = plain
T = tail
t = no tail
Sstt
sstt
Genotypes: 1 SSTT: 2 SSTt: 1 SStt: 2 SsTT: 4 SsTt: 2 Sstt: 1 ssTT: 2 ssTt: 1 sstt
Phenotypes: 9 striped, tail : 3 striped, no tail : 3 plain, tail : 1 plain, no tail
SSTt X SsTt
ST
St
sT
st
ST
SSTT SSTt SsTT SsTt
St
SSTt SStt
SsTt
Sstt
ST
Same as
above
Same as
above
Same as
above
Same as
above
St
Same as
above
Same as
above
Same as
above
Same as
above
S = striped
s = plain
T = tail
t = no tail
If they are the same
as above you do
NOT have to
rewrite the
genotype
Genotypes: 1 SSTT: 1SSTt: 1SsTT: 1SsTt: 1SSTt: 1SStt: 1SsTt: 1Sstt
Phenotypes: 6 Striped with Tail: 2 Striped with no tail (3:1 reduced)
SSTT X SsTt
ST
Same
ST
St
sT
st
SSTT SSTt SsTT SsTt
ST
ST
ST
Genotypes: 1 SSTT: 1 SSTt: 1 SsTT: 1 SsTt
Phenotypes: 4 Striped Tail (100%)
S = striped
s = plain
T = tail
t = no tail
Inheritance quiz
#1
#2
#3
#1
#2
#3
Width/thickness/petals
1. What is the trait for the flowers? __________________
Type of Hair
2. What is the trait for the animals? __________________
f (or narrow)
3. What is the recessive allele for the flower trait? _______
H (or straight)
4. What is the dominant allele for the animal trait? _______
#1
5. Which flower is heterozygous? ___________
#2
6. Which animal is homozygous dominant? __________
Ff
7. What is the genotype of flower #1? ________________
HH
8. What is the genotype of animal #2? ________________
Wide
9. What is the phenotype of flower #2? ________________
Straight Hair
10.What is the phenotype of animal #3? ________________
Punnett Square
F
f
Genotypic ratio:
f
Ff
ff
1 Ff : 1 ff
(2 Ff : 2 ff is OK)
Phenotypic ratio:
f
Ff
ff
1 fat : 1 skinny
(2 fat : 2 skinny is OK)
Review
In flowers, red color (R) is dominant to blue
color (r).
1. What possible genotypes produce a blue
flower? What possible genotypes
produce a red flower?
2. Explain how you could determine the
actual genotype of a red flower by
performing a genetic cross many times
and looking at the offspring phenotypes.
Review
•
•
•
How many sets of your 23 chromosomes
do you have (1, 2, 3, or 4?)
How many of each type of chromosome is
inherited from your mom?
How many of each type of chromosome is
inherited from your dad?
If parents have two copies of each
chromosome, how do they pass on
only one to their offspring?
• MEIOSIS is the process
of cell division that
decreases the number of
chromosomes to make
sperm or egg cells
Sperm or egg cells
Original cell
The purposes of Meiosis:
1. Split the total number of chromosomes in
half so that only ONE chromosome from
each pair is inherited from each parent.
2. Produce variation in offspring by
randomly sorting the chromosomes.
Meiosis
Original cell
•Diploid
(pairs of chromosomes)
Sperm or egg cells
•Haploid
(single chromosomes)
Fertilization
Sperm
Egg
Gametes:
(haploid sex cells)
Zygote:
(diploid embryo)
Fertilized egg