Download Lesson 12: Single Trait Inheritance lecture unit3Lesson12

Content Review:
• Nucleotides, DNA, genes, chromosomes, and
codons are all terms used to describe our
genetic information. Take each pair of
terms and describe their relationship.
• Nucleotides and genes
• Genes and Chromosomes
• DNA and codons
• Chromosomes and DNA
Lesson 12: Single Gene Inheritance
• relate your understanding of genes and DNA to
chromosomes;
• relate your understanding of alleles to Mendelian
concepts of segregation and dominance;
• understand how meiosis leads to the production of
haploid gametes;
• relate the outcome of meiosis to the establishment of
Punnett squares;
• extend your understanding of genetics to include
incomplete dominance (leaving pedigree analysis to
Lesson 14)
What did we inherit from our parents?
http://www.aiesec.org.nz/waikato/nzms/father.jpg
In organisms like humans,
chromosomes come in matched pairs.
How do we refer to the GENES we
inherited from our parents?
A
B
Genes come in
different forms,
called alleles
U
U
W
w
Example: A, B vs. O
alleles for blood type
HOMOZYGOUS for U gene
HETEROZYGOUS for W gene
How are chromosomes randomly passed
on to offspring?
Matched
chromosomes
pair up
Sex cells
= gametes.
5.9
Matched
chromosomes
separate
Ours are
HAPLOID
http://fig.cox.miami.edu/~cmallery/150/life/meiosis.pics.jpg
Meiosis
G
g
g
G
g
G
g
G
What happens after chromosomes are
divided in meiosis?
Haploid + Haploid
= Diploid
Meiosis followed by fertilization
g
G
You try it
first
G
g
GG
Gg
Gg
gg
Take a minute to talk about probability
g
G
g
G
What is the
probability of
getting Gg?
GG? gg?
1/4 1/4
1/4 1/4
What did Mendel tell us about the
inheritance of traits?
•Crossed peas for seven contrasting
characteristics
•Looked at offspring and “grand”
offspring
•Carefully, mathematically,
analyzed the data
CONCLUSION
Traits are controlled by factors
(alleles) that come in pairs
What else did Mendel tell us about the
inheritance of traits?
How are phenotype and genotype
related?
Flower color
is the
phenotype
P P
p p
(appearance)
PP
pp
Pp is the
genotype
(makeup of
alleles)
P p
Pp
Punnett squares predict offspring from
parents genotypes
Parent’s haploid gametes
PP
Pp
P
p
P
PP
Pp
p
Pp
pp
Pp
Diploid
progeny
pp
If I cross Pp purple by the white parent, what
kinds of “kids” will I see?
Pp x pp
Try it!
p
p
P
Pp
Pp
p
pp pp
p
Do you know any human single gene traits?
Check your partner’s
phenotype for these
traits.
Can you determine
their genotype?
First Thing Mendel Didn’t Know
RR
Rr
rr
Two doses of
“R” allele –
very red
One dose of
“R” allele –
pink
No doses of
“R” allele white
Mendel would have been surprised!
“R” vs. “r” now refers to whether or not allele makes a
protein, and “contributes” to phenotype
RR
Rr
“R” is contributing
“r” is non-contributing
rr
You mate two pink snapdragons. ____ is the
proportion of red offspring from this trait that
shows ________________.
Try it!
Try another one!
A gene called “Insulin-like growth factor” (I)
controls size in dogs. A Great Dane is homozygous
for the I allele, whereas a toy poodle is homozygous
for the “i” allele. A mating between the two gives a
middle sized dog.
Assume there is only this one gene that influences
size and determine what sizes (and in what
proportion) would be seen if the Great Dane mated
with the middle-sized GreatOodle.
Can you think of any traits in humans
controlled by incomplete dominance?
Try it!
Cross two
heterozygous
parents.
C1 = Curly hair
C2 = straight hair
Another example: not just ONE ethanolresponse gene:
GOOD ADH function =
contributing allele
GOOD ADH function =
Increased dosage desired
GOOD ALDH function =
contributing allele
GOOD ALDH function =
Few side effects
ADH
ALDH
With SOME Alcohol response genes
Therefore, if ALDH
works poorly, aldehyde
builds up. Drinker
Feels more sick.
ADH
ALDH
Alcohol dehydrogenase
Aldehyde dehydrogenase
How to designate alleles for incompletely
dominant traits?
http://english.gov.cn/images
http://www.travelinnermongolia.com
Rapid metabolism
of aldehyde
ALDH2*1 allele
Slow metabolism
of aldehyde
ALDH2*2 allele
Why not “A” vs. “a”?
“Brain Storm” by
alexiuus.deviantart.com
SNPs and alcoholism
http://www.travelinnermongolia.com
http://english.gov.cn/images
PMID: 9347089
Mongolian Chinese
Very low frequency of
ALDH2*2 allele
Han Chinese
Somewhat higher frequency
of ALDH2*2 allele
PROTECTS
from
ethanol
Rapid metabolism
of aldehyde
Slow metabolism
of aldehyde
abuse