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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?
In organisms like humans, chromosomes come in matched pairs.
http://www.aiesec.org.nz/waikato/nzms/father.jpg
How do we refer to the GENES we inherited from our parents?
Genes come in different forms,
called alleles
Example: A, B vs. O alleles for blood type
HOMOZYGOUS for U gene
U U
HETEROZYGOUS for W gene
W w
A B
How are chromosomes randomly passed on to offspring?
5.9
Matchedchromosomes
pair up
Matched chromosomes
separate
Sex cells = gametes.
Ours are HAPLOID
http://fig.cox.miami.edu/~cmallery/150/life/meiosis.pics.jpg
G
Meiosis
g G
g
G g G g
What happens after chromosomes are divided in meiosis?
Haploid + Haploid
= Diploid
Meiosis followed by fertilization
G
g G
g
You try it first
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 (appearance)
Pp is the genotype (makeup of alleles)
PP pp
Pp
P P p p
P p
Punnett squares predict offspring from parents genotypes
P p
P
p
Parent’s haploid gametes
Pp
Pp
PpPp
PP
PP
pp
pp
Diploid progeny
If I cross Pp purple by the white parent, what kinds of “kids” will I see?
Try it!Pp x pp
pp
p
p
P Pp Pp
pp pp
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
Two doses of
“R” allele – very red
One dose of “R” allele – pink
No doses of “R” allele - white
RR Rr rr
Mendel would have been surprised!
RR Rr rr
“R” vs. “r” now refers to whether or not allele makes a protein, and “contributes” to phenotype
“R” is contributing
“r” is non-contributing
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.
C1 = Curly hair
C2 = straight hair
Can you think of any traits in humans controlled by incomplete dominance?
Try it!
Cross two heterozygous parents.
Another example: not just ONE ethanol-response gene:
ADH
ALDH
GOOD ADH function = contributing allele
GOOD ADH function = Increased dosage desired
GOOD ALDH function = contributing allele
GOOD ALDH function = Few side effects
With SOME Alcohol response genes
ADH
ALDH
Alcohol dehydrogenase
Aldehyde dehydrogenase
Therefore, if ALDH works poorly, aldehyde
builds up. Drinker
Feels more sick.
How to designate alleles for incompletely dominant traits?
http://www.travelinnermongolia.com http://english.gov.cn/images
Rapid metabolism of aldehyde
Slow metabolism of aldehyde
ALDH2*2 allele ALDH2*1 allele
Why not “A” vs. “a”?
“Brain Storm” by alexiuus.deviantart.com
SNPs and alcoholism
PMID: 9347089
Very low frequency of ALDH2*2 allele
Mongolian Chinese
Somewhat higher frequency of ALDH2*2 allele
Han Chinese
http://www.travelinnermongolia.com http://english.gov.cn/images
Rapid metabolism of aldehyde
Slow metabolism of aldehyde
PROTECTS
from
ethanol
abuse
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