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