1. Dominant and Recessive

2. Doesn’t work like this recessive dominant

3. Homologous chromosomes Same genes, but possibly different versions

4. Allele  different versions of a gene Let’s look at a plant. On one of the chromosomes, there is a gene that determines flower color. Allele 1 has the following sequence: and codes for a red protein in the petals. Allele 2 has the following sequence: and produces a white protein.

5. Our plant chromosome

6. Red protein + Red flower White protein + White flower

7. Red protein White protein + Pink flower

8. A different plant chromosome Auxin: a plant cell growth hormone. As long as a plant cell has some auxin, it will grow to its full height. Mo’ auxin doesn’t mean mo’ height.

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11. Dominant Only need to have one copy of a dominant allele in order to see its effects in the cell (plant with one auxin gene is just as tall as the plant with two) Recessive Will not see the effects of a recessive allele if there are any dominant alleles of that gene on the other chromosome (DOESN’T mean you need two copies to see its effects)

12. Dominant alleles...... are NOT stronger... are NOT more common... are NOT “better”... are dominant because you’ll see the effect of their protein product no matter what else happens

13. Recessive alleles...... are NOT weaker... are NOT always rare... are NOT always harmful... are NOT bowing down to dominant alleles in any way... are recessive because the effect of their protein product can be masked by something else

14. More plant traits

15. What about our red/white alleles? Red protein White protein + Pink flower Alleles are codominant – you can see the effect of both proteins

16. Usually more than two alleles for each gene

17. 2 of each chromosome (well, only for half of us... )

18. X chromosome: Lots of genes! Y chromosome: Almost nothing on it; “genetic wasteland”

19. Red-green colorblindness Gene for protein that lets your brain tell the difference between red and green is on the X chromosome Two alleles: one that makes the protein properly, and one that doesn’t

20. Most colorblind people are male

21. Two chances to get a good copy Only one chance

22. Are there... Two identical alleles? The organism is homozygous for that trait. Two different alleles? The organism is heterozygous for that trait.