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Dominant and Recessive

Dominant and Recessive. Doesn’t work like this recessive dominant

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Page 1: Dominant and Recessive. Doesn’t work like this recessive dominant

Dominant and Recessive

Page 2: Dominant and Recessive. Doesn’t work like this recessive dominant

Doesn’t work like this

recessive dominant

Page 3: Dominant and Recessive. Doesn’t work like this recessive dominant

Homologous chromosomes

Same genes, but possibly different versions

Page 4: Dominant and Recessive. Doesn’t work like this recessive dominant

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.

Page 5: Dominant and Recessive. Doesn’t work like this recessive dominant

Our plant chromosome

Page 6: Dominant and Recessive. Doesn’t work like this recessive dominant

Red protein

Red protein

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Red flower

White protein

White protein

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White flower

Page 7: Dominant and Recessive. Doesn’t work like this recessive dominant

Red protein

White protein

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Pink flower

Page 8: Dominant and Recessive. Doesn’t work like this recessive dominant

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.

Page 9: Dominant and Recessive. Doesn’t work like this recessive dominant

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Page 10: Dominant and Recessive. Doesn’t work like this recessive dominant

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Page 11: Dominant and Recessive. Doesn’t work like this recessive dominant

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)

Page 12: Dominant and Recessive. Doesn’t work like this recessive dominant

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

Page 13: Dominant and Recessive. Doesn’t work like this recessive dominant

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

Page 14: Dominant and Recessive. Doesn’t work like this recessive dominant

More plant traits

Page 15: Dominant and Recessive. Doesn’t work like this recessive dominant

What about our red/white alleles?

Red protein

White protein

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Pink flower

Alleles are codominant – you can see the effect of both proteins

Page 16: Dominant and Recessive. Doesn’t work like this recessive dominant

Usually more than two alleles for each gene

Page 17: Dominant and Recessive. Doesn’t work like this recessive dominant

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

Page 18: Dominant and Recessive. Doesn’t work like this recessive dominant

X chromosome:Lots of genes!

Y chromosome:Almost nothing on

it; “genetic wasteland”

Page 19: Dominant and Recessive. Doesn’t work like this recessive dominant

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

Page 20: Dominant and Recessive. Doesn’t work like this recessive dominant

Most colorblind people are male

Page 21: Dominant and Recessive. Doesn’t work like this recessive dominant

Two chances to get a good copy

Only one chance

Page 22: Dominant and Recessive. Doesn’t work like this recessive dominant

Are there . . .

Two identical alleles?

The organism is homozygous for that

trait.

Two different alleles?

The organism is heterozygous for that

trait.

Page 23: Dominant and Recessive. Doesn’t work like this recessive dominant