Dominant and Recessive. Doesn’t work like this recessive dominant.
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Dominant and Recessive
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Transcript of Dominant and Recessive. Doesn’t work like this recessive dominant.
Dominant and Recessive
Doesn’t work like this
recessive dominant
Homologous chromosomes
Same genes, but possibly different versions
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.
Our plant chromosome
Red protein
Red protein
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Red flower
White protein
White protein
+
White flower
Red protein
White protein
+
Pink flower
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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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)
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
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
More plant traits
What about our red/white alleles?
Red protein
White protein
+
Pink flower
Alleles are codominant – you can see the effect of both proteins
Usually more than two alleles for each gene
2 of each chromosome(well, only for half of us . . . )
X chromosome:Lots of genes!
Y chromosome:Almost nothing on
it; “genetic wasteland”
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
Most colorblind people are male
Two chances to get a good copy
Only one chance
Are there . . .
Two identical alleles?
The organism is homozygous for that
trait.
Two different alleles?
The organism is heterozygous for that
trait.
