Three gene pairs located on separate autosomes determine...

Three gene pairs located on separate autosomes determine flower color and shape as well as plant height. The first pair exhibits incomplete dominance, where color can be red, pink (the heterozygote), or white. The second pair leads to the dominant personate or recessive peloric flower shape, while the third gene pair produces either the dominant tall trait or the recessive dwarf trait. Homozygous plants that are red, personate, and tall are crossed with those that are white, peloric, and dwarf. Determine the F1 genotype(s) and phenotype(s). If the F1 plants are interbred, what proportion of the offspring will exhibit the same phenotype as the F1 plants?

Transcript

00:01 We know for the parental generation that one parent is homozygous dominant and all of their genes are dominant.

00:07 And the other parent is homozygous recessive at both genes and so they have this genotype.

00:13 Now based on that, we can determine that the f1 generation is heterozygous because the first parent at the b gene can only give dominant b so all the offspring have to get a dominant b from them.

00:27 The second parent at the b gene has only recessive all the offspring have to get a recessive all of them.

00:35 And the e's are really similar.

00:37 One parent only has dominant, and so all offspring have to get a dominant from them, and the other parent is only recessive.

00:44 But when you cross this heterozygous individual with another heterozygous individual, so that way we can get an f2 generation, you get the expected 9 to 3 to 3 to 1 ratio.

01:05 Now this ratio is known if you do a lot of genetics.

01:09 Every time you do a die hybrid cross between two heterozygous individuals like we have right here, you have this ratio.

01:18 And the way that this breaks down is the four different phenotypes you would expect.

01:23 So out of these 16 options, right, 9 out of 16 have both dominant traits, meaning they have at least one dominant allele at each gene.

01:39 The threes are for having one dominant trait, but not the other.

01:44 So it might be having dominant b, but only recessive e's.

01:48 Or vice versa, having a dominant e, but only recessive bs.

01:53 Right.

01:53 And then out of all the the chances, there's only a 1 in 16 chance that two heterozygous individuals will have an offspring that has no dominant traits and only recessive alleles.

02:08 So once you know that, you can use that information to figure out an expected number of offspring for an f2 generation...

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