Co-dominance & Incomplete Inheritance

Dominance Inheritance ReviewIncomplete Inheritance

Co-dominance InheritanceSBI3U

Example of Dominance Inheritance● Hair texture

- Curly hair is dominant

- Straight hair is recessive

● Dimple trait- Dimple is dominant

- No dimple is recessive

More Examples

● Hitchhiker’s thumb- Straight is dominant

- Curved is recessive

● Tongue rolling- Rolling is dominant

- Not rolling is recessive

Your Genotype

● State your genotype for the following:– Hair texture

– Dimples

– Hitchhiker’s thumb

– Tongue rolling

Sample Problem #1● Dwarfism is a dominant trait. If both

parents with dwarfism phenotype have normal looking offspring,

a) Determine the genotype of the parents.

b) The percentage of their child looking normal.

c) The percentage of their grandkids from normal offsprings looking dwarfish given that their life partners are also normal.

Sample Problem #2● Breast cancer has been tracked to associate genes

BRCA1 & BRCA2, which are tumour suppressors and function to inhibit the growth of tumour (cell cycle genes). It is a recessive trait. That means, if the gene is negatively mutated and the offspring carry both mutated alleles, she is more likely to develop breast cancer.

a) Determine the phenotype of the genotype variants for this trait.

b) If the mother is heterozygous and the father has normal alleles, how many of their 6 children will:

I) be carriers of the cancer trait (heterozygous)

ii) be homozygous for normal BRCA1

iii)develop breast cancer.

Incomplete Dominance (Blending Inheritance)

● It is a cross between two organisms with two different phenotypes which produces offspring with a third phenotype that is a blending of the parental traits.

● Results in a combined phenotype.

● Thus, a total of 3 phenotypes are observed.

● Each phenotype has its own genotype.

Incomplete Dominance.... con’t

● The three phenotypes are:

Incomplete Dominance.... con’t

● The three phenotypes are:

- red, white, pink

Incomplete Dominance.... con’t

● The three phenotypes are:

- red, white, pink● The three

genotypes are:

Incomplete Dominance.... con’t

● The three phenotypes are:

- red, white, pink● The three

genotypes are:

- RR, WW, RW

Incomplete Dominance.... con’t

Going Back to Mendel

● Mendel got lucky.● He did not observe

these traits as they do not occur in pea plants.

Incomplete Dominance.... con’t

● A red hibiscus is crossed with a white hibiscus.

a) What are the genotypes of P?

b) What are the genotypes of F

1?

P:

Incomplete Dominance.... con’t

● A red hibiscus is crossed with a white hibiscus.

a) What are the genotypes of P?

b) What are the genotypes of F

1?

P: (HRHR) x (HWHW)

F1:

Incomplete Dominance.... con’t

● A red hibiscus is crossed with a white hibiscus.

a) What are the genotypes of P?

b) What are the genotypes of F

1?

P: (HRHR) x (HWHW)

F1: 100% HRHW

Incomplete Dominance.... con’t

● A red hibiscus is crossed with a white hibiscus.

c) Predict the phenotype ratio for self-pollinated hybrid hibiscus.

F1:

Incomplete Dominance.... con’t

● A red hibiscus is crossed with a white hibiscus.

c) Predict the phenotype ratio for self-pollinated hybrid hibiscus.

F1: (HRHW) x (HRHW)

F2:

Incomplete Dominance.... con’t

● A red hibiscus is crossed with a white hibiscus.

c) Predict the phenotype ratio for self-pollinated hybrid hibiscus.

F1: (HRHW) x (HRHW)

F2: 25% Red

50% Pink

25% White

Your Turn● A cross between a blue blahblah bird and a

white blahblah bird produces offspring that are silver. The colour of the blahblah birds is determined by just 2 alleles.

a) What are the genotypes of the parent blahblah birds in the original cross?

b) What is/are the genotype(s) of the silver offspring?

c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?

Your Turn..... Again

● The colour of fruit for plant “X” is determined by two alleles. When two plants with orange fruit are crossed, the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, and 25% yellow fruit. Determine the genotypes of the parent orange-fruited plants.

Co-dominance Inheritance● This occurs when

the dominancy (strength) of the allele changes unpredictably.

● The recessive and dominant traits appear together in the phenotype of the hybrid organism

Codominance Example

● Cattle can be red (RR), white (WW) or roan (RW).

● Predict what will happen if you cross a red cow (RR) with a roan (RW) bull.

Cows.... con’t

● What should the genotypes & phenotypes for the parent cattle be if the farmer only wanted cattle with red fur?

Moving along to cats.● A cross between a

black cat & a tan cat produces a tabby pattern.

a) What pattern of inheritance does this illustrate?

b) What percentage of kittens would have tan fur if a tabby is crossed with a black cat?