Complex Inheritance Patterns

Determine the Pattern of Inheritance

:Punnett Squares

Determine probability in certain inheritance patterns using Punnett Squares

Multiple Choice

Using a Punnett Square determine the parent genotypes if all the offspring are Tt.

• Tt x Tt

• tt x tt

• TT x tt

• Tt x tt

Complete Dominance

Mendelian Genetics

Trait: Phenotype: Yellow or green seeds

Yellow (Y) is Dominant to green (g)

Parent Generation YY x yy (purebreds)

F1 generation would be Tt (hybrids)

Phenotype ratio 4:0 Genotype Ratio 0:4:0

Cross the F1 generation via self fertilization

Tt x Tt = F2 generation

Phenotype ratio 3:1 Genotype Ratio 1:2:1

In an individual containing two allelic forms of a gene, one is expressed to the exclusion of the other.

Multiple Choice

Click the picture to enlarge.

What type of inheritance pattern is this?

• Complete

• Incomplete

• Co-Dominant

• Multiple Alleles

Another Example of Complete Dominance

• Seperate the gametes of both parents

• Enter Parent # 1 on the top and Parent # 2 on the side

• Cross as indicated in the diagram

Multiple Choice

Using a Punnett Square determine the phenotype ratio for a Heterozygous Tall Plant crossed with a short plant.

• Ratio 1:1

• Ratio 4:0

• Ratio 3:1

• Ratio 1:3

Can we determine the parent genotypes if we know the offspring?

• Yes we can, we use a TEST CROSS

• See Diagram on how to perform

Multiple Choice

There is a 100% probability that all the offspring have a phenotype that is heterozygous tall. Using a Punnett Square complete a test Cross to determine the parent genotypes.

• TT x Tt

• TT x tt

• TT x tt

• Tt x tt

Independent Assortment

• According to independent assortment, the inheritance of one gene/trait is independent to the inheritance of any other gene/trait

• Random orientation of pairs of homologous chromosomes in meiosis I

• The orientation of each homologous pair is random and is not affected by the orientation of any other homologous pair

  This means an allele on one chromosome has an equal chance of being paired with, or separated from, any allele on another chromosome

• Independent assortment will not occur if two genes are located on the same chromosome (linked genes)

Mendel's Dihybrid Crosses

• When Mendel crossed to purebred plants that were homozygous dominant for both and homozygous feccivve for both traits. He always got 16:0:0:0 ratio

• That is in the F1 generation all plants should Yellow and round seeds which are dominant

• However he noticed when he self fertilized F1 generation plants the two traits seemed to not affect one another and the phenotype ratio was always 9:3:3:1

Foil Method to Seperate Gametes

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Multiple Choice

In a flowering plant, tall (T) is dominant to short (t), and blue flowers (B) is dominant to white flowers (b).

A tall plant with white flowers (Ttbb) is crossed with a short plant with blue flowers (ttBb).

Use a 16 square Punnett square and provide the phenotype ratio

• 1

• 2

• 3

• 5

Using the Product Rule to determine genotype probability

Multiple Choice

In a flowering plant, tall (T) is dominant to short (t), and blue flowers (B) is dominant to white flowers (b).

A tall plant with white flowers (Ttbb) is crossed with a short plant with blue flowers (ttBb).

What is the chance that the offspring will be short with white flowers?

Use the product rule:

• 3/4

• 1/8

• 1/4

• 3/16

Example of Incomplete Dominance

Multiple Choice

In a species of birds, blue feathers (B) are incompletely dominant to the gene for white feathers (b). Individuals that are heterozygous (Bb) have light blue feathers.

A bird with light blue feathers is crossed with a white bird. What are the chances any of the offspring will have blue feathers?

• 0%

• 25%

• 50%

• 100%

Multiple Choice

In camellia flowers, petal color is controlled by codominance. When a red flower is crossed with a white flower, all of the offspring are covered in both red and white petals.

A scientist crosses a red flower (RR) with a red-and-white (RW) flower.

What are the predicted phenotypes of their offspring?

RR:RW:WW

• 4:0:0

• 1:2:1

• 2:2:0

• 0:2:2

How to Draw Antigens on the Surface of a RBC

Try this question on your own

Homozygous Type A= IAIA

Type O = ii

Genotype Ratio

AA:AO:BB:BO:AB:OO

0: 4: 0: 0: 0 :0

Phenotype Ratio to

A: B:AB : O

4: 0: 0: 0

None of the offspring will be Type O

Agglutination Test

• Anti serum A contains A antibodies that will react with the presence of blood that contains red blood cells that have A Antigens

• Anti serum B contains B antibodies that will react with the presence of blood that contains red blood cells that have B Antigens

• Anti serum D will react with the presence of blood that contains red blood cells are positive

• The blood type here show agglutination with Anti A and Anti D therefore this blood type is A+

Multiple Choice

Click on the image to enlarge

What blood type is this?

• AB+

• AB-

• 0-

• 0+

Other Multiple Allele Examples

Mendel implied that only two alleles, one dominant and one recessive, could exist for a given gene. We now know that this is an oversimplification. Although individual humans (and all diploid organisms) can only have two alleles for a given gene, multiple alleles may exist at the population level such that many combinations of two alleles are observed. Note that when many alleles exist for the same gene, the convention is to denote the most common phenotype or genotype among wild animals as the wild type (often abbreviated “+”); this is considered the standard or norm. All other phenotypes or genotypes are considered variants of this standard, meaning that they deviate from the wild type. The variant may be recessive or dominant to the wild-type allele.

Multiple Alleles and Rabbit Fur Colour

An example of multiple alleles is coat color in rabbits (Figure 1). Here, four alleles exist for the c gene. The wild-type version, C⁺C⁺, is expressed as brown fur. The chinchilla phenotype, c^chc^ch, is expressed as black-tipped white fur. The Himalayan phenotype, c^hc^h, has black fur on the extremities and white fur elsewhere. Finally, the albino, or “colorless” phenotype, cc, is expressed as white fur. In cases of multiple alleles, dominance hierarchies can exist. In this case, the wild-type allele is dominant over all the others, chinchilla is incompletely dominant over Himalayan and albino, and Himalayan is dominant over albino. This hierarchy, or allelic series, was revealed by observing the phenotypes of each possible heterozygote offspring.

Dominance in Fur Colour

• Full Colour Alleles (wild/brown) is dominant to all

• Chinchilla Alleles (light brown) is dominant to himilayan and albino

• Himalayan Alleles is dominant to albinos

• Albino Alleles are recessive and you need both recessive Alleles to be albino

• See the phenotype and genotyples