Mendelian GeneticsConcept 2: Analyzing the effects of complex genetic crosses such as incomplete/co- dominance, multiple alleles, pleiotropy, epistasis, polygenics, and lethal alleles.

We just need to practice…

Try… On Worksheets:Multiple Choice: 1, 2, 3, 5, 7, 8, 10, 13Genetics Problems: 1, 2, 6, 12, 13

Learning Goal: How are traits

passed down from

parents to offspring?

Try This!

A brown eyed male has 5 children with a blue eyed female. 4 of the children have brown eyes and 1 child has blue eyes. If brown eyes are dominant to blue eyes, what is the genotype of each parent?

Degrees of Dominance

Complete Dominance Homozygous Dominant and Heterozygous are

indistinguishable Monohybrid Phenotypic Ratio – 3:1

Incomplete Dominance Heterozygotes display a blended phenotype Monohybrid Phenotypic Ratio – 1:2:1

Codominance Heterozygotes display both traits (separate, distinguishable) Monohybrid Phenotypic Ratio - 1:2:1

Degrees of Dominance

Not cut and dry… Organism Biochemical Molecular

Multiple Alleles

Many alleles for one gene Blood Type

Example: If a male with blood type AB has children with a female with blood type O, what is the predicted phenotypic ratio of their children?

Multiple Alleles

Example: If a male with blood type AB has children with a female with blood type O, what is the predicted phenotypic ratio of their children?

Type AB male x Type O Female IAIB ii

IA IB

ii

Multiple Alleles

Example: If a male with blood type AB has children with a female with blood type O, what is the predicted phenotypic ratio of their children?

Type AB male x Type O Female IAIB ii

IA IB

i IAi IBii IAi IBi

Multiple Alleles

Example: If a male with blood type AB has children with a female with blood type O, what is the predicted phenotypic ratio of their children?

Type AB male x Type O Female IAIB ii

IA IB

i IAi IBii IAi IBi

Predicted Phenotypic Ratio:

Multiple Alleles

Example: If a male with blood type AB has children with a female with blood type O, what is the predicted phenotypic ratio of their children?

Type AB male x Type O Female IAIB ii

IA IB

i IAi IBii IAi IBi

Predicted Phenotypic Ratio:

1 Type A: 1 Type B

Pleiotropy

One gene that has multiple effects on phenotypic characters Sickle cell Cystic fibrosis

Epistasis

One gene having an effect over another gene Mouse coat colour

Example: In corn, a dominant allele I inhibits kernel colour, while the recessive allele i permits colour when homozygous. At a different locus, the dominant allele P causes purple kernel colour, while the homozygous genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring?

Epistasis Example: In corn, a dominant allele I inhibits kernel

colour, while the recessive allele i permits colour when homozygous. At a different locus, the dominant allele P causes purple kernel colour, while the homozygous genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring? (no colour=yellow)

IiPp x IiPp

Phenotypes:

P pP PP Ppp Pp pp

I iI II Iii Ii ii

Epistasis Example: In corn, a dominant allele I inhibits kernel colour,

while the recessive allele i permits colour when homozygous. At a different locus, the dominant allele P causes purple kernel colour, while the homozygous genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring? (no colour=yellow)

IiPp x IiPp

Phenotypes:Yellow I___Purple iiP_Red iipp

P pP PP Ppp Pp pp

I iI II Iii Ii ii

Epistasis Example: In corn, a dominant allele I inhibits kernel colour,

while the recessive allele i permits colour when homozygous. At a different locus, the dominant allele P causes purple kernel colour, while the homozygous genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring? (no colour=yellow)

IiPp x IiPp

Phenotypes:Yellow I___ 1 x ¾ = ¾ = 12/16Purple iiP_ ¾ x ¼ = 3/16Red iipp ¼ x ¼ = 1/16

P pP PP Ppp Pp pp

I iI II Iii Ii ii

Epistasis Example: In corn, a dominant allele I inhibits kernel colour,

while the recessive allele i permits colour when homozygous. At a different locus, the dominant allele P causes purple kernel colour, while the homozygous genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring? (no colour=yellow)

IiPp x IiPp

Phenotypes:Yellow I___ 1 x ¾ = ¾ = 12/16Purple iiP_ ¾ x ¼ = 3/16Red iipp ¼ x ¼ = 1/16

P pP PP Ppp Pp pp

I iI II Iii Ii ii

Predicted Phenotypic Ratio:

Epistasis Example: In corn, a dominant allele I inhibits kernel colour,

while the recessive allele i permits colour when homozygous. At a different locus, the dominant allele P causes purple kernel colour, while the homozygous genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring? (no colour=yellow)

IiPp x IiPp

Phenotypes:Yellow I___ 1 x ¾ = ¾ = 12/16Purple iiP_ ¾ x ¼ = 3/16Red iipp ¼ x ¼ = 1/16

P pP PP Ppp Pp pp

I iI II Iii Ii ii

Predicted Phenotypic Ratio:

12 Yellow: 3 Purple: 1 Red

Polygenic Inheritance

Two or more genes affecting one phenotypic character Quantitative characters – continuum rather than

“either/or” Skin colour in humans Spike weed height

Number of phenotypic classes possible = #alleles+1

Try This! The height of spike weed is a result of polygenetic

inheritance involving three genes, each of which can contribute an additional 5cm to the base height of the plant, which is 10cm. The tallest plant (AABBCC) can reach a height of 40cm.

A) If a tall plant (AABBCC) is crossed with a base-height plant (aabbcc), what is the height of the F1 plants?

B) How many phenotypic classes will there be in the F2?

c) What is the probability of seeing a 20cm plant in the F2 generation?

A) If a tall plant (AABBCC) is crossed with a base-height plant (aabbcc), what is the height of the F1 plants?

The parental cross produced 25cm tall F1 plants, all AaBbCc plants with 3 units of 5 cm added to the base height of 10cm.

B) How many phenotypic classes will there be in the F2?

General Rule: number of phenotypic classes resulting from a cross of heterozygotes equals the number of alleles involved plus one.

(AaBbCc ) 6 alleles + 1 = 7

6 dominant alleles: 40 cm5: 35 cm4: 30 cm3: 25 cm2: 20 cm1: 15 cm0: 10 cm

c) What is the probability of seeing a 20cm plant in the F2 generation?

Phenotype: 20cm

Genotype: 2 dominant alleles

AaBbCc x AaBbCc

AAbbcc ¼ x ¼ x ¼ = 1/64AaBbcc ½ x ½ x ¼ = 1/16 = 4/64 AabbCc ½ x ¼ x ½ = 1/16 = 4/64 aaBBcc ¼ x ¼ x ¼ = 1/64aaBbCc ¼ x ½ x ½ = 1/16 = 4/64 aabbCC ¼ x ¼ x ¼ = 1/64

Different ways of getting the same thing… add!

15/64

Lethal Alleles

Recessive lethal allele 2:1 ratio if lethal before birth Cystic fibrosis

Dominant lethal allele Must show effects after reproductive age

Why? Huntington’s Disease

Environmental Effects

Hydrangeas Plant a tin can next to them and see what happens!

Don’t forget about pedigrees!

We just need to practice…

On Worksheets for Concept 2:Multiple Choice: 4, 6, 9, 11, 12, 14, 15, 16Genetics Problems: 3, 4, 5, 7, 8, 9, 10, 11, 14

Learning Goal: How are traits

passed down from

parents to offspring?