Genetics non mendelian

Other Patterns of Inheritance

Beyond Dominant and Recessive Alleles

Incomplete Dominance

- A case in which one allele is not completely dominant over another- The heterozygous phenotype lies

somewhere between the two homozygous phenotypesR R

W

W

RW RW

RW RW

CC – Curly hair x SS - Straight hair

CS – Wavy hair x CS

Incomplete Dominance

C C

S

S

CS CS

CS CS

SpongeBob loves growing flowers for his pal Sandy! Her favorite flowers, Poofkins, are found in red, blue, and purple. Use the information provided and your knowledge of incomplete dominance to complete each section below.

Incomplete Dominance

1. Write the correct genotype for each color if R represents a red gene and r represents a blue gene.

Red - ____________Blue - ____________Purple - __________

Incomplete Dominance

2. What would happen if Spongebob crossed a Poofkin with red flowers with a Poofkin with blue flowers. a. Give the phenotypes and genotypes for the offspring.b. How many of the plants would be have red flowers? _____ %c. How many of the plants would have purple flowers? ______ %d. How many of the plants would have blue flowers? ______%

Incomplete Dominance

3. What would happen if SpongeBob crossed two Poofkins with purple flowers?

a. Give the phenotypes and genotypes for the offspring.

b. How many of the plants would be have red flowers? _____ %

c. How many of the plants would have purple flowers? ______ %

d. How many of the plants would have blue flowers? ______%

Incomplete Dominance

4. What would happen if SpongeBob crossed a Poofkins with purple flower with a Poofkin with blue flower?

a. Give the phenotypes and genotypes for the offspring.

b. How many of the plants would be have red flowers? _____ %

c. How many of the plants would have purple flowers? ______ %

d. How many of the plants would have blue flowers? ______%

Incomplete Dominance

5. Cow color can be white CW or black CB. Mixing white and black makes spotted cows CWCB. A black cow and a spotted cow mate. What offspring could they have at what possibilities?

Incomplete Dominance

Codominance

- The genetic situation in which both alleles in heterozygous individual are fully expressed in the phenotype.

A A

B

B

AB AB

AB AB

1. In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette.

Codominance

1. Cross a checkered chicken with a black chicken.

Codominance

Parents: ____x _____

Determine the genotype, phenotypes and give the ratio of its phenotype.

2. Cross two checkered chickens

Codominance

Parents: ____x _____

Determine the genotype, phenotypes and give the ratio of its phenotype.

Codominance

Codominance: Neither allele masks the other so that effects of both alleles are observed in heterozygote without blending

IA = IB > i

IA and IB are codominant. IA and IB are completely dominant over i.

Codominance

Phenotype Genotype Gene Product

Antibodies Present

Type A IAIA or IAi Antigen A Anti-B

Type B IBIB or IBi Antigen B Anti-A

Type AB IAIB Antigen A andAntigen B

Neither Anti-A norAnti-B

Type O ii none Anti-A andAnti-B

A heterozygous type B man and a type AB woman want to have a child.

a. What are the chances of that they will have a type B child?

b. What are the chances that their child will be a type O carrier?

c. Other than a blood type B, what other blood types could their child have?

Codominance

Antigens on Red Blood Cells

IAi IBi

IAIB

Inheritance of Rh Factor

Phenotype Genotype*

Gene Product

Antibodies Present

Rh Positive RR or Rr Rhesus Protein

None

Rh Negative

rr None None unless exposed

*There are multiple alleles for the Rhesus protein (R1, R2, R3, etc.) and all are dominant to the multiple alleles for the absence of Rhesus protein (r1, r2, r3, etc.) .

C+ > cch > ch > c

Parents: C + cch x c hch

Determine the genotype, phenotypes and give the ratio of its phenotype.

Multiple Alleles

Parents: cchch x chc

Determine the genotype, phenotypes and give the ratio of its phenotype.

Multiple Alleles

Parents: cchc x chc

Determine the genotype, phenotypes and give the ratio of its phenotype.

Multiple Alleles

Multiple Alleles

• Multiple alleles: three or more alleles exist for one trait

(Note: A diploid individual can only carry two alleles at once.)

Blood Type

Allele

Type A IA

Type B IB

Type O i

1. What is the expected genotypic ratio among children born to a mother having the genotype Iai and a father with the phenotype AB?

2. One parent has the blood type A and the other blood type B. What are the genotypes of the parents if they produce children with only blood type AB?

Multiple Alleles

3. One parent has the blood type A and the other blood type B. What are the genotypes of the parents if ½ of the offspring are AB and the other ½ A?

4. One parent has blood type A and the other blood type B. What are the genotypes of the parents if the offspring produce the following blood types: ¼ AB, ¼ A, ¼ B and ¼ O?

Multiple Alleles

Multiple Alleles and Codominance

Type A, Rh positive x Type B, Rh negative(father is Type O, Rh negative) (mother is Type O)

Phenotypic Ratio of Offspring

Lethal Alleles

Example: Manx catML = tailless, lethal in homozygotem = tail

Tailless male x Tailless female

Egg

1:2 ratioof kittensthat are born

Sperm

x

MM(early

embryonicdeath)

Mm(Manx)

M

M

m

m

Mm(Manx)

Mm(Manx)

Mm(Manx)

mm(non-Manx)

Lethality in Manx cats

causes altered ratio

2:1 ratio from cross between

two yellow mice results from a lethal

allele.

Hierarchy of Dominance

Example: hair curlingSw = wooly Sc= curly Swa= wavy s =

straightSw> Sc> Swa> s

Hierarchy of Dominance

Sw> Sc> Swa> s

Dad Colavito has wavy hair.Mom Colavito has curly hair.Their daughter Jean has straight hair.What are the expected genotypic and phenotypic ratios for their offspring?

Hierarchy of Dominance

Sw> Sc> Swa> s

Dad C x Mom CWavy Curly

Pleiotropic Effects

One gene affects many phenotypic characteristics

Allele S S’

Gene Product Hemoglobin A Hemoglobin S

Cell Shape Round Sickled under low O2 tension

Response to Malaria

Susceptible Resistant in SS’ genotype

Polygenic Traits

Definition

• Some traits are determined by the combined effect of two or more pairs of alleles. These traits are called polygenic traits.

• Each pair of alleles adds something to the resulting phenotype.

• Other names for polygenic traits are multi-factorial traits, or quantitative traits.

Polygenic traits are continuous

• Because so many alleles contribute to the final phenotype, a variety of phenotypes can occur!

• Polygenic inheritance is responsible for many phenotypic traits. Examples include skin pigmentation, height, intelligence and stature. (note that these traits all result from the interaction of the genes with environmental

factors)

Polygenic Inheritance -Discontinuous Variation.

• A characteristic shows DISCONTINUOUS VARIATION if it can be used to divide up the members of a species into two distinct groups.

• e.g. Can roll tongue vs Cannot roll tongue.

• Such information is often presented in a bar chart.

Polygenic Inheritance -Continuous Variation.

• A characteristic shows CONTINUOUS VARIATION when it varies amongst the members of a species in a smooth continuous way from one extreme to another, and does not fall into distinct groups.

• e.g. Height – varies from very small to very tall. Also, skin colour, weight

• Such information is often presented in a HISTOGRAM.

Effect of Environment• Many of these characteristics are

influenced by the environment.• Polygenic inheritance +

environmental factors = phenotypic characteristic which shows a wide range of continuous variation and a normal pattern of distribution.

Many characteristics which show continuous variation (e.g. Height, foot size, etc.) are influenced by

the environment• They are dependant on favourable

environmental conditions for their full phenotypic expression.

• For example, regardless of how many dominant alleles for height that a person inherits, he or she will not reach their full potential for height without consuming an adequate diet during childhood and adulthood.

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Examples of Polygenic Traits

• Pepper Color

Gene 1: R=red r=yellow

Gene 2: Y=absence of chlorophyll (no green)

y=presence of chlorophyll (green)

Pepper Color

• Possible genotypes:

• R-/Y- : red (red/no chlorophyll)• R-/yy : brown/orange

(red/chlorophyll)• rr/Y- : yellow (yellow/no chlorophyll)• rr/yy : green (yellow/chlorophyll)

Pepper Color

• Try crossing a brown pepper (RRyy) with a yellow pepper (rrYY).

• Which trait will your offspring (F1 generation) produce?

• What traits are produced when you cross two of the peppers found in the F1 generation?

More Polygenic Traits

• Chicken Combs:

– There are 4 different comb shapes that can appear in a chicken.

– Comb shape is controlled by two genes found on two different pairs of chromosomes.• Gene 1: R• Gene 2: P

Chicken Comb Example:

• 4 different phenotypes result:

• Rose Combs (R-pp)• Walnut Combs (R-P-)• Pea Combs (rrP-)• Single Combs (rrpp)

Another example of a polygenic trait:

• Hair Color– Hair color is controlled by alleles on

chromosomes 3, 6, 10, and 18. – The more dominant alleles that appear

in the genotype, the darker the hair!

Polygenic inheritance

In humans, most traits that have anything to do with size, shape, and color are controlled by multiple sets of genes.

(e.g. AaBbCc – three sets for one trait)What if you did the following cross? AaBbCc x AaBbCc – each parent contribution?3 dominant (ABC) / 3 recessive (abc)2 dominant/1 recessive (ABc, AbC, aBC)1 dominant/2 recessive (Abc, aBc, abC)

The number of dominant alleles determines how dark (or how big) the phenotype will be…AABBCC (very dark) aabbcc (very light)

Note the following Punnett Square…

Record the number of Dominant Alleles in the

Punnett Square

Practice Problem

The length of a stem is controlled by three genes – A_B_C_

aabbcc – 4 cm tallAABBCC – 16 cm tallEach upper case allele represents an

equal portion of the trait.Suppose a 16 cm tall plant was

crossed with a plant 4 cm tall. How tall is the F1?

F1 – 100% AaBbCcBase height (4 cm) + # of upper case alleles (3 @ 2cm

each)

4 + 6 = 10cm tall plants (AaBbCc)

Sex Linkage and Polygenic Inheritance

Normal Body Cells

• In the nucleus of every body cell there are 46 chromosomes

• 22 homologous pair and one pair of sex chromosomes

Female and Male Sex Chromosomes

Red Green Colour Blindness

• Inability to distinguish between red and green

• A red green colour blind person does not see the number 29 on the right

• In humans normal vision is completely dominant to red-green colour blindness

Genetics of Colour Blindness

• Normal vision C• Red-green colour blindness c• Heterozygous females are called

carriers• Work out the genotypes of the

following family tree

Answers

• Carrier mother XCXc

• Nomal father XCY

• Normal daughter XCXC

• Carrier daughter XCXc

• Normal son XCY• Colour-blind son XcY

Haemophilia

• Haemophiliacs cannot make the blood clotting protein Factor VIII.

• It caused by a recessive allele carried on the X but not the Y chromosome

• Hence is sex-linked

Family Tree of Haemophilia

Muscular Dystrophy

• Skeletal muscles loose their normal structure and fibrous tissue develops in their place

• Caused by a recessive allele carried on the X chromosome and is sex-linked

Family Tree of Muscular Dystrophy