1. Non-Mendelian Genetics
S-B-8-1_Non-Mendelian Heredity PowerPoint
Heredity
Non-Mendelian Genetics

2. S-B-8-1_Non-Mendelian Heredity PowerPoint
Principle of Dominance 
Law of Segregation
Law of Independent Assortment
Review the main points of Mendelian Heredity. Remind students that Mendel was lucky. The traits he studied on the pea plant were on different chromosomes, governed by a single gene and behaved as either dominant or recessive. Because of their simplicity, Mendel was able to recognize patterns of heredity.
Any hereditary outcome that does not fit Mendel’s Principles and Laws is considered non-Mendelian.

3. Non-Mendelian Heredity
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Non-Mendelian Heredity
does not fit Mendel’s Laws
is not governed by one autosomal gene
Most inheritable traits are non-Mendelian. Autosomal is a chromosome that is not a sex (X or Y) chromosome.

4. S-B-8-1_Non-Mendelian Heredity PowerPoint
Incomplete Dominance
Heterozygotes look different from a homozygotes
Blending of phenotypes
Remind students that in Mendelian dominance, a heterozygote is indistinguishable from homozygous dominant individual. Notice that the probabilities for the genotypes still work, the phenotypic ratios change because the heterozygote is a new phenotype.
RR x RIRI
RRI

5. Codominance: Both alleles of a gene pair are expressed.
Example: Human Blood Types
Human blood type is determined by codominant alleles. There are three different alleles: IA, IB, and i. The IA and IB alleles are codominant, and the i allele is recessive.
The possible human phenotypes for blood group are type A, type B, type AB, and type O.
Type A and B individuals can be either homozygous (IAIA or IBIB, respectively), or heterozygous (IAi or IBi, respectively). Type O is IOIO.
What do you think the genotype of a Roan Cow is? IRIW
S-B-8-1_Non-Mendelian Heredity PowerPoint

6. Codominance: More Examples
Rhododendron coloration
Roan coloration in cows (red coat with white blotches)
S-B-8-1_Non-Mendelian Heredity PowerPoint

7. S-B-8-1_Non-Mendelian Heredity PowerPoint
THINK-PAIR-SHARE
Distinguish between incomplete dominance and codominance.
How many phenotypes are seen when codominance is possible?
Red color (R) in snapdragons shows incomplete dominance to white snapdragons (RI). The heterozygotes are pink. If pink snap dragons are crossed with a white snapdragon, what are the genotypic/ phenotypic ratios?
Incomplete dominance –there is a blending of the two phenotypes. Codominance-both alleles are expressed.
Three, but the heterozygote expresses both alleles present.
There should be approximately 50% pink and 50% white snapdragons.
How many phenotypes would be seen if you have codominant alleles and a recessive allele? 4 R RI
RRI
RIRI

8. S-B-8-1_Non-Mendelian Heredity PowerPoint
Multiple Alleles
When 4 or more possible phenotypes exist within a population
Blood type
Eye & hair color
Fur in mammals
Explain that the blood types, IA and IB refers to the antigens located on the blood cell. If one of the chromosomes carries the IA allele, then that cell will produce that antigen, if one of the chromosomes carries the IB allele, then that antigen is made by the cell. If both alleles are present, both are expressed. What is this an example of? Codominance
Stress that although there may be multiple alleles within a population, an individual will only have 2. Why? Received one from each parent.
Explain that one allele could be dominant over another but recessive to a different allele. In mice, agouti (the wild type) is dominant to black. Both agouti and black is dominant to albino. The series are often written as: agouti > black > albino.

9. Problems with Multiple Alleles
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Problems with Multiple Alleles
A woman with type O blood marries a man with type AB blood. What are the possible blood types that a child of theirs could inherit?
STEP 1: ♀ ii ♂ IAIB
STEP 2: i IA , IB
STEP 3:
Step 1: Indentify the genotypes of the parents. The woman is O so she must be homozygous recessive or ii. The man is AB so he is IAIB.
Step 2: Determine the number and kinds of gametes the parents can make. How many kinds of gametes can the mother make? 1 How many kinds can the father make? 2 What is the formula for figuring this out? 2n, where n is the number of heterozygous gene pairs present in the parent.
Step 3: Make your grid. How many rows and columns? It is a 2 x 1 grid
Step 4: Put the in the gamete alleles at the head of the column and row.
Step 5: Fill in the boxes. What are the possible genotypes of their offspring? IAi , IBi
Step 6: What are the possible phenotypes? Type A and Type B, and an equal chance of either.
IA IB
STEP 4: i
IAi IBi
STEP 5:
STEP 6:
There’s a 50% chance that their baby will be Type A or Type B.

10. Polygenic Inheritance
S-B-8-1_Non-Mendelian Heredity PowerPoint
Polygenic Inheritance
Poly-many genic-gene
More than one gene on more than one loci or on more than one chromosome.
Give the appearance of gradation
Hair & skin color
Height
Body size
Many times, more than one gene determines the trait. The multiple genes allow for continuous variations of certain traits within the population.
Notice with one gene, 2 allele there is only 3 variations in height. As we add numbers of genes, the numbers of variations increase. What do you think would happen if we those genes had multiple alleles as well? Increase variation within the population

11. S-B-8-1_Non-Mendelian Heredity PowerPoint
THINK-PAIR-SHARE
Black fur (BBl) is completely dominant to brown fur in rabbits, but brown fur (BBr) is dominant to white (b). A hybrid brown doe (BBrb) is crossed with a hybrid black buck (BBlb). What are the expected phenotypes of the offspring? Ratios?
The cross will produce: 2 of 4, or 1 in 2, will be black, a 1 in 4 possibility for a brown or white.
Have a student volunteer make the Punnett square on the board.

12. S-B-8-1_Non-Mendelian Heredity PowerPoint
Linked Traits
When the loci of two genes are located close together on the same chromosome
Red hair, freckles, and fair skin are linked.
Explain that during the crossing over phase of meiosis the genes are too close together. Often they break apart as a group and get mixed up as a set. Which of Mendel’s Laws does this violate? The law of independent assortment. Sometimes they do break apart, but it does not occur with the same frequency as independently assorted alleles.

13. S-B-8-1_Non-Mendelian Heredity PowerPoint
Sex-Linked Traits
Genes located on a sex (X or Y) chromosome
♀XX & ♂XY
Some forms of hemophilia
Red-green colorblindness
Remind students that homologous chromosomes, 1-22, are autosomes. The 23rd pair are the sex chromosomes, X and Y. The X and Y are not homologous chromosomes. Each carry different sets of genes. Normally, XX are females and XY are males, however, sex is a phenotype, not a genotype. Many of the sex-linked traits are carried on the X chromosome. Since males only have one X chromosome, recessive genes will be expressed. Females can only express the recessive trait if both XX chromosomes have the recessive allele, which is rare since it requires the mother to be a carrier and the father to be affected.
(In humans, the Y chromosome codes for the development of testes and the X chromosomes has the gene for testosterone (male hormone) receptors. In order to be “male” both genes must be functioning. It is possible for a person to have the genotype XY but if either gene is nonfunctioning, the phenotype will be a female. Being female is the “default” condition in humans)

14. Red-Green Colorblindness
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Red-Green Colorblindness
If you are red-green colorblind, you have difficulty distinguishing between red and green hues.

15. S-B-8-1_Non-Mendelian Heredity PowerPoint
Hemophilia
Hemophilia is the failure (lack of a gene code) to produce certain substances needed to clot the blood. It is possible for a hemophiliac to bleed to death from a bruise.
This is a pedigree chart for hemophilia in Queen Victoria’s the descendants. It seems that Queen Victoria was a carrier for hemophilia, which she passed to her children and through their marriages, introduced the gene to many of the royal houses of Europe. See,
Pedigree charts are used to show the phenotypes for a particular gene as well as their ancestors. What do we call people that are heterozygous for hemophilia? Carriers Notice that only females are carriers. Why is this important? It means that the trait is sex-linked or found on the X-chromosome. How are males and female descendants distinguished on a pedigree chart? Males are represented with squares and females with circles. How are marriages distinguished from siblings? The line from male to female indicate a marriage, lines originating on top of the square or circle that “T” together are siblings. How many generations are shown here? There are 8 generations (from Edward & Victoria to William and Harry).

16. S-B-8-1_Non-Mendelian Heredity PowerPoint
Barr Bodies
The inactive X chromosome found in female (XX) somatic cells
Not found in normal males (XY) .
Explains calico coloring in cats.
Murray Barr discovered the dark spot on the edge of the nucleus of female somatic cells. Mary Lyon proposed that it is one of the X chromosome which is randomly turned off sometime during development. It is supported by the fact that Barr bodies are not found in XY males but can be seen in XXY males (Klinefelter's syndrome). Also, mice that inherit only one X chromosome, grow-up to be fertile females.
The nucleus of a cell. The arrow is pointing to the inactive X chromosome, the Barr Body.

17. S-B-8-1_Non-Mendelian Heredity PowerPoint
Calico Cats
Mosaic coloration occurs when, sometime during development, an inactive X chromosome (Barr Body) is switched while the other X chromosome is switched off.

18. Solving Sex-Linked Problems
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Solving Sex-Linked Problems
A woman who is a carrier for red-green colorblindness marries a man with normal sight. What percent of the male and female children will be red-green colorblind or carriers?
STEP 6:
STEP 1: ♀ XX' ♂ XY
50% ♀ Normal
50% ♀Carriers 50% ♂Normal 50% ♂ Colorblind
STEP 2: X, X' X, Y
Step 1: The woman is a carrier for red-green colorblindness, so she is heterozygous for this trait, XX' . Since the man can see normally, he has the normal X chromosome.
Step 2: Female X and X‘ genes, while the Male makes X and Y (The male is similar to a heterozygote since he can make two different kinds of gametes)
Step 3: Make the grid. How big will it need to be? 2 X 2
Step 4: Put the in the gamete alleles at the head of the column and row.
Step 5: Fill in the boxes. What are the possible genotypes of their offspring? XX, XX‘, XY, X‘Y
Step 6: What are the possible phenotypes? Half of their daughters are expected to be carriers and half of their sons are expected to be red-green colorblind.
STEP 3:
X Y
STEP 4: X X'
XX XY
STEP 5:
XX' X'Y

19. S-B-8-1_Non-Mendelian Heredity PowerPoint
THINK-PAIR-SHARE
Wild Type 1 2 3 4 5 6 7 8
Homozygous
Heterozygous
Is the trait sex-linked? How do you know?
How could we tell if female #5 is heterozygous if she never has children?
What are the expected phenotypic ratios from a cross between #3 & #7?
No, It is an autosomal gene because males can be carriers.
The alleles could be incompletely dominant or codominant and therefore has a different genotype.
Half the offspring is expected to have the wild type phenotype, the other half is expected to show heterozygous phenotype.