1. Other Laws of Inheritance
Mendelian Genetics: characteristics controlled by dominant and recessive paired alleles
Many traits follow the patterns outlined by Mendel’s Laws, many do not.

2. Incomplete Dominance
Offspring heterozygous for a trait have an intermediate appearance.
Neither allele is completely dominant over the other
Ex: Snapdragon flowers
Homozygous Red x Homozygous White
Results in all PINK flowers

3. Showing a Cross for Incomplete Dominance
Use a capital letter for each allele since each influence trait equally
RR (homozygous red) x WW (homozygous white)
What is phenotype ratio of offspring?
RW x RW (heterozygous pink)
How is this ratio different from the offspring
of Mendel’s Monohybrid cross? (Tt xTt)

4. Codominance
If individual is heterozygous, both alleles for gene are expressed.
Ex: Chickens
Black feathers (BB) x White Feathers (WW)
Offspring (BW) are checkered and have both black and white feathers

5. Try a codominant cross:
Checkered (BW) x checkered (BW)
Checkered (BW) x white (WW)
Checkered (BW) x black (BB)

6. Ex: Roan Cattle Offspring of pure red and pure white cows
Have both red and white hair

7. Multiple Alleles A gene that has more than two alleles.
Each individual can only have two alleles
Ex: Human Blood Types

8. Possible Blood Types:
A, B, AB, O
There are 3 alleles for blood type (A, B, O)
A and B are codominant alleles (IA, IB)
O is a recessive allele (i)

9. Six genotypes are possible for blood:
IA IA
IA IB
IB IB
IA i
IB i
i i
What blood types would they have?

10. Ex: Type A (homozygous) x Type B
What are the blood types of the offspring?

11. IB IB x IA IA IA i x i i IA IB x i i Try a Cross:
What blood types do the offspring have?
IB IB x IA IA
IA i x i i
IA IB x i i
If a Type A mother and a Type B Father produce a type O child, what are the parent’s genotypes?

12. Environmental Influences on Gene Expression
Ex: temperature, nutrition, light etc.
Ex: Coat color in Himalayan rabbits
Black fur present only on areas of body that are colder. (ear, nose, feet and tail)

13. Ice Pack placed on fur = fur turns black
If rabbit kept in warm environment, all fur is white.

14. Genetic Research and Testing
To study genes for different traits it is best to use an organism that grows and reproduces quickly an produces many offspring.
Can do controlled breeding experiments
Can do forced “inbreeding”
Ex: Drosophila melanogaster (fruit fly)

15. Genetic Tests Test Cross:
To determine if an individual is homo or heterozygous for a trait.
Breed to a homozygous recessive.
Ex:
Drosophila: red eyes dominant over white.
To see if red eyed fly is hetero/homo, breed to white eyed fly

16. Sex Determination Humans have 23 pairs of chromosomes
22 pairs are autosomes
1 pair are sex chromosomes
These pictures are called karyotypes!
I’m a BOY!
I’m a GIRL!

17. Sex Determination XX = female, XY = male
Males can give Y chromosome or X chromosome
Females can only contribute X
There is always a 50% chance of being boy or girl

18. Sex Linked Traits
If allele is found on an X or a Y chromosome it is inherited differently in males and females.
Ex:
Calico Cats
Color Blindness
Hemophilia
Duchenne Muscular Dystrophy

19. Calico Cats: (Codominant X Linked Trait)
X chromosome has gene for black or orange fur (codominant)
Only females can be “Calico” XBlackXOrange
Males can only be Black or Orange
they have only one X chromosome and one Y
I’m always a girl!

20. Colorblindness: (Recessive X linked trait)
Certain colors cannot be distinguished from others (usually red or green)
Most often seen males
Females are more likely to be “carriers”
Father cannot pass gene to son, only mother

22. Hemophilia: (Recessive X-linked trait)
Blood has trouble clotting
XHXh Carrier female
XHY Normal Male
XhY Affected Male
XhXh Affected Female
XHXH Normal Female

23. Examples of Crosses for Hemophilia

24. Queen Victoria of England passed this gene onto some of the royal family offspring
She must have been a “carrier”
Queen Victoria

25. Chromosomal Disorders
Due to the presence of absence of an entire chromosome or part of a chromosome.
Can be determined by doing a Karyotype from blood or amniotic fluid

26. Amniocentesis: Prenatal test
Grow cells from amniotic fluid around fetus.
Helps to rule out major chromosomal abnormalities

27. Nondisjuction Nondisjunction:
homologous chromosomes fail to separate properly during meiosis.
Results in egg or sperm with one or more extra chromosomes.

28. Nondisjunction
Normal Meiosis

30. What is Wrong?

31. Nondisjunction of Sex Chromosomes Klinefelter’s Syndrome (XXY)
2 X’s from mother, Y from father
Often tall, long arms and legs
May have some gynomastia and small testicles

32. Turner’s Syndrome (XO)
Offspring has only one X (always female)
Usually sterile, short, thick neck

33. Nondisjunction of Autosomes Trisomy 21 (Down’s Syndrome) (47, +21)
Most commonly seen chromosomal disorder resulting in live birth
Extra Chromosome 21

34. Other trisomys can happen as well
Babies may make it to term but usually don’t live very long (nonviable)
Ex: Trisomy 18, Trisomy 13

35. Gene Linkage
When alleles for different traits are located on the same chromosome
They tend get inherited together.
They are “linked”
They do no “assort independently”

36. Ex: Red hair and freckles

37. Crossing Over and Linked Genes
Crossing Over: homologous chromosomes
line up during synapsis and exchange
material.
Increases variation in offspring.

38. Sometimes linked
genes will separate
when crossing over
occurs.
The closer genes are
on the chromosome,
the less chance they
will be separated during
crossing over

39. Autosomal Genetic Disorders
Caused by defective alleles on autosomes
Can be recessive or dominant

40. Sickle Cell Anemia: (Autosomal recessive)
Red blood cells have a sickle shape
Very fragile and break easily
Clump up on blood vessels (causing pain)

41. Reduces oxygen carrying capacity of red blood cells
Caused by a single flaw in gene
One nitrogenous base in DNA sequence is different
Cause wrong amino acid in protein chain for hemoglobin, changing it’s shape
Hemoglobin doesn’t transport oxygen as well

42. Mostly found in people of African American descent
(1 in 500 births heterozygous)
If disorder has negative effects why so common in population?
Malaria is a deadly disease common in Africa
Heterozygous individuals for sickle cell have malarial resistance, more likely to survive than people who aren’t carriers.
I spread malaria!

43. Phenylketonuria (PKU):(Autosomal recessive)
Enzyme that breaks down amino acid phenylalanine doesn’t function
Chemical builds up in system and eventually forms substances that can damage the brain and cause mental retardation
Can test for it at birth and treat with a low phenylalanine diet

45. Tay-Sachs Disease: (Autosomal Recessive)
Incurable inherited disorder that damages the brain
Enzyme doesn’t function that helps breakdown lipid in brain.
Brain tissue deteriorates
Most often found in eastern European Jews
Death occurs several years after birth

46. Gene-Chromosome Theory
Explains the hereditary patterns that Mendel and others observed.
The genetic characteristics of an organism are determined by the genes for different traits present on their chromosomes.

47. Mutations
Sometimes a genetic disorder is caused by a mutation of a gene.
The mutation can only be passed to the next generation if it happens in a sex cell.
Mutagenic Agents:
Exposure to x-rays
Radiation
Certain chemical toxins