1. Complex Patterns of Heredity
Chapter 12

2. Human Inheritance Humans have 23 pairs of chromosomes
These are made of about 100,000 genes
Scientists usually study disease causing genes because they can easily be traced
They often prepare a Pedigree – a family record that shows how a trait is inherited over several generations.

3. Pedigree
Carriers – usually, Heterozygous; they do not express the recessive allele, but they pass it along to their offspring.
Square = Male
Circle = Female
No shading = normal
Shaded = displays trait
Half/Half = Carrier

4. A Pedigree of Hemophilia in the Royal Families of Europe

5. Simple Dominant Heredity
Many traits are inherited just as the rule of dominance predicts.
Remember that in Mendelian inheritance, a single dominant allele inherited from one parent is all that is needed for a person to show the dominant trait.

6. Patterns of Inheritance
Phenotypes repeated in a predictable pattern from generation to generation
Genetic Disorders – diseases or debilitating conditions that have a genetic basis

7. Patterns of Inheritance
Traits controlled by a Single Allele
More than 200 human traits are determined by a single dominant allele
Ex. Huntington’s Disease
More than 250 other traits are determined by homozygous recessive alleles
Both parents must have this allele in order for their offspring to have the disease.
Ex. Cystic Fibrosis & Sickle cell anemia

8. Inheritance Patterns Recessive Allele Inheritance Patterns
Unaffected parents can have affected offspring
The phenotype can skip a generation
Individuals with no signs of the allele can be carriers
Dominant Allele Inheritance Patterns
Affected offspring must have at least one affected parent
The phenotype appears in every generation without skipping
Two unaffected parents have no affected offspring

9. Sometimes Heredity Follows Different Rules
Incomplete Dominance: Appearance of a third phenotype
Codominance: Expression of both alleles
Multiple phenotypes from multiple alleles
Sex determination
Sex-linked inheritance
Polygenic Inheritance

10. Incomplete Dominance
With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits. 
RED Flower x WHITE Flower ---> PINK Flower

11. R = allele for red flowers W = allele for white flowers red x white ---> pink RR x WW ---> 100% RW

12. Codominance
The genetic gist to codominance is pretty much the same as incomplete dominance.  A hybrid organism shows a third phenotype --- not the usual "dominant" one & not the "recessive" one ... but a third, different phenotype. 
In COdominance, the "recessive" & "dominant" traits appear together in the phenotype of hybrid organisms.

13. Codominance Example red x white ---> red & white spotted
With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.

14. R = allele for red flowers W = allele for white flowers red x white ---> red & white spotted RR x WW ---> 100% RW

15. Examples of Codominance
A very very very very very common phenotype used in questions about codominance is roan fur in cattle.  Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together).  A good example of codominance. Another example of codominance is human blood type AB, in which two types of protein ("A" & "B") appear together on the surface of blood cells.

16. Codominance and Blood Types
Blood transfusion can only take place between two people who have compatible types of blood.
Human blood is separated into different classifications because of the varying proteins on the surface of blood cells.
These proteins are there to identify whether or not the blood in the individual's body is it's own and not something the immunity system should destroy.

17. Patterns of Inheritance
Traits controlled by Multiple Alleles
Controlled by 3 or more alleles of the same gene that code for a single trait
Ex. Blood types
A & B are codominant – both are expressed when together; and both are dominant to O.
A person can only have type O blood if they receive the “O” allele from both parents.

18. Human Blood Types

19. ABO Blood type and genetics
The protein's structure is controlled by three alleles;
i, IA and IB.
i, the recessive of the three,
IA and IB are both codominant when paired together.
If the recessive allele i is paired with IB or IA, it's expression is hidden and is not shown.
When the IB and IA are together in a pair, both proteins A and B are present and expressed.
The individual's blood type is determined by which combination of alleles he/she has.
There are four possible blood types in order from most common to most rare: O, A, B and AB.
O blood type represents an individual who is homozygous recessive (ii) and does not have an allele for A or B.
Blood types A and B are codominant alleles.
Codominant alleles are expressed even if only one is present. The recessive allele i for blood type O is only expressed when two recessive alleles are present.
Blood type O is not apparent if the individual has an allele for A or B.
Individuals who have blood type A have a genotype of IAIA or IAi and those with blood type B, IBIB or IBi,
An individual who is IAIB has blood type AB.

20. Blood type Chart

21. Blood type practice Use a Punnett Square!
A woman has type A blood. Her father has type O blood. The woman marries a man with type O blood. What is the chance that they will have a child with type A blood?
What is the chance that the couple from question 1 will have a child with type AB blood?
*Show me your answers when you are finished. Keep these in your notes!

22. Multiple Phenotypes from Multiple Alleles
Although each trait that we have studied so far only has two alleles, it is common for more that two alleles to control a trait in a population
For instance, Pigeons – three colors possible (red, blue, chocolate)
However, each pigeon can have only two of these alleles
Complete P.S. Lab 12.2 to observe multiple alleles in how coat color in rabbits is inherited.

23. Sex determination
Remember that in humans the diploid number of chromosomes is 46, or 23 pairs.
There are 22 matching pairs of homologous chromosomes called autosomes.
The 23rd pair differs in males and females, they determine the sex of an individual (sex chromosomes)
X females (XX)
Y males (XY)
Complete a punnett square to determine the expected ratio of males to females produced given their possible gamete contribution

24. Sex-linked inheritance
Traits controlled by genes located on sex chromosomes are called sex-linked traits
Read about Thomas Hunt Morgan’s research with fruit flies on pg Complete a punnett square to show how the allele for red eye color is a sex-linked trait.

25. Patterns of Inheritance
Polygenic Traits
Most human characteristics are controlled by several genes (2 or more)
Ex. Skin color – 3 to 6 genes
Ex. Eye color
Some are also affected by the environment
Ex. Height – nutrition and disease

26. Eye Color Activity

27. Patterns of Inheritance
Sex-Linked Traits
Are found only on the X chromosome
Ex. Colorblindness (recessive)
Ex. Hemophilia (recessive)

28. Patterns of Inheritance
Sex-Influenced Traits
Influenced by male or female sex hormones
Ex. Patterned Baldness
Homozygous baldness-both will lose hair
Heterozygous-men will lose hair but women will not

29. Nondisjunction
Nondisjunction is the failure of homologous chromosome pairs to separate properly during meiosis. The result of this error is a cell with an abnormal (too few or too many) number of chromosomes.

30. Nondisjunction

31. Patterns of Inheritance
Disorders due to Nondisjunction
Monosomy (45 Chromosomes)
Trisomy (47 Chromosomes)
Trisomy-21 (Down’s Syndrome)
Klinefelter’s (XXY)-male w/ some female traits
Turner’s (XO)-female appearance
Single Y chromosome do not survive

32. Environmental Effects
Genes are inherited from parents, but sometimes their expression is modified by environmental factors.
An example is the snowshoe hare we discussed earlier in the year-these hares have dark fur in the summer and white fur in the winter.

33. Snowshoe Hare

34. Detecting Human Genetic Disorders
Genetic Screening – examination of genetic makeup
Karyotype: a picture of chromosomes grouped in pairs and arranged in sequence.
Screening of Blood: look for certain proteins
Genetic Counseling-medical guidance informing of problems that could affect their offspring.

35. Human Karyotype

36. Detecting Human Genetic Disorders
Amniocentesis: removal of small amount of amnionic fluid surrounding the fetus
Chorionic Villi Sampling: tissue that grows between the mother’s uterus and the placenta (between the 8th and 10th week)
Screening Immediately after Birth:
Ex PKU (Phenylketonuria)-body cannot metabolize the amino acid phenylalanine
Special diet lacking phenylalanine

37. Karyotyping