1. Beyond Mendel’s Laws of Inheritance

2. Rules of Probability
Addition Rule- probability that any one of two or more mutually exclusive events will occur is calculated by adding the individual probabilities.
Example- the chance of getting heads or tails on a coin toss
heads- ½ tails – ½ ½ +1/2 = 1

3. Rules of Probability
Multiplication- probability that two or more independent events will occur together Ex- What is the chance that two coins tossed together will both land heads up? probability of 1 head- ½ probability of 2 heads ½ x ½ = 1/4

4. Probability Problems Chance of rolling a three on a die? 1/6
Chance of getting any other number other than three? 5/6
Chance of rolling a 1 and then a 2 and then 4?
1/6 x 1/6 x 1/6 = 1/216
Parents are PP and pp- chance that offspring will be Pp? 1 x 1 = 1
Parents are PpYy x Ppyy chance that offspring will be ppYy? Pp= ½ x ½ Yy= ½ x 1 total=1/8

5. Incomplete dominance
Heterozygote shows an intermediate, blended phenotype
example:
RR = red flowers
rr = white flowers
Rr = pink flowers
make 50% less color
RR
WW
RW RR RW WW

6. Incomplete dominance P F1 100% 1:2:1 F2 X true-breeding red flowers
white flowers
100%
100% pink flowers F1
generation
(hybrids)
self-pollinate
25%
white F2
generation
red
1:2:1
50%
pink

7. Codominance
There are two or more alleles that are dominant in a phenotype.
Both alleles are expressed in heterozygous condition.
Ex: Red – RR, white – WW, red and white - RW

8. Multiple Alleles 2 alleles affect the phenotype equally & separately
not blended phenotype
human ABO blood groups
3 alleles
IA, IB, i
IA & IB alleles are co-dominant
glycoprotein antigens on RBC
IAIB = both antigens are produced
i allele recessive to both

9. Polygenic inheritance
Some phenotypes determined by additive effects of 2 or more genes on a single characteristic
phenotypes on a continuum
human traits
skin color
height
weight
intelligence
behaviors

10. Sex linked traits 1910 | 1933 Genes are on sex chromosomes
as opposed to autosomal chromosomes
first discovered by T.H. Morgan at Columbia U.
Drosophila breeding
good genetic subject
prolific
2 week generations
4 pairs of chromosomes
XX=female, XY=male

11. Hemophilia XHXh XHY Hh x HH XH XHXh XH Y Xh XHXH XHXH XHY XHY XH Xh XH
sex-linked recessive
Hemophilia
XHXh
XHY
Hh x HH XH
XHXh XH Y
male / sperm Xh
XHXH
XHXH
XHY
XHY XH Xh
female / eggs XH
XHY
XHXh
XHXh
XhY
XhY Y
carrier
disease

12. Pedigree Analysis
Used to predict inheritance based on past phenotypes

13. Autosomal Recessive Inheritance-
cystic fibrosis
Generation skipped

14. Autosomal Dominant Inheritance-Huntington Disease
Generations are not skipped

15. Human disorders The family pedigree
Recessive disorders: •Cystic fibrosis •Tay-Sachs •Sickle-cell
Dominant disorders:
-Huntington’s

16. Practice Question
Sickle cell anemia is caused by the mutation of a single base pair in the gene for hemoglobin. This mutation results in hemoglobin molecules that form long chains in low-oxygen settings and stretch the blood cells into their characteristic sickled shape. What would the result be if a different base pair in the sickle cell hemoglobin gene were to become mutated?
A. The effects of sickle cell would be increased
B. The effects of sickle cell would be reduced
C. The new mutation would increase resistance to malaria
D. It is impossible to predict what the effect would be without knowing more about the mutation

17. Practice Problem
In the cross AaBBcc x aaBbCc, what is the probability of an offspring that is aaBbcc?
A 1/2
B 1/4
C 1/8
D 1/16

18. Practice Problem
What type of inheritance pattern is illustrated above?

19. Genetics of Sex X Y X XX XY X XX XY
In humans & other mammals, there are 2 sex chromosomes: X & Y
2 X chromosomes
develop as a female: XX
gene redundancy, like autosomal chromosomes
an X & Y chromosome
develop as a male: XY
no redundancy X Y X XX XY X XX XY
50% female : 50% male

20. Discovery of sex linkage
true-breeding
red-eye female
true-breeding
white-eye male X P
Huh! Sex matters?!
100%
red eye offspring F1
generation
(hybrids)
100%
red-eye female
50% red-eye male
50% white eye male F2
generation

21. Genes on sex chromosomes
Y chromosome
few genes other than SRY
sex-determining region
master regulator for maleness
turns on genes for production of male hormones
X chromosome
traits other than sex determination
mutations: (all are recessive)
hemophilia
Duchenne muscular dystrophy
color-blindness
Duchenne muscular dystrophy affects one in 3,500 males born in the United States.
Affected individuals rarely live past their early 20s.
This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin.
The disease is characterized by a progressive weakening of the muscles and loss of coordination.

22. X-inactivation Female mammals inherit 2 X chromosomes XH XHXh Xh
one X becomes inactivated during embryonic development
condenses into compact object = Barr body
which X becomes Barr body is random
patchwork trait = “mosaic”
patches of black
XH
XHXh
Xh
tricolor cats can only be female
patches of orange

23. Sex Linked Traits Usually found on the X chromosome
Only if she is homozygous recessive, will she exhibit the trait
Expressed more with males since they have only one X

24. Sex Linked diseases in humans
Duchenne muscular dystrophy
Hemophilia
Colorblindness

25. Hemophilia in the Russian Family

26. Linked Genes
Are physically close to each other and get inherited together even with crossing over
The greater the distance between the genes, the greater the chance of separation during crossing over

27. Map Units
Morgan and Sturtevant developed the genetic map that shows a list of ordered loci on a chromosome
The distance between the genes is called a map unit
A recombinant frequency of 1% = 1 map unit

28. Example
If the black body gene (b) is 17% or 17 map units from the vestigal wing gene (vg) and the cinnabar eye gene (cn) is 9.75% or 9.75 map units from the b gene, what are the order of the genes on the chromosome?

29. Cytogenic Maps
Locates genes with respect to chromosomal features as stained bands

30. Alternative Systems

31. Nondisjunction

32. Remember this
Down Syndrome

33. Aneuploidy- too many or too few
Plants- are actually less serious
Animals (one too many or too few chromosomes), are very serious or fatal due to gene imbalances

34. XO Turner Syndrome- Monosomy

35. XXY- Klinefelter Syndrome

36. XYY- Jacob’s Syndrome Tall, thin, larger build More prone to acne
Increased testosterone levels

37. Genomic Imprinting
Some traits vary depending on which parent passes it on
The section of DNA has a methyl group (-CH3) added on
Certain cancers can be stimulated this way
Fragile X syndrome can come from father

38. Mitochondrial Defects
These defects originate in the mitochondrial DNA. Some examples are:
Some forms of Diabetes
Some forms of Deafness
Multiple sclerosis
Some forms of epilepsy

39. Environmental effects
Phenotype is controlled by both environment & genes
Human skin color is influenced by both genetics & environmental conditions
Coat color in arctic fox influenced by heat sensitive alleles
The relative importance of genes & the environment in influencing human characteristics is a very old & hotly contested debate
a single tree has leaves that vary in size, shape & color, depending on exposure to wind & sun
for humans, nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence tests
even identical twins — genetic equals — accumulate phenotypic differences as a result of their unique experiences
Color of Hydrangea flowers is influenced by soil pH

40. Human Genetic Diseases to Know
Huntington’s (AD)
Colorblindness (SR)
Hemophilia (SR)
Cystic Fibrosis (AR) Sickle cell anemia (AR) PKU (AR) Tay Sachs (AR)