1. Chapter 9.1~ Mendel & The Gene Idea

2. Mendelian genetics Character: heritable feature, i.e., fur color
Trait : variant for a character, i.e., brown
True-bred: all offspring of same variety
Hybridization: crossing of 2 different true-breds
P generation: parents
F1 generation: first generation

3. Leading to the Law of Segregation
Alternative versions of genes (alleles) account for variations in inherited characteristics
Org inherits 2 alleles per character
dominant allele - fully expressed in orgs appearance. recessive allele - no noticeable effect on appearance
The alleles for each character segregate (separate) during gamete production (meiosis).
Mendel’s Law of Segregation

4. Genetic vocabulary…….
Punnett square: predicts the results of a genetic cross between individuals of known genotype
Homozygous: pair of identical alleles for a character
Heterozygous: two different alleles for a gene
Phenotype: an organism’s traits
Genotype: an organism’s genetic makeup
Testcross: breeding of a recessive homozygote X dominate phenotype (but unknown genotype)

5. Practice monohybrid crosses
TRAIT KEY
Hairline: W= widow’s peak w= straight hairline
Tongue: R = can roll r = can’t roll
Earlobes F = free hanging f = attached
Eye shape L = almond shaped = round shaped
Blood type A = type A blood B = type B blood
Hair C = curly c = straight
Freckles K = freckles k = no freckles
Middle toe D = short d = long
Fingers S = six s = five
Lip size T = thick lips t = thin lips
Knuckle H = hair on middle knuckle h = no hair on middle knuckle
Thumb B = hitchhikers b = straight thumb
Practice monohybrid crosses
Reporting results… %, fraction, ratios…
Phenotypic results:
Genotypic results:

6. The Law of Independent Assortment
Law of Segregation involves 1 character. What about 2 (or more) characters?
Monohybrid cross vs. dihybrid cross
The two pairs of alleles segregate independently of each other.
Mendel’s Law of Independent Assortment

7. Cross a with Results: YR Yr yR yr yR yr YyRR YyRr yyRR yyRr yyrr Yyrr
6/16
2/16

8. Practice Slide
Results:

9. Using the rule of multiplication to find particular genotypes or phenotypes
What is the probability of getting a yyRR if a is crossed with a ?
Complete a monohybrid cross for each character & then multiply the two fractions.
… so chance of getting a yy if cross a Yy & yy?
… chance of getting a RR if cross a Rr & Rr?

10. Using the rule of multiplication to find particular genotypes or phenotypes
What is the probability of getting a green round if a is crossed with a ?
Complete a monohybrid cross for each character & then multiply the two fractions.
… so chance of getting a green if cross a Yy & yy?
… chance of getting a round if cross a Rr & Rr?

11. Extending Mendelian Genetics, I
Incomplete dominance: appearance between the phenotypes of the 2 parents.
Results in 3 possible phenotypes – one being intermediate.
Ex: snapdragons

12. Molecular explanation for incomplete dominance
One allele carries the code for a functional protein and the other doesn’t. Since there’s only one copy of the functional allele, not enough proteins are synthesized which results in the intermediate phenotype in the heterozygote.
How is this different from complete dominance?

13. Extending Mendelian Genetics, II
Codominance: two alleles affect the phenotype in separate, distinguishable ways.
Ex: human blood types
Multiple alleles: more than 2 possible alleles for a gene.

14. Extending Mendelian Genetics, III
Pleiotropy: genes with multiple phenotypic effect. Ex: sickle-cell anemia

15. Extending Mendelian Genetics, IV
Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. Ex: mice coat color
B = black
b = brown
C = pigment production
c = no pigment production

16. Epistasis Problem
 In a certain breed of plants, D produces dark red color and is dominant over d which produces a light red color.  Another gene determines in which cells the pigment will be synthesized.  Allele w allows synthesis of the pigment throughout the petals but the mutant allele W prevents pigment production. 
D = dark red
d = light red
w = pigment production
W = no pigment production
You cross two plants that are DdWw.
What will be the genotype and phenotype ratios of the crosses?
Possible phenotypes:
Dark red = 3/16
Light red = 1/16
White = 12/16 (3/4) DW Dw dW dw
DDWW
DDWw
DdWW
DdWw
DDww
Ddww
ddWW
ddWw
ddww

17. Possible genotypes: DDWW = 1/16 DDWw = 2/16 (1/8) DdWW = 2/16 (1/8)
Same problem continued… DW Dw dW dw
DDWW
DDWw
DdWW
DdWw
DDww
Ddww
ddWW
ddWw
ddww

18. Extending Mendelian Genetics, V
Polygenic Inheritance: an additive effect of two or more genes on a single phenotypic character Ex: human skin pigmentation and height

19. Human disorders
The family pedigree – trace a character through generations
Square = male, circle = female, shaded = has trait

20. What is it about the recessive allele that causes the disease phenotype?
codes for malfunctional protein or none at all
Hetero normal b/c dom allele produces enough of the needed protein

21. Recessive Human Genetic Disorders
Tay-Sachs
fatal genetic lipid storage disorder in which harmful quantities of a fatty substance called ganglioside GM2 build up in tissues and nerve cells in the brain.
Cystic fibrosis
Build up of mucus in the lungs and digestive tract due to the lack of a transport protein in the cell membranes.

22. Sickle-cell Substitution of single amino acid in hemoglobin of RBC
1/400 African Americans
1/10 are hetero for it
Treatment = blood transfusions
Hetero have disease b/c alleles are codom on molecular level.
High hetero b/c they are res to malaria!

23. Cystic fibrosis
Build up of mucus in the lungs and digestive tract due to the lack of a transport protein in the cell membranes.
Most lethal in US
1/2500 whites of Euro decent have it
1/25 are carriers
Antibiotic & pounding

24. Dominant Human Genetic Disorders
•Huntington’s
results from genetically programmed degeneration of brain cells, called neurons, in certain areas of the brain. This degeneration causes uncontrolled movements, loss of intellectual faculties, and emotional disturbance.

25. •amniocentesis
•chorionic villus sampling (aka: CVS)
Testing

26. Quiz tomorrow on ch 14
Get out snowflake problems, ch 12 review sheet w/ aliens on it, pedigree practice sheet… we’re going over them.
Photosnythesis labs due Fri.

27. Ch 9 The Chromosomal Basis of Inheritance
Chromosomal theory in inheritance – mendelian genes have specific loci on chromosomes & it is the chromosomes that undergo segregation & independent assortment
Morgan traced genes to specific chrom
fruit flies
Prolific breeders
New gen every 2 wks
Only 4 pair chrom.
Normal (wild type) = lower case of mutant w/ +
Mutant = lower case

28. Use different symbols with these problems…
Lower case of mutant
+ = dominant
So… b+ = gray
b = black
vg+ = normal wings
vg = vestigial wings

29. b+ b vg+ vg x bbvgvg
b+ vg+
b+ vg
b vg+
b vg

31. Recombination Frequency

32. Using recombination frequencies to construct a genetic map – ordered list of the genetic loci along a chromosome
Farther apart 2 genes are – higher probability x-over will occur.

33. AP Bio 12/16 Do It Now…
What fraction of offspring would you expect to be bald if you crossed a bald man with a woman who is heterozygous for the bald allele.

34. Sex Linked Traits – traits that are determined by genes on the X chromosome
Unique patterns of inheritance
Why? Males need only 1 rec allele to have a sex linked disorder
Colorblindness, hemophilia (blood won’t clot), baldness, duchenne muscular dystrophy
All recessive disorders

35. More men than women have sex linked traits.
Explanation:
XH XH = Homozygous Dominant Woman
XH Xh = Heterozygous Woman
Xh Xh = Homozygous Recessive woman so hemophilia
XH Y = Dominant male so no hemophilia
Xh Y = Recessive male so hemophilia

36. So… males only need one recessive allele to have a sex linked trait since they only have one X
Women have 2 X chromosomes so they have to inherit 2 recessive alleles to have a sex linked trait.

37. Males inherit sex linked traits from their mothers.
Why? B/c males inherit their X chromosomes from their moms – their dads give them their Y chromosomes.
So… men inherit baldness from their moms!

38. Sex linked trait problems:
Cross a woman heterozygous for baldness with a man who is not bald.
Hint: show chromosomes too
XB Xb XB Y
XBXB
XBXb
XBY
XbY
¼ chance that child will be bald. ½ chance that they have a boy that’s bald.

39. Everyone should be able to see a 12

40. Nomal =5 color blind = 2

41. X inactivation in female mammals
1 of the 2 X chromosomes in each cell becomes almost completely inactivated during embryonic development.
Barr body – condensed form of inactive X located along inside of nuc mem
Random from cell to cell… mosaic of active X s
Ex: calico cats, human females lacking sweat glands

47. 15.5 from ch 15 study guide 2 normal color-sighted individuals produce the following children & grandkids.

48. #1 from ch 15 study guide p 108

49. Scientists use recombination frequencies to determine the order of genes on a chromosome. Try to figure out the order of these 5 genes given the following recombination frequencies.
D B C A E