1. Mendelian Genetics
Chapter 11

2. Genetics What is Genetics? The scientific study of heredity
What is Heredity? – the passing of traits from parents to offspring

3. Inheritance You get your genes from your parents
In meiosis, half of the chromosomes in a pair come from the Dad, half come from the Mom
Chromosome: Thread-like structure within the nucleus that contains the genetic information passed from one generation of cells to the next
What we know today is based on the work of Gregor Mendel – Austrian monk

4. “The Father of Modern Genetics”
Gregor Mendel
– Austrian monk who laid groundwork for understanding biological inheritance
– studied 7 inherited traits in pea plants (true-breeding) of his monastery garden
– COUNTED the plants and compiled data (QUANTITATIVE APPROACH to science)
Paper was published in 1866,
but not enough was understood
to truly value this work.

5. Key terms to know
Allele – each form of a gene for a certain trait (R or r)
Gene – sequence of DNA that codes for a protein and thus determines a trait
Genotype – combination of alleles for a given trait
(RR or Rr or rr)
Phenotype – Appearance of trait
(round seeds or wrinkled seeds)
Homozygous - when you have 2 of the same alleles for a given trait (RR or rr)
Heterozygous – when you have 2 different alleles for a trait (Rr)

6. Key terms to know
Dominant – Allele that is expressed, Represented by a Capitol letter.
Recessive – Allele that is masked or hidden, Represented by a lowercase letter.
F1 generation: Filial or First Generation
Test cross (Punnett square): determine the genotype of an individual with a dominant phenotype

7. Characters and Traits
Character – heritable feature that varies among individuals (ex. Flower color)
Trait – each variant for a character
(ex. Purple vs. white flowers)
Originally believed that traits blended together to give offspring results

8. Figure A genetic cross

9. Mendel chose to use plants that were true-breeding…
P generation – parentals; true-breeding (On their own create identical offsprings) parents that were cross-pollinated
F1 generation – hybrid offspring of parentals that were allowed to self-pollinate
F2 generation – offspring of F1’s

10. Figure 14.2 Mendel tracked heritable characters for three generations

11. Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants
Section 11-1
Seed Shape
Seed Color
Seed Coat
Color
Pod
Shape
Pod Color
Flower Position
Plant Height
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
Green
White
Constricted
Yellow
Terminal
Short
Round
Yellow
Gray
Smooth
Green
Axial
Tall
*Flower color – purple (P) vs. white (p)
Seed coat color and flower color are often put in for one another – thus, the EIGHT traits!!!
Go to Section:

12. Mendel’s 4 ideas…
Alternative versions (alleles) of genes account for variations in inherited characters.
For each character, an organism inherits two alleles, one from each parent.
If the two alleles differ, the dominant allele is expressed in the organisms appearance, and the other, a recessive allele is masked.
The two alleles for each character segregate during gamete production.
(Law of Segregation)

13. Figure 14.3 Alleles, alternative versions of a gene

14. Figure 14.4 Mendel’s law of segregation (Layer 2)

15. From the law of segregation……
Came the Law of Independent Assortment
Genes for different traits can segregate independently during the formation of gametes.
In other words…..
Just because a seed is round does not mean that it has to be green.

16. Figure 14.5 Genotype versus phenotype

17. Probability & Genetics

18. Punnett Square
Device for predicting the results of a genetic cross between individuals of a known phenotype.
Developed by R.C. Punnett
Rules:
1. must predict possible gametes first
2. male gametes are written across top, female
gametes on left side
3. when read Punnett, start in upper left corner
and read as if a book
4. WRITE OUT GENOTYPES IN ORDER

20. Example…… Character – flower color Alleles – Purple (P) and white (p)
Note: Purple is dominant with a capital letter and white is recessive shown with a lowercase of dominant trait
Genotypic combos possible –
two dominants: PP (homozygous dominant)
two recessives: pp (homozygous recessive)
One of each: Pp (heterozygous)

21. Phenotypic possibilities – physical appearance
PP – purple
pp – white
Pp – purple (white is masked, but still part of genotype)

22. Monohybrid crosses – only one character considered
Steps to do:
Write out genotypes of parents
Write out possible gametes produced
Draw 4 box Punnett square
Put male gametes on top, female on left side
Fill in boxes
Determine genotypes by reading Punnett starting from top left
Determine phenotypes by reading from genotype list
Ex.
White flowered plant X Purple flowered plant
Yellow peas X Green peas
Tall plant X short plant

23. Dihybrid (Two-Factor)Cross
Because genes separate independently we can determine the possible outcomes of a two-factor cross.
Example: Mendel’s Peas
F1 Hybrids for Shape and Color: RrYy
Foil – First, Last, Inner, Outer
Possible gametes passed on to offspring:
RY, ry, rY, and Ry – Place in order (dominant to recessive) RY, Ry, rY, ry then place on cross

25. Beyond Dominant and Recessive
Incomplete Dominance
One allele is not completely dominant over the other – something in the middle is expressed
Ex. Red and White Snapdragons
Result can be heterozygous (Rr) or two separate dominant alleles (RW) each resulting in a mixture of both alleles
Incomplete dominance & co-dominance. Go over on the day you assign worksheet (01/08/08?)

26. Another way that incomplete dominance can be expressed
Red= RR
White= WW
RW= pink- each allele is equally expressed to result in a blended product

27. One way to express incomplete dominance
RR (Red) X rr (White)= (Rr)Pink
Rr- results in a blended result of PINK

28. Beyond Dominant and Recessive
Codominance
Both alleles are expressed in the phenotype
Ex. Cow Hair Color
RR – Red
WW – White
RW – Roan (Red & White)
Practice
Codominance/Incomplete Dominance #1-4

29. Beyond Dominant and Recessive
Multiple Alleles
Genes have more then two alleles
Ex. Blood Type
Type A blood- AA or AO alleles
A is dominant to O
Type B blood- BB or BO alleles
B is dominant to O
Type AB- codominant- A and B alleles
A nor B is dominant so both are expressed on organisms RBC
Type O- recessive- OO alleles
Both alleles must be recessive in order to have type O.

30. More on blood types…..
The blood type determines what antibodies are located within the blood. Type A blood has type B antibodies. If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, the antibodies clump the blood - can cause death.
Type AB blood has no antibodies, any blood can be donated to them - they are called the "universal acceptors"
Type O blood has no surface markers on it, antibodies in the blood do not react to type O blood, they are called the "universal donors"

32. Polygenic Traits
Traits that are controlled by the interaction of several genes.
Example:
Reddish brown eyes in varying degrees found in fruit flies is controlled by 3 genes
Human skin color is controlled by 4 different genes which result in a variety of skin color.

33. Sex-linked Genetics
Ex. Colorblindness

34. Sex Chromosomes- last pair (23rd) in a karyotype
MALE KARYOTYPE
FEMALE KARYOTYPE

35. Sex Chromosomes- last pair (23rd) in a karyotype
Male – XY and Females – XX
The 23rd pair of chromosomes will determine the gender of an individual
Very few genes are located on the Y chromosome……Most are located on the X
Sex linked alleles will ALWAYS be tracked on the X chromosome ONLY when we conduct practice genetic problems

36. Sex-Linked Genes Ex. Colorblindness is carried on the sex-chromosomes
It is a recessive trait – Xc
How many genes do females need to express the trait (colorblindness)?
2 Xc Xc
How many genes do males need to express the trait (colorblindness)?
1 XcY

37. Sex-Linked Punnett Square
Let C = Normal Vision and c = Colorblind
Cross: Normal Male ( ) x Carrier Female ( )

38. Sex-Linked Punnett SquareC
Let C = Normal Vision and c = Colorblind
X Y x X X = Normal Male x Carrier Female
X Y X C C c
1st put male genotype on the top of the table & female genotype on the left side C C c

39. Sex-Linked Punnett SquareC
C – Normal Vision and c - Colorblind
X Y x X X - Normal Male x Carrier Female
X Y X C C c C
2nd, cross them
X X X Y C C C C C c c c

40. Sex-Linked Punnett SquareC
C – Normal Vision and c - Colorblind
X Y x X X -Normal Male x Carrier Female
X Y X
3rd, list the sex and appearance
of each possible offspring C C c C
Offsprings:
1 Normal Female
1 Normal (Carrier) Female
1 Normal Male
1 Colorblind Male
X X X Y C C C C C c c c

41. PRACTICE and HW
Complete problems 1-3 on the sex linked genetic practice problems sheet NOW!
Complete the remaining 3 Co-dominant and Incomplete dominant practice problems and Sex Linked practice problems # 4-8 from today’s class for HW