1. Genetics
Chapter 8

2. Origins of Genetics Heredity Character Trait
The passing of characters from parents to offspring
Character
Inherited characteristic (ex. flower color)
Trait
Single form of a characteristic (ex. purple flower)

3. Genes Control the expression of traits (i.e. flower color)
Have two parts - alleles
One allele is from Mom other from Dad.

4. Alleles Dominant - the expressed allele of the gene
Capital letter Ex. P
Recessive - the allele that was not expressed
Lower case letter Ex. p
Homozygous (Homo = same)
Two alleles are the same
Ex. PP or pp
Heterozygous (Hetero = different)
The alleles are different
Ex. Pp

5. Modern Terms Genotype Phenotype The set of alleles for a Gene
Ex. PP, Pp or pp
Phenotype
Physical appearance
Ex. Purple or White Flowers
The dominant allele determines phenotype
Ex. Pp  Purple Flower or PP  Purple Flower
If both alleles are recessive then the individual will express the recessive phenotype.
Ex. pp  White Flower

6. Homozygous- genes are the same HH hh
Heterozygous- genes are different Hh

7. Probability The likelihood that a specific event will occur
Expressed in multiples ways:
Fractions ½
Percentages 50%
Decimals .5
Ratios 3:1 or 3 to 1
Probability = # of one kind of possible outcome
Total # of all possible outcomes

8. Y Y y y Monohybrid Crosses Cross 1 character – Seed Color
Yellow Seeds are dominant – Y
Green Seeds are recessive – y
Cross a Homozygous Dominant Yellow with a Green.
Cross:
TT X tt
Genotype Ratio:
4Yy
Phenotype Ratio:
4 Yellow
Probabilities:
Being Yellow:
4 out of 4
Being Green:
0 out of 4 Y Y y Y y Y y y Y y Y y

9. P p p p Monohybrid Crosses Cross 1 character – Flower Color
Purple Flowers are dominant – P
White Flowers are recessive – p
Cross a Heterozygous with a homozygous recessive
Cross:
Pp X pp
Genotype Ratio:
2 Pp; 2 pp
Phenotype Ratio:
2 Purple
2 White
Probabilities:
Being Purple:
2 out of 4
Being White: P p p P p p p p P p p p

10. Incomplete Dominance
Inheritance that is intermediate between two parents
Ex. Snapdragon with red flowers are crossed with a snapdragon with white flowers  a snap dragon with pink flowers is produced.
Neither the allele for red flowers nor the allele for white flowers is dominant.

11. R R W W Incomplete Dominance Cross: RR X WW R W R W R W R W
Genotype for red flowers: RR
Genotype for white flowers: WW,
Genotype for pink flowers: RW.
Cross a red with a white.
Genotype Ratio:
4 RW
Phenotype Ratio:
4 Pink Flowers
Probabilities:
Red Flower:
0 out of 4
White Flower
Pink Flower:
4 out of 4
Cross: RR X WW R R W R W R W W R W R W

12. R W W W Incomplete Dominance Cross: RW X WW R W W W R W W W
Genotype for red flowers: RR
Genotype for white flowers: WW,
Genotype for pink flowers: RW.
Cross a pink with a white.
Genotype Ratio:
2 RW; 2WW
Phenotype Ratio:
2 Pink; 2 White
Probabilities:
Red Flower:
0 out of 4
White Flower
2 out of 4
Pink Flower:
Cross: RW X WW R W W R W W W W R W W W

13. Codominance Case in which both forms of the character are displayed.
Both traits are displayed
Ex. The ABO blood groups
Neither IA nor IB are dominant is dominant over the other.
Both are dominant over i.
When both IA and IB are present they are codominant and the individual is type AB

14. Blood Types Blood Typing IA IB i IA IB i O B AB A ii IBi IAi IBIB IAIB
IAIA IA IB i

15. Blood Typing IAIA X ii IA IA i i IAi
Cross a homozygous type A with a type O
Homozygous type A: IAIA
Type O: ii
Genotype Ratio:
4 IAi
Phenotype Ratio:
4 Type A
Probabilities:
Type A: 4 out of 4
Type O: 0 out of 4
IAIA X ii IA IA
IAi i i

16. Blood Typing IAIB X ii IA IB i i IBi IAi Cross a type AB with a type O
Homozygous type A: IAIB
Type O: ii
Genotype Ratio:
2 IAi; 2 IBi
Phenotype Ratio:
2 Type A
2 Type B
Probabilities:
Type A: 2 out of 4
Type B: 2 out of 4
IAIB X ii IA IB
IBi
IAi i i

17. Sex-Linked Traits Body cell has 46 chromosomes -
44 autosomes, 2 sex chromosomes.
Gamete (egg/sperm) has 23 chromosomes –
22 autosomes, 1 sex chromosome
Sex-Linked Gene
A gene located only on the X or Y
Most are carried on the X chromosome
Males have only one X chromosome
Male who carries a recessive allele on the X chromosome will exhibit the sex-linked condition

18. Hemophilia (Heme: blood, philia: liking of)
Condition that impairs the blood’s ability to clot
A sex-linked trait
Carriers and victims contain the recessive allele on their X-chromosomes
Only females can be carriers  XHXh
Because males only have one X chromosome
Males CAN NOT be carriers only victims.

19. Sex Linked Traits Xh XH XH Y XHY XhY XHXH XHXh The normal gene: XH
The hemophilia gene: Xh
Cross a normal male with a carrier female
Genotype Ratio:
1 XHXh: 1 XHXH: 1 XhY: 1XHY
Phenotype Ratio:
1 norm. female:
1 carrier female:
1 norm. male:
1 hemophilic male
Probabilities
Normal Female:
1 out of 2
Carrier Female:
Normal Male:
Hemophilic male:
XHY X XHXh
Xh XH
XHY
XhY
XHXH
XHXh XH Y

20. Sex Linked Traits XH Xh Xh Y XhY XHY XhXh XHXh The normal gene: XH
The hemophilia gene: Xh
Cross a hemophilic male with a carrier female
Genotype Ratio:
1 XHXh: 1 XhXh: 1 XHY: 1XhY
Phenotype Ratio:
1 carrier female:
1 hemophilic female:
1 norm. male:
1 hemophilic male
Probabilities
Hemophilic Female:
1 out of 2
Carrier Female:
Normal Male:
Hemophilic male:
XhY X XHXh
XH Xh
XhY
XHY
XhXh
XHXh Xh Y

21. Genetic Disorders Sickle Cell Anemia
Recessive disorder among African Americans
Caused by a mutated allele that produces a defective hemoglobin protein.
Hemoglobin in RBC’s bind and transport oxygen through the body

22. Genetic Disorders Cystic Fibrosis
Fatal hereditary recessive disorder among Caucasians.
Clogging of the airways and lungs with thick mucus and the blockage of ducts of the liver and pancreas.
There is no known cure.

23. Genetic Disorders Albinism Recessive
Body is unable to produce an enzyme necessary to make melanin.
Melanin is a pigment that gives color to hair, skin and eyes

24. Pedigrees
A family history that shows how a trait is inherited over several generations
Helps to track down the carriers (heterozygotes) of recessive disorders.
Reading Pedigrees
A shaded box – affected male …………
A shaded circle - affected female……….
A clear box - normal male…………..
A clear circle - normal female………...

25. Pedigree Practice ? ? I II III IV
A man and woman marry. They have five children, 2 girls and 3 boys. The mother is a carrier of hemophilia, an X-linked disorder. She passes the gene on to two of the boys who died in childhood and one of the daughters is also a carrier. Both daughters marry men without hemophilia and have 3 children (2 boys and a girl). The carrier daughter has one son with hemophilia. One of the non-carrier daughter’s sons marries a woman who is a carrier and they have twin daughters. What is the percent chance that each daughter will also be a carrier? I II
III IV
Legend:
Hemophilic Male: ………
Hemophilic Female: …...
Normal Female: ………
Normal Male: ……… ? ?

26. Pedigree Practice
The non-carrier normal daughter in the 2nd generation must have a genotype of XHXH her normal husband must have the genotype XHY; therefore, it is not possible for any of their children to have hemophilia or be a carrier of the trait.
XHXh
XHY
XHY
XHXh
XhY
XhY
XHY
XHXH
XHY
XHXh
XHY
XHY
XHXH
XhY
XHY
XHXH
Probability of XHXh?
Probability of XHXh?

27. Pedigree Practice
However, when their normal son (genotype XHY) marries a woman who is a carrier of the trait (genotype XHXh), then the probability that each of his twins will be a carrier is 1 out of 2 (50%).
XH Xh
XhY
XHY
XHXh
XHXH XH Y
XHXh
XHY
XHY
XHXh
XhY
XhY
XhY
XHXH
XHY
XHXh
XHY
XHY
XHXH
XhY
XHY
XHXH
Probability of XHXh?
Probability of XHXh?