1. Chapter 14~ Mendel & The Gene Idea

3. Mendelian genetics Trait True-breeding Hybridization
variant for a character ex: purple
True-breeding
all offspring same variety
Hybridization
Cross of two pure breeding
P generation = parents
F1 generation = first filial generation

4. Leading to the Law of Segregation
Alleles = Different versions of genes
one from each parent
If the two alleles are different
the dominant allele is expressed
the recessive allele is “hidden”
Mendel’s Law of Segregation
The alleles for each character segregate during gamete production

5. Genetic vocabulary…….
Punnett square: predicts the results of a genetic cross between individuals of known genotype
Homozygous: alleles are the same
Heterozygous: two alleles are different
Phenotype: an organism’s traits (what you SEE)
Genotype: an organism’s genetic makeup: TT, Tt, tt
Testcross: cross with a homozygous recessive x dominant phenotype (but unknown genotype)

7. The Law of Independent Assortment
Monohybrid cross vs. dihybrid cross
The two pairs of alleles segregate independently of each other.
Mendel’s Law of Independent Assortment

8. LE 14-8 P Generation YYRR yyrr Gametes YR yr YyRr F1 Generation
Hypothesis of
dependent
assortment
Hypothesis of
independent
assortment
Sperm 1 YR 1 Yr yR yr
Sperm 4 4 1 4 1 4
Eggs 1 YR yr 2 1 2 1 YR
Eggs 4
YYRR
YYRr
YyRR
YyRr 1 YR
F2 Generation
(predicted
offspring) 2
YYRR
YyRr 1 Yr 4
YYRr
YYrr
YyRr
Yyrr 1 yr 2
YyRr
yyrr 1 yR 4
YyRR
YyRr
yyRR
yyRr 3 4 1 4 1 yr 4
Phenotypic ratio 3:1
YyRr
Yyrr
yyRr
yyrr 9 16 3 16 3 16 3 16
Phenotypic ratio 9:3:3:1

9. Genes working together
Incomplete dominance: blending of the phenotypes of the 2 parents.
Ex: snapdragons
Codominance: two alleles affect the phenotype in separate ways
Ex: human blood types A & B
Multiple alleles: more than 2 possible alleles for a gene.
Ex: human blood types

10. LE 14-10 P Generation Red CRCR White CWCW Gametes CR CW Pink CRCW
F1 Generation
Gametes 1 1 2 CR 2 CW
Sperm 1 2 CR 1 2 CW
Eggs
F2 Generation 1 CR 2
CRCR
CRCW 1 2 CW
CRCW
CWCW

14. Gene Interaction Pleiotropy: genes with multiple phenotypic effect.
Ex: sickle-cell anemia
Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus.
Ex: mice coat color
Polygenic Inheritance: an additive effect of two or more genes on a single phenotypic character Ex: human skin pigmentation and height

15. Pleiotropy

16. Epistasis LE 14-11 BbCc BbCc Sperm BC bC Bc bc BC BBCC BbCC BBCc BbCc9 3 4 16 16 16

17. Polygenic inheritance
Quantitative variation usually is additive effect of two or more genes on a phenotype
Skin color in humans is an example

18. Human disorders The family pedigree: Recessive disorders:
Diagram showing family relationships:
Circle - female
Square - Male
Recessive disorders:
•Cystic fibrosis
•Tay-Sachs
•Sickle-cell
Dominant disorders: •Huntington’s

19. Recessive trait (attached earlobe)
LE 14-14b
First generation
(grandparents) Ff Ff ff Ff
Second generation
(parents plus aunts
and uncles)
FF or Ff ff ff Ff Ff ff
Third
generation
(two sisters) ff FF or Ff
Attached earlobe
Free earlobe
Recessive trait (attached earlobe)

20. Dominant trait (widow’s peak)
LE 14-14a
First generation
(grandparents) Ww ww ww Ww
Second generation
(parents plus aunts
and uncles) Ww ww ww Ww Ww ww
Third
generation
(two sisters) WW ww or Ww
Widow’s peak
No widow’s peak
Dominant trait (widow’s peak)

21. TESTING
•Amniocentesis: (between week: 15-18) Prenatal diagnosis of chromosomal abnormalities
•CVS = Chorionic villi (villus) sampling (10-12 weeks)

24. Bozeman: Mr. Anderson