1. Chapter 11 – law of segregation, law of ind. assortment
Mendel and the Gene Idea

3. Allele for purple flowers
Homologous
pair of
chromosomes
Locus for flower-color gene
Allele for white flowers

4. The Testcross
How can we tell the genotype of an individual with the dominant phenotype?
Could be DD or Dd
The answer is to carry out a testcross: breeding the mystery individual with a homozygous recessive individual
If any offspring display the recessive phenotype, the mystery parent must be heterozygous. Same thing for a 2 trait but testcross would
involve the double recessive.

5. 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

6. Using a dihybrid cross, Mendel developed the law of independent assortment
This principle states that the alleles for a trait separate when gametes are formed. These allele pairs are then randomly united at fertilization.
Genes located near each other on the same chromosome tend to be inherited together – these are called linked genes and we will do work them!

7. The Spectrum of Dominance
Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical
In codominance, two dominant alleles affect the phenotype – both expressed!
In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

9. LE 14-12 20/64 15/64 6/64 1/64 AaBbCc AaBbCc aabbcc Aabbcc AaBbcc
Fraction of progeny
6/64
1/64

10. Pedigree Analysis
A pedigree is a family tree that describes the interrelationships of parents and children across generations
Inheritance patterns of particular traits can be traced and described using pedigrees
Males = squares, females = circles
The trait is shaded in

11. 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)

12. 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)

13. Recessively Inherited Disorders
Many genetic disorders are inherited in a recessive manner
Recessively inherited disorders show up only in individuals homozygous for the allele
Carriers are heterozygous individuals who carry the recessive allele but are phenotypically (look) normal, so they don’t know they have bad genes!

14. Cystic Fibrosis http://www. muschealth. com/video/Default. aspx
Cystic fibrosis is the most common lethal genetic disease in the United States,striking one out of every 2,500 people of European descent - why???
The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes –so lungs full of mucus
Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine (so stunted growth)

15. Sickle-Cell Disease – Watch HHMI video
Sickle-cell disease affects one out of 400 African-Americans
The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells
Symptoms include physical weakness, pain, organ damage, and even paralysis

16. Dominantly Inherited Disorders
Some human disorders are due to dominant alleles
One example is achondroplasia, a form of dwarfism that is lethal when
homozygous for the
dominant allele

17. Blue Fugates of Kentucky: mutant enzyme

18. Marfans – Defective connective tissue

19. Color blindness inheritance – mostly seen in males
Color blindness inheritance – mostly seen in males. How would females get it??

20. Are you color blind? Try to read these!