1. Final Concepts for Chapter 11 Mendelian Genetics
Codominance
Complete dominance
Dihybrid cross
Genotype
Genotypic ratio
Heterozygous
Homozygous
Incomplete dominance
Monohybrid cross
Phenotype
Phenotypic ratio
Probability
Punnett square
Testcross
Expected/predicted results
Actual/observed results
Karyotype
Amniocentesis
Linked genes
Sex-linked disorders
Autosomal disorders
Allele
Dominant
Recessive
P-generation
F1 generation
F2 generation
Law of independent assortment
Law of segregation
Chromosomes
Pure breed
Trait

2. Independent Assortment vs. Linked Genes
Mendel did not know about chromosomes when he proposed the Law of Independent Assortment.
The pea traits he studied happened to be located on different chromosomes – so they did assort independently.

3. Independent Assortment vs. Linked Genes
Question: How many traits do you have?
Question: How many chromosomes (per cell) do you have?
Question: Is it possible to have only one trait per chromosome?
No, lots of genes are carried or linked together on the same chromosome.

4. Independent Assortment vs. Linked Genes
Do the punnett square for the following cross – assume independent assortment.
Cross two heterozygous tall, heterozygous red flowered plants
T=tall R=red flower
t= short r = white flower

5. Independent Assortment vs. Linked Genes
What is the phenotypic ratio?
TtRr x TtRr TR Tr tR tr
TTRR
TTRr
TtRR
TtRr
TTrr
Ttrr
ttRR
ttRr
ttrr TR Tr tR tr

6. Independent Assortment vs. Linked Genes
9:3:3:1 ratio
9 = tall and red
3 = tall and white
3 = short and red
1 = short and white
PROBABILITY:
From this cross, 48 offspring were produced.
How many offspring would you expect to be tall and red?
How many would expect to be tall and white?
How many would you expect to be short and white?

7. Independent Assortment vs. Linked Genes
Now, do the following cross BUT the genes for tallness and red flowers are linked.
Cross two heterozygous tall, heterozygous red flowered plants
T=tall R=red flower
t= short r = white flower

8. Independent Assortment vs. Linked Genes
Hint
T t
R r
TtRr X TtRr
Is it possible to produce a Tr gamete?

9. Independent Assortment vs. Linked Genes
TtRr X TtRr
What is the phenotypic ratio? tr TR
TTRR
TtRr
ttrr
3:1
3 = Tall and Red
1 = Short and white TR tr

10. Independent Assortment vs. Linked Genes
So… out of the 48 offspring, if the genes are linked, how many would be
1. tall and red?
2. tall and white?
3. short and red?
4. short and white?
Answer:
tall and red = 36 tall/white = 0
short and white = 12 short/red = 0
EXPECTED RESULTS!

11. Independent Assortment vs. Linked Genes
Is it possible for our Actual Results to show any flowers that are tall/white or short/red?
Yes – how?
Crossing over

12. Crossing over occurs in meiosis
Pieces of the chromosomes actual switch places.

13. Complete vs Incomplete Dominance

14. Codominance – the alleles are equally dominant
Roan Cow Human Blood Type

15. Fill in the genotypes on the pedigree.
Sex-linked Traits
Traits carried on the X chromosome
Fill in the genotypes on the pedigree.

16. Autosomal disorders
Disorders carried on non-sex chromosomes (first 22 pairs)
Some are autosomal dominant
Huntington’s disease
Most are autosomal recessive
Sickle-cell anemia
Cystic fibrosis

17. Question: How do you know if the pure bred dog you just paid big bucks for is actually pure?
GG?
Gg?

18. Test Cross
Cross using a homozygous recessive individual with a dominant individual to determine if the dominant individual is heterozygous or homozygous dominant (pure)
Why use a homozygous recessive individual?

19. Test Cross
Do the punnett squares for each case:
GG x gg Gg x gg

20. Test Cross
All offspring produced should show the dominant characteristics if the dominant parent is pure (GG) for the trait.