1. Start-up for Tuesday, November 13, 2012
Complete the following crosses. Show your work in Punnett Squares.
T = Talll R = Round
t = Short r = Wrinkled
A. Single Trait = If you cross a heterozygous tall plant with a short plant, what percent of the offspring do you expect to be tall?
B. Two traits = What is the phenotypic ratio if you cross a pure tall round pea plant with a short wrinkled pea plant?

2. Genetics – Mendelian Exceptions Multiple Alleles and Sex-linked Genes
Chapter 14 Section 2
Objectives: Students will
A) Identify the genotypes of males compared to females
B) Define sex-linked traits
C) Complete punnett squares for sex-linked traits
D) Predict offspring outcomes of multiple allele crosses
E) Read and predict genetic outcomes from pedigrees

3. Exceptions to Mendel’s Laws
The elegance of Mendel’s experiments was partly due to the complete consistency between his observations and hypotheses he developed.
However, after Mendel’s work was rediscovered, it became clear that the simple Mendelian model did not adequately predict experimental observations in all situations.

4. 2. Codominance – Smiley Face Lab 3. Multiple Alleles
Exceptions to Mendel’s Laws
Variations on Mendel
1. Incomplete Dominance
2. Codominance – Smiley Face Lab
3. Multiple Alleles
4. Polygenic Inheritance
5. Sex-linked Traits

5. A) Identify the genotypes of males compared to females.
Human males are the heterogametic sex with two different sex chromosomes, (XY).
Human females are the homogametic sex (XX).
During fertilization, what is the probability that a female will result?
50%

6. Obj. B) Define sex-linked traits
Chromosomes carry genes. Genes are located on autosomes and sex chromosomes.
Genes on
Autosomes – body traits
Sex chromsomes- sex traits
However, certain genes present in the sex chromosomes control the body traits.
The characters which are controlled by such genes are called sex-linked traits and transmission of such traits from one generation to next is called sex-linked inheritance

7. Discovery and types of Sex linked inheritance
Obj. B) Define sex-linked traits
Discovery and types of Sex linked inheritance
Was first discovered by Thomas H. Morgan in 1910 on Drosophila melanogaster (fruit flies).
It can be classified into three types depending upon the chromosomes (X or Y) having sex linked genes.
1. X – Linked inheritance
2. Y - Linked inheritance
3. XY - Linked inheritance

8. Obj. B) Define sex-linked traits
Certain sex-linked genes are located only on X chromosomes and their alleles are absent in Y chromosomes.
These genes are called X–linked genes;
Their mode of inheritance is called X-linked inheritance
This pertains to the inheritance of traits which are controlled by genes located in the non-homologous part of X-chromosomes
Examples: Colorblindness, Hemophilia,
Duchenne Muscular Dystrophy
1. X- Linked inheritance

9. Color blindness – the inability to see red and green
Obj. C) Complete punnett squares for sex-linked traits
Color blindness – the inability to see red and green
XBXB Normal female
XBXb Carrier female
XbXb Affected female
XBY Normal Male
XbY Affected male

10. Sex-linked Recessive Practice
Obj. C) Complete punnett squares for sex-linked traits
Sex-linked Recessive Practice
Trait: Color blindness
Cross: Carrier female x Color Blind male
XBXb x XbY Use genotypes on previous slide. Xb Y
Phenotypes:
25% Carrier Females
25% Color Blind Females
25% Normal Males
25% Color Blind Males
XBXb
XBY XB Xb
XbXb
XbY

11. Sex-linked Recessive Example
Obj. C) Complete punnett squares for sex-linked traits
Sex-linked Recessive Example
Trait: Color blindness
Cross: Carrier female x Normal male
XBXb x XBY XB Y
Phenotype:
25% Normal Females
25% Carrier Females
25% Normal Males
25% Color Blind Males
XBXB
XBY XB Xb
XBXb
XbY

12. Obj. B) Define sex-linked traits
See page 345 for a list
X – Linked Recessive:
1. Affects males more than females
2. No female offspring of an affected male are affected, the trait skips generations in pedigrees. When is there an exception?
Exception to this pattern occurs in the rare instance when the affected male mates with a female carrier, producing an affected female offspring.
X – Linked Dominant:
1. Affected male produce all affected female offspring and no affected male offspring
2. Approximately half the offspring of affected females are affected, regardless of their sex.

13. Multiple Alleles
It is generally accepted that a gene has two alternative forms called Alleles.
Usually, one of the two alleles of a gene is dominant over the other, which is recessive e.g, Tall (TT)
But in many cases, several alleles of a single gene govern the concerned trait and is known as Multiple alleles.
Both prokaryotes and Eukaryotes show multiple alleles.
Examples:
1. Human Blood Type
2. Fur color in rabbits and other mammals.

14. Multiple Alleles – Blood type
Obj. D) Predict offspring outcomes of multiple allele crosses
Multiple Alleles – Blood type
Safe to Transfuse to
A, AB
B, AB AB
A, B, AB, O
Safe to Transfuse From
A, O
B, O
A, B, AB, O O

15. Obj. D) Predict offspring outcomes of multiple allele crosses
Example: homozygous male Type B (IBIB)
x heterozygous female Type A (IAi)
Genotype: IB IB
50% = IAIB
50% = IBi IA
IAIB
IBi
Phenotype:
50% = AB blood type
50% = B blood type i

16. Obj. D) Predict offspring outcomes of multiple allele crosses
Practice: male Type O (ii) x female type AB (IAIB) i IA IB
Genotype:
IAi
IBi
50% = IAi
50% = IBi
Phenotype:
50% A blood type
50% B blood type

17. Obj. E Read and predict genetic outcomes from pedigrees
Pedigree Symbols
Always read the legend
Male =
Female=
Sexual Union=
Offspring=

18. Obj. E) Read and predict genetic outcomes from pedigrees
Shaded = color blind
No shade = normal vision
What does a line between a male and female indicate?
What do the circles and squares beneath this mean?
What are the genotypes of the following individuals:
Individual #8, Generation III
Individual #3, Generation II
Individual #2, Generation III
Sexual Union
Children
XbY
XBXb
XBXb

19. Hemophilia Obj. C) Complete punnett squares for sex-linked traits
Hemophilia is another sex-linked trait.
Hemophilia is characterized by delayed blood clotting. People with hemophilia can easily bleed to death from very minor wounds.
Otherwise called “Bleeders disease”.
Hemophilia is sex-linked recessive trait (hh) and the genes are located on X chromosomes.
It is more common in men and rare in women.

20. Understanding Check – Sex-linked
This disease appeared as a mutant in Queen Victoria and from her it was transmitted to her descendants.
“Royal disease” = Hemophilia, Bleeder’s Disease
XH XH Normal female
XH Xh Carrier female
XH Y Normal Male
Xh Y Affected male
Xh Xh Affected female
Cross a carrier female with a normal male. Identify the phenotypes.

21. _______ x _______ Understanding Check – Multiple Alleles
Cross a heterozygous type B blood type with a AB blood type
_______ x _______
Phenotype Percentages: