1. What word is written here?
Most color blind people can easily read what is written in the picture above. That means, if you fail the test, you probably have the full range of color sensitivity that is attributed to color-sighted people.

2. Complex Patterns of Inheritance
Topics:
Sex Determination
Sex Linkage
Sex Influenced

3. Sex Determination
Sex Chromosome was discovered by the work of Thomas Hunt Morgan.
He study the fruit flies’ chromosomes.

4. Fruit Flies

5. He discovered that females have XX chromosomes and males have XY chromosomes.
Sex chromosomes determine the sex of an organism.

6. Females have homologous X sex chromosomes while the males have X and Y sex chromosomes.
When gametes are produces each egg in a female will receive one X chromosome.
In males, each sperm will either receive an X or Y chromosome.

8. Sex Linkage
Thomas Hunt Morgan also discovered that genes are also carried on these sex chromosomes.
Genes that are carried on either the X or Y chromosome are called sex-linked genes.
Genes found on other 44 autosomes are called autosomal genes.

9. Fruit Fly Eye Color

10. Fruit Fly Eye Color Legend
Order of dominance
Phenotype
Allele symbol
Possible Genotype
Dominant Over
Wild Type E1
E1E1, E1E2, E1E3, E1E4
Apricot, Honey, White
Apricot E2
E2E2, E2E3, E2E4
Honey, White
Honey E3
E3E3, E3E4
White E4
E4E4
none

12. Morgan’s Conclusion
Morgan crossed a white-eyed female (XrXr) with a red eyed male (XRY).

13. For example, he noticed that male flies got white eyes way more often than female flies.
Seeing as white eye color is recessive to red eye color the only way white could show up would be if that gene was by itself and not have the dominant red gene to mask it.
He concluded that the X chromosome must carry the gene for eye color.

14. Sex Linked Traits In Humans

15. Color Blindness Color blindness is an example of sex linkage.
People who have the dominant allele for color vision can see all the colors in the visible spectrum.
Red-green color blindness is the inability to distinguish red from green which, is a recessive condition.

20. For a woman to be color-blind both alleles for red-green color vision must be recessive.
In men however, one recessive allele on the X chromosome will result in color blindness because the Y chromosome does not carry the gene.

21. Genotypes for Red-Green Vision
X = the location or loci of the gene
A or a = the alternative form of the gene
XAXA a woman with normal vision
XAXa heterozygous female carrier
XaXa a color-blind woman
XAY a man with normal vision
XaY a color-blind man

22. EXAMPLE
A woman, that is a carrier for the colorblindness, has a child with a man who has normal color vision. What are the possible genotypes and phenotypes of the offspring?

24. SEX INFLUENCED TRAITS
A phenotypic characteristics that are controlled by a pair of alleles found on the autosomes chromosomes but not on the sex chromosomes (the X and Y chromosomes).
The trait’s expression is influenced by gender (presence of hormones such as: estrogen, progesterone, testosterone, etc.).

25. Sex-influences traits can vary in the degree of the phenotypic expression.
Pattern Baldness – the gene for baldness is dominant over the gene for keeping hair.
The difference between the sexes expression of this trait is exhibited in the following ways:

26. Pattern Baldness

27. *Baldness is dominant in males and recessive in females*
B or b = the alternative form of the gene
Male
BB = baldness
Bb = baldness
bb = normal hair line
FEMALE
BB = baldness
Bb = normal hair line
bb = normal hair line
*Baldness is dominant in males and recessive in females*

28. EXAMPLE
A boy who is wondering if he might be bald later on in his life. When he checks the family gene pool, his mother is not bald but his grandfather is (on his mother’s side) and his dad has a normal hair line. Create two Punnett squares to help him determine the possibility of being bald later in his life.

29. Punnett Square 1

30. Punnett Square 2

31. Check For Understanding