1. Gene-Linked Traits Agenda: Hand in Blood Type Questions Spotlight
Review/Take Up Questions
Gene Linkage
Sex-Linkage
Dihybrid Cross Problems and Sex-Linkage Problems

2. Summary From Last Class
Blood type is controlled for by one gene and the interactions between 3 alleles, referred to as IA IB Ii alleles
Blood type refers to the antigen present on the membrane of red blood cells.
Your body produces antibodies to antigens, not present inside of you. These antibodies clot red blood cells.
Therefore, AB individuals (both antigens present) are universal recipients and type O are universal donors (no antigens present)

3. Revisiting Incomplete Dominance
Traits exhibiting incomplete dominance are an excellent way to prove genes do not mix.
Despite exhibiting a blending of alleles, the F2 generation still produces white and red phenotypes

4. Looking at Incomplete Dominance on the Cellular Level
The individual alleles coding for plant colour, still must sort independently
Or else the red and white phenotypes would not reappear in the F2 generation of plants

5. Using your knowledge of dihybrid crosses, what do you think the expected phenotype for the F1 generation would be if these two plants were crossed?
Assume, purple flower and long pollen are dominant alleles and both plants have heterozygous genotypes.

6. The F1 generation would be PpLl
Now what if you cross-fertilized the F1 generation?
What would your phenotype ratios be?
Recall 9:3:3:1

7. The results of this particular experiment are:
This evidence indicates some alleles do not sort themselves independently. How is this possible?

8. Linked Genes One chromosome can code for thousands of genes.
Therefore genes on the same chromosome, tend to go together in pairs and are inherited together.
This is referred to as a linked gene

9. Crossing Over and Linked Genes
Linked genes, do not always have to be inherited together.
Recall crossing over in prophase I of meiosis, the exchange of genetic material

10. Due to crossing over, genes which were previously linked become unlinked. Happens very rarely
If the linked genes were close together on the chromosome, would they be more or less likely to become unlinked?

11. Why Does This Happen?

12. What is Hemophilia?
The individual is lacking the ability to produce proteins in their blood to help it clot, when a cut occurs.
The trait coding for these proteins are on the X chromosome. The trait coding for no proteins is recessive.

13. Why Are Males Affected More?
Genes on your sex chromosomes can also be linked
Traits controlled or coded for be genes on your sex chromosomes are referred to as sex-linked

14. The human x chromosome is estimated to contain about 2000 genes
The Y chromosome contains fewer than 100! Most of these genes are responsible for sex determination

15. Males only have one copy of the X chromosome (XY)
Females have two copies of the X chromosome (XX)

16. Due to this, any X-linked genetic conditions, males will be much more susceptible to because they only have one copy of the X chromosome
While females are ‘protected’ from genetic disorders on the X chromosome because they have two copies of X chromosome

17. Practice Problem
Imagine you are a mother, who is eight months pregnant. You and your husband have had genetic screening done and you find out, that you are a carrier for hemophilia (heterozygous), while your husband does not have the allele for hemophilia.
What are the chances you will have a son with hemophilia?
What are the chances you will daughter with hemophilia?
Let X and Y represent the sex chromosomes
Let H represent normal allele
Let h represent the hemophilia allel

18. Red-Green Color Vision is another trait located on the X chromosome.
Red-green color deficiency is a controlled for by a recessive gene. Much like the hemophilia gene.

20. Summary
One chromosomes contains many genes. Traits/genes located on one chromosome tend to go together and do not follow the law of independent assortment.
Similarly, the X chromosome codes for many traits, including hemophilia and red-green colour deficiency
Hemophilia and red-green colour deficiency are both X-linked recessive conditions
Males are more susceptible to X-linked conditions because they only contain one copy of the X chromosome

21. Quiz on Tuesday November 23
Blood Type
Monohybrid cross problems
Dihybrid cross problems
Sex linked problems
Incomplete dominance
Around 8 questions