Gene-Linked Traits

Summary From Last ClassBlood 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)

Revisiting Incomplete DominanceTraits 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

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

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.

The F1 generation would be PpLlNow what if you cross-fertilized the F1

generation?

What would your phenotype ratios be?Recall 9:3:3:1

The results of this particular experiment are:

This evidence indicates some alleles do not sort themselves independently. How is this possible?

Linked GenesOne 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

Crossing Over and Linked GenesLinked genes, do not always have to be

inherited together. Recall crossing over in prophase I of meiosis,

the exchange of genetic material

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?

Why Does This Happen?

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.

Why Are Males Affected More?Genes on your sex chromosomes can also be

linkedTraits controlled or coded for be genes on

your sex chromosomes are referred to as sex-linked

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

Males only have one copy of the X chromosome (XY)

Females have two copies of the X chromosome (XX)

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

Practice ProblemImagine 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 chromosomesLet H represent normal alleleLet h represent the hemophilia allel

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.

SummaryOne 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

Quiz on Tuesday November 23Blood TypeMonohybrid cross problemsDihybrid cross problemsSex linked problemsIncomplete dominanceAround 8 questions