Theoretical Genetics4.3.2-4.3.11

Sydney Foil, Jasmine Delaine, Cameron Folmar, Stephanie Weng

Alleles: one member of a pair of genes that codes for distinct traits

Genotypes: the alleles of an organism Phenotypes: the characteristics of an

organism

Genotypes and Phenotypes

The genotypes of offspring can determined using a monohybrid cross◦ A monohybrid cross is a genetic cross using a

single trait with two alleles (both heterozygous)

Genotypes and Phenotypes

Using punnett squares you can find out the ratio of phenotypes.

Phenotype Ratios

Activity Punnett square worksheet

◦ Work in groups of two or three

Some genes can have more than just two alleles.

Although these genes can have multiple alleles individuals can only have two. ◦ Example: the gene of the A, B, AB, and O blood

types. This gene contains three alleles.

Genes Have Multiple Alleles

The alleles of IA and IB are dominant while the i is recessive. ◦ When both dominant alleles are present they form the blood group AB

Codominant alleles are pairs of alleles that both affect the phenotype when present in the heterozygote.

Codominance and Multiple Alleles

Phenotype Genotype

A IAIA or IAi

AB IAIB

B IBIB or IBi

O ii

The mother always passes on an X chromosome to her offspring

The father can pass either an X or Y chromosome to his offspring

Some genes are present on the X chromosome and absent from the shorter Y chromosome in humans

Determining Gender

When the gene controlling the characteristic is located on the sex chromosome ◦ We associate the characteristic with gender

Sex-linked genes are carried on the X chromosome ◦ Because females have two X chromosomes, they

carry two copies of the sex-linked gene while the males only carry one because they only have one X chromosome.

◦ Example: Hemophilia and color blindness

Sex Linkage

Hemophilia: XH is the allele for normal blood clotting, this is dominant over the allele Xh (the recessive gene which causes hemophilia)

If the mother is heterozygous, she is then a carrier of the disease and passes it on to her offspring◦ This means the dominant and recessive alleles

are present.

Sex Linkage Continued

Heterozygous: contains two different alleles ◦ Ex: Rr (one recessive, one dominant) ◦ Ex: AB blood type

Homozygous: having identical alleles for the same trait◦ Ex: RR or rr

Heterozygous or Homozygous

Because a female has two X chromosomes she can carry either both recessive/dominant genes or she can have one of each (with respect to sex linked genes).

If female carriers are heterozygous they can pass it onto their offspring.

Heterozygous or Homozygous

Basketball:◦ Six teams of five each◦ Each team at a lab table◦ Write answer on white board◦ Get the question right first, chance to shoot

Game Time

"IB Biology Notes - Theoretical Genetics." IB Guides - Free International Baccalaureate Study Guides, Notes, Videos and Powerpoints. 2010. Web. 10 Feb. 2012. <http://www.ibguides.com/biology/notes/theoretical-genetics>.

"Multiple Alleles." Redirecting... Web. 10 Feb. 2012. <http://www.hobart.k12.in.us/jkousen/Biology/multalle.htm>.

Pitocchelli, Jay. "Lecture Notes for Genetics." Saint Anselm College : Saint Anselm College. 2001. Web. 10 Feb. 2012. <http://www.anselm.edu/homepage/jpitocch/genbio/geneticsnot.html>.

"X and Y Chromosomes." Science Photo Library. Web. 10 Feb. 2012. <http://www.sciencephoto.com/media/94963/view>.

Works Cited