Overview/Review of Basic Genetics

Genetic material (DNA) is stored within structures called chromosomes.

In sexually reproducing organisms (e.g. mammals and birds), an individual has two copies of each type of chromosome.

Every species has a specific number of chromosomes (in humans there are 23 pairs of chromosomes = 46 total).

Genes (sequences of DNA which encode proteins) are found on chromosomes.

Overview/Review of Basic Genetics

DifferentGenes

Each chromosome in a pair has the same genes in the same order.

However, specific genes can be variable and the two chromsomes may not have the same gene variant.

Variants of a specific gene are known as alleles.

Example: There is a gene in humans that controls basic eye color. There are two alleles: Blue (b) and Brown (B).

The genotype of an individual is the set of alleles the individual has.

Question: What are the possible genotypes for eye color?

Answer: BB or Bb or bb

Overview/Review of Basic Genetics

The phenotype of an individual is the physical characteristic formed by their specific alleles.

Example: An individual with the brown alleles (BB) has a brown eyed phenotype. An individual with two blue alleles (bb) has a blue eyed phenotype.

Question: Does an individual with 1 brown and 1 blue allele (Bb) have one brown eye and one blue eye?

Answer: No. The brown allele is dominant over the blue allele (which is recessive). An individual with both alleles (heterozygous) has the phenotype of the dominant allele. Thus the Bb genotype = Brown phenotype.

Overview/Review of Basic Genetics

Another example: Many plants can have flowers of different colors.

Overview/Review of Basic Genetics

Bougainvillea

Snap Dragons

Bougainvillea on Campus

In many plants, flower color is controlled by a single gene.

There are alleles for Red (R) and White (W) and sometimes other colors (e.g., yellow).

A plant with an RR genotype has a red phenotype.A plant with a WW genotype has a white phenotype.A plant with an RW genotype has a pink phenotype.

Neither R nor W are dominant. They are called incompletely or partially dominant alleles and the observed phenotype of a heterozygote is in between the phenotype of either homozygote ( a blend).

Overview/Review of Basic Genetics

Question: Can you predict phenotype from genotype?

Answer: Yes. For eye color we know that BB and Bb are always brown and bb is always blue.

Question: Can you predict genotype from phenotype?

Answer: No. While we know a blue eyed person must have a bb genotype, a brown eyed person could have either Bb or BB. All we know for sure is they have at least 1 B.

Overview/Review of Basic Genetics

An individual’s chromosomes are inherited from their parents. One from the father and one from the mother.

When an individual has children, half of its chromosomes (one from each chromosome pair) will go into the child.

The process by which a specific chromosome (and therefore specific alleles) goes into a child is random.

What does any of this have to do with math?

Pretend you are going to breed a pair of plants with pink flowers.

Question: What are the phenotypes of these plants? What are the genotypes?

Answer: Phenotypes are both pink. Genotypes are both RW.

Questions: What are the possible genotypes and phenotypes of the offspring? What is the probability of getting these genotypes and phenotypes?

You may know the answer, but do you know the mathematics behind it…

What does any of this have to do with math?