Do Now• If a diploid pea plant has one copy of a gene

(allele) for green seed color, and one copy for yellow, what is the probability it will produce a haploid pollen grain with the yellow version?

• If a second diploid pea plant with the same genetic make-up produced a haploid egg cell, what is the chance it will have the yellow version?

• If pollen and egg cells from the two plants are randomly combined, what is the probability the diploid offspring will have 2 of the yellow versions of the gene for seed color?

Is your phenotype Tounge rolling on

Non-tounge rolling?

Phenotype: a physical trait or characteristic of an

organism (i.e. brown hair, blue eyes, shiny feathers,

penicillin allergy… anything really)

Genotype = the alleles an individual has for a gene, represented by letters

• There are 70,000+ genes on those chromosomes… lets look at 1.

BRCA1

• BRCA1 is a gene associated with hereditary breast and ovarian cancer risk, located on chromosome 8.

Phenotype: Increased Breast Cancer Risk (Carrier)

Genotype: Nn

• Lets simplify things and say there’s a low risk (normal) allele (N) and a high risk mutant allele (n).

• What is this person’s risk of passing a mutant allele on to their child?

N n

The Rules of Inheritance are Universal

• In diploid organisms (like people, mammals, some plants, and many other eukaryotic organisms), every individual has two copies of each gene.

• In humans, the tongue rolling phenotype (T) is dominant over not being able to roll (t).

• Therefore, if you can roll your tongue, you’re genotype is TT or Tt. If you can’t, you must be tt.

Dominant Alleles

• A dominant allele is one which hides the presence of a recessive allele, and is typically represented with a capital letter.

• Example: If the Dd genotype has phenotype D, D is dominant to d.

Two VERY important terms

• Homozygous: having 2 of the same alleles for a gene (i.e. QQ or pp)– May be homozygous dominant or

homozygous recessive– Aka “purebred”

• Heterozygous: having 2 different alleles for a gene (i.e. Qq or Pp)– Aka “hybrid”

Which is Haploid?Which is Diploid?

Haploid

Diploid

Words to Know• Allele – A certain form of a gene (like T or t)

• Heterozygous – having two different alleles

• Homozygous – having two copies of the same allele

• Dominant / Recessive – two common types of alleles. The DOMINANT allele determines the trait in heterozygotes that have both forms.

Which is Genotype?Which is Phenotype?

Phenotype

Genotype

bb

Which is Homozygous?Which is Heterozygous?

Heterozygous

Homozygous

Genetic Crosses

Yy x Y yYy Y yYy Y y

Y Y

y y

Y

Y

y

y

3:1

1:2:1