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”
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.
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