Introduction to Genetics Ms. Stewart November 5, 2013

Why are we like our parents? Why do we look like our brothers and sisters?  It’s because of our genes  Each of us receives traits, in the form of genes, from our mother and father  The passing of these genes from parents to children is called inheritance  If you inherit your genes from your parents, why don’t you look exactly like them?

The Work of Gregor Mendel  Gregor Mendel – the Father of Genetics - Studied genetics using pea plants - Determined that biological inheritance is determined by genes.  Genetics: The study of inheritance

Important Terms  A trait is a specific characteristic that varies from person to person. –Eye color, height, curling your tongue, cheek dimples  A gene is a sequence of DNA that codes for a protein and determines a trait.  Different forms of genes are called alleles.

The Principal of Dominance States that some alleles are dominant and others are recessive.

 Dominant alleles always “over power” recessive alleles. An organism with a dominant allele for a particular trait will always show that trait. -Always represented with a capital letter (A, B, C) Ex – the allele for brown eyes is dominant over the allele for blue eyes. (BB)  Recessive alleles show only when a dominant allele is not present. -Always represented with a lower case letter (a,b,c) -Ex – If your mother has blue eyes (bb) that are recessive, but your dad has brown eyes (BB) that are dominant, what color will your eyes be?

Example  Purple flowered plants x White flowered plants = All purple offspring  What does this tell us about the genes for purple and white?  That the purple gene is Dominant  And the white gene is Recessive

 Probability – the likelihood that an event will occur. -Probability can be used to predict the outcomes of genetic crosses. What’s the chance that a quarter will land on heads?

Punnett Squares  Punnett Squares – used to predict genetic variations that will come from a cross.  B = Brown eyes (dominant) b = green eyes (recessive) Example: Example:  Father: Bb Mother: bb  Probability of brown eyed child: ____ Probability of a green eyed child:____

Important Terms  Phenotype – the physical appearance of the organism. (what the off spring LOOKs like) Example – Jose has brown eyes  Genotype – the genetic makeup of an organism. usually expressed in capital and lowercase letters(HH, hh, Hh) usually expressed in capital and lowercase letters(HH, hh, Hh)  Example – BB is the genotype for brown eyes  Homozygous/ purebred – Both alleles are the same. (bb or BB)  Heterozygous/ Hybrid – Has different alleles (Bb)

 If we say something is homozygous dominant, what will you look for?  If we say something is heterozygous dominant, what will you look for?  What about homozygous recessive?

Practice  Identify the following as either homozygous dominant or heterozygous dominant or homozygous recessive.  Key B= brown, W= white P=pink  BB PP  Bb ww Pp WW Ww

 If 2 traits are being studied, the Punnett square would have 2 times the amount of boxes.  B= Brown Eyesb= green eyes  E = big eyes e = small eyes  Father = bbEe Mother = Bbee

What is the probability of the child having big, brown eyes? What is the probability of the child having small, green eyes? What is the probability of the child having small, brown eyes? What is the probability of the child having big, green eyes?

Using the diagram, name the genotypes and phenotypes of the parents?

 Principal of Independent Assortment – genes from different traits can segregate independently during the formation of gametes.  What this means in English – Just because you have a 50% chance of having children with blue eyes does not mean that half of your children will definitely have blue eyes.

Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.  Incomplete Dominance – when one allele is not completely dominant over another.  In this case, the heterozygous phenotype is a mix between the 2 homozygous phenotypes.  Ex – Red flower and a White flower may result in a pink flower.

 Codominance – both alleles contribute to the phenotype. You can see BOTH phenotypes at the SAME time.  Ex – in bunnies an allele for black fur can be codominant with the allele for white fur. This results in white fur with black spots.

Examples of Incomplete Dominance and Co-dominance  ance_patterns.htm ance_patterns.htm ance_patterns.htm