 Genes & AllelesGenes & Alleles  Genotype & PhenotypeGenotype & Phenotype  Homozygous & Heterozygous Homozygous & Heterozygous Created by Sima Mathew and Jennifer Dietz

Gregor Mendel known as:: THE FATHER OF GENETICS. - laid the foundations for the SCIENCE OF GENETICS through his study of inheritance patterns of traits in pea plants.

What is heredity or inheritance?  Passing of traits from parent to offspring or from one generation to the next.  Genes are the coded instructions that define our traits.

How are genes inherited?  Humans have 2 sets of chromosomes for a total of 46 chromosomes. Each parent contributes only 1 set of chromosomes to their child.  When a sperm cell (23 chromosomes) and an egg cell (23 chromosomes) join during fertilization, it results in a zygote (46 chromosomes).

What is a trait?  Notable feature or quality in a person. What are the two types of traits?  Physical traits are traits that can be seen such as eye or hair color  Behavioral traits demonstrate the way one acts such as “the fetching behavior of golden retrievers”.

Phenotype  Phenotype is another word for physical trait (in other words, it describes how someone looks)  Examples of phenotypic words are: tall, short, brown hair, straight hair, fat, skinny, fair skin, freckles, etc. Can you think of anymore? On your notes, write at least 4 phenotypic words that describe YOU!

REMEMBER!!  Phenotype describes things you can see!!!

What do you think person’s phenotype would be?

How would you describe this phenotype?

Remember??  REMEMBER: Mom gives you one half of your genes, and your dad gives you the other half….  sperm + egg = YOU! Together, these two genes (one from mom and one from dad) represent your genotype  Each gene is represented by one letter.

Genotype  Genotype is the genetic makeup of an organism’s traits represented by letters Genotype codes for phenotype T = tall t = short

Two different forms of the same gene = The factors that carry all traits =

Example  Gene = height  Alleles = tall; short

Example  Gene = eye color  Alleles = green, blue, brown

Example  Gene – hair texture  Alleles – straight, wavy, curly

Example  Gene – thumb  Alleles – hitchhiker’s thumb, straight thumb

Dominant vs. Recessive  Think of a person who never lets you talk during a conversation – that person DOMINATES the conversation. A Dominant Allele: allele that is expressed (the one that you see). A Recessive Allele: allele that is masked or hidden (not shown)

Which allele is expressed over another and represented by a capital letter? Which allele is usually masked or appears less in the population and represented by a lowercase letter?

Dominant or Recessive? AFrhGtdAFrhGtd

Check Yourself A – dominant F - dominant r – recessive h - recessive G - dominant t - recessive d - recessive

 When both alleles are the SAME it is called  When the alleles are DIFFERENT it is called B = brown hairb = red hair homozygous for brown hair heterozygous for brown hair homozygous for red hair HOMOZYGOUSHETEROZYGOUS

Homozygous or Heterozygous? RR Jj tt Hh aa

Check Yourself RR - homozygous Jj - heterozygous tt - homozygous Hh - heterozygous aa - homozygous

You inherit two alleles for each gene (trait). 1 from MOM! 1 from DAD!  PHENOTYPE – physical characteristics that you SEE  Ex. Straight hair, red hair, freckles, lactose intolerant, tall, blue eyes  GENOTYPE – genetic makeup represented by letters  Ex. RR, Tt, Ffgg, YyEePp

 Principle of Dominance: when there is a dominant allele and a recessive allele inherited together for a particular gene, the dominant allele will ALWAYS be expressed. Mendel’s 1 st Law of Inheritance Dominant Brown hair allele Recessive red hair allele Express the dominant allele for brown hair