Name_________________________________________  Period Number_________________

Genetics and Heredity

Unit 3

State Standard

Develop and use a model to describe why structural changes to genes (mutations) located on chromosomes may affect proteins and may result in harmful, beneficial, or neutral effects to the structure and function of the organism.  [Clarification Statement:  Emphasis is on conceptual understanding that changes in genetic material may result in making different proteins.] [Assessment Boundary:  Assessment does not include specific changes at the molecular level, mechanisms for protein synthesis, or specific types of mutations.]

Genes are located in the chromosomes of cells, with each chromosome pair containing two variants of each of many distinct genes. Each distinct gene chiefly controls the production of specific proteins, which in turn affects the traits of the individual. Changes (mutations) to genes can result in changes to proteins, which can affect the structures and functions of the organism and thereby change traits. (MS-LS3-1)


Directions: Put a check in the box next to completed items.

Day 1: Mendel’s Experiment                                        Name________________ Per_______


For an A, do all Day one lessons

For a B, do all of the “On Your Own, including the summary, plus one discussion item

For a C, Do all of the “On Your Own,” including the summary

On Your Own:

Story: Mendel’s Experiment

     Once upon a time (1860's), in an Austrian monastery, there lived a monk named Mendel, Gregor Mendel. Monks had a lot of time on there hands and Mendel spent his time crossing pea plants. As he did this over & over & over & over & over again, he noticed some patterns to the inheritance of traits from one set of pea plants to the next. By carefully analyzing his pea plant numbers (he was really good at mathematics), he discovered three laws of inheritance.

Mendel's Laws are as follows:

1. the Law of Dominance

2. the Law of Segregation

3. the Law of Independent Assortment

     Now, notice in that very brief description of his work that the words "chromosomes" or "genes" are nowhere to be found.  That is because the role of these things in relation to inheritance & heredity had not been discovered yet. What makes Mendel's contributions so impressive is that he described the basic patterns of inheritance before the mechanism for inheritance (namely genes) was even discovered.

Hail to the "Father of Genetics" !

     There are a few important vocabulary terms we should iron-out before diving into Mendel's Laws.

GENOTYPE = the genes present in the DNA of an organism.  We will use a pair of letters (ex: Tt or YY or ss, etc.) to represent genotypes for one particular trait.  There are always two letters in the genotype because (as a result of sexual reproduction) one code for the trait comes from mama organism & the other comes from papa organism, so every offspring gets two codes (two letters).

Let's Summarize:

Genotype = genes present in an organism (usually abbreviated as two letters)

TT = homozygous = pure

Tt = heterozygous = hybrid

tt = homozygous = pure

PHENOTYPE = how the trait physically shows-up in the organism.  Wanna know the simplest way to determine an organism's phenotype ?  Look at it.  Examples of phenotypes: blue eyes, brown fur, striped fruit, yellow flowers.

 ALLELES = (WARNING - THIS WORD CONFUSES PEOPLE; READ SLOW) alternative forms of the same gene.  Alleles for a trait are located at corresponding positions on homologous chromosomes.

Remember just a second ago when explaining genotypes I said that "one code (letter) comes from ma & one code (letter) comes from pa"? Well "allele" is a fancy word for what I called codes.

     For example, there is a gene for hair texture (whether hair is curly (c) or straight (C)).  One form of the hair texture gene codes for curly hair.  A different code for of the same gene makes hair straight.  So the gene for hair texture exists as two alleles --- one curly code, and one straight code.

     Getting back to our abbreviations, we could use a "C" for the curly allele, and a "c" for the straight allele.  A person's genotype with respect to hair texture has three possibilities: CC, Cc, or cc.  So to review some vocab, homozygous means having two of the same allele in the genotype (2 big or 2 little letters --- CC or cc).  Heterozygous means one of each allele in the genotype (ex: Cc).

     Now I could tell you which genotypes create curls & which do not, but then I'd be stealing some of Mr. Mendel's thunder.  More on that in a minute ........

Share the summary with your table partner. Write and discuss questions. Then, share with the class.

Practice: Discuss with a table partner.


           Is it homozygous or heterozygous? ____________ Explain. __________________________