Crash Course on Heredity

Gregor Mendel, an Austrian monk, published his work on garden _peas_ in 1866. It became the basics for the study of genetics!

He formulated three laws of inheritance:

The Law of Dominance- When an organism has genes that call for two different versions of the same trait, the _dominant_ gene will be expressed, while the other is masked.

Dominant trait (allele) is Capitalized ex. T

Recessive trait (allele) is written in _small_ case letters ex. t

The Law of Segregation- traits (alleles) occur in pairs and are _separated_ from each other during sex cell (gamete) formation

The Law of Independent Assortment- during the making of sex cells (meiosis), genes for one traits are _separated_ independently from the genes of a different trait. (This is only true if the traits are on separate chromosomes. Mendel got lucky on this one!)


Here is some vocabulary to be sure to know:

Allele: different _forms_ of the same gene

Meiosis: the making of a sex cell

Gamete: an egg or _sperm_

Phenotype: the form that is shown- the outward, _physical_ appearance of a trait

Genotype- the specific _genetic_ make up of an organism

Homozygote- having two of the _same_ alleles for a particular trait (pure)

Heterozygote- having two _different_ alleles for a particular trait. (hybrid)

Now it is time to study the probability of offspring using Punnet squares

A punnet square is a square diagram that is used to predict a particular cross or breeding experiment. It helps us determine the probability of offspring having a particular genotype.



Genetics Basics


All cells in the body contain the same _DNA_.

  • Only some of these genes are turned _on_ and others are silent.

Chromosome pairs carry alleles for the same trait.

  • We all have two alleles for each gene- one from each _parent_
    • One on each member of the homologous pairof chromomsomes.
      • Homologous is a pair of chromosomes that carry alleles for the same _trait_.

Each chromosome has hundreds or thousands of genes.

  • Each gene codes for a particular _protein_ (1 gene=1 protein).

Humans have 46 chromosomes, or _23_ homologous pairs.

Elephants have 56, mosquitos have 6.

Sex chromosomes: in humans, females are _XX_ and males are _XY_

The Y chromosome is much _smaller_ than the X, so it is missing many genes. This means many genes on the X chromosome do not have a partner and it will be expressed in males.

ex. color blindness, baldness, hemophilia

Gene Expression: While genes determine our traits, the environment can affect the _expression_ of genes.

ex. fur color of Himalayan rabbit after exposure to cold air.

Genetic mutations in a cell can result in uncontrolled cell _division_. Cancer can be caused by either heredity or environmental factors like radiation, chemicals or virus.


Transcription and Translation

Crash Course on Transcription and Translation

Transcription and Translation youtube


  • The genetic instructions that is used as a ___________ code to make an organism.
    • If your genes and chromosomes are the instruction manuel for your body than the DNA would be the paper it is printed on.
  • The DNA stands for deoxyribonucleic acid and is found in the ___________ of a cell.
  • DNA is shaped like a double _______. Discovered by Watson and Crick.
  • The smallest unit of DNA is a nucleotide illustrated below. It has three parts: deoxyribose ___________, phosphates and a nitrogen base. yo
  • DNA is made up of 4 bases.
    • Adenine must pair with thymine, A=T or T=A
    • Guanine always pairs with cytosine, G=C or C=G
  • The two strands of DNA with its opposite nitrogen base pairs are called ____________ DNA and are connected by a hydrogen bond.


DNA replication

  • When the cell is ready to duplicate, the DNA divides in ______ and creates an exact copy of itself!
    • DNA genetic code is unzipped by an enzyme that breaks the weak ___________ bond between the bases.
    • The split side acts as a template (pattern) for complimentary _______ bases.
  • Once the DNA duplication is complete, the cell divides in half forming _______ identical cells.


  • Any change in the __________ of nucleotides in a DNA molecule can create a gene mutation.
  • If the mutation is in the sex cell it can be inherited, if it is in a __________ cell it can't.
  • Mutations may involve addition, ___________ or substitution of one nitrogen base for another.
  • Things that cause mutations include ____ light, radiation and toxic chemicals.
  • Chromosome mutations are caused when a person inherits too many or too few chromosomes.
    • Chromosome mutations affect many genes at once. Most are lethal.
    • Down's Syndrome: Non-lethal mutation caused by inheritance of an extra copy of chromosome 21.

DNA Candy Lab!


How do genes direct the production of PROTEINS?

Protein Synthesis: Your body functions depending on the order of the nitrogen bases in your genes.

A codon is a sequence of _______ bases in DNA.

Each codon represents a specific amino acid which is then strung together to make _________ which build and runs your body.


The steps to making proteins from DNA:

Transcription = the sequence of _____ bases are transfered from the nucleus to the ribosomes

  1. The DNA unzips when an enzyme breaks its weak __________ bonds.
  2. m-RNA called the messenger RNA reads (______________) the exposed DNA code by forming a complimentary strand of RNA from the nitrogen bases of the DNA. The DNA serves as the template of information to be read.

    Base pairs: A=T, C=G in DNA In the RNA, the Thymine is replaced by Uracil so A=U and C=G.

  3. The m-RNA travels from the nucleus to the ___________ in the cytoplasm for the next step, translation.


Translation = the _____ base sequence code in the mRNA transfers to the ___________ and specific amino acids are formed. A protein is synthesized.

  1. T-RNA (transfer RNA) travels in groups of three base pairs with a specific amino acid. The tRNA ____________ the mRNA code on the ribosome by reading its complementary opposite code from the corresponding 3 adjacent nitrogen bases on the mRNA (codon). This causes the animo acids to be positioned close together so they can join together.
    • There are _____ different amino acids in cells.
  2. The amino acids join together in different orders to create different ___________!

Proteins participate in every process of a cell. They control the function and structure of your body in every way imaginable!


Genetic Technology

a. Selective breeding produces animals and plants with ________ traits


  • breeding plants for food crops like corn or _______
  • animals for livestock such as cows or pigs
  • animals for pets such as ______, cats and birds

b. Genetic engineering or gene splicing inserts _______ of one organism into the genes of another.

  • ____________ _____________ are used to cut and copy the DNA segments.
    • ex. copying a gene into a plant that kills insects
  • Organism that receives the new gene will begin to make the protein coded for by that gene.
  • The new protein will be ____________ as the one produced by the original organism.
  • Bacteria are often used because they are simple and reproduce quickly.
    • ex. human _______ for diabetics and _________ hormones are grown from artifically using bacteria. Both of these are safe to use because they are identical to normal human hormones.

How does selective breeding compare with genetic engineering?

c. New technologies are making it easier to diagnose and treat genetic disease though we cannot yet cure them.

Gene Therapy- finding genes with mutations that cause disease can be fixed using hormones and enzymes from genetically engineered organisms.

Karyotype: a ____________ of an organism's chromosomes

Can determine if a person has __________ Syndrome- a chromosome disorder.

Gel Electrophoresis (or DNA fingerprinting) creates banded patterns based on a person's DNA base sequence.

First the DNA is broken down into segments then the sections of DNA are fed into an electrophoresis machine that organizes the segments based on _______.

The unique pattern of DNA is like a __________. The more closely related people are to each other the more similar their DNA fingerprinting.

This phemonemon is being used to solve ___________ cases that haven't been resolved for decades.

Gel electrophoresis is also useful in taxonomy and the genetic relationship between plants and animals (and early _______) are being rethought because of this new technology.

Gel Electrophoresis virtual lab

Using genes to trace human history