Exploring Genetics

With Sai, Rayna, and Nataly


What are Genetics?

Genetics is the study of heredity and the variation of inherited characteristics.

Keywords to Know When Studying Genetics

Chromosome- Thread-like bearing genes that are found in the nucleus of a cell.

Sex Chromosome- one of the pair of chromosomes that determine the gender of an organism. There is a x-chromosome and a y-chromosome.

DNA- Deoxyribose Nucleic Acid-a molecule found in the nucleus of a cell which codes for an individual's genetic makeup

Gene- A length of DNA carrying a code for a certain feature

Sexual Reproduction- When the genetic material of a male and female combine to create offspring that differs genetically from both parents

Asexual Reproduction- When a single cell or set of cell reproduces on its own to create offspring that inherit all the parents genetic features

Genotype- The genetic makeup of an organism

Phenotype- The physical appearance of an organism

Allele- One of the alternative forms of a gene that governs a characteristic

Homozygous- an organism that has two alleles for a trait

Heterozygous- an organism that has two different alleles for a trait


There are two types of traits, dominant traits and recessive traits. Dominant traits show up more often, while recessive traits are more rare. If a individual with dominant traits breed with an individual with recessive traits it will result in hybrid offspring. Hybrid offspring is when an organism seems to have the dominant/recessive trait, but in reality it will have the other trait. For example the organism may seem to have a dominant trait, but really contains recessive traits.

How Punnett Squares Were Discovered

One of the simplest ways of predicting the probability of inheriting a specific trait is called a Punnett Square. Punnett squares are named for an English geneticist, Reginald Punnett. He discovered some basic principles of genetics, including trait linkage and trait determination. He worked with Feathers. Gregor Mendel did the famous pea plant expiriment. He found that tall pea plants are dominant over short pea plants. With Punnett Squares, you can predict the genotypes and phenotypes of the offspring of a homozygous tall pea plant and a homozygous short pea plant. Seeing this is what made Reginald Punnett invent the Punnett square. It is a simple way of seeing all of the possible combinations of genotypes that can occur in children, given the genotypes of their parents. It also shows us the odds of each of the offspring genotypes occurring.

Punnett Squares

Genotype and Phenotye

On way you can think of it is GENotype is for the genes as in it is the instructions for a trait and PHenotype is the physical characteristics that are determined by the genotype. For example non red hair(R) is dominant to red hair(r)

The genotypes would be RR, Rr, Rr, rr

These would be the phenotypes as in the physical features:

RR= non red hair

Rr= non red hair because dominant overpowers rescessive

Rr= non red hair because dominant overpowers rescessive

rr= red hair

Dominant an Rescessive

A dominant trait is a trait that appears more often in people
say that blond hair is recessive and brown is dominant.
And say that one parent has blond and the other has brown
The blond trait would be a lowercase r and the brown trait would be an uppercase R. Now say here's the DNA of each parent the brown haired parent had one parent with blond hair and one with brown so that person's dna is Rr. he other one had both blond so theirs is rr. Since dominant traits overpower recessive any dominant DNA wins. So if you have RR, rR, or Rr, then you get the dominant trait. You only get the recessive trait with an rr.

How to use a punnet square?

On the left side of the square you put the male parent traits, and on the top of the square the female parent traits. So if the male and female traits were R and r, the possible genotypes are RR, Rr, Rr, and rr


Homozygous is when an organism has two of the same alleles for a trait(RR,tt,FF,yy)

Heterozygous is when an organism has two different alleles for a trait(Rr,Tt,Ff,Yy)

Now can you help determine which is He or Ho?

Dd _____ ff _____ Tt _____ bb _____ BB _____ FF _____

TT _____ Bb _____ DD _____ Ff _____ tt _____ dd _____

Now can you help us determine the phenotypes for each genotype?

Brown hair is dominant to blond hair

BB ________________ Bb ________________ bb ________________

Brown eyes is dominant to blue eyes.

BB ________________ Bb ________________ bb ________________

If curly hair (C) is dominant to straight hair (c)

give us the genotypes for the specific phenotype.

Curly = _______________ Straight = _______________

Freckles (F) are dominant to no freckles (f).

(there is more than 1 answer for each question)

Freckles = _____________ No Freckles = _________________