What exactly are Chromosomes, DNA and Genes?Introduction to Genetics

Introduction to Genetics Video

Chromosome

•46 inside every cell•Chromosomes are in the cell in pairs. •One came from mom and one came from

dad.

Mom’s Chromosome

Dad’s Chromosome

DNA - deoxyribonucleic (say: dee-ox-see-ri-bo-nyoo-clay-ik) acid

•Long strands of genetic code•Makes up chromosomes in plants and

animalsDNA

Genes

•Tiny pieces of DNA that are instructions for specific traits

Traits

•Things that you inherit from your parents•Examples: Hair color, eye color and

having freckles or not•Through sexual reproduction you

inherited a set of traits

Traits•Pairs of letters are used to define genes in

your body•CAPTIAL LETTERS are used to represent

DOMINANT genes• lower case letters are used to represent

recessive genes•Dominant trait: If you receive even one of

these in the pair, you will get a specific trait.•Recessive trait: You have to have two of

these in the pair to get a specific trait

Genotypes

•The letter associated with the gene▫Example: W (dominant widow’s peak) w

(recessive no widow’s peak)

Phenotypes

•This is the "outward, physical manifestation“•The actual physical trait

▫Example: You have a widow’s peak.

Allele

•Allele: The single letter such as the a or the A.

Heterozygous – having two different alleles

•AA•bb

Homozygous – having the same alleles

•Aa•Bb

Purebred or Hybrid?

•Purebred: AA or aa•Hybrid: Aa

Practice:B – brown hair b – red hair

My genes: Bb

What color hair will I have?

Is Bb the phenotype or the genotype?

Are my genes heterozygous or homozygous?

Practice:A – attached earlobe a – unattached earlobe

My genes: aa

What will my earlobes do?

Is attached earlobe the phenotype or the genotype?

Is my genotype homozygous or heterozygous?

Practice:D – dimples d – no dimples

My genes: DD

Do I have dimples or not?

What is the genotype?

Is my genotype heterozygous or homozygous?

Quiz F – freckles f – no freckles

My genes: FF

Do I have freckles or not?

What is the phenotype?

What is the genotype?

Is my genotype heterozygous or homozygous?

Which parent carried the dominant gene?

Mom has blue eyes (bb)

Dad has brown eyes (BB or Bb)

Daughter has

blue eyes (bb)

Therefore, Dad must have the Bb genotype, because he must have given her the “b” allele. His “b” allele is masked by his “B”/dominant allele.

What is a PUNNETT SQUARE?•A tool to predict the probability of

certain traits in offspring that shows the different ways alleles can combine

•A way to show phenotype & genotype•A chart that shows all the possible combinations of alleles that can result when genes are crossed

Punnett Squares Video

Using a PUNNETT SQUARE

To set up a Punnett square, draw a large square, and then divide it into 4 equal sections (also squares). It should look something like this:

Using a PUNNETT SQUARE•Now you need two parents to mate, ones

with a known genotype

• For example, Brown hair (genotype BB) and blonde hair (genotype Bb). BB x Bb

• In this scenario, the Mom has brown hair. The dad blonde hair.

Using a PUNNETT SQUARE

Place one of the parents on top, and one on the left. You should get a something similar to this:

B b

B

B

Using a PUNNETT SQUARE

•The two-letter combinations are the possible genotypes of offspring

•They are: BB, Bb, BB, and Bb genotypes

•From this it is possible to determine the probability (chance) that a baby will have a brown phenotype (2/4 or 50%) or a blonde phenotype (2/4 or 50%)

Does it work with animals and plants?

•Yes, all of this works the same way in determining the outcome of combining animals and plants.

•How can we relate this to selective breeding?

•How can we relate this to genetic engineering?