Genes to Traits

Genes

• Gene- a piece of DNA that makes a certain protein – Example: Gene for tongue-rolling

• Allele- different forms of a gene– Example: One allele is for tongue-rolling, the other

allele is for not tongue-rolling

Gregor Mendel

• Austrian monk in 1800s.• Bred pea plants together for experiments.• Experiment:

X X

Where did the White Flower come from?

• Dominant allele- the allele that is shown when the two alleles are different or they are both the strong allele– Example: Purple color in Mendel’s peas

• Recessive allele- the allele that is only shown if you have two copies of it– Example: White color in Mendel’s peas

Take a guess!• What do you have? Which allele is dominant?

• Freckles?• Dimples?• Nearsightedness?• 5 fingers?• Dwarfism?• Roll tongue?• First toe longest?• Attached ear lobe?• Widow’s Peaks?• Cleft Chin?• Hitchhiker’s Thumb?

Take a guess!• What do you have? Which allele is dominant?

• Freckles?• Dimples?• Nearsightedness?• 5 fingers?• Dwarfism?• Roll tongue?• First toe longest?• Attached ear lobe?• Widow’s Peaks?• Cleft Chin?• Hitchhiker’s Thumb?• Thumb crossing, L or R?

Dominant Traits are NOT

necessarily more common nor are they “stronger”

or “better”!

If you have freckles…

• Having freckles is dominant (F)– No freckles is recessive (f)

• What could your two alleles be if you HAVE freckles?

• What if you don’t have freckles?

More Vocabulary

• Genotype- The two alleles a person has– Example: RR or Rr or rr

• Phenotype- The trait that you see– Example: Rolls tongue, can’t roll your tongue

Tongue-rolling is dominant (R) to not tongue-rolling (r).

• What are the three possible genotypes and their corresponding phenotypes?

Genotype possibilities Phenotype they show

Tongue-rolling is dominant (R) to not tongue-rolling (r).

• What are the three possible genotypes and their corresponding phenotypes?

Genotype possibilities Phenotype they show

RR Tongue-rolling

Rr Tongue-rolling

rr Not tongue-rolling

More Vocab

• Homozygous- two of the SAME alleles– Example:

• Heterozygous- two different alleles– Example:

What trait will you see?

6 fingers per hand (F) is dominant to 5 fingers (f)

• If a person is homozygous recessive, what trait will he show?

• If a person is heterozygous, what trait will he show?

• If a person is homozygous dominant, what trait will he show?

What trait will you see?Genotype (letters) Phenotype (trait shown)

Homozygous recessive

Heterozygous

Homozygous dominant

What if…

• A man who can roll his tongue (RR) has a baby with a woman who cannot roll her tongue (rr). What chance does the baby have of rolling his/her tongue?

What if…

• A person with freckles (Ff) has babies with his partner who also has freckles (Ff). What is the chance that their baby will have freckles?

The B allele is for brown eyes. The b allele is for blue eyes. B is dominant allele. b is the recessive allele.

• Geraldo has the genotype BB. What will his phenotype be?

• Vanessa has the genotype bb. What will her phenotype be?

• If Geraldo and Vanessa have a baby, what eye color do you think the baby will most likely have? Why?

• Do you think that Geraldo and Vanessa can possibly have a child with blue eyes? Why or why not?

Sex-linked Traits

• These traits are located on the sex chromosomes.

• Autosomal traits: located on chromosomes other than sex chromosomes (1-22)

Sex-linked traits

• Colorblindness is a recessive trait on the X-chromosome. If a heterozygous female (____) has kids with a normal male (____), what chance do their male/female kids have of being colorblind?

Statistics on X-linked diseases

• Colorblindness– 8% of males– 0.5% of females

• Hemophilia– 1/5,000 births in males– 1/20,000 births in females

• Duchenne muscular dystrophy– 1/3500 males– ~0 females?