Mendelian Genetics1. Pick up the handouts.

2. If you didn’t take or finish the exam, see me about making it

up.

Homework Worksheet due tomorrow.

(Heads up: There will be a bunch of practice worksheets this week, because we will be learning a skill that takes practice!)

Family Project due probably Monday March 9. Details forthcoming, I’m just letting you know so you can plan on putting aside some time late next week to work on it. It will require you to get some information from

family members: Parents, siblings, grandparents, aunts, uncles, cousins. It’s okay if you’re adopted or not in contact with someone anymore, but if you have concerns, please discuss them with me! :)

Review

With your partner, talk and look up definitions for these terms:ChromosomeGeneGameteTrait

ReviewChromosome: A very long, tightly-

wound strand of DNA. Contains thousands of genes.

Gene: A segment of a chromosome that codes for one protein.

Gamete: A haploid sex cell (sperm and egg).

Trait: The physical characteristic you get from the proteins made by one or more genes.

Genes and Traits This unit is going to be about how we

quantify traits, and how we can predict what versions of genes you, your relatives, and your offspring must have based upon limited information.

(Our next unit will then be taking this same skill and applying it to whole populations.)

Today, there will be several new vocab words. Prepare yourselves!

Genes and Traits First, a new word, because saying “version

of a gene” every time is powerfully tiresome.

Allele: A version of a gene. For instance, when we’re talking about the gene for hair color, different alleles may be for black hair, brown hair, blonde hair, and red hair. (Every gene has at least two alleles. Most of

them have more, but for the sake of simplicity, we’ll usually talk about them in terms of just two.)

With your partner: Pick any two human traits that could be coded for by a gene. What could be different alleles of that gene?

Genes and Traits

If a gene is a segment of a chromosome that codes for a kind of protein, and an allele is a version of a gene, what do you think an allele is in terms of DNA and chromosomes?

Genes and Traits

The gene is the region of the chromosome, the allele is the particular sequence of bases.

Genes and Traits

There are two other words that I introduced to you ages and ages ago, does anybody recall what they mean?

Genotype and Phenotype

Genes and Traits

Genotype: Your particular combination of alleles.Think “Genotype = Your type of

gene”

Phenotype: Your particular trait or combination of traits. Think “Phenotype = Your

physical type”

Genotypes and Phenotypes

Take out the handout w/ the three students’ chromosomes, and the chart.

These are the chromosome #3s for three people.Why do they each have two

chromosome #3s?What observations do you have

about them?

Genotypes and Phenotypes When we’re talking about

genotypes, scientists represent the alleles with letters. Usually, each gene will have one kind of

letter, like the letter R. Then, the different alleles are represented by the R being either upper-case or lower-case.

What trait does the gene represented by letters R code for? The other letters?

Genotypes and Phenotypes

Compare these students’ tongue-rolling genotypes. What do you notice?

Genotypes and Phenotypes Both of Joaquin’s chromosomes have a

tongue-rolling gene with exactly the same sequence of bases. So do both of Darnell’s, though his sequence of bases is different from Joaquin’s.

Jer, on the other hand, has a tongue-rolling gene with one allele on one chromosome, and a different allele on the other chromosome. His two copies of that gene has different sequences from each other.

What does this mean in terms of the proteins these students are making?

Genotypes and Phenotypes

We express genotypes as that individual’s two alleles written together, like this:

Joaquin has the genotype rrDarnell has the genotype RRJer has the genotype Rr

By convention, if the two alleles are different, we always write the capital letter first.

Genotypes and Phenotypes

Take a moment and fill out the middle column for all three students. Use the information from their chromosomes to correctly write their genotypes. Ignore the “yes and no”

business, we’ll get to that in a moment.

Genotypes Alleles aren’t just randomly given a

capital or lower-case letter. The capital letter means something.

Some alleles are dominant. If either of your chromosomes has that allele, you will have that trait. We use capital letters for dominant alleles.

Recessive alleles will only give you that trait if you don’t have the dominant allele anywhere. We use lower-case letters for recessive alleles.

Genotypes

Look at the chromosomes.What kind of alleles do the three

students have for tongue-rolling?Which, if any, of them will have

the dominant version of the tongue-rolling trait?

Genotypes

Who remembers what the roots “homo-” and “hetero-” mean in words?

Genotypes

Who remembers what the roots “homo-” and “hetero-” mean in words?

Latin/Greek RootsHomo: Same

Homosexuality, homogenous, homogenized, homeostasis

Hetero: DifferentHeterosexuality, heterogenous,

heterodox

GenotypesHeterozygous: A genotype with two

different alleles. Tt, Yy, Uu, Kk…Notice: hetero + zygote

Homozygous: A genotype with two of the same allele.Homozygous dominant: Both alleles

are dominant. TT, YY, UU, KK…Homozygous recessive: Both alleles

are recessive. tt, yy, uu, kk…

Genotypes

Look again at your chromosomes.Find every instance where someone is

homozygous dominant.

Genotypes

Look again at your chromosomes.Find every instance where someone is

homozygous recessive.

Genotypes

Look again at your chromosomes.Find every instance where someone is

heterozygous.

Genotypes and Phenotypes

Homozygous dominant and heterozygous people will always have the dominant version of that trait. Only homozygous recessive people will have the recessive version. Discuss with partner in just 15 seconds: why?

Phenotypes Let’s finish by analyzing

phenotypes for Joaquin, Darnell, and Jer. Where it says “Yes,” it means that

students has the listed version of the trait.

Where it says “No,” it means that student doesn’t have that version of the trait.

How can we figure out what is the dominant phenotype and what is the recessive phenotype?

Genotypes and Phenotypes

Your homework gives you practice with genotypes and phenotypes, heterozygous and homozygous, dominant and recessive. Some points to clarify:Why does everyone have two

alleles for every gene?

Genotypes and Phenotypes

Your homework gives you practice with genotypes and phenotypes, heterozygous and homozygous, dominant and recessive. Some points to clarify:Why does everyone have two

alleles for every gene? Because you have 2 chromosomes of every kind, and each chromosome carries one allele for a gene.

Genotypes and Phenotypes

Your homework gives you practice with genotypes and phenotypes, heterozygous and homozygous, dominant and recessive. Some points to clarify: For each gene, do you think you got

both alleles from Mom? Both alleles from Dad? One allele from each?

Genotypes and Phenotypes Your homework gives you practice with

genotypes and phenotypes, heterozygous and homozygous, dominant and recessive. Some points to clarify: For each gene, you received one allele

from Mom, and one allele from Dad. This is because you came from the zygote created from the fusion of their two haploid gametes, each containing one copy of the chromosome.

Can we tell just by looking at this piece of paper which chromosome Joaquin, Darnell, or Jer got from Mom and which he got from Dad?

Genotypes and Phenotypes Your homework gives you practice with

genotypes and phenotypes, heterozygous and homozygous, dominant and recessive. Some points to clarify: Dominant alleles don’t just come from one

kind of parent, they have an equal chance of coming from Mom or from Dad. The only way to tell which allele came from whom is by looking at their genotypes as well as yours.

Genotypes and Phenotypes

Use this time to work on your homework. Get REALLY GOOD at understanding allele vs gene, homozygous vs heterozygous, dominant vs recessive. If you are confused, ask! HELP ME HELP YOU. If you don’t get this now, you’re so going to be toast for the next two weeks. Sad face. :(