Download Genotypes and Phenotypes

Mendelian Genetics
1. 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:
 Chromosome
 Gene
 Gamete
 Trait
Review
 Chromosome: 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 lowercase.
 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 tonguerolling 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 rr
 Darnell has the genotype RR
 Jer 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 Roots
 Homo: Same
Homosexuality, homogenous,
homogenized, homeostasis
 Hetero: Different
Heterosexuality, heterogenous,
heterodox
Genotypes
 Heterozygous: 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. :(