Transcript Genetics - Montville.net

Do Now!!  True or False?
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1. Certain thoughts or experiences of a mother mark or
alter the hereditary makeup of an unborn child.
2. Color blindness is more common in males than in
females.
3. A person may transmit characteristics to offspring
which he/she does not show.
4. Certain inherited traits may be altered by the stars,
planets or moon early in development.
5. The total number of male births exceeds female
births each year.
 Allele: Version of a gene
 Dominant: shields recessive trait

(ex: B=brown eyes)
 Recessive: masked by dominant

(ex: b=blue eyes)
 Heterozygous: 2 different alleles

(ex: Bb)
 Homozygous: 2 of the same alleles

(ex: BB, bb)
 Genotype: organism’s set of genes

(ex: BB, Bb, bb)
 Phenotype: physical appearance

(ex: brown or blue eyes)
Chapter 10: Genetics!
Objectives
 To distinguish
between heredity and inheritance
 To describe Mendel’s experiments in heredity
 To compare heterozygous vs. homozygous and
dominant vs. recessive.
Say whaaat??
 Maria and Lucy are bi-racial twins… how is this
possible??
 Let’s brainstorm…
Do Now!! 
 Ariel and Prince Eric are curious to see
what their babies will look like! Eric is
heterozygous for black hair and Ariel has
the recessive trait of red hair. Both are
recessive for blue eyes. If they have 32
children, how many can we EXPECT to
have red hair and blue eyes?
Do Now!! 
 Mickey Mouse is heterozygous for round
ears and homozygous for black eyes. Minnie
Mouse is homozygous for floppy ears and
heterozygous for black eyes. Determine
phenotype ratios.
Genetics: the study of heredity by which
traits are passed from parents to offspring
Gregor Mendel
o The father of genetics!
o First to develop rules that
accurately predict patterns of
heredity
o Discovered how traits were
inherited in a population using
pea plants
The beginning of genetics…
 The passing of traits to the next generation
–
inheritance or heredity
 Mendel performed cross-pollination and self-
fertilization in pea plants
 Mendel followed various traits in the pea plants
he bred
7 Traits Mendel Studied
Pollination: transfer of pollen from anthers to
stigma in flowers
1) self pollination
occurs within the
same flower or same
plant
2) cross pollination
occurs between
different plants
Mendel’s Crosses with Pea Plants
P1
parental
generation
Pure tall
plants
X
Pure short
plants
Cross Pollination
F1
F2
first filial
generation
All Tall plants
Self Pollination
second filial
generation
787 tall plants, 277 short plants
3 to 1 ratio
Generations
 P Generation
 Parents
 Pure bred
 F1 Generation
 Hybrid – 2
different types
of genes for a
trait
 F2 Generation
 3:1 ratio
Mendel’s 3 Laws of Inheritance
Law of Dominance- Each trait is controlled by 2
1.
factors:
•
•
Dominant- what is expressed
Recessive- masked in presence of dominant
P1
F1
F2
Mendel’s 3 Laws of Inheritance (cont.)
2. Law of Segregation- Each allele separates into
different gametes (when does this happen??)
Ex. Ww – one W goes in one sperm and the other w
goes into another sperm
Ww
W
w
Mendel’s 3 Laws of Inheritance (cont.)
3. Law of Independent
Assortment- Gene pairs
(homologous) will
separate randomly into
gametes during meiosis
*Chromosomes line up
randomly at metaphase
plate
Do Now!!  (P. 6)
 What were the results of Mendel’s experiments
for F1 and F2 generations?
 What are his 3 laws?
 What is a gene?
Definitions
o Gene – segment of DNA on a chromosome
that codes for a particular protein
*genes
occur in
pairs
Allele – alternative form of a gene
T = tall
t = short
Recessive
Lowercase
letter (usually
hidden)
Dominant
capital
letter (shields
recessive trait)
G = green
pods
g = yellow
pods
More alleles!
Phenotype –
physical
characteristics
of an organism
(Ex: Blue eyes or Brown Eyes)
Genotype
-genetic makeup of an organism
(genes)
-alleles received from parents
(internal information
Ex: BB, Bb, bb)
Genotype vs. Phenotype
TT
genotype
Tall
phenotype
Homozygous – when both alleles
of a pair are the
same
homozygous
dominant
homozygous
recessive
TT
tt
Heterozygous – when both alleles
of a pair are not
the same
heterozygous
(tall)
Tt

If Jon Snow is heterozygous
for black hair… (H=Black,
h=blonde)
 1. What is Jon Snow’s genotype?
 2. What is Jon Snow’s
phenotype?

Beyonce is BB. (B= brown eyes,
b=blue eyes)
 1. What is her genotype?
 2. What is her phenotype?
 3. Is she heterozygous or
homozygous? Explain.
Genotypic vs. Phenotypic
Ratios
 Phenotype


Ratio of different physical traits
Ex) Brown eyes ¼ or 25%
 Genotype


Ratio:
Ratio:
Ratio of the different possible alleles
Ex) Tt = ¼ or 25%
Monohybrid Cross
 R=
Can roll your tongue
 r= Can’t roll your tongue
 Genotype
R
Ratio:
R
 Phenotype
Ratio:
r
r
Lets Try a Monohybrid together!
1) Daffy Duck is heterozygous for black feathers.
Daisy Duck is homozygous for yellow feathers. Set
up a punnett square and determine probabilities of
their potential offspring. (Both genotype and
phenotype ratios!)
2) B = Black
b = yellow
DO NOW!! 
Sleeping Beauty has freckles. Her prince
charming is heterozygous for no freckles.
What are the chances of her children having
freckles? Please show your work.
Test cross – an individual with
unknown genotype is crossed
with a homozygous recessive
individual
 used
to determine
the genotype of
any individual
whose
phenotype is
dominant
Lets Try a Test Cross
 Spongebob
squarepants doesn’t know
whether or not he is Homozygous Dominant
or Heterozygous for his yellow color. The
recessive trait is a white sponge. Let’s say
that we perform a “test cross” on spongebob
(spongebob + a white female sponge) and all
of the baby sponges are yellow. What would
spongebob’s genotype be?
What is a dihybrid Cross?
A
dihybrid cross allows us to predict possible
outcomes of offspring that will have 2 traits
simultaneously.

Ex: what would you get if you crossed a Brownhaired brown-eyed male with a blonde-haired
blue-eyed female? How many of the children
would have brown hair and brown eyes? Brown
hair and blue eyes? Blonde hair and brown
eyes? Blonde hair and blue eyes?
Setting up Dihybrid Crosses
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1. Labels!!
2. Determine parent genotypes
3. Determine gametes (alleles to be passed
down)
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The FOIL method
4. Set up punnet square
5. Determine outcome

Phenotype Ratio
Dihybrid Crosses

Looking at two different traits
 Ex. Hair color and eye color
B=brown eyes
 b=blue eyes

R=Brown hair
 r=blonde hair

Mother is heterozygous for both traits
 Father is heterozygous for eye color and
homozygous dominant for hair color

Example
More Practice
 Mickey Mouse is heterozygous for Round
ears and homozygous for Black eyes.
Minnie Mouse is homozygous for Floppy
ears and heterozygous for Black eyes.
Determine phenotype ratios. (B=black eyes,
b=brown eyes, R=round, r= floppy.)
Gene Linkage
 There are several
genes on a chromosome
 Gene Linkage:
 When two genes are close to each other on the
same chromosome
Gene Linkage (cont.)
o Linked genes on a chromosome results in an
exception to Mendel’s law of independent
assortment
o Linked genes usually do not segregate
independently
Drosophila melanogaster (Fruit Flies)
o First organism
with linked genes
o Linked genes
typically travel
together during
crossing over
Chromosome Map
 A map of genes on chromosomes
 Crossing over occurs more frequently
genes that are far apart
between
Polyploidy
o
o
Cells that contain more than 2 homologous sets of
chromosomes
Ex. A triploid organism (3n) - means that it has
three complete sets of chromosomes.
Strawberries are octoploid!!
Pedigree
Shows history
of a trait in a
family
Allows
researchers to
analyze traits
within a family
In a pedigree…
You can see how a genetic disorder runs in
a family.
Carriers are individuals who are
heterozygous for an inherited disorder but
do not show symptoms.
Carriers can pass the allele for the disorder
to their offspring
Symbols for Pedigree
Worksheet!!
Do Now!! 
 Fill in the genotypes for the following pedigree (shows
recessive trait)
 B=brown eyes
 b = blue eyes
Incomplete dominance
o
o
o
Heterozygous phenotype is intermediate
between two homozygous phenotypes:
o In between two extremes
Heterozygous phenotype appears blended.
Ex: Four O’clock flowers
+
 Both traits are dominant and expressed (no
blending)
 Ex: Roan Cows
 white hair (HW) is codominant with red hair (HR)
 cows with genotype (HRHW) have coats with a
mixture of red and white hairs (roan)
 Red + White = RED AND WHITE
Do Now!! 
 What is the difference between incomplete and
codominance?
 Cross a roan cow with a red cow.
Multiple alleles – 3 or more alleles that control a
trait
 Example: blood type!
 Possible alleles: IA, IB,
i
 Which genotypes are heterozygous? Homozygous?
GENOTYPES
RESULTING PHENOTYPES
IAIA
IAi
IBIB
IBi
IAIB
Type A
Type AB
ii
Type O
Type B
Antigens vs. Antibodies
 Antigen: substance foreign to the body that causes
an immune response:
 Can act as surface markers
 EX: type A antigens on surface of type A blood
cells
 Antibody: protein that reacts with specific antigen:
 EX: Type B blood contains anti-A antibodies
Which is the universal donor?
Universal acceptor?
Determine Blood Type
 Determine the possible offspring of the following
crosses
 1. AB and O
 2. Homozygous A and heterozygous B
 3. AB and AB
What do you see?
What do you see?
Sex Linked Traits
 Traits located on the sex chromosomes
(X or Y)
 X linked: gene is located on the X chromosomes
 Y linked: gene is located on the Y chromosome
 Ex: color-blindness
is X-linked!
*If X-linked, can males be carriers?
What are the chances of having a girl?
 How
would you go about solving it?
Sex-Linked Traits
A man who is color blind marries a
woman that is heterozygous for color
blindness. What is the chance of having
a color blind boy?
Polygenic Traits
o Polygenic traits arise from the interaction of
multiple pairs of genes.
Worksheet!!