Download Heredity Review Sheet - Old Saybrook Public Schools

1/20/15
What is genetics?
DNA CRAPSHOOT
l 
The study of heredity
l 
l 
Mendel takes control
Mendel
l 
l 
He changed biology
FOREVER.
He used pea plants
l 
l 
l 
l 
Ordinary pea plants are
self pollinators; meaning
the offspring will be
identical to parent
This is called true
breeding
Mendel’s mixes
l 
He studied 7 traits
l 
l 
He “neutered” the flower
by cutting away the male
parts; this prevented self pollination
Then he dusted the
neutered flower with
pollen from another
flower
From generation to generation
l 
Trait—specific
characteristic, like height
or color
Hybrid— offspring of
crosses between
parents with different
traits (a combo)
Inheritance—receiving
characteristics from
parents
Gene—sequence of DNA
that codes for a protein,
(characteristic).
l 
The parent’s were
called the P (parental)
generation
Each successive
generation was labeled
the F generation, like
F1, F2, F3, etc.
P
F1
F2
1
1/20/15
Mendel’s Conclusion
l 
Inheritance is determined by “factors” passed
from one generation to the next
l 
More Conclusions
l 
Allele for short gene
One gene exists in two contrasting forms
l 
This factor is the gene!
For example, there are two genes for the height
trait:
l 
l 
l 
1. short gene
2. tall gene
The different forms are called alleles
Allele for tall gene
Something peculiar
Detective Mendel
When Mendel bred a white and purple flower
(P generation), the F1 generation was all
purple
l  So what happened to the white trait?
l 
l 
How did it appear?
How do the alleles separate?
l 
l 
Let’s assume:
l 
l 
1. Purple is the dominant allele
2. When the purple allele is present it masks the
white allele
Therefore, in order to see the white allele
expressed, the purple allele can not be
present
l  The alleles must be separated!
Mendel produced a F2
generation by self
pollinating the F1 to find
out if the “missing trait”
was truly gone.
l 
The separation,
(segregation) occurred
during sex cell
(gamete) formation.
A gamete will carry only
one type of allele
l 
2
1/20/15
Gene expression: which
version of the trait will we see?
When female and male gametes combine to
form offspring, that offspring will get one
allele from mom and one from dad
l  If just one gamete carries the dominant allele,
purple, than the offspring will be purple
l  In order to see the recessive allele, BOTH
gametes must carry the recessive allele
l 
l 
l 
l 
l 
l 
l 
Probability; The Punnett
Square
l 
l 
T
t
How to?
Dad’s Allelles
Likelihood that a
particular event will
occur
Past outcomes do not
affect future outcomes
Can use probability to
predict genetic crosses
Mom’s Allelles
l 
Possible
Allele
Combo
for
Offspring
Possible
Allele
Combo
for
Offspring
Possible
Allele
Combo
for
Offspring
Possible
Allele
Combo
for
Offspring
t
T t
t t
tall
short
T t
t t
tall
short
l 
l 
T
Heterozygous tall male
mated with a short
female
What’s the prediction?
T
t
Genotypes
Tt = 2/4 =1/2 = 50%
tt = 2/4 =1/2 = 50%
Phenotypes
Tall = 2/4 =1/2 = 50%
short = 2/4 =1/2 = 50%
1:1
l 
l 
Probability predicts
average outcome, not
precise numbers!
The largest the number
of offspring, the more
likely the actual number
will be close to the
predicted number
t
t
t
Tt
t
Average
1:1
t
Dominant alleles are written with a capital letter; Tall = T
Recessive alleles for the same trait are written in lower case of
the same letter for the dominant trait; short = t
Organisms with two of the same allele are called homozygous
l  TT
l  tt
Organisms with two different alleles are heterozygous
l  Tt
Genotype—genetic makeup, designated by letters
l  TT, tt, or Tt
Phenotype—physical characteristic, description, based on
genotype
l  TT, Tt = Tall
l  tt = short
t
tt
T
t
t
Tt
tt
t
Tt
tt
1:1 or 50:50
Total = 100
Tall = 53
Short = 47
3
1/20/15
Monohybrid
l 
l 
One pair of alleles
being studied; one trait
Example
l 
l 
l 
l 
l 
l 
Phenotype
¾ = tall
¼ = short
3:1
t
T
TT
Tt
t
Tt
tt
Heterozygous x
heterozygous
Dominant = tall = T
Recessive = short = t
Principle of Dominance
l 
l 
l 
Some alleles are
dominant and others
recessive
Organism that carry a
dominant allele will
always express that
form
Can only express the
recessive allele when
the dominant allele is
not present
Law of Independent
Assortment
l 
Mendel’s Principles
l 
l 
T
Trait = height
One allele = tall
One allele = short
The cross
l 
Genotype
¼ = TT
2/4 = Tt
¼ = tt
1:2:1
Alleles for different characteristics are
distributed to gametes independently
l 
Principle of Dominance
Principle of Segregation
Principle of Independent
Assortment
Law of Segregation
l 
l 
l 
A parent has two alleles
Offspring must have
two alleles
The alleles for a
characteristic must be
separated during the
formation of egg and
sperm so baby gets 1
allele from mom, 1 from
dad to make the set
complete
Pedigree
l 
Chart which shows the genetic relationships within a
family
Female
Male
Children
Marriage
Individual
II-6
Carrier
Does not express trait
Expresses the trait
*Note: Children go in order
of birth.
4
1/20/15
Pedigree of Queen Victoria and her
descendants tracing the gene for
Hemophilia
Advancing past simple
Mendelian Genetics
l 
l 
Incomplete dominance
Codominance
l  Multiple alleles
l  Polygenic traits
l  Sex-linked traits
l 
Incomplete dominance
l 
l 
Neither gene is dominant;
Both contribute to the
phenotype
When a genotype is
heterozygous, there is a
blending
Codominance
l 
l 
l 
The dominant does not
mask the recessive
Both alleles are
displayed in the
phenotype
Example:
B
l 
l 
B = Black
W = White
W
W
Multiple alleles
B
BW
BW
BW
BW
Multiple Alleles: Blood Types
A gene that has more than two allele
Does not mean an individual can have more
than two alleles!
l  Only means that more than two versions of
the gene (allele) exist in the population
l 
l 
5
1/20/15
Personality Traits By Blood
Type
Type O:
Compatibility by Blood Groups:
Type O's are outgoing, and very social. They are initiators, although they don't always
finish what they start.
and popular, they
love
to be AB
the center of attention and
A isCreative
most compatible
with
A and
appear very self confident.
Type A:
B is most compatible with B and AB
While outwardly calm, they have such high standards (perfectionists) that they tend to be
balls of nerves on the inside. Type A's are the most artistic of the blood groups. They can
AB is mosttrustworthy,
compatible
AB, B, A and O
be shy, are conscientious,
and with
sensitive.
Type B:
is most
compatible
with
andand
ABcontinue it until
Goal oriented andOstrong
minded,
type B's will
startO,
a task
completed, and completed well. Type B's are the individualists of the blood group
categories and find their own way in life.
Type AB:
Type AB's are the split personalities of the blood groups. They can be both outgoing and
shy, confident and timid. While responsible, too much responsibility will cause a
problem. They are trustworthy and like to help others.
Polygenic traits
l 
l 
Traits controlled by two
or more genes
Show a wide range of
phenotypes
Sex-linked traits
l 
Practice
l 
l 
l 
l 
Cross an AB dad with
an O Mom
Who can Dad donate
donate to? AB
Who can Mom donate
to? O, A, B, AB
What blood type do the
potential offspring
have? IAi = type A ; 50 %
IBi
IA
IB
i
IAi
IBi
i
IAi
IBi
= type B ; 50%
•  Can
two blood type B parents have a blood type O
child? Show the punnet square.
• Can a type O Dad and a Type B mom have a type A
child? Show your work.
AaBbCc X AaBbCc
(each square shows the number of dark skin alleles in the genotype)
Gametes
ABC
ABc
AbC
Abc
aBC
aBc
abC
abc
ABC
6
AABBCC
5
AABBCc
5
AABbCC
4
AABbCc
5
AaBBCC
4
AaBBCc
4
AaBbCC
3
AaBbCc
ABc
5
AABBCc
4
AABBcc
4
AABbCc
3
AABbcc
4
AaBBCc
3
AaBBcc
3
AaBbCc
2
AaBbcc
AbC
5
AABbCC
4
AABbCc
4
AAbbCC
3
AAbbCc
4
AaBbCC
3
AaBbCc
3
AabbCC
2
AabbCc
Abc
4
AABbCc
3
AABbcc
3
AAbbCc
2
AAbbcc
3
AaBbCc
2
AaBbcc
2
AabbCc
1
Aabbcc
aBC
5
AaBBCC
4
AaBBCc
4
AaBbCC
3
AaBbCc
4
aaBBCC
3
aaBBCc
3
aaBbCC
2
aaBbCc
aBc
4
AaBBCc
3
AaBBcc
3
AaBbCc
2
AaBbcc
3
aaBBCc
2
aaBBcc
2
aaBbCc
1
aaBbcc
abC
4
AaBbCC
3
AaBbCc
3
AabbCC
2
AabbCc
3
aaBbCC
2
aaBbCc
2
aabbCC
1
aabbCc
abc
3
AaBbCc
2
AaBbcc
2
AabbCc
1
Aabbcc
2
aaBbCc
1
aaBbcc
1
aabbCc
0
aabbcc
Red/Green Color Blindness
When the gene is found only on the X
chromosome and not the Y
Do you see the faint brown circle?
Do you see a 15 or a 17?
6
1/20/15
Sex-linked traits Practice
Y linked- Holandric traits
100% Daughters = Normal
100% Sons = Color Blind
XC
Xc
Xc
Cross a Normal vision father with
a color blind mother.
Normal
Y
Color
Blind
XCXc
XcY
Normal
Color
Blind
XCXc
XcY
Ear hair distribution… you jealous ladies?
Dihybrid
l 
l 
The cross
2 pairs of alleles are studies; 2 traits
Example
l 
l 
l 
l 
l 
l 
Color
Seed appearance
One allele = yellow
One allele = green
One allele = round
One allele = wrinkled
Color
Yellow = dominant = Y
Green = recessive = y
l  Round = dominant = R
l  Wrinkled = recessive = r
l  Heterozygous x heterozygous
l 
l 
YyRr x YyRr
Seed appearance
The Punnett Square
YR
YyRr x YyRr
?
?
?
YR
Yr
?
YR
?
yR
yR
?
yr
yr
?
Yr
?
YR
Yr
YYRR YYRr
yR
yr
YyRR
YyRr
Yr
YYRr
YYrr
YyRr
Yyrr
yR
YyRR
YyRr
yyRR
yyRr
yr
YyRr
Yyrr
yyRr
yyrr
7
1/20/15
Key
Dominant = yellow = Y
Recessive = green = y
Dominant = round = R
Recessive = wrinkled = r
AYS
ALWKE A
MA !!!!
Y
KE
YR
YR
yellow
round
yR
yr
yellow
round
yellow
round
yellow
round
YYRR
YYRr
YyRR
yellow
round
yellow
wrinkled
yellow
round
Yr YYRr
yellow
round
yR YyRR
yellow
round
yr YyRr
Thomas Hunt Morgan
Yr
YYrr
yellow
round
YyRr
yellow
wrinkled
Yyrr
YyRr
yellow
wrinkled
YyRr
Yyrr
green
round
green
round
yyRR
green
round
yyRr
yyRr
green
wrinkled
yyrr
l 
Genotype
1/16 = YYRR
2/16 = 1/8 = YYRr
2/16 = 1/8 = YyRR
4/16 = ¼ = YyRr
1/16 = YYrr
2/16 = 1/8 = Yyrr
1/16 = yyRR
2/16 = 1/8 = yyRr
1/16 = yyrr
l 
l 
Applied Mendel’s
principles to the fruit fly,
Drosophila
melanogaster
Found them applicable!
Discovered sex-linked
traits
Phenotype
9/16 = yellow round
3/16 = yellow wrinkled
3/16 = green round
1/16 = green wrinkled
1: 3 : 3 : 1
Nature vs Nurture
Chromosome number
Genes provide the plan
l  Environment also play role in the outcome
l 
l 
l 
l 
The body cells of an organism
has a unique number of
chromosomes
l  Human = 46
l  Donkey = 62
l  Potato = 48
l  Dog = 78
Half of those chromosomes
come from mom, the other
have come from dad
The pair are considered Mitosis: Identical daughter cells
homologous chromosomes
Meiosis: Cells are halved.
Meiosis
l 
l 
Note that almost all chromosomes come in homologous pairs.
l 
The parents carry two
complete sets of genes
When gametes are
formed, the set of two
must be separated so
that the offspring will only
receive one set from one
parent and one from
another (making a new
but complete set)
The number of
chromosomes is cut in
half by separating
homologous
chromosomes
8
1/20/15
Mitosis vs Meiosis:
The Visual
Diploid vs. Haploid
l 
l 
Meiosis:
To get from dip to hap
A cell that contains both
pairs of homologous
chromosomes (body cell) is
diploid
l  2N
l  Humans 2N =46
A cell that contains only 1 of
the homologous
chromosome (gamete) is
called haploid
l  N
l  Humans N = 23
Meiosis I
l 
l 
l 
Prophase I
l 
l 
l 
During interphase, each
chromosome duplicates
Each chromosome pairs
with its corresponding
homologous chromosome
l  THIS IS THE KEY TO
UNDERSTANDING
MEIOSIS!
The four chromatids are
called a tetrad
Prophase I: The Visual
Nuclear membrane breaks down
Each chromosome pairs with its corresponding
homologous chromosome (forms tetrad)
First opportunity for variation!!!!
l 
As homologous chromosomes pair up to form tetrads,
portions of chromatids are exchanged—crossing over
Tetrad; Homologous
Chromosomes
9
1/20/15
Metaphase I
Metaphase I: The visual
Chromosome line up in the middle
Spindle fibers attach to the chromosome
l  Second opportunity for genetic variation!!!!
l 
l 
l 
Random alignment of homologous chromosomes
will determine which new cell gets what—
independent assortment
Homologous
Chromosomes
Line Up
Anaphase I
l 
l 
l 
Telophase I & Cytokinesis
Fibers pull the
homologous
chromosomes apart
toward opposite end of
the cell
Tetrad now eliminated
Only sister chromatids
remain
l 
l 
Nuclear membrane form
The cell separates into two cells
l 
l 
Tetrad
(4 chromatids)
These new cells are different from the diploid cell
that entered into meiosis I
AND these new cells are different from each other
2
Chromatids
Telophase I & Cytokinesis:
The Visual
Meiosis II
l 
l 
Two new cells enter a second round of meiotic
division
Chromosome replication does not occur
What we started with
2 new cells different from the cell at start
AND different from each other
10
1/20/15
Telophase & Cytokinesis
l 
l 
Evidence of
Crossing over
l 
4 new cells produces
All four cells are haploid
Called gametes
1 2
l 
l 
l 
Prophase II: Meiosis I results in two unique daughter cells
Metaphase II: Chromosomes line up in middle
Anaphase II: Sister chromatids are separated and moved to
34
opposite end of cell
1
12
12 3
1
34
4
Meiosis vs Mitosis
Meiosis results in 4 genetically different
haploid cells
l  Mitosis results in 2 identical diploid cells
l 
2
2 3
1
1 all blue
1 red/blue
1 red/blue
2 all blue
1 blue/red/blue
5
6
3 blue
3 red
3
1 2
Before crossing over
3
1 red/blue/red
2 red
1 blue/red
1 all red
1 red/blue
1 2
3
Girl vs Boy
l 
In a girl, the cell
divisions are uneven
l 
l 
l 
Large = egg
3 small = polar bodies
All 4 haploids of boy
gametes (sperm) are
equal and functional
11