Download Genetics - Killeen ISD

• “The Father of Genetics”
• Austrian Monk during
the 19th century
(1822-1884)
• Studied Pea plants
https://www.youtube.com/watch?v=GTiOETaZg4w
•
Peas were good choice.
– Readily available
– Easy to self-pollinate and cross-pollinate
•
Good experimental choices.
– Only chose “either-or” traits (purple OR white)
– Started with true-breeding (purebred) plants
– Followed for 3 generations (P, F1, F2)
•
Kept good quantitative data.
– Very large sample sizes


Cross-pollinate 2 purebred
plants
(P generation)
Resulting offspring
(F1 generation)
were all with dominant
trait
So where did the
“white” go?
Mendel allowed F1
plants to self-pollinate
to see if they really
had “lost” the white
Approximately ¾
of F1 plants
produced seeds
that grew into
purple flower
plants
The remaining ¼
made white
flower plants
•
Alternate versions of hereditary “factors” account
for variation in inherited traits
•
For each trait, an organism inherits 2 “factors”
(one from each parent)
 If
the “factors” differ, one is dominant and
other is recessive
 The
2 “factors” for each trait separate
during gamete production (meiosis)
• Law of segregation - when sex cells are made…
the 2 factors separate…1 per gamete
Mathematically
proven through
both generations

Allele pairs separate independently during the
formation of gametes. Traits are transmitted to the
offspring independently of one another






Genotype
• Combination of genes (ex: Tt)
Phenotype
• traits (ex: tall)
Homozygous
• Two of same allele (ex: TT or tt)
Heterozygous
• One of each allele (ex: Tt)
Dominant
• Gets expressed; use capital letter
Recessive
• Gets covered; use lowercase letter
 Where
are the “factors” that Mendel
discovered?
• On our chromosomes
 How
do these “factors” get passed on to
offspring?
• Through the gametes during fertilization
 What
do we call these “factors” now?
• Alleles (different forms of the same genes)
 Why
can’t we use mitosis to make
gametes?
• Mitosis makes diploid cells with two sets of
chromosomes (2n = diploid)
* gametes must be haploid (n) having only one
set of chromosomes
 What is the main goal of meiosis?
• Meiosis produces cells with only one set of
chromosomes which are haploid gametes
 Father
genotypes always goes on top
 Mother genotypes always goes on the
side
 Practice on your sheet! This is a
monohybrid
 1st square: AA x aa
 2nd square: PP x pp
• List genotypes & phenotypes
• List types of alleles
 Homozygous
 Heterozygous
 Crosses
can be larger then
the simple 4 square- this is
called a dihybrid
• Some you may see as: AaBb x
AaBb
• When you cross this, you should
“cross multiply” each
individual by itself…
• i.e. (Aa)(Bb) x (Aa)(Bb)
 This will now look like this 
 Mendel’s
Laws:
• Independent assortment- allele pairs separate
independently during the formation of gametes. Traits
are transmitted to the offspring independently of one
another
• Segregation- when sex cells are made, the 2 factors
separate… 1 per gamete
 Discoveries: factors
located on our
chromosomes, through gametes during
fertilization, now known as alleles (different
forms of the same gene)
Fertilization – fusing of sperm & egg
Zygote – fertilized egg (diploid) which develops into
an embryo
Meiosis – type of cell division that produces egg &
sperm; occurs in ovaries & testes
Homologous Chromosomes- Carry same type of genes
(though not necessarily the same version of that gene)
Draw a dihybrid punnett square: 5 across, 5 down:
making 25 squares… do not take up your whole page!
Use your lines on the sheet!!
Mendel’s Laws:
• Independent assortment- allele pairs separate
independently during the formation of gametes. Traits
are transmitted to the offspring independently of one
another
• Segregation- when sex cells are made, the 2 factors
separate… 1 per gamete
 Discoveries: factors located on our chromosomes, through
gametes during fertilization, now known as alleles
(different forms of the same gene)
 Why can’t we use mitosis to make gametes?
 Where are alleles located?
 How do alleles get passed down?

Fertilization – fusing
of sperm & egg
Zygote – fertilized
egg (diploid) which
develops into an
embryo
Meiosis – type of cell
division that produces
egg & sperm; occurs
in ovaries & testes
Meiosis is process to split
chromosome # in half
Result: 4 cells each with 1 of
each type of chromosome
Meiosis I – halves the
chromosome #
Meiosis II – reduces amount of
DNA by half
 Meiosis
starts out with 1 cell that is
DIPLOID (2n), (has both sets of
chromosomes), and ends with 4 cells that
are HAPLOID (n), (have only 1 set of
chromosomes).
•
Homologous chromosomes
– Carry same type of genes (though not necessarily
the same version of that gene)
– Ex: chromosome pair #1…both have gene for eye
color in same spot…one codes for blue, other for
brown
Draw each in their circle!
KEY
TERM: Synapsis Homologous chromosomes pair up
(prophase I) WRITE THIS DEFINITION DOWN!!
KEY
TERM: Tetrad Group of 4 chromatids together during
synapsis WRITE THIS DEFINITION DOWN!!
KEY
TERM: Chiasma (chiasmata) Crossing of non-sister chromatids
(see crossing over) WRITE THIS DEFINITION DOWN!!
Metaphase I: tetrads line up
Anaphase I: homologous chromosomes separate
Draw each in their circle!
Works just like mitosis
MITOSIS

cell division that produces
2 genetically identical
diploid daughter cells
MEIOSIS

ex. Somatic or body
cells

This type of cell division
produces identical
daughter cells which leads
to the development of
tissues and organs
cell division that produces
4 genetically different
haploid daughter cells
ex. Gametes or sex
cells

This type of cell division
produces gametes which
are all different and unique.
The
positioning of
tetrads in
metaphase
determines
variability of
resulting
gametes
 If
diploid # is 4 chromosomes
• 2 x 2 = 4 possible gametes
 If
diploid # is 6 chromosomes
• 2 x 2 x 2 = 8 possible gametes
 If
diploid # is 46 chromosomes (like us!)
• 2 x 2 x 2 x …x 2 = 8 million possible gametes
And possibility after fertilization…
8 million x 8 million = 64 trillion possible individuals
Crossing over
during meiosis I,
nonsister chromatids of
homologous
chromosomes switch
places
Results in even more
genetic variability
 Page
111 comparing mitosis and meiosis
• Work on this as individual work!!
• No cell phones, no talking!
 Law
of Independent Assortment:
• this law simply put means that for a certain
trait, the gamete can have either allele that is
present in the mother/father. So during
meiosis, the 2 alleles will randomly move to
opposite poles and 1 of those gametes
produced will be fertilized
 Law
of Segregation:
• Mendel's Law of Segregation says that the
two factors that govern a trait separate from
each other and go into different gametes. In
meiosis I the homologous chromosomes pair
up and separate from each other - just like
Mendel said, even though he didn't know
about meiosis.
4
people per lab table
 Draw what each phase looks like on the
paper
 Write down what happens in each phase
 Write the genetic material name (i.e.
chromatin, chromosome, tetrad, sister
chromatids)
 Page
112 Front page only
• Label each phase, and put the correct number of
order each phase goes in
• Label every structure within each phase
• Write down the definitions of the new terms
under the correct phase they belong to:
 Tetrad
 Synapsis & Chiasma (Crossing over)
 Homologous pairs
 Haploid cells
• Write a brief statement of what is going on in
each phase under the phases
 Purebred-
Homozygous dominant or recessive
 Hybrid- heterozygous traits
 Dominant- Capital letter-covers recessive trait
 Recessive- lower case letter- gets covered,
unless homozygous
 Genotype- the letters used to represent the
alleles
 Phenotype- physical appearance



Parent genotypes listed
on edges
Fill in spaces…big letter
listed first
List genotype (G) and
phenotype (P) including
fractions, percent’s, or
ratios
G: 4/4 Aa
P: 4/4 red
Use information to
make a punnett
square under basics
Include the genotype
and phenotype ratios
and what they mean
(T=tall, t=short, P=purple, p=white)
TtPp x TtPp
(T=tall, t=short, P=purple, p=white)
TP
TP
Tp
tP
tp
Tp
tP
tp
(T=tall, t=short, P=purple, p=white)
TP
Tp
tP
tp
TP
TTPP
TTPp
TtPP
TtPp
Tp
TTPp
TTpp
TtPp
Ttpp
tP
TtPP
TtPp
ttPP
ttPp
tp
TtPp
Ttpp
ttPp
ttpp
How many different phenotypes is that?
(T=tall, t=short, P=purple, p=white)
TP
Tp
tP
tp
TP
TTPP
TTPp
TtPP
TtPp
Tp
TTPp
TTpp
TtPp
Ttpp
tP
TtPP
TtPp
ttPP
ttPp
tp
TtPp
Ttpp
ttPp
ttpp
P: 9/16 tall, purple
3/16 tall, white
3/16 short, purple
1/16 short, white
 1st
– Work on page 114 (individual work)
• Raise hand when finished to get your grade
 2nd
– Bikini Bottoms 1 (pg119), you can
work individually or in groups
• Raise hand when finished to get your grade
To
determine
genotype of
a dominant
phenotype
organism
 What
happens if you test 2 traits at the
same time? (dihybrid cross)
 What
if you cross purebred yellow-round
with purebred green-wrinkled?
• Will traits “stick” to each other?
• Will traits “split up” from each other?
Alleles are segregated (and inherited) separately
 Law
of Independent Assortment
• Alleles for different traits are inherited
independently or separately from each other.
• This occurs in Metaphase I…
 Law
of Segregation
• Every individual has two alleles of each gene
and when gametes are produced, each gamete
receives one of these allele.
 Happens during Anaphase I the homologous
chromosomes separate (each chromatid has one
allele per gene)
 Mendel’s
laws still apply, but many traits
due to more complicated relationships
between alleles


A single dominant allele
inherited from one
parent is all that is
needed for a person to
show the dominant trait.
Ex:
-Earlobes attached
is recessive trait
- Flower color in
peas
 Cross
a person who is heterozygous for
dimples and a person who is recessive for
no dimples
 Use the letter D & d for your dominant and
recessive traits
 Write down how many will have and will not
have the trait

Dominant partially covers
recessive; heterozygotes will
have an in-between
phenotype
Ex:
curly-wavy-straight hair

Sample:
• G: 4/4 Hh
• P: 4/4 wavy
 Cross
a person who has straight hair (hh)
with a person who has curly hair (HH)
 Write
down the genotypes and phenotypes
 Both
alleles dominant…
both expressed (no
blending in hetero’s)
Ex:
Human blood grps
Sickle Cell
Sample Problem
Type AB – IAIB
• Cross a Sickle Cell Anemia (AA) with a
person who is normal (NN)
• Cross a heterozygous and a normal


Sample #1:
• G: 4/4 NA P: 4/4 s-c trait
Sample #2:
• G: 2/4 NN, 2/4 NA
• P: 2/4 normal, 2/4 s-c
Some traits have more than 2 possible alleles
Ex: Human blood has A, B, and O
Which other
pattern
does this
reflect?
codominance
 Practice
doing your punnett squares at
the bottom of 115, under Codominance
and Multiple alleles
 Blood
types:
• O= ii
• A= IA
• B=IB
 Ranges
from complete dominance to
incomplete dominance to codominance
 Reflects
expression of alleles, NOT one
allele “covering up” another
 Does
not reflect prevalence in population
• Recessive allele may be more common
If a black bunny (a dominant trait) is mated
with a white bunny. The baby bunny is
gray. What type of inheritance pattern does
this express? Prove this with using a
Punnett Square.
 For
Question 1,
T=tall, t=short
 1. Cross a plant that is homozygous
tall with a plant that is homozygous
short.
 What
are the Phenotypes?
 What are the Genotypes?
• In humans, sex-linked genes are the ones on the
X chromosome
• Fathers pass these on to their daughters only and
mothers pass these on to both sons & daughters
• Males more likely to have recessive sex-linked
traits
Sex-linkage – Sample Problem
XX - female
XY - male
 Ex: male-pattern
baldness; hemophilia;
color-blindness
Due to more than one
gene controlling a trait
Has an “additive
effect”
Ex: human eye color,
skin color, hair color,
height
•
Ranges from complete dominance to
incomplete dominance to codominance
•
Reflects expression of alleles, NOT one
allele “covering up” another
•
Does not reflect prevalence in population
– Recessive allele may be more common
Ex: Flower color differs based
on pH of soil
 Phenotype
depends on environment &
genes
 Ex: nutrition, physical activity, education,etc
 Norm of reaction = range of phenotype
governed by a gene
• Some traits have no range (blood type)
• Some traits have large range (esp. polygenic)
 Not
easy to study
• Generations too long
• Not enough offspring
• Cannot selectively breed
 Must
find alternative methods to figure
out human inheritance patterns
Traces traits through a family
Used to determine genotypes & phenotypes
Used to predict probability of certain traits in future offspring
Purple = has
disease
Phenylketonuria
(PKU)
Is this trait due to a dominant or recessive gene?
What are the genotypes for each individual?
•
Cystic fibrosis (recessive)
– 1/2500 whites of European descent
– 4% of whites are carriers (heterozygous)
– Cl- transport is abnormal…thick mucus
 Phenylketonuria(PKU)
recessive)
(autosomal
• rare condition in which a baby is born w/o the
ability to properly break down amino acid called
phenylalanine.
• products containing aspartame should be avoided
• Phenylalanine plays a role in the body's
production of melanin, the pigment responsible
for skin & hair color. Therefore, infants with the
condition often have lighter skin, hair, and eyes
 Tay-Sachs
Disease (recessive)
• 1/3600 of Ashkenazic (European) Jews
• Dysfunctional enzyme that does not break down
brain lipids
• Seizures, blindness, motor & mental degeneration
 Duchenne’s
Muscular Dystrophy
(sex-linked
recessive)
• Muscles atrophy
• Gene carried on X
chromosome
 Recessives
should be rare so chance
that 2 people will have exact same
recessives are low
 Chances
related
 Lethal
increase if the 2 people are
recessive traits much more
common than lethal dominant traits…
 Sickle-Cell
Disease (codominance)
• 1/400 African Americans
• Substitution of 1 amino acid in hemoglobin
• Abnormal cell shape = less oxygen = many other
symptoms (pleitropic)
• Heterozygotes may/may not have symptoms
 Codominance – both hemoglobins made
 Increases resistance to malaria
 Hemophilia
• X-Linked recessive pattern (males are more
affected, females carriers)
• 1/5000 males inherited bleeding disorder
• Blood doesn’t clot properly, may cause
spontaneous bleeding, excessive bruising, bleed
excessively during teething time, swollen bruised
joints, frequent falling
 Recessives
should be rare so chance that
2 people will have exact same recessives
are low
 Chances
increase if the 2 people are
related
 Lethal
recessive traits much more
common than lethal dominant traits…
 Sickle-Cell
Disease
 Achondroplasia
• Type of dwarfism
• 1/10,000 people
 Huntington’s
disease
• Degenerative disease of
nervous system
• starts ~35-45 yrs of age
(after reproductive age)
 Heart
disease
 Diabetes
 Cancer
 Alcoholism
 Schizophrenia
 Manic-depression
Male but often sterile; often with feminine characteristics
Male; perhaps taller than normal
 XXX
• female; nondistinguishable from XX
 X0
• Turner’s syndrome
• Female; typically sterile
 0Y
• Not viable; would not be born








For Question 1, R=red, r=white
1. A) If a pure-bred red is crossed with a pure-bred
white, what will the offspring be?
B) Which inheritance pattern is this?
For Questions 2, R=red, r=white
2. This plant shows incomplete dominance…
If a pure-bred red is crossed with a pure-bred
white, what will the offspring be?
For Question 3, R=red, W=white
3. A) If a pure-bred red is crossed with a pure-bred
white, what will the offspring be?
B) Which inheritance pattern is this?
 4.
What is the name for this type of
picture?
 5. What gender is this person?
 6. What defect does this person have?
Purple = has disease
White = does not have disease
7. Is this trait due to a dominant or recessive gene?
8. What is the likeliest genotype for Daniel?
 9.
Why can’t mitosis be used to make
new sperm or egg cells?
 10. In which phase of meiosis do
tetrads form?
 11. What is a tetrad?
 12. What does Mendel’s law of
independent assortment state?
 13. What does Mendel’s law of
segregation state?