Transcript Unit 7 Genetics

About Mendel
and Genetics
PG 101
• “The Father of Genetics”
• Austrian Monk during
the 19th century
(1822-1884)
• Studied Pea plants
https://www.youtube.com/watch?v=GTiOETaZg4w
Mendel’s Laws
INDEPENDENT ASSORTMENT
 Allele pairs separate independently during the
formation of gametes. Traits are transmitted to the
offspring independently of one another


LAW OF SEGREGATION
 When
sex cells are made, then 2 “factors”
separate… 1 per gamete
Law of
Segregation
Mathematically
proven through
both generations
Why did Mendel succeed?
PG 101
•
•
•
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
Mendel’s
Experiments
(additional
notes)

Cross-pollinate 2
purebred plants
(P generation)

Resulting offspring
(F1 generation)
were all with dominant
trait
Results for
F1 generation
So where did the
“white” go?
Mendel allowed F1
plants to self-pollinate
to see if they really
had “lost” the white
Results for F2 generation
Approximately ¾
of F1 plants
produced seeds
that grew into
purple flower
plants
The remaining ¼
made white
flower plants
Other traits… same results
Mendel’s Hypotheses (bottom of pg 101)
•
Alternate versions of hereditary “factors” account
for variation in inherited traits
•
For each trait, an organism inherits 2 “factors” (one
from each parent)
Mendel’s Hypotheses

If the “factors” differ, one is dominant and
is recessive

The 2 “factors” for each trait separate during
gamete production (meiosis)
 Law
other
of segregation - when sex cells are made…
the 2 factors separate…1 per gamete
Important Terms (Top of pg 101)






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
Putting it all together…

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)
Putting it all together…

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
Punnett Square Basics

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 (make your square)
 List
genotypes & phenotypes
 List
types of alleles
Homozygous
Heterozygous
Punnett Square Basics

Crosses can be larger then the
simple 4 square- this is called a
dihybrid
 Some
AaBb
you may see as: AaBb x
 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 
RECAP

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)
Bell Ringer PG 102
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!!
Individual work- yes for a grade!

Punnett square exercises
 Do
the entire front page –get a check mark!
 We
will work on the back page at a latter time!
Recap of Mendel!





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?
Human Life
Cycle Events PG
102
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
How do we get to
haploid? PG 103
Meiosis is process to split
chromosome # in half, making
HAPLOID (n) CELLS (4)
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

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
•
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
Meiosis I: Reduce to Haploid PG 103
Draw each in their circle! Label & write the notes part under each
KEY
TERM: Synapsis Homologous chromosomes pair up
(prophase I) WRITE THIS DEFINITION DOWN!!
Meiosis I: Reduce to Haploid
KEY
TERM: Tetrad Group of 4 chromatids together during
synapsis WRITE THIS DEFINITION DOWN!!
Meiosis I: Reduce to Haploid
KEY
TERM: Chiasma (chiasmata) Crossing of non-sister chromatids
(see crossing over) WRITE THIS DEFINITION DOWN!!
Meiosis I: Reduce to Haploid
Metaphase I: tetrads line up
Anaphase I: homologous chromosomes separate
Meiosis II: Reduce DNA Amount
Draw each in their circle! Label & write the notes part under each
Works just like mitosis
Mitosis vs. Meiosis
Mitosis

cell division that produces
2 genetically identical
diploid daughter cells
ex. Somatic or body
cells

Meiosis

cell division that produces 4
genetically different haploid
daughter cells
ex. Gametes or sex
cells
This type of cell division
 This type of cell division
produces identical
produces gametes which
daughter cells which leads
are all different and unique.
to the development of
tissues and organs
Mitosis vs Meiosis
So Many Possibilities…
The
positioning of
tetrads in
metaphase
determines
variability of
resulting
gametes
So Many Possibilities… PG 104

If diploid # is 4 chromosomes
2

If diploid # is 6 chromosomes
2

x 2 = 4 possible gametes
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
So Many Possibilities…
Crossing over
during meiosis I,
nonsister chromatids of
homologous
chromosomes switch
places
Results in even more
genetic variability
Bell Ringer
 Page
104 comparing mitosis and meiosis
 Work
 No
on this as individual work!!
cell phones, no talking!
Meiosis related to Mendel’s Laws
Bottom of PG 103
 Law
of Independent Assortment:

IA: a certain trait, the gamete can have either allele
that is present in mom or dad

MII: the 2 alleles will randomly move to opposite poles
and 1 of those gametes produced will be fertilized
How do Mendel’s Laws Relate to
Meiosis? PG 110

Law of Independent Assortment
 Alleles
for different traits are inherited independently
or separately from each other.
 This
occurs in Metaphase I…
Meiosis related to Mendel’s Laws
 Law
of Segregation:
 LoS:
2 factors that govern a trait separate from
each other and go into different gametes
 MI:
Homologous chromosomes pair up and
separate form each other- just like Mendel
said, even though he didn't know about
meiosis
How do Mendel’s Laws Relate to
Meiosis? PG 103

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)
Group Activity
4
people per lab table
 Draw
what each phase looks like on the
paper
 Write
 Write
down what happens in each phase
the genetic material name (i.e.
chromatin, chromosome, tetrad, sister
chromatids)
Elbow partner work!

Page 105 Front page only - Stages of Meiosis
 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
 Haploid
 Write
pairs
cells
a brief statement of what is going on in
each phase under the phases
Punnett Squares PG102

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
Punnett Square Basics PG 101 – review

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
Genotype vs Phenotype PG 101
Cross 2 heterozygous tall, purple pea plants
with each other… PG 102
(T=tall, t=short, P=purple, p=white)
TtPp x TtPp
Cross 2 heterozygous tall, purple pea plants
with each other…
(T=tall, t=short, P=purple, p=white)
TP
TP
Tp
tP
tp
Tp
tP
tp
Cross 2 heterozygous tall, purple
pea plants with each other…
(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?
Cross 2 heterozygous tall, purple
pea plants with each other…
(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
Work For Today!

1st – Work on page 106 (individual work) Problem
Solving/Critical Thinking
 Raise

hand when finished to get your grade
2nd – Genetic problems (pg106), Individual work
 Raise
hand when finished to get your grade
Bell Ringer
 Finish
up your homework! You will have 10
minutes to complete it and turn it in!
(problem solving & genetic problems)
Testcross
To
determine
genotype of
a dominant
phenotype
organism
Mendel’s Other Law

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?
Law of Independent Assortment
Alleles are segregated (and inherited) separately
Quiz time!
Bell Ringer
 Individual
 Page
work!
105- cell division concept map! You
may listen to music while doing this
assignment…
Beyond Mendels’ Laws

Mendel’s laws still apply, but many traits due to
more complicated relationships between alleles
Simple Dominance PG 107

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 a
recessive trait
- Flower color in peas
Sample Punnett Problem
 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
Incomplete Dominance

Dominant partially covers
recessive; heterozygotes
will have an in-between
phenotype
Ex:
curly-wavy-straight hair
Sample Punnett Problem
 Cross
a person who has straight hair (hh)
with a person who has curly hair (HH)
 Write
down the genotypes and
phenotypes
Codominance

Both alleles dominant… both
expressed (no blending in
hetero’s)
Ex:
Human blood groups
Sickle Cell
Sample Problem
Type AB – IA IB
Sample Punnett Problem
 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
Multiple Alleles
Some traits have more than 2 possible alleles
Ex: Human blood has A, B, and O
Which other
pattern
does this
reflect?
codominance
Sample Punnett Squares

Practice doing your punnett squares at the bottom of
107, under Codominance and Multiple alleles

Blood types:
 O=
ii
 A= IA IA
 B= IB IB
or IA i
or IB I
 AB= IA IB
Summary of “Dominance”

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
Sex-linked Gene Inheritance PG
108
 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
traits
more likely to have recessive sex-linked
Sex-linkage – Sample Problem
XX - female
XY - male
Sex-linked Inheritance

Ex: male-pattern baldness;
hemophilia; color-blindness
Sample Punnett Problem PG 108

Cross a woman who is normal with a man who is colorblind

Cross a woman who is a carrier for hemophilia with a
normal man

Cross a color-blind woman with a normal man
Bell Ringer pg 114
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.
Polygenic Inheritance pg 108
Due to more than one
gene controlling a trait
Has an “additive effect”
Ex: human eye color, skin
color, hair color, height
The frequency of
phenotypes of traits is
controlled by PI follows a
bell shaped curve
Nature vs Nurture
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)
Mendelian Inheritance in Humans
 Not
easy to study
 Generations
 Not
enough offspring
 Cannot
 Must
too long
selectively breed
find alternative methods to figure out
human inheritance patterns
Pedigrees PG 108
Traces traits through a family
Used to determine genotypes & phenotypes
Used to predict probability of certain traits in future offspring
Pedigree Practice
Purple = has
disease
Phenylketonuria
(PKU)
Is this trait due to a dominant or recessive gene?
What are the genotypes for each individual?
Human Disorders
•
Cystic fibrosis (recessive)
– 1/2500 whites of European
descent
– 4% of whites are carriers
(heterozygous)
– Transport is abnormal…thick
mucus
Human Disorders

Phenylketonuria(PKU) (autosomal recessive)
 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
Human Disorders

Tay-Sachs Disease (recessive)
 1/3600
of Ashkenazic (European) Jews
 Dysfunctional
brain lipids
 Seizures,
enzyme that does not break down
blindness, motor & mental degeneration
Human Disorders
 Duchenne’s
Muscular Dystrophy
(sex-linked
recessive)
 Muscles
 Gene
atrophy
carried on X
chromosome
Recessives in the Population
 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…
Human Disorders
 Sickle-Cell
 1/400
Disease (codominance)
African Americans
 Substitution
of 1 amino acid in hemoglobin
 Abnormal
cell shape = less oxygen = many
other symptoms (pleitropic)
 Heterozygotes
symptoms
may/may not have
Codominance
made
Increases
– both hemoglobins
resistance to malaria
Human Disorders

Sickle-Cell Disease
Human Diseases
 Hemophilia
 X-Linked
recessive pattern (males are
more affected, females carriers)
 1/5000
 Blood
males inherited bleeding disorder
doesn’t clot properly, may cause
spontaneous bleeding, excessive
bruising, bleed excessively during
teething time, swollen bruised joints,
frequent falling
Human Dominant Disorders

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)
Bell Ringer PG 114
 In
chickens, rose comb (R) is dominant to
single comb (r). A homozygous rose combed
rooster is mated with a single combed hen. All
of the chicks in F1 generation were kept
together as a group for several years. They
were allowed to mate only within their group.
What is the expected phenotype of the F2
chicks? (use percentages).
Multi-factor Disorders PG 109
 Heart
disease
 Diabetes
 Cancer
 Alcoholism
 Schizophrenia
 Manic-depression
Trisomy 21 – Down Syndrome PG
117
Klinefelter’s Syndrome XXY (XXXXY)
Male but often sterile; often with feminine characteristics
XYY- Syndrome
Male; perhaps taller than normal
Other Aneuploids- pg 109
(write it down)!
 XXX
 female;
nondistinguishable from XX
 X0
 Turner’s
syndrome
 Female;
typically sterile
 0Y
 Not
viable; would not be born
PG 114
 Human
blood types are one example of
_________ ____ traits.
 _____________
_____________ is when there are
more than 1 gene controlling a trait and has
an “additive effect”.
 ________________
traces traits through a family,
determines phenotypes & genotypes, and
can predict probability of certain traits in
future offspring.
Quiz
For Question 1, R=red, r=white
 1. A) If a pure-bred red is crossed with a purebred 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?

Quiz

4. What is the name for this type of picture?

5. What gender is this person?

6. What defect does this person have?
Quiz
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?
Quiz

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?