Mendel and Genetics

Transcription

Mendel and Genetics

Mendel and Genetics
Mr. Nagel
Meade High School
Warm Up
Meiosis Review
• Consider the following about Meiosis:
– How many daughter cells are created?
– How many chromosomes are in each daughter?
– What words could be used to describe the
daughter cells?
– What events in Meiosis lead to nearly infinite
possibilities in genetic variation?
IB Syllabus Statements
• 4.1.1
– State that eukaryote chromosomes are made of DNA and proteins.
• 4.1.2
– Define gene, allele and genome.
• 4.3.1
– Define genotype, phenotype, dominant allele, recessive allele, codominant
alleles, locus, homozygous, heterozygous, carrier and test cross.
• 4.3.2
– Determine the genotypes and phenotypes of the offspring of a monohybrid cross
using a Punnett grid.
• 10.1.4
– State Mendel’s law of independent assortment.
• 10.1.5
– Explain the relationship between Mendel’s law of independent assortment and
meiosis.
http://click4biology.info/c4b/4/gene4.1.htm
Question?
• What is inheritance?
Inheritance: Passing on traits by
transmitting them from parents to offspring
– How does it relate to you personally?
– Why does it matter to you and your future
family members?
Once Upon a Time…
• Gregor Mendel (1865) – Austrian Monk
– A PAIR of factors control the expression of
each inherited trait in an organism
• Sutton (1900)
– These factors are on chromosomes
• Modern Thought
– These factors are called GENES and are
segments of DNA
Give “Peas” A Chance
• Why use pea plants?
– What physical features could you monitor?
Factors Observed by Mendel
Mendel’s First Experiment
• What are the genotypes
for each seed?
• Which trait is
dominant?
• Which trait is
recessive?
• Is the parental
Spherical seed
homozygous or
heterozygous?
Down With the Lingo?
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Gene
Allele
Genome
Dominant
Recessive
Homozygous
Heterozygous
Self-Pollination
Cross-Pollination
Parental Generation
Filial Generation
Independent Assortment
Segregation
Genotype
Phenotype
Down With the Lingo?
• Gene – segment of DNA on a chromosome that controls a particular
trait
• Allele – equivalent of Mendel’s ‘factor’ - several alternative forms of a
gene {one from each parent}
• Genome – entire genetic makeup of an organism
• Dominant – dominates the other factor of the trait
• Recessive – masked in the presence of a dominant factor
• Homozygous – when both alleles of a pair are the same
• Heterozygous – when both alleles of a pair are NOT the same
• Self-Pollination – mating with self (same plant)
• Cross-Pollination – mating with a different plant
• Parental – original generation
• Filial – children (generation of offspring)
• Independent Assortment – there is no connection AT ALL between
any given inherited trait (color and height, etc.)
• Segregation – two factors (alleles) that a parent possess for a trait
are separated during egg/sperm formation
• Genotype – genetic makeup of an organism
• Phenotype – external appearance of an organism
Mendel and Meiosis
• Discuss with a partner:
– What does independent assortment mean
in terms of what is observed in Meiosis?
• Hint: Linkage is when two traits are known to
commonly exist together.
– What does segregation mean in terms of
what is observed in Meiosis?
• Hint: Disjunction is when the chromosomes
separate, sending one trait to each sex cell.
Punnett Grids
• Graphical
representation of
possible offspring
• Each parent occupies
one side
• Each parental gene
occupies one side of a
‘box’
• Based on ideas of
Probability
– In Meiosis, there is a
50/50 possibility that
each trait is passed
on. (Think coin flip)
Parental
Genes
Mom 1
Mom 2
Dad 1
Kid 1
Kid 2
Dad 2
Kid 3
Kid 4
Punnett Grids
Punnett Grids
• What are the two
parental genotypes?
parental phenotypes?
• What are the offspring’s
genotypes? Ratio?
phenotypes? Ratio?
Homozygous Dominant (YY)
x
Homozygous Recessive (yy)
parental genotypes?
genotypes? Ratio?
phenotypes? Ratio?
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
Homozygous Dominant (YY)
x
Heterozygous (Yy)
parental genotypes?
genotypes? Ratio?
phenotypes? Ratio?
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
Heterozygous (Yy)
x
Heterozygous (Yy)
parental genotypes?
genotypes? Ratio?
phenotypes? Ratio?
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
Warm Up
Intro to Genetics Review
• How are Mendel’s laws associated with our
understanding of Meiosis?
– Independent Assortment?
– Segregation?
• Consider the trait for silliness. S (silliness) is
dominant over s (serious). Create a Punnett
Grid of a mating of two parents that are silly
but produce a serious child.
•
4.3.2
–
•
10.2.1
–
•
State that a human female can be homozygous or heterozygous with respect to sex-linked genes.
4.3.10
–
•
Describe the inheritance of colour blindness and hemophilia as examples of sex linkage.
4.3.9
–
•
Define sex linkage.
4.3.8
–
•
State that some genes are present on the X chromosome and absent from the shorter Y chromosome in humans.
4.3.7
–
•
Explain how the sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans.
4.3.6
–
•
Describe ABO blood groups as an example of codominance and multiple alleles.
4.3.5
–
•
State that some genes have more than two alleles (multiple alleles).
4.3.4
–
•
Calculate and predict the genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal
genes.
4.3.3
–
•
Determine the genotypes and phenotypes of the offspring of a monohybrid cross using a Punnett grid.
Explain that female carriers are heterozygous for X-linked recessive alleles.
4.3.11
–
Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of
inheritance.
Dihybrid Cross
Parental
Genes
Dad 1
Dad 2
Dad 3
Dad 4
Mom 1
Kid 1
Kid 2
Kid 3
Kid 4
Mom 2
Kid 5
Kid 6
Kid 7
Kid 8
Mom 3
Kid 9
Kid 10
Kid 11
Kid 12
Mom 4
Kid 13
Kid 14
Kid 15
Kid 16
Homozygous Dominant (TTYY)
x
Homozygous Recessive (ttyy)
Parental
Genes
Dad 1
Dad 2
Dad 3
Dad 4
Mom 1
Kid 1
Kid 2
Kid 3
Kid 4
Mom 2
Kid 5
Kid 6
Kid 7
Kid 8
Mom 3
Kid 9
Kid 10
Kid 11
Kid 12
Mom 4
Kid 13
Kid 14
Kid 15
Kid 16
Heterozygous (TtYy)
x
Heterozygous (TtYy)
Parental
Genes
Dad 1
Dad 2
Dad 3
Dad 4
Mom 1
Kid 1
Kid 2
Kid 3
Kid 4
Mom 2
Kid 5
Kid 6
Kid 7
Kid 8
Mom 3
Kid 9
Kid 10
Kid 11
Kid 12
Mom 4
Kid 13
Kid 14
Kid 15
Kid 16
Codominant I
• Imagine a cat that
is black, and
another that is
white.
– What if all the
offspring were
gray?
– What if half the
offspring were gray
and half were
white?
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
Codominant II
• Consider two
parents, one with
type A blood and
one with type B.
– How could a child
of this mating have
type O blood?
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
Sex-Linked I
• Imagine a
colorblind mom
mating with a noncolorblind dad.
– What predictions
could you make
about the
offspring?
– What do you notice
about the boys?
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
Sex-Linked II
• Imagine a
hemophilic dad
mating with a nonhemophilic mom.
– What predictions
could you make
about the
offspring?
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
Testcross
• What if we know
the offspring
phenotypes and/or
genotypes, but
don’t know one of
the parents?
• Breed with a
homozygous
recessive!
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
•
Fun
With
Traits
Pick a few traits from the list
below:
– Dominant
•
•
•
•
•
•
•
•
Widow’s peak
Dimples
Bent little finger
Mid-digital hair
Dwarfism
L-over-R Thumb folding
Detached Earlobes
Tongue Rolling
– Recessive
• Hitch-hiker’s Thumb (90’)
• Chin cleft
– Sex-Linked
• Hemophilia
• Red-green Colorblindness
• Male Pattern Baldness
– Co-Dominant
• Blood type
• Flower Color (Red/White)
• Map out a Punnett
Square based on the
trait you selected, where
mom and dad are both
heterozygous for the
condition or trait.
Where are Genes Located?
• http://www.ncbi.nl
m.nih.gov/books/N
BK22266/
Assessment
• Imagine a parent
that is blue and
another that is red.
– Construct a Punnett
Square for each that
demonstrates this
mating if:
• ALL the offspring are
Blue.
• ALL the offspring are
Purple.
• HALF of the offspring
are Red. (2)
Parental
Genes
Dad 1
Dad 2
Mom 1
Kid 1
Kid 2
Mom 2
Kid 3
Kid 4
Warm Up
Genetics Review
• Consider a parent with type A blood.
– What type of parental mating would determine
the parent’s genotype? What is called?
– The parent is found to have the genotype Ao.
List the possible offspring with a parent with
genotype AB.
– What was the probability of having a child with
the type blood:
• AB
•A
Gizmo
• Observe outcomes predicted in Punnett
Grids for:
– Single Trait
– Two traits
– Aliens
– Codominance
Warm Up
Genetics Review
• Consider the following situation.
– Two parents, one possessing Nagel’s Disease
and one perfectly healthy, mate. Describe the
mode of inheritance and construct a Punnett
Grid if:
• None of the children are visibly affected. (2 possible)
• Half of the children are visibly affected.
• Only the male offspring have the disorder.
•
4.3.12
–
Deduce the genotypes and phenotypes of individuals in pedigree charts.
Pedigrees
http://www.sciencecases.org/hemo/hemo.asp
Pedigrees
• Let’s take a look at
Queen Victoria’s son
Leopold’s family. His
daughter, Alice of
Athlone, had one
hemophilic son (Rupert)
and two other children—
a boy and a girl—whose
status is unknown.
– What is the probability
that her other son was
hemophilic?
that her daughter was a
carrier? Hemophilic?
that both children were
normal?
Pedigrees
• Now for the Spanish
connection: Victoria’s youngest
child, Beatrice, gave birth to
one daughter, one normal son,
and two hemophilic sons.
– Looking at the pedigree of the
royal family, identify which of
Beatrice’s children received
the hemophilic gene; why can
you make this conclusion?
• Notice that Beatrice’s
daughter, Eugenie, married
King Alfonso XIII of Spain and
had six children, one of whom
was the father of Juan Carlos,
the current King of Spain.
– Would you predict that Juan
Carlos was normal, a carrier,
or a hemophilic?
– What is the probability that her
unnamed son was
hemophilic?
Pedigrees
• Lastly, the royal line of
Russia.
– What are the
probabilities that all four
of the girls were carriers
of the allele hemophilia?
– Supposing Alexis had
lived and married a
normal woman, what are
the chances that his
daughter would be a
hemophiliac?
– What are the chances
his daughters would be
carriers?
– What are the chances
that his sons would be
hemophiliacs?
Pedigree Practice
• Use the worksheets in small groups to
determine the genotypes and phenotypes
of the given subjects.
Warm Up
Chi Square Test for Dihybrid Cross
•
•
•
Chi Square Problem: An ear of corn has a total of 381 grains, including 216 Purple &
Smooth, 79 Purple & Shrunken, 65 Yellow & Smooth, and 21 Yellow & Shrunken.
Hypothesis: This ear of corn was produced by a dihybrid cross (PpSs x PpSs) involving
two pairs of heterozygous genes resulting in a theoretical (expected) ratio of 9:3:3:1.
Objective: Test the hypothesis using chi square and probability values. In order to test
your hypothesis you must fill in the columns in the following Table.
http://waynesword.palomar.edu/lmexer4.htm
Warm Up
Chi Square Test for Dihybrid Cross
•
•
•
•
Chi Square Problem: An ear of corn has a total of 381 grains, including 216 Purple &
Smooth, 79 Purple & Shrunken, 65 Yellow & Smooth, and 21 Yellow & Shrunken.
Hypothesis: This ear of corn was produced by a dihybrid cross (PpSs x PpSs) involving
two pairs of heterozygous genes resulting in a theoretical (expected) ratio of 9:3:3:1.
Objective: Test the hypothesis using chi square and probability values. In order to test
your hypothesis you must compare your value to that on the chart.
Degrees of Freedom = ???
http://waynesword.palomar.edu/lmexer4.htm
Probability Lab
• Using pennies, we will model births to
determine population statistics…
• Then we will use math to make similar
predictions…
• Lastly, we will use pedigrees to illustrate
why inbreeding allows recessive traits to
become expressed frequently!
Warm Up
Inheritance
• Given the parents AaBbCcDd and aabbccdd:
– What are the chances of a child aabbCcDd?
– What are the chances of a child AaBbCcDd?
– What are the chances of a child AABBCCDD?
– What are the chances of a child aaBbccDd?
•
•
10.3.1
– Define polygenic inheritance.
10.3.2
– Explain that polygenic inheritance can contribute to continuous variation
using two examples, one of which must be human skin colour.
Polygenes
• Polygenes have an additive effect… the
more dominants you have, the more
intense the feature:
– Fingerprint Ridge Count
– Eye Color
– Skin Color
Warm Up
Meiosis
• What event in Meiosis I accounts for the
shuffling
of
traits
amongst
non-sister
chromatids?
• Given a parent AaBb, what is the probability
that AB will be passed on?
– Which of Gregor Mendel’s laws dictates this?
– Could this rule ever be broken?
• 10.2.1
– Calculate and predict the genotypic and phenotypic ratio of
offspring of dihybrid crosses involving unlinked autosomal
genes.
• 10.2.3
– Explain how crossing over between non-sister chromatids of a
homologous pair in prophase I can result in an exchange of
alleles.
• 10.2.4
– Define linkage group.
• 10.2.5
– Explain an example of a cross between two linked genes.
• 10.2.6
– Identify which of the offspring are recombinants in a dihybrid
cross involving linked genes.
Heterozygous (TtYy)
x
Heterozygous (TtYy)
Parental
Genes
Dad 1
Dad 2
Dad 3
Dad 4
Mom 1
Kid 1
Kid 2
Kid 3
Kid 4
Mom 2
Kid 5
Kid 6
Kid 7
Kid 8
Mom 3
Kid 9
Kid 10
Kid 11
Kid 12
Mom 4
Kid 13
Kid 14
Kid 15
Kid 16
What would you do?
• William Bateson &
R.C. Punnett (early
1900s)
• Sweet pea plants
– PpLl x PpLl
•
•
•
•
P = purple eyes
p = red eyes
L = long pollen
l = round pollen
Phenotype
Expected
(9:3:3:1)
Observed
Purple, Long
3911
4831
Purple, Round
1303
390
Red, Long
1303
393
Red, Round
435
1338
TOTAL
6952
6952
Why does this happen?
• Genes located on the same chromosome exhibit this
behavior if they are close to each other, but…
• Genes on far ends of the same chromosome act ‘nearly
independent’… thus Gregor Mendel got really lucky!
A
B
A a
B b
a
b
Trait
Phenotype
Alleles
Chromosome
Seed form
round-wrinkled
R-r
7
Seed color
yellow-green
I-i
1
Pod color
green-yellow
Gp-gp
5
Pod texture
smooth-wrinkled
V-v
4
Flower color
purple-white
A-a
1
Flower location
axial-terminal
Fa-fa
4
Plant height
tall-dwarf
Le-le
4
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/Linkage.html
Read about it!
• http://biology.clc.uc.edu/courses/bio105/s
ex-link.htm
So what?
• Genes can be mapped based on their
distance apart
– Closer = less likely crossing over occurs
• A map unit is 1 cM, or centimorgan, and
represents a 1% cross over rate
– Shout out to Morgan’s work with flies and
discovering crossing over
Gene Maps In The Modern Age
• http://www.ncbi.nlm.nih.gov/books/NBK22
266/
Recombinants
• Recombinants
– Products of meiosis with allelic combinations
different from those of the haploid cells that
formed the meiotic diploid.
– RESULT OF CROSSING OVER!
• Re-combined DNA
– These appear as the lower than expected
values in the observed matings

Mendel and Genetics

Transcription

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