Download Genetic Inheritance

Paper Bag Project
1.
Make Paper Bag according to guidelines for traits
2.
Fill in phenotype column of table
3.
Fill in genotype column of table
4.
Fill in alleles on chromosomes
5.
Act out meiosis to create gametes
6.
Mate animals (fertilization)
7.
Use Punnet squares to predict traits of baby
8.
Give birth and decorate baby to match inherited genotype
Paper Bag Project
• Genetic Traits – inherited characteristics of a living organism
(examples: hair color, number of limbs, ability to make insulin)
• Phenotype – the observable version of a trait expressed
(examples: brown hair, four limbs, diabetic)
• Allele – the genetic sequence that codes for each distinct possible phenotype for a trait
(examples: the alleles for hair color are brown, black, red, and blonde; the alleles for
insulin would be all of the different variations of insulin that exist in the human
genome, some of which have mutations that make it not work as well or at all)
• Genotype – in humans, the pair of alleles that determine each trait, because humans
get one set of genes from mom and one set from dad – with the exception of the genes
on the X and Y chromosomes (example: if you have black hair, your genotype may
include the black allele from one parent and a brown allele from the other parent)
• Dominant Allele – the allele that is expressed as the phenotype of an organism when
paired with a “competing” allele (in the example above, black is dominant over brown)
• Recessive Allele – the allele that is NOT expressed as the phenotype of an organism
when paired with a “competing” allele that is dominant over it (in the example above,
brown is recessive to black)
Inheritance
Gregor Mendel – “Father of Genetics”
• Did experiments with pea plants in mid-late 1800’s to show
basic patterns of inheritance
• Genetic Traits – inherited characteristics of a living organism
• Allele – the genetic sequence that codes for each distinct possible phenotype for a trait
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Seed Shape
(round or wrinkled)
Seed Color
(yellow or green)
Seed Coat color (gray or white)
Pod Shape
(smooth or constricted)
Pod Color
(green or yellow)
Flower Position (axial or terminal)
Plant Height
(tall
or short)
Traits
Alleles (genes)
Inheritance
Gregor Mendel – “Father of Genetics”
• Phenotype – the observable version of a trait expressed
• Found that when two plants with different alleles are crossed, the
offspring look like one of the parents, rather than a blending of both
parents  Principle of Dominance: Some alleles are dominant and
others are recessive
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
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Seed Shape
(round or wrinkled)
Seed Color
(yellow or green)
Seed Coat color (gray or white)
Pod Shape
(smooth or constricted)
Pod Color
(green or yellow)
Flower Position (axial or terminal)
Plant Height
(tall
or short)
Traits
Alleles (genes)
Dominant
Alleles
Recessive
Alleles
round
yellow
gray
smooth
green
axial
tall
Phenotypes
wrinkled
green
white
constricted
yellow
terminal
short
Homozygous
recessive
Homozygous dominant
genotypes
or Heterozygous
Inheritance
Gregor Mendel – “Father of Genetics”
• Phenotype - The observable physical characteristic of a trait
• Genotype - The genetic combination of alleles for a trait
• Letters are used to represent the alleles (usually correspond to the dominant
phenotype – Example: “P” for purple if purple flowers are dominant over white)
Upper Case Letters = Dominant Allele
Lower Case Letters = Recessive Allele
traits
alleles
genotypes = phenotypes
homozygous
dominant
 Seed Shape:
 Seed Color:
 Pod Shape:
 Pod Color:
 Plant Height
round (R) or wrinkled (r)
yellow (Y) or green (y)
smooth (S) or constricted (s)
green (G) or yellow (g)
tall (T) or short (t)
RR = round
YY =
SS =
GG =
TT =
homozygous
recessive
rr = wrinkled
yy =
ss =
gg =
tt =
heterozygous
Rr = round
Yy =
Ss =
Gg =
Tt =
Practice Questions
1.
Which of the following are genotypes and which are phenotypes:
Brown hair
Heterozygous
Bb
Webbed Fingers
Homozygous recessive
Down Syndrome
For each statement below, underline any genotypes and put a box around
any phenotypes.
2. Robert and his wife are both carriers for Tay Sach’s disease.
3. Maria inherited an allele for brown hair from her mother and an allele
for black
hair from her father; and now she has black hair.
4. My mother has brown hair and I had blonde hair until I was ten.
5. Ron’s parents both have brown eyes, but they are both heterozygous
for eye
color. As a result, Ron has blue eyes.
6. If you have a widow’s peak, you are homozygous recessive for this
trait.
Practice Questions
Inheritance
Paper Bag Project
• Which of the following are traits
and which are alleles?
 Gender
 Eye Shape
 Eye Color
 Hair Color
male (XY) or female (XX)
oval (E) or slit (e)
brown (B), blue (b),
green (g), yellow (y)
black (H), brown (h),
 Eyelashes
yellow(y)
present (L), not present (l)
 Tail (Y-linked)
 Ear Shape
 Nose Shape
present (T), not present (t)
round (R), pointed (r)
triangle (N), circle (n)
(X-linked)
Traits
Alleles
Most
Dominant
Most
Recessive
Genotype
EE
Ee
Bg
bg
nn
hy
lY
LY
Xt
Phenotype
Meiosis
Cell division that results in production of gametes (sex cells)
• Eggs (females) – occurs in ovaries
• Sperm (males) – occurs in testes (singular = testis)
https://www.youtube.com/watch?v=_5OvgQW6FG4
Fertilization (enables mixing of genes from two
different individuals which helps create genetic variation
among individuals)
Meiosis
Meiosis is similar to mitosis, but results in the formation of gametes: four
cells each having only one set of chromosomes (a total of 23 chromosomes)
• Recall that “normal” cells are diploid, they have two sets of 23 chromosomes (one set
from mom, one set from dad) for a total of 46 chromosomes
• Gametes are haploid, they have one copy of each chromosome – either from mom or
dad (the other copy ended up in the sister gamete)
These cells have two
sets of 3 chromosomes,
humans have 2 sets of
23 chromosomes
These cells have one
set of 3 chromosomes,
human gametes have
one set of 23
chromosomes
Meiosis
• Homologous chromatids or homologous chromosomes have the same
genes but are not identical
• Sister chromatids are exact copies of one another
homologous chromatids
homologous chromosomes
sister chromatids
Review of Mitosis
Interphase
DNA Replication
1. Prophase
• Chromatin condenses to
form chromosomes
• Mitotic spindle begins to form
2. Metaphase
• Mitotic spindle attaches to
chromatid pairs and pulls them
into alignment at center of cell
3. Anaphase
• Centromeres replicate
• Mitotic spindle pulls chromatids
apart to opposite sides of cell
4. Telophase
• The cell membrane invaginates and
pinches off between the two daughter cells
Meiosis
Similar to mitosis, but results in four cells each having only one copy of
each chromosome (a total of 23 chromosomes)
• Recall that “normal” cells have 23 sets of chromosomes
(one from mom, one from dad) for a total of 46 chromosomes
1. DNA replication during interphase
2. DNA condenses to form 92 chromatids
3. Homologous chromatids from mom and dad
pair up and crossing over occurs
4. 46 homologous chromatid pairs line up at
center of cell
5. Homologous chromatid pairs are separated
into two halves of cell (random assortment)
6. Cytokinesis divides cell into two cells
(each daughter cell gets 23 pairs, 46
chromatids total, each chromatid pair is
either derived from mom or dad)
http://www.johnkyrk.com/meiosis.html
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
http://www.cellsalive.com/meiosis.htm
Meiosis
Similar to mitosis, but results in four cells each having only one copy of
each chromosome (a total of 23 chromosomes)
• Recall that “normal” cells have 23 sets of chromosomes
(one from mom, one from dad) for a total of 46 chromosomes
http://www.johnkyrk.com/meiosis.html
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
http://www.cellsalive.com/meiosis.htm
1. DNA replication during interphase
2. DNA condenses to form 92 chromatids
3. Homologous chromatids from mom and dad
pair up and crossing over occurs
4. 46 homologous chromatid pairs line up at
center of cell
5. Homologous chromatid pairs are separated
into two halves of cell (random assortment)
6. Cytokinesis divides cell into two cells
(each daughter cell gets 23 pairs, 46
chromatids total, each chromatid pair is
either derived from mom or dad)
7. 23 chromatid pairs line up at center of each
daughter cell (46 chromatids total)
8. Centromeres divide and 46 chromosomes are
separated into two halves of cell
9. Cytokinesis divides two cells into four cells
(each gamete gets 23 chromosomes)
Mitosis vs. Meiosis
• Mitosis results in two daughter cells that are both genetically identical to the
original cell
• Meiosis results in four gamete cells that are each genetically identical due to
crossing over and random assortment
46 chromosomes
46 chromosomes
(one set of 23 from
each parent)
92 chromatids
92 chromatids
(crossing over occurs between
homologous chromosomes)
46 chromosomes
46 chromosomes
(random assortment divides
mom and dad chromosomes)
23 chromosomes
Diploid cells
(identical to original cell)
(haploid cells = gametes)
Meiosis
Genetic variation comes from
• Mutations
• Crossing Over
• Random Assortment
Results in four genetically
unique haploid cells (gametes)
Predicting Inheritance
Gregor Mendel – “Father of Genetics”
• Found that alleles show up in predictable patterns and that
some alleles show up more often than others
• Punnett Square – tool used to predict probability of a
particular phenotype
Phenotype: White
Genotype: pp
(homozygous
recessive)
Phenotype: Purple
Genotype: PP
(homozygous
dominant)
Mr. Anderson: Mendelian Genetics
https://www.youtube.com/watch?v=N
WqgZUnJdAY
Learn Biology: How to Draw a Punnett Square:
https://www.youtube.com/watch?v=prkHKjfUmMs
Predicting Inheritance
• Homozygous (Pure-Breeds) - both alleles are the same
Pure-Breed Dominant Crosses result in:
100% chance dominant phenotype
Pure-Breed Recessive Crosses
result in:
100% chance recessive phenotype
Predicting Inheritance
• Heterozygous (Hybrids) - both alleles are different
• Carriers – heterozygous for a recessive trait
Both parents have
the dominant
phenotype but are
carriers for the
recessive allele
Hybrid Crosses result in:
75% chance dominant phenotype
25% chance recessive phenotype
Inheritance
Gregor Mendel – “Father of Genetics”
• Found that alleles can be tracked through multiple
generations and probabilities determined
First Generation:
100% chance dominant phenotype
Second Generation:
75% chance dominant phenotype
Third Generation:
63% chance dominant phenotype
100% chance
75% chance
75% chance
0% chance
Summary of Mendel’s Principles
Gregor Mendel’s work forms the basis of modern genetics:
• Genes are passed from parent to offspring
• Some forms of genes (alleles) are dominant while others are recessive
• Genes randomly segregate (random assortment) when gametes are formed
= Law of Segregation
• The alleles for different genes usually segregate independently of one another
= Law of Independent Assortment
Linked genes (genes that occur very close
to one another on a chromosome) are the
exception (for example, freckles and the
gene for red hair are close together on the
same chromosome)
Solving Punnett Squares
If a round pea plant (AA) is crossed
with a wrinkled pea plant (aa), what
percent of the offspring will be:
• Round?
• Wrinkled?
If two heterozygous round pea
plants are crossed, what percent of
the offspring will be:
• Round?
• Wrinkled?
If a heterozygous round pea plant is crossed
with a homozygous wrinkled pea plant, what
percent of the offspring will be:
• Round?
• Wrinkled?
Solving Punnett Squares
Predicting phenotype gets more
complicated when you look at more
than one trait at a time
Parents
Depending on how the
chromosomes independently
assort determines the
genotype, and thus
phenotype, of the resulting
progeny (offspring)
Offspring
Honors
Solving Punnett Squares
If a round, yellow pea plant (AABB)
is crossed with a wrinkled, green
pea plant (aabb), what percent of
the offspring will be:
• Round and yellow?
• Round and green?
• Wrinkled and yellow?
• Wrinkled and green?
Honors
Other Types of Inheritance
• Complete Dominance (what we have been studying):
 Homozygous dominant genotype  dominant phenotype
 Heterozygous genotype  dominant phenotype
 Homozygous recessive genotype  recessive phenotype
Other Types of Inheritance
• Complete Dominance
• Codominance
 Homozygous genotype  one phenotype
 Heterozygous genotype  both phenotypes
R
R
W
RW
RW
W
RW
RW
R1
R1
R2
R1R2
R1R2
R2
R1R2
R1R2
Other Types of Inheritance
• Complete Dominance
• Codominance
 Homozygous genotype  one phenotype
 Heterozygous genotype  both phenotypes
Other Types of Inheritance
• Complete Dominance
• Codominance
• Incomplete Dominance
 Homozygous genotype  one phenotype
 Heterozygous genotype  new phenotype
(usually an intermediary between both)
C = curly
C
C
S
CS
CS
S
CS
CS
CS = wavy
S = straight
Other Types of Inheritance
• Complete Dominance
• Codominance
• Incomplete Dominance
 Homozygous genotype  one phenotype
 Heterozygous genotype  new phenotype
(usually an intermediary between both)
Pink = new genotype
Other Types of Inheritance
Hemophilia
• Complete Dominance
• Codominance
• Incomplete Dominance
• Sex-Linked
 X-linked: gene lies on X
chromosome (males only
have one copy of the gene)
 Y-linked: gene lies on Y
chromosome (only males
have the gene)
 Contributes to slightly
younger mortality rate in
males – males are more
likely to have a genetic
disease
Phenotypic Expression Varies
• Complete Dominance
• Codominance
• Incomplete Dominance
• Sex-Linked
 X-linked: gene lies on X
chromosome (males only
have one copy of the gene)
 Y-linked: gene lies on Y
chromosome (only males
have the gene)
 Contributes to slightly
younger mortality rate in
males – males are more
likely to have a genetic
disease
Hemophilia
Phenotypic Expression Varies
• Complete Dominance
• Codominance
• Incomplete Dominance
• Sex-Linked
 X-inactivation disables one
x-chromosome in each cell
(females and males each
only use one x-chromosome)
 can lead to unique
phenotypes in females
Phenotypic Expression Varies
• Polygenic Traits
https://www.youtube.com/watch?v=Zf2hnFhyJFI
 Controlled by more than
one gene
 Most common type of
expression
There are three known gene pairs that control eye
color. The bey 2 gene on chromosome 15 contains a
brown and blue allele, the bey 1 gene on chromosome 15
contains a brown gene, and the gey gene on chromosome
19 contains a green allele and a blue allele. All four
alleles must be blue to produce a blue eyed person.
There are two layers to the iris, the anterior and the external, or front and back layers. To produce blue eyes,
there is no pigment found in the front layer. The brown pigment melanin is deposited in the back layer only. It
appears blue because of reflection and diffraction of light. In green eyes, a small amount of melanin is
deposited in the front layer of the iris along with the melanin found in the back layer. The additional pigment to
the amount needed for blue eyes, causes the eye to appear green. To produce gray eyes, the dark pigment is
distributed in the front layer of the iris and over the blue background it appears gray. In brown eyes there is so
much pigment in the front layer, that the blue behind is completely covered up. Some people have so much
pigment in the front layer that their eyes appear very dark brown or black. Hazel, blue-green, gray-blue eye
colors are produced by different amounts of pigmentation and the pattern in which the pigment is placed.
Albino eyes are have no pigment at all in either layer of the iris. The iris appears pink or red because of the
reflection of blood vessels in the back of the eye. The pattern in which the pigment is deposited is also
determined by genetics. The pigment may be deposited in rings, clouds, radial stripes, or spread over the entire
iris. (from http://www.sewanee.edu/)
Sources of Genetic Diversity
During Interphase (DNA Replication)
• Mutations – create new alleles
During Meiosis
• Random Assortment (law of segregation) – mixes up
chromosomes inherited from mother and father
• Crossing Over – mixes up genes that occur on the same
chromosome
(“Linked genes” occur adjacent or very close to one another on the same
chromosome and so are almost always inherited together)
During Sex
• Fertilization – mixes up genes from two different partners
Genetic
Disorders
Inherited
New Mutations (“De Novo”)
(from mom or dad or both)
(new point mutations or chromosomal)
Complete Dominance
Incomplete Dominance
Codominance
Sex-Linked
Polygenic Traits
meiosis
Gametes
(egg / sperm)
Tay Sachs (one wrong letter)
http://www.pbs.org/wgbh/nova/genome/program.html
How do mutations during
meiosis affect an organism
differently than mutations
during mitosis?
Pedigrees
• Graphically shows the lineage of a disorder in a particular family
• Be able to tell if disorder is dominant, recessive, or sex-linked from a
pedigree
• Be able to predict the chance that an indicated couple will have a child
with the disorder
Autosomal Dominant Pedigree
How can we tell?
Autosomal Recessive Pedigree
How can we tell?
Pedigrees
Sex-Linked Pedigrees
How can we tell?
Which is X-linked and which is Y-linked?
Is the X-linked dominant or recessive?
Honors
Practice Problems
1.
What are gametes? Where are they made in the body? How are they made?
2.
What are the eight phases of meiosis? What occurs during each phase? How
does meiosis differ from mitosis?
3.
How do crossing over and random assortment “mix up” genes so that children
are genetically different from their parents?
4.
At each step of meiosis, is the cell haploid or diploid?
5.
If an allele is dominant and two heterozygous individuals mate, what is the
chance that their child will have the dominant phenotype?
6.
If two alleles are codominant and two heterozygous individuals mate, what is
the chance that their child will have both phenotypes?
7.
If two individuals mate and their child has a phenotype completely different
from both parents, what was the genotype of the parents?
8.
If a disorder is X-linked and a normal man mates with a woman who is a
carrier, what is the chance that they will have a boy with the disorder? What is
the chance that they will have a girl with the disorder?