Download APDC Unit XI Meiosis

Unit XI: Meiosis & Inheritance
Chapter 10 - Meiosis
Chapter 36* - Reproduction
(Parts of this will actually move to Unit 12)
QUICK UNIT this time  Test is soon!
WHAT YOU NEED TO KNOW:
• Terms associated with genetics problems: P, F1, F2,
dominant, recessive, homozygous, heterozygous,
phenotype, genotype.
• How to derive the proper gametes when working a
genetics problem.
• The difference between an allele and a gene.
• How to read a pedigree.
Two Types of Reproduction
• Asexual
• One “parent”
• All genes passed on “as
is”
• Very little genetic
variation
• Typically involves “just
splitting”
• Sexual
• Two “parents”
• Shuffling of gene
combinations
• Greater genetic variation
• Typically involves meiosis
• Sexual Reproduction
• Why bother?
Chromosome Terms
• Homologous chromosomes
• Carry same type of genes
(though not necessarily 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
• Sex chromosomes
• Determine gender of offspring (Y determines)
• In humans, X & Y (male XY; female XX)
• Autosomes
• The other chromosomes…in humans, #1-22
Human Karyotypes
Map of homologous chromosome pairs
Life Cycle Terms
• Somatic cell – a regular body cell
• Diploid (2n)  has both sets of chromosomes
• In humans, diploid = 46 chromosomes
• Gamete – a reproductive cell
• Haploid (1n)  has one set of chromosomes
• in humans, haploid = 23 chromosomes
Human Life
Cycle Events
Fertilization – joining of
sperm & egg
Zygote – fertilized egg
(diploid)
Meiosis – production of
haploid sex cells;
occurs in ovaries &
testes
Other Life Cycles
All share same
alternation
between
fertilization and
meiosis
Animals – 2n dominates
Fungi – 1n dominates
Plants – alternation of
generations
How do we get to
haploid?
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 I: Reduce to Haploid
KEY
TERM:
Synapsis
Homologous chromosomes pair up (prophase I)
Meiosis I: Reduce to Haploid
KEY
TERM:
Tetrad
Group of 4 chromatids together during synapsis
Meiosis I: Reduce to Haploid
KEY
TERM:
Chiasma (chiasmata)
Crossing of non-sister chromatids (see crossing over)
Meiosis I: Reduce to Haploid
Metaphase I: tetrads line up
Anaphase I: homologous chromosomes separate
Meiosis II: Reduce DNA Amount
Works just like mitosis
Mitosis vs Meiosis
Mitosis vs Meiosis
So Many Possibilities…
The positioning
of tetrads in
metaphase
determines
variability of
resulting
gametes
So Many Possibilities…
• 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
So Many Possibilities…
Crossing over
during meiosis I, nonsister
chromatids of
homologous
chromosomes switch
places
Results in even more
genetic variability
Mendel and the Gene Idea
Mendel’s Experiment
Start with 2 purebred
plants
Cross-pollinate
Allow to fertilize
Plant resulting seeds
to get F1 generation
• P (parental) generation = true breeding plants
• F1 (first filial) generation = offspring
• F2 (second filial) generation = F1 offspring
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
About ¾ were purple
flower plants
About ¼ made white
flower plants
Led to
Law of Dominance:
If both types
present, one factor
masks other
Other traits… same results
MENDEL’S PRINCIPLES
1. Alternate version of genes (alleles) cause variations in
inherited characteristics among offspring.
2. For each character, every organism inherits one allele
from each parent.
3. If 2 alleles are different, the dominant allele will be
fully expressed; the recessive allele will have no
noticeable effect on offspring’s appearance.
4. Law of Segregation: the 2 alleles for each character
separate during gamete formation.
Law of Segregation
• Alternate versions of genes (alleles) account for variation in
inherited traits
• For each trait, an organism inherits 2 alleles (one from each
parent)
• Law of Segregation: Can only pass on ONE of these to gametes –
why?
• When in meiosis does this occur?
Law of Segregation
Mathematically
proven through both
generations
Remember
Punnett squares?
What do the letters on
outside represent?
Letters on inside?
dominant (P), recessive (p)
• homozygous = 2 same alleles (PP or pp)
• heterozygous = 2 different alleles (Pp)

Mendel’s Other Law
• Remember metaphase I…what controls how those
tetrads align themselves?
• Are the genes on one chromosome “linked” to the ones on
other chromosomes?
• So, are they inherited independently of each other…or linked
to each other?
Phenotype:
expressed physical traits
Genotype: genetic make-up
Law of Independent Assortment
• Assuming the genes are on different chromosomes, they
are inherited independently of each other…
• (Ex: just because you got your Mom’s freckles does not mean you
inherited her widow’s peak)
• Occurs due to random alignment of tetrads in metaphase I
Punnett Square
• Device for predicting offspring from a cross
• Example: Pp x Pp (P=purple, p=white)
Genotypic Ratio:
Phenotypic Ratio:
Testcross: determine if dominant trait is
homozygous or heterozygous by crossing with
recessive (pp)
Law of Independent Assortment
• What happens if you test 2 traits at the same time?
(dihybrid cross)
• Monohybrid will have typical 3:1 results
• Ex: YY x yy  Yy x Yy  ¾ yellow, ¼ green
• 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 segregate (and passed on) separately from each other
What if the genes are on the SAME chromosome?
• Monohybrid cross: study 1 character
• eg. flower color
• Dihybrid cross: study 2 characters
• eg. flower color & seed shape
Dihybrid Cross
• Example:
AaBb x AaBb
The laws of probability govern
Mendelian inheritance
• Rule of Multiplication:
• probability that 2+ independent events will occur together
in a specific combination  multiply probabilities of each
event
• Ex. 1: probability of throwing 2 sixes
• 1/6 x 1/6 = 1/36
• Ex. 2: probability of having 5 boys in a row
• ½ x ½ x ½ x ½ x ½ = 1/32
• Ex. 3: If cross AABbCc x AaBbCc, probability of
offspring with AaBbcc is:
• Answer: ½ x ½ x ¼ = 1/16
The laws of probability govern
Mendelian inheritance
• Rule of Addition:
• Probability that 2+ mutually exclusive events will occur 
add together individual probabilities
• Ex. 1: chances of throwing a die that will land on 4 or
5?
• 1/6 + 1/6 = 1/3
Segregation of alleles and fertilization as chance events
Extending Mendelian Genetics
The relationship between genotype and phenotype
is rarely simple
Complete Dominance:
heterozygote and homozygote
for dominant allele are
indistinguishable
• Eg. YY or Yy = yellow seed
Incomplete Dominance: F1
hybrids have appearance that
is between that of 2 parents
• Eg. red x white = pink flowers
Codominance: phenotype of both alleles is expressed
• Eg. red hair x white hairs = roan horses
Multiple Alleles: gene has 2+ alleles
• Eg. human ABO blood groups
• Alleles = IA, IB, i
• IA,IB = Codominant
Blood Typing
Phenotype
(Blood Group)
Genotype(s)
Type A
IAIA or IAi
Type B
IBIB or IBi
Type AB
IA IB
Type O
ii
Blood Transfusions
• Blood transfusions must match blood type
• Mixing of foreign blood  clumping  death
• Rh factor: protein found on RBC’s (Rh+ = has
protein, Rh- = no protein)
Blood Typing Problem:
• A man who is heterozygous with type A blood
marries a woman who is homozygous with type B
blood. What possible blood types might their
children have?
Polygenic Inheritance: the effect of 2 or more
genes acting upon a single phenotypic character
(eg. skin color, height)
Nature and Nurture: both genetic and
environmental factors influence phenotype
Hydrangea flowers vary in shade and intensity of color
depending on acidity and aluminum content of the soil.
Mendelian Inheritance in Humans
Pedigree: diagram that shows the relationship
between parents/offspring across 2+ generations
Woman =
Man =
Trait expressed:
Pedigree Analysis
Genetic Disorders
Autosomal Recessive
•
•
•
•
Cystic fibrosis (CF)
Tay-Sachs disease
Sickle-cell disease
Phenylketonuria (PKU)
Autosomal Dominant
• Huntington’s disease (HD)
• Lethal dominant allele
Animal Reproduction
• Both asexual & sexual reproduction in animals (some do both)
• Asexual reproduction may include…
• Budding – new individuals grow off of a part of adult
• Fragmentation (& regeneration) – body breaks into parts & all of them
can grow into adults
• Advantages *best in stable environments*
• Don’t need partner (good for isolated or nonmotile)
• Multitudes of offspring in short time (colonize quickly)
Reproductive Cycles & Patterns
• Most animals have reproductive cycles
WHY?
• allows for conserving energy & reproducing
at optimal times
• Controlled by variety of hormonal &
environmental cues
Such as…?
- temp, day-length, rainfall, etc
- Ex: light  pineal gland  melatonin
 pituitary  gonads
Reproductive Cycles & Patterns
• Parthenogenesis – egg develops into adult
• Ex: Daphnia – asexual when conditions good, sexual when under stress
conditions…why?
Reproductive Cycles & Patterns
• Parthenogenesis – egg develops into adult
• Ex: whiptail lizards…lost “maleness”, but still use sex act to stimulate
egg/offspring production; alternate between “male behavior” and
“female behavior”
• What evolutionary advantage?
Reproductive Cycles & Patterns
• Hermaphroditism –
• Has both male & female parts
• Sequential hermaphoriditism 
• Selective advantage?
Reproductive Mechanisms
• Internal Fertilization
• Fewer zygotes, more care
• External fertilization
• More zygotes, less care
Complex Reproductive Structures
Human Male
• Structures
• Check out the pic…testes most important!
• Hormone Patterns
• FSH & LH
• Stimulate testes to act
• Testosterone
• Make sperm
• Secondary sex characteristics
Spermatogenesis vs Oogenesis
• 4 sperm cells
• 1 egg cell (& 3 polar bodies)
• Production starts at puberty, • Production before birth, but
lasts much longer
arrested until puberty
• Sperm must be modified
• Egg cell keeps most of the
before viable (tails,
organelles & cytoplasm… VERY
acrosomes, etc)
LARGE
Complex Reproductive Structures
• Human Female
• Structures
• Ovaries!
• Hormone Patterns
• FSH
• Stimulates follicle
• LH
• Stimulates ovulation
• Estrogen
• Sex characteristics; ovaries
• Progesterone
• Get uterus ready
Animal Development
• Epigenesis
• Determined by genome & egg’s organization of cytoplasm
• Fertilization
• Acrosome action: “hat” drops off enzyme to eat thru
• Cortical reaction: Ca+ released; changes membrane charge
• Activation of egg…fertilization
Animal Development
• Cleavage
• Mitosis…but cells do not separate
Animal Development
Gastrulation
Infolding; forms 3-layered embryo
How do they know how to do this?
Animal Development
• Organogenesis
•
•
•
•
Folds and splits and clusters
Ecto = nervous
Meso = muscles & bones
Endo = linings
Animal Development
• Morphogenesis
• Changes in cell shape, position, and adhesion
The End
Warm-Up
1. What is the pattern of inheritance of the trait
(shaded square/circle) shown in the pedigree?
1. How many chromosomes are in a human cell that
is:
a) Diploid?
c) Monosomic?
b) Triploid?
d) Trisomic?
THE CHROMOSOMAL BASIS
OF INHERITANCE
What you must know:
• How the chromosome theory of inheritance connects
the physical movement of chromosomes in meiosis to
Mendel’s laws of inheritance.
• The unique pattern of inheritance in sex-linked genes.
• How alteration of chromosome number or
structurally altered chromosomes (deletions,
duplications, etc.) can cause genetic disorders.
• How genetic imprinting and inheritance of
mitochondrial DNA are exceptions to standard
Mendelian inheritance.
Chromosome theory of inheritance:
• Genes have specific locations
(loci) on chromosomes
• Chromosomes segregate and
assort independently
Chromosomes tagged to reveal a specific gene (yellow).
Thomas Hunt Morgan
• Drosophila melanogaster – fruit fly
• Fast breeding, 4 prs. chromosomes (XX/XY)
• Sex-linked gene: located on X or Y chromosome
• Red-eyes = wild-type; white-eyes = mutant
• Specific gene carried on specific chromosome
Sex determination
varies between
animals
Sex-linked genes
• Sex-linked gene on X or Y
• Females (XX), male (XY)
• Eggs = X, sperm = X or Y
• Fathers pass X-linked genes to daughters, but not sons
• Males express recessive trait on the single X (hemizygous)
• Females can be affected or carrier
Transmission of sex-linked recessive traits
Sex-linked disorders
• Colorblindness
• Duchenne muscular dystrophy
• Hemophilia
X-Inactivation
Barr body = inactive X chromosome; regulate gene
dosage in females during embryonic development
•
•
Cats: allele for fur
color is on X
Only female cats can
be tortoiseshell or
calico.
Human development
• Y chromosome required for development of testes
• Embryo gonads indifferent at 2 months
• SRY gene: sex-determining region of Y
• Codes for protein that regulates other genes
Genetic Recombination: production of offspring with new
combo of genes from parents
• If offspring look like parents  parental types
• If different from parents  recombinants
• If results do not follow Mendel’s Law of Independent
Assortment, then the genes are probably linked
Linked genes: located on same chromosome and tend to be
inherited together during cell division
Crossing over: explains why some linked genes get separated
during meiosis
• the further apart 2 genes on same chromosome, the
higher the probability of crossing over and the higher the
recombination frequency
Calculating recombination frequency
Linkage Map: genetic map that is based on
% of cross-over events
• 1 map unit = 1% recombination frequency
• Express relative distances along chromosome
• 50% recombination = far apart on same chromosome
or on 2 different chromosomes
Exceptions to Mendelian
Inheritance
Genomic Imprinting
• Genomic imprinting: phenotypic effect of gene
depends on whether from M or F parent
• Methylation: silence genes by adding methyl groups
to DNA
Non-Nuclear DNA
• Some genes located in
organelles
• Mitochondria, chloroplasts,
plastids
• Contain small circular DNA
• Mitochondria = maternal
inheritance (eggs)
Variegated (striped or spotted) leaves result from mutations in
pigment genes in plastids, which generally are inherited from
the maternal parent.
Genetic Testing
Reasons for Genetic Tests:
• Diagnostic testing (genetic disorders)
• Presymptomatic & predictive testing
• Carrier testing (before having children)
• Pharmacogenetics (medication & dosage)
• Prenatal testing
• Newborn screening
• Preimplantation testing (embryos)
Prenatal Testing
• May be used on a fetus to detect genetic disorders
• Amniocentesis: remove amniotic fluid around fetus
to culture for karyotype
• Chorionic villus sampling: insert narrow tube in
cervix to extract sample of placenta with fetal cells
for karyotype
Nondisjunction: chromosomes fail to separate
properly in Meiosis I or Meiosis II
Karyotyping can detect nondisjunctions.
Down Syndrome = Trisomy 21
Nondisjunction
Klinefelter Syndrome: 47XYY, 47XXY
Nondisjunction
Turner Syndrome = 45XO
Chromosomal Mutations
Chromosomal Mutations
Nondisjunction
• Aneuploidy: incorrect # chromosomes
• Monosomy (1 copy) or Trisomy (3 copies)
• Polyploidy: 2+ complete sets of chromosomes;
3n or 4n
• Rare in animals, frequent in plants
A tetraploid mammal. Scientists think this species may have arisen when an
ancestor doubled its chromosome # by errors in mitosis or meiosis.
Review Questions
1. What is the pattern of inheritance of the trait
(shaded square/circle) shown in the pedigree?
1. How many chromosomes are in a human cell that
is:
a) Diploid?
c) Monosomic?
b) Triploid?
d) Trisomic?
Chi-Square Analysis Practice
• Two true-breeding Drosophila are crossed: a normal-winged, red-eyed female
and a miniature-winged, vermillion-eyed male. The F1 offspring all have normal
wings and red eyes. When the F1 offspring are crossed with miniature-winged,
vermillion-eyed flies, the following offspring resulted:
• 233 normal wing, red eye
• 247 miniature wing, vermillion eye
• 7 normal wing, vermillion eye
• 13 miniature wing, red eye
• What type of conclusions can you draw from this experiment? Explain your
answer.
Definitions:
Closing Questions
• Sex-linked
gene
1. A white-eyed female fruit-fly is mated with a redeyed male. What genotypes and phenotypes do you
• Barr body
predict for the offspring?
• SRY gene
2. Neither Tim nor Rhoda has Duchenne muscular
• Linked
dystrophy (X-linked recessive disorder), but their
genes
firstborn son has it. What is the probability their 2nd
• Linkage
child will have it?
map
3. Colorblindness is a sex-linked recessive trait. A
colorblind male and a female with normal vision
have a son who is colorblind. What are the parents’
genotypes?
Closing questions
1. What is a Barr body?
2. How are linkage maps constructed? (See your
textbook)
3. What does a frequency of recombination of 50%
indicate?
Fake Quiz!
• PURPOSE:
• Take note of what you know and what you do not know!
• You do NOT need to write full sentences – use short,
quick phrases
Fake Quiz!
• 1. What was Mendel’s basic experiment? What was
result of F1 (first set of offspring)? Why?
• What was result of F2? Why?
• 2. Which is better – sexual or asexual reproduction?
Defend! (What defense would you have for the opposite
choice?)
• 3. What are the events of G1,S,G2? What are the events
of Pro I? Meta I? Ana I? Why is meiosis II even needed?
Fake Quiz!
• 4. Identify 3 processes/events that contribute to genetic
variation. For each, describe what it means and when it
happens.
• 5. What does the law of independent assortment state?
When do these events happen?
• 6. What does the law of segregation state? When do
these events happen?
FRQ - Unit X: Meiosis & Reproduction
• 35. -- 3 points maximum (4 available) –
• NOTE: if it says “TWO”, only the first two mentioned are
eligible for grading – be careful!
• A) 2 maximum
• 1 – copy DNA, make sister chromatids, etc
• 2 – sisters pulled apart (not homologous chroms!)
• 3 – sisters align (in preparation for pulling apart)
• 4 – cell/cytoplasm/CM actually splits into 2
• 5 – chromatin coils to chromosomes (easier to pull)
FRQ - Unit X: Meiosis & Reproduction
• 35. -- 3 points maximum (4 available) –
• NOTE: Must state both parts – FOLLOW THROUGH!
• B) 2 maximum
• 1 – # divisions (1 vs 2) OR # resulting cells (2 vs 4)
• 2 – ploidy of daughter cells (haploid vs diploid)
• 3 – crossing over (yes vs no)
• 4 – hom-chrom separate/ind.assort/synapsis (Y vs N)
FRQ - Unit X: Meiosis & Reproduction
• 36. -- 3 points maximum –
• NOTE: if it says “TWO”, only the first two mentioned are
eligible for grading – be careful!
• A) 2 maximum
B) 1 maximum
• 1 – faster
- genetic
• 2 – more offspring overall
variation!!!
• 3 – less overall energy
• 4 – no mate required
• 5 – no gonads/meiosis
• 6 – 100% genes passed on
FRQ - Unit X: Meiosis & Reproduction
• 37. -- 4 points maximum –
• NOTE: for parth, must address mate issue!
• A) 2 maximum
• 1 – DEFINE  adult forms from non-fertilized egg
• 2 – SEL ADV  no mate required
• Less energy
• Less time
• No limitation due to lack of available mates
FRQ - Unit X: Meiosis & Reproduction
• 37. -- 4 points maximum –
• NOTE: follow through…why are there more babies?
• B) 2 maximum
• 1 – DEFINE  orgs with both male & female gonads
• 2 – SEL ADV  more babies because both fertilized OR no
need for mate because can self-fertilize
MC - Unit X: Meiosis & Reproduction
• Most Missed MC
• 9 – A - Did you draw it?
• After S, have 4 double-stand chroms = 8 strands DNA
• After meiosis, have 2 chroms (1/2), and 2 DNA strands (1/4)
• 1 – B – Segregation = when the hom-chroms split
• Happens during meiosis
MC - Unit X: Meiosis & Reproduction
• Most Missed MC
• 24 – D – If on same chrom, would not ind-assort
• Because not linked, must take into account all possibilities
• 11 – C – What happened here?
• Meiosis daughter cells NOT same as parents (are haploid)
• 17 – D – 22 pairs+XX = 46  is somatic, not gamete
• Female = XX