Download Dominant Gene

Unit 3: Genetics
1. Explain the significance of Mendel`s experiments and
observations and the laws derived from them.
a. Explain the concept of independent events.
b. Understand that the probability of an independent event is not altered by the outcomes of previous
events.
Heredity
All organisms pass on their characteristics from generation to generation through INHERITANCE.
2 kinds of characteristics inherited:
Species characteristics: each species always passes on their own traits.
Individual Characteristics: even though we inherit things equally from both parents, offspring is always
different from their parents because we are a combination of both parents (i.e. mother's hair colour,
father's build, mother's nose, etc.)
Heredity is controlled by a chemical code in our DNA.
This genetic code is present in the chromosomes of the gametes (egg and sperm).
Environment
Even though we inherit traits from our parents, our environment will affect the full potential of what we
inherit.
Example: Food: people in Canada are bigger and taller than 100 years ago
Exercise: stronger, healthier bodies
Sunlight: lightens hair, darkens freckles
Independent Events
Another factor that will affect what we inherit are independent events.
An event that takes place that no previous event has an effect on.
Example: you broke your finger when you were six and it is now crooked. You will not pass this
crooked finger on to any of your offspring, it is an independent event.
Probability
In genetics, we use a mathematical process called probability. Probability is the chance that an event will
occur (i.e. the chance that you will have curly hair or blue eyes).
When determining probability, we do not consider items like the environment or independent events.
In-Class Discussion
How does heredity affect you?
What traits have you received that are NOT affected by the environment or independent events?
What traits have you received that have been affected by the environment or independent events
Instructions:
1. In groups of 2 or 3, discuss the 3 questions above, make a list of traits that have been inherited, and a
list of traits that have been affected/altered.
2. Look at the list of traits that your group has made and decide which ones are most common and which
ones are not as common....decide what this might have to do with the terms "dominant" and "recessive".
List of Traits:
Recessive:
Dominant or
Dominant and Recessive Genes
Dominant Gene: determine the expression of the genetic trait in offspring. Dominant gene is given an
upper case (capital) letter.
Recessive Gene: genes that are overruled by dominant genes. Recessive gene is designated by a
lower case letter.
Other Examples:
To determine some other examples of traits that are dominant or recessive, we will conduct a class
survey.
http://www.uni.edu/walsh/genetics.html
Review...
1. What does the term "heredity" mean?
2. What is the difference between a dominant and a recessive trait? Provide an example of each.
1. Explain the significance of Mendel`s experiments and
observations and the laws derived from them.
c. Describe Mendel`s experiments and observations.
d. Describe the relationship between genotype and phenotype.
e. Use the concept of the gene to explain Mendel`s Laws.
f. Describe the ideas of dominant and recessive traits with examples.
h. Explain the law of segregation.
GENETICS
GENETICS: the branch of biology that studies the ways in which hereditary
information is passed on from parents to offspring.
GREGOR MENDEL:
(1822-1884) first to study heredity (monk).
studied pea plants (traits) and came up with some basic principles.
Peas: easy to grow, mature quickly, show sharply contrasting traits (tall vs. short,
yellow vs. green, wrinkled vs. smooth).
Easy to cross pollinate for humans.
Kept careful records.
Mendel and His Experiments
Gregor Mendel: Austrian monk
1822-1884
studied garden peas
Mendel studied peas and cross-fertilized them by hand. Peas had specific traits that he
studied.
Crosses:
Round seeds X Wrinkled (parents)
Round Seeds (offspring)
Tall plants X Short plants (parents)
Tall Plants (offspring)
Yellow seed coats X Green seed coats (parents)
Yellow seed coats (offspring)
Mendel discovered that genes control the traits of a plant. Genes are located on
chromosomes.
Mendel also discovered that some genes are dominant over others (recessive). Ex) round
seeds dominant over wrinkled seed
tall plants dominant over short plants
yellow seed coat dominant over green seed coats
Dominant Gene: determine the expression of the genetic trait in offspring. Dominant gene is
given an upper case (capital) letter.
Recessive Gene: genes that are overruled by dominant genes. Recessive gene is designated
by a lower case letter.
For each trait, an organism gets one gene form the mother and one gene from the father.
Mendel's Laws of Heredity:
1. Inherited characteristics are controlled by genes. Genes happen in pairs. During
fertilization 2 genes come together to form a pair.
2. Principle of Dominance one gene masks the effect of another. The gene for round
seed coats masks the effect of the gene for wrinkled seed coats. Round is dominant over
wrinkled.
3. Law of Segregation: Genes separate during the formation of sex cells. Organisms get
one gene from each parent for a particular trait. During the formation of gametes (sex
cells), alleles (form of a gene) separate randomly so that each gamete receives one or the
other. The Law of Segregation deals with meiosis, which will be talked about later.
Genotype: refers to the genes that an organism has for a particular trait. Ex) RR, Rr, rr; a round seed coat
can have genotype RR or Rr, a wrinkled seed coat has only one genotype rr. YOU CAN'T TELL THE
GENOTYPE BY JUST LOOKING AT AN ORGANISM
Phenotype: refers to the observable traits of an organism, the traits that you see, Ex) there are only 2
phenotype for seed coat, wrinkled and smooth.
Homozygous: an organism contains 2 genes for one trait that are the same, Ex) RR or rr : the organism is
pure for the trait.
Heterozygous: an organism contains 2 genes for one trait that are different. Ex) Rr
Alleles: two or more alternate forms of a gene.
Ex)
Recessive
seed coat alleles
R (smooth)
Dominant
r (wrinkled)
Review....
1. List and explain one of the new terms learned last day.
2. What was one of Gregor Mendal's laws?
1. Explain the significance of Mendel`s experiments and
observations and the laws derived from them.
g. Consider the value of the punnett square by creating examples of mono and dihybrid
crosses.
Monohybrid Cross
Mono (one)
Hybrid (result from crosses between parents that are genetically not alike)
Monohybrid Cross: a cross that involved one pair of contrasting genes for one trait.
Ex) Dealing with the trait of Seed Coat
Round seed coat X Wrinkled seed coat
(parent)
RR
rr
Crossed Again
Hybrid Offspring
X
(F1 generation)
Round Seed Coat
Rr
Rr
(F = filial)
RR
(F2 generation)
Rr
Rr
rr
Punnet Square for Monohybrid Cross
Punnet Square: chart used by geneticists to show the possible combinations of alleles in
offspring.
Wrinkled Parent (homozygous)
r
r
R
Round Parent
(homozygous)
R
(F1 generation)
all _ Rr, heterozygous
Round Parent (heterozygous)
R
r
R
Round Parent
(heterozygous)
r
(F2 generation)
_ RR homozygous dominant, _ Rr heterozygous and _ rr homozygous (recessive)
Monohybrid Cross Genotypic Ratio
1 RR (homozygous dominant) : 2Rr (heterozygous) : 1rr (homozygous recessive)
Monohybrid Cross Phenotypic Ratio
3 round : 1 wrinkled
3 with the dominant trait showing : 1 with the recessive trait showing
3/4 or 75% : 1/4 or 25%
Lets look at this in more detail.
X
RR
rr
(parents)
sex cells
R R
sex cells
r
r
Rr
(F1 generation)
X
Rr
sex cells
R r
(F2 generation)
RR
Rr
round
Rr
rr
wrinkled
Examples:
1. Brown eyes (B) are dominant over blue eyes.
If a parent homozygous for blue eyes produce
offspring. What are the chances that the offspring has brown eyes? blue eyes?
Parent A = BB
Parent B = bb
2. In plants, tall (T) is dominant over short (t). Two plants, that are tall, are crossed and produce
a plant that is short. Determine the genotype of the parents.
short plant = tt
3. In guinea pigs, curly hair (C) is dominant over straight hair (c). If two guinea pigs that have curly hair
and are straight hair carriers mate, what is the chance they have a straight haired offspring?
Genotype of parents =
1. Explain the significance of Mendel`s experiments and
observations and the laws derived from them.
g. Consider the value of the punnett square by creating examples of mono and dihybrid crosses.
Review Question....
1. Both a hen and a rooster are heterozygous trait carriers.
They both have a trait to be black (B) and a
trait to be white (b). Black is the dominant colour, what will the phenotypes and genotypes of their
offspring be?
Dihybrid Cross
Di = 2
Hybrid: result from crosses between parents that are genetically not alike.
Dihybrid cross: a cross that involves 2 traits.
Example of a dihybrid cross:
Yellow Round
X Green Wrinkled
(parent)
(gametes YR)
yyrr
YYRR
(gametes yr)
Crossed Again
(F1 generation)
X
Yellow Round
YyRr
(gametes = YR, Yr, yR, yr)
YyRr
(gametes = YR, Yr, yR, yr)
(F2 generation)
1 YYRR, 2 YyRR, 2 YYRr, 4 YyRr, 1 YYRR, 2 yyRr, 1 yyrr, 1 YYrr
Punnet Square for Dihybrid Cross
yyrr
YYRR
Parent
Yellow & Round
(homozygous)
Green and Wrinkled Parent (homozygous)
yr
yr
YR
YR
(F1 Generation)
_ YyRr (yellow & round, heterozygous)
YyRr
Yellow & Round Parent (heterozygous)
YR
YyRr
Yellow & Round
Parent
(heterozygous)
Yr
yr
YR
Yr
yR
yr
Dihybrid Cross Phenotypic Ratio
9/16 Yellow & Round : 3/16 Yellow & Wrinkled : 3/16 Green & Round : 1/16 Green & Wrinkled
**Remember** Dihybrid Cross = 9 : 3 : 3 : 1
yR
Examples....
1. Black coat colour (B) in cocker spaniels is dominant to white coat colour (b). Solid coat pattern (S)
is dominant to spotted pattern (s). A male that is black with a solid pattern mates with two females.
The mating with female A which is white, solid, produces four pups: 2 black, solid, and two white,
solid. The mating with female B, which is black, solid, produces a single pup, which is white, spotted.
Indicate the genotypes of the parents.
2. In guinea pigs, black coat colour (B) is dominant to white (b), and short hair length (S) is dominant to
long (s). Indicate the genotypes and phenotypes from the following crosses:
a) Homozygous for black, heterozygous for short-hair guinea pig crossed with a white, long-haired guinea
pig.
b) Heterozygous for black and short-hair guinea pig crossed with a white, long-hair guinea pig.
c) Homozygous for black and long-hair crossed with a heterozygous black and short-hair guinea pig.
2. Discuss the relationship among chromosomes, genes, and
DNA.
h. Examine incomplete dominance, alleles, sex determination, and sex-linked traits in the context of
human genetics.
i. Discuss several human genetic disorders such as hemophilia, sickle-cell anemia, Down`s syndrome,
and Tay-Sach`s disease.
Test Cross
There is an organism showing the dominant trait but it is unknown if the organism is
homozygous or heterozygous, it's genotype is unknown. To figure out the genotype you
cross the unknown genotype and a homozygous recessive genotype.
If the offspring all show the dominant trait, the unknown genotype is homozygous
dominant.
If any of the offspring show the recessive trait, the unknown genotype was heterozygous
dominant.
Determine the genotype of the parent plants by looking at the phenotypes of the
offspring from the following cross.
Round, yellow X Wrinkled, green
1/4 round, yellow, 1/4 round, green, 1/4 wrinkled, yellow, 1/4 wrinkled, green
Incomplete Dominance
The lack of a dominant gene. Both alleles contribute to the phenotype of a
heterozygote. Produces an offspring with traits unlike either parent.
Ex)
Red snapdragon (RR) X White snapdragon (WW)
F1Generation
All Pink Snapdragons (RW)
RW X RW
F2 Generation
RW
R
W
1 RR (red) : 2RW (pink) : 1 WW (white)
Codominance
Two dominant genes are expressed at the same time in the heterozygous organism.
Ex) Shorthorn Cattle
Red (HRHR) X White (HWHW)
Roan Calf - it has intermingling of white and red hair
F1 Generation (all) HRHW X HRHW
F2 Generation
HR HW
HR
Hw
1 HRHR : 2HRHW : 1HWHW
Multiple Alleles
The problem we have dealt with so far only have dealt with 2 alleles - the dominant
allele and the recessive allele. The dominant allele controlled the trait.
Multiple Alleles - when more than 2 different alleles exist for a trait.
Ex) the fruit fly Drosophilz - many different eye colors are possible.
Dominant Hierarchy
Red (wild type) eyes : most common
Apricot
Honey
White
Note: a drosophila can only have 2 different genes at one time, but many alleles are possible.
When using multiple alleles we no longer use upper and lower case letters. Capital
letters with subscript numbers are used.
Red (wild type) eyes E1E1 OR E1E2, E1E3, E1E4
Apricot E2E2, E2E3, E2E4
Honey E3E3, E3E4
White E4E4
Ex) Human Blood Typing: example of codominance and multiple alleles
The ABO blood typing system in humans is determined by a set of 3 alleles - multiple
alleles. IA, IB, i
Different combinations of these alleles in people produce 4 different blood types.
Type A, Type B, Type AB, Type O
Genotype Phenotype
IAIA or IAi Type A Blood
IBIB or IBi Type B Blood
IAI B Type AB Blood *
ii Type O Blood
* This is codominance - different alleles expressing their full phenotype in a heterozygote,
giving a new phenotype.
Exceptions to Mendel's Laws Example Questions...
1. For ABO blood groups, the A and B genes are codominant, but both
A and B are dominant
over type O. Indicate the blood types possible from the mating of a male who is blood type O
with a female of blood type AB.
2. Could a female with blood type AB ever produce a child with blood type AB? Could she ever
have a child with blood type O?
Exceptions to Mendel's Laws Example Questions...
3. Thalassemia is a serious human genetic disorder that
causes severe anemia. The homozygous condition
(TmTm) leads to sever anemia. People with thalassemia
die before sexual maturity. The heterozygous condition
(TmTn) causes a less serious form of anemia. The
genotype TnTn causes no symptoms of the disease.
Indicate the possible genotypes and phenotypes of the
offspring if a male with the genotype TmTn marries a
female of the same genotype.
Review...
1. What is incomplete dominance? Provide an example.
2. What is meant by the term "multiple alleles?" Provide an
example.
3. What is co-dominance?
2. Discuss the relationship among chromosomes, genes, and
DNA.
h. Examine incomplete dominance, alleles, sex determination, and sex-linked traits in the context of
human genetics.
i. Discuss several human genetic disorders such as hemophilia, sickle-cell anemia, Down`s syndrome,
and Tay-Sach`s disease.
Incomplete Dominance
Examples...
A cross between a blue blahblah bird and a white blahblah bird
produces offspring that
are sliver. The color of blahblah birds is determined by just two alleles.
a) What are the genotypes of the parent blahblah birds in the
original cross?
b) What is/are the genotyp(s) of the silver offspring?
c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?
Incomplete Dominance Examples...
1. The color of fruit for Golgi plants is determined by two alleles.
When two plants with orange
fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit,
50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited
plants?
Co-dominance Example Problem...
1. Predict the phenotypic ratios of offspring when a
homozygous white cow is crossed
with a roan bull?
2. What should the genotypes and phenotypes for parent cattle be if a farmer wanted only
cattle with red fur?
Multiple Alleles Example Problem...
1. Remembering what you learned about blood types, what are
of children in the following families?
a) Heterozygous type A mother, Homozygous type A father?
b) Homozygous type B mother, type AB father?
c) type AB mother, type AB father?
the possible phenotypes
2. Discuss the relationship among chromosomes, genes, and
DNA.
h. Examine incomplete dominance, alleles, sex determination, and sex-linked traits in the contexts of
human genetics.
i. Discuss several human genetic disorders such as hemophilia, sickle-cell anemia, Down`s syndrome,
and Tay-Sach`s disease.
j. Discuss the similarities and differences between sex chromosomes and somatic chromosomes.
Sex - Linked Traits
Sex-linked traits : controlled by genes located on the sex chromosomes.
In humans the sex chromosomes go as follows:
Female = XX Male = XY
The X chromosomes are relatively the same size.
In a female you have two homologous X chromosomes.
- -
- Locus: the actual site of the gene
on a chromosome.
X
X
In a male you have one large X chromosome and a smaller Y chromosome. The Y
chromosome is shorter than the X chromosome. Some of the genes on the X
chromosome may be missing on the Y chromosome.
There is nothing to match.
- -
X
Y
Most sex-linked traits are determined by genes found on the X chromosome but not on
the Y chromosome.
Sex-linked disorders in Humans:
1. Color-Blindness: person can't perceive certain colors, usually red and green.
: more common in males than females.
: Females may be carriers for it, because they have the recessive allele for color-blindness on
one X chromosome and the normal dominant allele on the other X chromosome.
Female Carrier Normal Female Color-blind Female
XX'
XX
X'X'
Every male gets an X chromosome from its mother and a Y chromosome from his father.
Mother = XX
Father = XY
Male Offspring
XY
Mother a Carrier
Father
XX'
XY
Male Offspring XY or X'Y
There is a 50% chance that the male son will have color blindness.
Since the Y chromosome is smaller than the X, the Y chromosome has no spot for
color vision. When a son gets the defective color blind allele from his mother the
color blindness is expressed and the son is color blind.
In order for a female to be color blind, she must inherit the color blind allele from
both parents and this is a rare event.
Mother
XX'
Father
X'Y
Color-Blind Female Offspring X'X'
Remember: color-blindness is transmitted only through the female.
2. Hemophilia: sex-linked disorder in which the blood is unable to clot because it
lacks a certain blood-clotting protein.
: the recessive gene for hemophilia is carried on the X chromosome.
: Most affected individuals are male.
: Females with one recessive genes are carriers but show no sign of the illness.
: Smallest cut or bruise can cause the person to bleed severely.
Pedigree
- means of tracing sex-linked traits in family trees through a pictorial representation
- females are represented by circles, males are represented as squares.
- matings are shown by horizontal lines connecting two individuals
- offsprings are connected by vertical lines to the mating line
- different shades or colors added to the symbols represent carious phenotypes
- each generation is listed on a separate row labeled with Roman Numerals
Pedigree
Review...
1. Explain why it is more likely for a male child to be born
colorblind if his father is normal, but his mother is a carrier for
colorblindness.
2. Discuss the relationship among chromosomes, genes, and
DNA.
a. Describe how the genetic code is carried on the DNA.
i. Discuss several human genetic disorders such as hemophilia, sickle-cell anemia, Down`s syndrome,
and Tay-Sach`s disease.
Chromosomes
Chromosomes: long threads of genetic material found in the nucleus of cells
: made up of nucleic acids and proteins
: humans have 46 chromosomes (23 pairs)
Genes: located on the chromosomes
- made up of DNA
- units of instruction, located on chromosomes that produce or influence a specific trait in
offspring.
DNA-deoxyribonucleic acid: carries the genetic code, carries genetic information.
Diploid Chromosome Number: (2n) the full compliment of chromosomes. Everyday
cells in the body, except sex cells have a diploid chromosome number (ex- Humans
= 46)
Haploid Chromosome Number: (n) one half of the full compliment of chromosomes. Sex
cells have haploid chromosome number (ex- Humans=23)
Homologous Pairs/Homologous Chromosomes: are similar in size, shape, and gene
arrangement. Get one from each parent (ex - 23 pairs in humans).
Karyotype: pictures of chromosomes arranged in homologous pairs.
Sex Chromosomes: chromosomes that determine the sex of an individual. Ex) Human pair
#23 XY = male XX = female
Somatic Chromosome/Autosomes: chromosomes not involved with sex determination.
Ex) Human pairs #'s 1-22.
Monosomy: is the presence of a single chromosome in place of a homologous pair.
Ex) Turner's Syndrome: a female that has a single X chromosome (pair #23). Only females,
do not develop sexually, tend to be short and have thick wide necks.
Trisomy: the presence of three homologous chromosomes in place of homologous pair.
Ex) Down's Syndrome: an extra chromosome for pair #21. Often called trisomy 21.
Characteristics include round full face, enlarged creased tongue, short height, large forehead
and decreased mental capabilities.
Ex) Klinefelter Syndrome: 3 sex chromosomes
(XXY). Appears to be male, @ puberty
produces large amounts of female
hormones. Sterile.
2. Discuss the relationship among chromosomes, genes, and
DNA.
b. Outline the process of replication.
d. Describe the process of transcription.
e. Describe the functions of mRNA, tRNA, amino acids, and ribosomes in protein synthesis.
Protein Synthesis
1. Transcription
2. Translation
2. Discuss the relationship among chromosomes, genes, and
DNA.
f. Describe the causes and effects of both chromosomes and gene mutations.
Mutations Handout
2. Discuss the relationship among chromosomes, genes, and
DNA.
k. Using examples from living organisms discuss the importance of asexual and sexual reproduction to
their growth and survival.
Asexual vs. Sexual Reproduction
a. Asexual Reproduction
Asexual cell division = mitosis - producing 2 daughter cells identical to the parent
cell.
Asexual reproduction in organisms involves one parent with the offspring looking
identical to nearly identical to the parent.
Cloning is a type of asexual reproduction.
Budding is a type of asexual reproduction (ex. hydra, strawberries).
There is no variation in traits with asexual reproduction, this is dangerous because
what happens if there is a change in environment.
b. Sexual Reproduction:
Sexual cell reproduction = meiosis - producing gametes that have genetic variation.
Animals that reproduce sexually have male and female sexes. They produce gametes
through the process of meiosis.
Humans reproduce sexually.
In sexual reproduction there is diversity and genetic variation.
An advantage of sexual reproduction is that there is variety in the population and some
organisms may be better able to survive (survival of the fittest); or if there is an environmental
change some organisms may survive while others may not.
2. Discuss the relationship among chromosomes, genes, and
DNA.
c. Compare mitosis and meiosis.
Mitosis...
The process in which the cell triggers itself to asexually reproduce forming
2 identical
daughter cells from 1 parent cell
Necessary for growth and to replace injured cells
Before the mother cell splits, the chromosomes in it have duplicated into 2 sets.
When the mother cell splits, 1 set
of chromosomes goes to each of the
2 daughter cells.
The process a cell goes through to
duplicate itself is called the cell cycle,
and looks like this:
Mitosis
Cell division occurs in a series of stages, or phases.
1st INTERPHASE
Chromosomes are copied (# doubles).
Chromosomes appear as threadlike coils (chromatin) at the
start, but each chromosome and its copy (sister chromosome)
change to sister chromatids at end of this phase.
centromere
2nd: PROPHASE
Mitosis begins (cell begins to divide)
Centrioles (or poles) appear and begin to move to
opposite ends of cell.
Spindle fibers form between the poles.
3rd: METAPHASE
Chromatids (or pairs of chromosomes) attach to the
spindle fibers.
sister chromatids
4th: ANAPHASE
Chromatids (or pairs of chromosomes) separate and begin
to move to opposite ends of the cell.
sister
chromatids
split
5th: TELOPHASE
Two new nuclei form
Chromosomes appear as chromatin (threads rather than
rods)
Mitosis ends
6th: CYTOKINESIS
Cell membrane moves inward to create two daughter cells each with its own nucleus with identical chromosomes.
One final note...
- During telophase in plant cells, a cell plate forms in the center and grows outward
creating a cell wall (rather than the cell membrane pinching inward).
cell plate
Review...
1. What happens, most importantly, during interphase?
2. What is the end result of mitosis?
2. Discuss the relationship among chromosomes, genes, and
DNA.
c. Compare mitosis and meiosis.
Meiosis...
Is the process that takes place in the sex organs of all living organisms in
order to
produce haploid sex cells (also known as gametes).
This process is absolutely essential, otherwise at fertilization, when two gametes unite
together, there would be too many chromosomes!
In humans, meiosis reduces the number of chromosomes from 46 to 23, so that every
sperm or egg cell has 23 chromosomes. At fertilization, 23 chromosomes from the sperm
unite with 23 chromosomes from the egg to produce the original 46 chromosomes.
Meiosis: two divisions of chromosomes
a. MEIOSIS I = first round of divisions; stage where the chromosome # is reduced by half
i) INTERPHASE I: as in interphase of mitosis, it is the period during which the cell grows and
replicates its chromosomes
ii) PROPHASE I
Early Prophase I:
- chromosomes appear as long, thin threads
- nucleoli starts to disappear and centrioles move to opposite ends of the
cell
Middle Prophase I:
- the chromosomes come together in homologous pairs through the
process of synapsis (intertwining)
- each homologous pair is composed of chromatids and is referred to as a
tetrad
- intertwined chromatids may break and exchange segments = crossing
over
- tetrads become shorter and thicker
Late Prophase I:
- centrioles are at opposite poles
- spindle formation is complete
- nucleus begins to dissolve
iii) METAPHASE I
- each tetrad moves onto a spindle
and
attaches to a single fibril at the equator
iv) ANAPHASE I
- centromeres do not divide and homologous
chromosomes move apart to opposite poles in a
process called segregation
- now, half the number of double stranded
chromosomes at each pole
v) TELOPHASE I
- the two sets of double stranded chromosomes
become enclosed in new nuclei
- chromosomes remain double stranded and disappear
- cytokinesis occurs creating two haploid daughter
cells that are NOT identical
b) MEISOSIS II: occurs in both haploid daughter cells at the same time
Interkinosis: basically interphase, except there is no replication of chromosomes
i) PROPHASE II
- nuclear membrane dissolves
- centrioles move and spindles form
- double-stranded chromosomes shorten and
thicken
ii) METAPHASE II
- double-stranded chromosomes attach the
spindle and line up at the equator
iii) ANAPHASE II
iv) TELOPHASE II
- the centromere holding each pair of sister
chromatids together dissolves
- sister chromatids move to opposite poles
- nuclear membranes are restored, spindles
disappear, and cytokinesis occurs
- results in 4 haploid daughter cells that are
different from each other and the parent cell
Review...
1. What is the end result of meiosis?
2. Why must our sex cells be produced through meiosis and not
mitosis?
2. Discuss the relationship among chromosomes, genes, and
DNA.
g. Consider the purposes and techniques of gene mapping.
Genetic Engineering
Activities
Gene Mapping
there are approximately 100 thousand genes in the nucleus of each human cell among
the 46 chromosomes.
Human Genome
all the genes that make up the 'master blue print'
3 billion base pairs of nucleotide bases that make up DNA
Human Genome Project
to identify the full set of genetic instructions contained in our cells and to read the complete
text written in DNA.
Worked on by 100's of biologists, chemists, engineers, mathematicians, etc. all over the
world.
Will revolutionize our understanding of how genes control the function of the human body.
Provide new strategies to diagnose, treat, prevent human diseases.
Estimate to take 15 years.
1) complete maps of the 46 chromosomes
2) sequence the DNA in chromosomes
it's like shedding an encyclopedia and trying to put it back together again so it can be read.
Consider:
Body made of several trillion body cells.
Each cell has 46 chromosomes in nucleus.
Each chromosome is made of DNA with thousands genes.
3 billion base pairs make of DNA.
3. Delineate the impact of biotechnology on our society.
a. Describe the basic processes involved in the production of recombinant DNA.
b. Discuss examples of current uses of recombinant DNA technology in the agricultural and
pharmaceutical industries.
c. Discuss techniques of genetic screening.
d. Consider the implications of genetic screening of adults, children, and fetuses.
Research Project
4. Discuss the application of population genetics to the
study of evolution.
a. Describe the concepts of the deme and gene pool.
b. Consider the Hardy-Weinberg principle.
c. Describe the factors which influence genetic drift.
d. Consider the relevance of the gene pool and the idea of mutations to the concept of evolution.
Population Genetics
Activities