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Genetics.notebook
Unit 3: Genetics
October 26, 2012
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.
Jun 24­1:36 PM
Oct 23­2:58 PM
Heredity
• All organisms pass on their characteristics from generation to generation through INHERITANCE.
• 2 kinds of characteristics inherited:
1.
Species characteristics: each species always passes on their own traits.
2.
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.)
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
• Heredity is controlled by a chemical code in our DNA.
• Another factor that will affect what we inherit are independent events.
• This genetic code is present in the chromosomes of the gametes (egg and sperm).
• An event that takes place that no previous event has an effect on.
Oct 23­2:58 PM
• 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.
Oct 23­3:03 PM
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Probability
In­Class Discussion
How does heredity affect you?
• 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.
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".
Oct 23­3:07 PM
List of Traits:
Dominant or Recessive:
Oct 23­3:09 PM
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
Oct 24­9:13 AM
Oct 24­9:28 AM
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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.
October 26, 2012
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.
Oct 24­9:14 AM
GENETICS
GENETICS: the branch of biology that studies the ways in which
hereditary information is passed on from parents to offspring.
GREGOR MENDEL:
• (1822­1884) 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.
Oct 24­9:14 AM
Mendel and His Experiments
• Gregor Mendel: Austrian monk
1822­1884
studied garden peas
• Mendel studied peas and cross­fertilized 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)
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Jun 24­1:36 PM
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• 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 geneis
designated by a lower case letter.
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.
• For each trait, an organism gets one gene form the mother and one gene
from the father.
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Jun 24­1:36 PM
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
Review....
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.
1. List and explain one of the new terms learned last day.
Homozygous: an organism contains 2 genes for one trait that are the same, Ex) RR or rr : the organism is pure for the trait.
2. What was one of Gregor Mendal's laws?
Heterozygous: an organism contains 2 genes for one trait that are different. Ex) Rr
Alleles: two or more alternate forms of a gene.
Ex) seed coat alleles
Dominant
R (smooth)
Recessive
r (wrinkled)
Oct 24­9:35 AM
Oct 24­9:41 AM
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Monohybrid Cross
1. Explain the significance of Mendel`s experiments and observations and the laws derived from them.
• Mono (one)
• Hybrid (result from crosses between parents that are genetically not
alike)
g. Consider the value of the punnett square by creating examples of mono and dihybrid crosses.
• Monohybrid Cross: a cross that involved one pair of contrasting genes for
one trait.
Oct 24­9:41 AM
Jun 24­1:36 PM
Ex) Dealing with the trait of Seed Coat
Punnet Square for Monohybrid Cross
Punnet Square: chart used by geneticists to show the possible combinations
of alleles in offspring.
Round seed coat X Wrinkled seed coat
(parent)
rr
Crossed Again
Hybrid Offspring X
RR
(F1 generation)
Round Seed Coat
(F = filial)
Rr
Wrinkled Parent (homozygous)
r
r
Rr
RR
(F2 generation)
Rr
Rr
rr
R
Round Parent
(homozygous)
R
(F1 generation)
all _ Rr, heterozygous
Jun 24­1:36 PM
Jun 24­1:36 PM
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Monohybrid Cross Genotypic Ratio
1 RR (homozygous dominant) : 2Rr (heterozygous) : 1rr (homozygous recessive)
Round Parent (heterozygous)
r
R
Monohybrid Cross Phenotypic Ratio
R
3 round : 1 wrinkled
Round Parent
(heterozygous)
3 with the dominant trait showing : 1 with the recessive trait showing
r
3/4 or 75% : 1/4 or 25%
(F2 generation)
_ RR homozygous dominant, _ Rr heterozygous and _ rr homozygous (recessive)
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Jun 24­1:36 PM
Lets look at this in more detail.
Examples:
X
RR
rr
(parents)
sex cells
R R
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?
sex cells
r
r
Rr (F1 generation) X
Rr
Parent A = BB
Parent B = bb
RR
(F2 generation)
Rr
Rr
round
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sex cells
R r
rr
wrinkled
Oct 24­1:03 PM
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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.
October 26, 2012
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 =
short plant = tt
Oct 24­1:06 PM
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.
Oct 24­2:24 PM
Oct 24­1:18 PM
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?
Oct 24­1:00 PM
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Example of a dihybrid cross:
Yellow Round
Dihybrid Cross
X Green Wrinkled
(parent)
Di = 2
Hybrid: result from crosses between parents that are genetically not alike.
Dihybrid cross: a cross that involves 2 traits.
(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
Jun 24­1:36 PM
Jun 24­1:36 PM
Punnet Square for Dihybrid Cross
YyRr
yyrr Green and Wrinkled Parent (homozygous)
YYRR
Parent
Yellow & Round
(homozygous)
yr
yr
YR
YR
(F1 Generation)
_ YyRr (yellow & round, heterozygous)
YR
YyRr
Yellow & Round Parent (heterozygous)
Yr
yr
yR
YR
Yellow & Round
Yr
Parent
(heterozygous)
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
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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:
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.
a) Homozygous for black, heterozygous for short­hair guinea pig crossed with a white, long­haired guinea pig.
b) Heterozygous for black and short­hair guinea pig crossed with a white, long­hair guinea pig.
Oct 24­1:20 PM
c) Homozygous for black and long­hair crossed with a heterozygous black and short­hair guinea pig.
Oct 24­1:26 PM
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, sickle­cell anemia, Down`s syndrome, and Tay­Sach`s disease.
Oct 24­1:29 PM
Oct 24­2:27 PM
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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.
Jun 24­1:36 PM
Jun 24­1:36 PM
Incomplete Dominance
Determine the genotype of the parent plants
by looking at the
phenotypes of the offspring from the following cross.
The lack of a dominant gene. Both alleles contribute to the phenotype of a
heterozygote. Produces an offspring with traits unlike either parent.
Round, yellow X Wrinkled, green
Ex)
1/4 round, yellow, 1/4 round, green, 1/4 wrinkled, yellow, 1/4 wrinkled, green
Red snapdragon (RR) X White snapdragon (WW)
F1Generation
All Pink Snapdragons (RW)
RW
F2Generation
X RW
R W
R
W
1 RR (red) : 2RW (pink) : 1 WW (white)
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Jun 24­1:36 PM
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Codominance
• Two dominant genes are expressed at the same time in the heterozygous
organism.
Ex) Shorthorn Cattle
Red (H RHR) X White (HW HW )
Roan Calf ­ it has intermingling of white and red hair
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.
Red (wild type) eyes : most common
F1 Generation
(all) HRHW X HRHW
Dominant Hierarchy
Apricot
Honey
F2 Generation
HR HW
HR
White
Note: a drosophila can only have 2 different genes at one time, but many alleles
are possible.
Hw
1 HRHR : 2HRHW : 1HW HW
Jun 24­1:36 PM
• When using multiple alleles we no longer use upper and lower case
letters. Capital letters with subscript numbers are used.
Jun 24­1:36 PM
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
Red (wild type) eyes E1E1 OR E1E2, E1E3, E1E4
Apricot E2E2, E2E3, E2E4
Honey E3E3, E3E4
White E4E4
Genotype Phenotype
IAIA or IAi Type A Blood
IB IB or IB i 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.
Jun 24­1:36 PM
Jun 24­1:36 PM
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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.
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.
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?
Oct 24­1:39 PM
Review...
1. What is incomplete dominance? Provide an
example.
2. What is meant by the term "multiple alleles?"
Provide an example.
Oct 24­1:40 PM
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, sickle­cell anemia, Down`s syndrome, and Tay­Sach`s disease.
3. What is co­dominance?
Oct 24­1:41 PM
Oct 24­1:41 PM
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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?
October 26, 2012
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?
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?
Oct 24­1:41 PM
Co-dominance Example Problem...
1. Predict the phenotypic ratios of offspring when a
homozygous white cow is crossed with a roan bull?
Oct 24­1:42 PM
Multiple Alleles Example Problem...
1. Remembering what you learned about blood types, what are
the possible phenotypes of children in the following families?
a) Heterozygous type A mother, Homozygous type A father?
b) Homozygous type B mother, type AB father?
2. What should the genotypes and phenotypes for parent
cattle be if a farmer wanted only cattle with red fur?
c) type AB mother, type AB father?
Oct 24­1:42 PM
Oct 24­1:42 PM
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Sex - Linked Traits
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, sickle­cell anemia, Down`s syndrome, and Tay­Sach`s disease.
• Sex­linked traits : controlled by genes located on the sex chromosomes.
• In humans the sex chromosomes go as follows:
Female = XXMale = 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.
j. Discuss the similarities and differences between sex chromosomes and somatic chromosomes.
X
Oct 24­1:43 PM
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
X
Jun 24­1:36 PM
Sex­linked disorders in Humans:
1. Color­Blindness: 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 color­blindness on one X chromosome and the normal dominant allele on
the other X chromosome.
Female Carrier
Normal Female
Color­blind Female
XX' XXX'X'
• Most sex­linked traits are determined by genes found on the X
chromosome but not on the Y chromosome.
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Jun 24­1:36 PM
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• Every male gets an X chromosome from its mother and a Y chromosome
from his father.
Mother = XX
Father = XY
Male Offspring
Male Offspring
• 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.
XY
Mother a Carrier
XX'
• 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.
Father
XY
Mother
XX'
Father
X'Y
Color­Blind Female Offspring X'X'
XY or X'Y
Remember: color­blindness is transmitted only through the female.
There is a 50% chance that the male son will have color blindness.
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Jun 24­1:36 PM
Somatic Cells: are all the cells of an organism except the sex cells.
2. Hemophilia: sex­linked disorder in which the blood is unable to clot
because it lacks a certain blood­clotting protein.
: the recessive gene for hemophilia is carried on the X
chromosome.
What is a somatic chromosome based on what you know about somatic cells?
: 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.
Jun 24­1:36 PM
What is the difference between sex chromosomes and somatic chromosomes?
Oct 26­9:43 AM
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Pedigree
Pedigree
­ means of tracing sex­linked 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
Oct 24­1:45 PM
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.
Jun 24­1:36 PM
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, sickle­cell anemia, Down`s syndrome, and Tay­Sach`s disease.
Oct 24­1:46 PM
Oct 24­1:46 PM
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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. October 26, 2012
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).
DNA­deoxyribonucleic acid: carries the genetic code, carries genetic information.
Jun 24­1:36 PM
Karyotype: pictures of chromosomes arranged in homologous pairs.
Jun 24­1:36 PM
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 1­22.
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 #28). Only females, do not develop sexually, tend to be short and have thick wide necks.
Jun 24­1:36 PM
Jun 24­1:36 PM
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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.
October 26, 2012
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.
Ex) Klinefelter Syndrome: 3 sex chromosomes (XXY). Appears to be male, @ puberty produces large amounts of female hormones. Sterile.
Jun 24­1:36 PM
Protein Synthesis
1. Transcription
Oct 24­2:41 PM
2. Discuss the relationship among chromosomes, genes, and DNA.
f. Describe the causes and effects of both chromosomes and gene mutations.
2. Translation
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2. Discuss the relationship among chromosomes, genes, and DNA.
Mutations Handout
k. Using examples from living organisms discuss the importance of asexual and sexual reproduction to their growth and survival.
Jun 24­1:36 PM
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.
Jun 24­1:36 PM
Oct 24­2:42 PM
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.
Jun 24­1:36 PM
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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:
2. Discuss the relationship among chromosomes, genes, and DNA.
c. Compare mitosis and meiosis.
Oct 24­2:40 PM
Mitosis
1st INTERPHASE
Oct 24­1:47 PM
Cell division occurs in a series of stages, or phases.
3rd: METAPHASE
• Chromatids (or pairs of chromosomes) attach to
the spindle fibers.
• 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.
sister chromatids
centromere
4th: ANAPHASE
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.
Jun 24­1:36 PM
• Chromatids (or pairs of chromosomes) separate
and begin to move to opposite ends of the cell.
sister
chromatids
split
Jul 28­2:05 PM
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5th: TELOPHASE
• Two new nuclei form
• Chromosomes appear as chromatin (threads
rather than rods)
• Mitosis ends
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).
6th: CYTOKINESIS
• Cell membrane moves inward to create two
daughter cells ­ each with its own nucleus with
identical chromosomes.
Jul 28­2:05 PM
Review...
1. What happens, most importantly, during
interphase?
cell plate
Oct 24­1:48 PM
2. Discuss the relationship among chromosomes, genes, and DNA.
c. Compare mitosis and meiosis.
2. What is the end result of mitosis?
Oct 24­1:49 PM
Oct 24­1:50 PM
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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
Oct 24­1:50 PM
­ each tetrad moves onto a spindle
and attaches to a single fibril at the
equator
iv) ANAPHASE I
Oct 24­1:52 PM
v) TELOPHASE I
iii) METAPHASE 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
­ 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
­ 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
Oct 24­1:52 PM
Oct 24­1:52 PM
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October 26, 2012
b) MEISOSIS II: occurs in both haploid daughter cells at the same time
iii) ANAPHASE II
Interkinosis: basically interphase, except there is no replication of chromosomes
­ the centromere holding each pair of
sister chromatids together dissolves
­ sister chromatids move to opposite poles
i) PROPHASE II
­ nuclear membrane dissolves
­ centrioles move and spindles form
­ double­stranded chromosomes
shorten and thicken
iv) TELOPHASE II
ii) METAPHASE II
­ double­stranded chromosomes
attach the spindle and line up at the
equator
Oct 24­1:53 PM
Review...
­ 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
Oct 24­1:55 PM
2. Discuss the relationship among chromosomes, genes, and DNA.
1. What is the end result of meiosis?
2. Why must our sex cells be produced through
meiosis and not mitosis?
Oct 24­1:56 PM
g. Consider the purposes and techniques of gene mapping.
Oct 24­2:53 PM
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October 26, 2012
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
Jul 28­2:05 PM
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.
Jul 28­2:05 PM
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.
Research Project
c. Discuss techniques of genetic screening.
d. Consider the implications of genetic screening of adults, children, and fetuses.
Oct 24­2:44 PM
Oct 24­2:54 PM
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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 Hardy­Weinberg principle.
c. Describe the factors which influence genetic drift.
Population Genetics
Activities
d. Consider the relevance of the gene pool and the idea of mutations to the concept of evolution.
Oct 24­2:46 PM
Jul 28­2:05 PM
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