Download Ch. 11 Intro to Genetics

UNIT IV
Chapter 11
Introduction to Genetics
Introduction to Genetics
I. Ancient Concepts of Genetics
A. Domestication of Plants and Animals
1. Necessary step in human societies (going
from hunter/gatherer to agriculture and herding)
2. Gradual process
3. Dogs sheep, goats, oxen,
horses, camels domesticated
10,000 to 12,000 years ago
4. Cultivated plants developed
(date palms, cereal crops, rice,
corn) at same time
B. ‘Myths and Mutants’
1. Work with animals led to recognition of
heritable traits in humans
Heredity- biological inheritance
2. Stories of heritable deformities in humans
appear in myths and legends (e.g. cyclops,
giants, etc.)
a. 60 birth defects on Babylonian clay
tablets (5000 years ago)
b. Knowledge of traits played role in
shaping social customs and more (e.g.
choosing a wife/husband)
C. Early Theories
1. Theory of Blending of Inheritance- e.g.
giraffe result of mating of camel with leopard.
+
=
2. Democritus (300 B.C.)- idea that tiny
particle (pangenes) controlled inheritance of
particular traits.
a. Each part of body
contained these particles
responsible for inheritance of
that specific part
b. Periodically these particles
joined to form sperm and ova.
3. Pangenisis- (inheritance of acquired
characteristics) theory of Jean Baptiste
Lamarck- late 18th century. Any change in animal
or plant after it had been born or sprouted but
before it had reproduced was passed onto
offspring when it did reproduce.
a. Modified ideas of Democritus
(inheritance of pangenes)
b. Environment could induce changes
(e.g. long neck of giraffe, ‘acquired’
large claw of fiddler crab
c. Errors quite obvious
4. Preformation- 17th century. Sperm and
egg discovered- thought contained miniatures
of adults
II. The Work of Gregor Mendel
A. Gregor Mendel (1822-1884)
“Father of Genetics”
Genetics- branch of biology that studies
heredity
1. Discovered basic principles of
heredity- still apply today
2. Conducted carefully planned
experiments
a. Selected pea plants for study
1). Easy to grow, take little space,
easily observable traits
2). Can be self-pollinated or
cross-pollinated
To cross-pollinate pea plants,
Mendel cut off the male parts of
one flower and then dusted it with
pollen from another flower. The
resulting seeds were crosses
between the two plants
b. Applied math with biology. (analyzed
results according to principles of probability
and statistics
B. Genes and Dominance
1. Mendel studied 7 different pea plant traits
trait- specific characteristic, such as seed color or
height
a. Each trait has contrasting
characters (e.g. green seed
color or yellow seed color)
b. Mendel crossed plants with 7
contrasting characters.
c. P (parental) generationeach original generation
d. F1 generation – offspring of
P generation (“filial”- Latin word
for “son”)
e. Hybrids- offspring of crosses
between parents with different
traits.
2. Mendel’s experiments
a. First set of experiments- crossed
purebred tall plants with purebred short
plants
Purebred- organism that always produces the
same trait in offspring. (homozygous)
1). Offspring (F1
generation) were all Tall
no blending. Short trait
seemed to disappear
2). From this, Mendel concluded 2 things
a). Biological inheritance is determined by
factors passed from one generation to the
next (we now call genes). Said these
occurred in two contrasting forms (e.g.
tall/short) different forms called alleles
b). Principle of Dominance- States that
some alleles are dominant and others are
recessive
Dominant alleletrait always shows
Recessive allelewill only have that
form when dominant
allele for trait is not
present
b. Second set of experiments- Mendel
wanted to answer the question- “did recessive
. they still present in F1
alleles disappear or were
plants
1). Allowed F1 hybrid plants to produce F2
by self-pollination
2). 25% of offspring showed recessive
characteristics
3). Explained as follows: The
Principle of SegregationMendel said that alleles for
tall and short in F1 plants
were separated (segregated)
from each other during the
formation of sex cells
(gametes)
III. Probability and Punnett Squares
A. Genetics and Probability- Mendel realized
principles of probability could be used to explain
results of genetic crosses.
1. Probability- likelihood that a
particular event will occur.
2. Alleles segregate randomly like
a coin flip. 50/50 chance each
time.
B. Punnett Square- tool used to represent the
possible gene combinations from a genetic cross.
parent
gametes
Dominant Allele
Possible offspring
Recessive allele
homozygous
heterozygous
1. Phenotype- physical characteristics (what
they look like. (e.g. tall, short)
2. Genotype- genetic makeup (e.g. TT, Tt, tt)
TT
tt
C. Independent Assortment- Mendel wanted to
find out if alleles separated independantly (is the
inheritance of one characteristic linked to another.
E.g. Must a round seed by yellow?)
1. Two-Factor Cross- Mendel experimented
to determine if alleles segregated
independently
2. Mendel’s two-factor
experimental results were very
close to 9:3:3:1 ratio predicted by
punnett square. Proved that genes
that segregate independently do
not influence each other’s
inheritance. Principle of
Independent Assortment
D. Beyond Dominant and Recessive Alleles
1. Incomplete Dominance- one allele is not
completely dominant over another (phenotype
is a uniform blend, original colors do not
show)
2. Codominance- similar to incomplete
dominance. Both original alleles contribute to
phenotype of organism and are shown
In certain varities of chickens, black and white feather colors
are caused by codominant alleles. Thus the heterozygous
phenotype, speckled black and white, is a result of the
expression of both alleles
3. Multiple Alleles- More than two possible
alleles exist for a trait (e.g. blood type, eye
color)(deals with one gene)
4. Polygenic traits- trait produced by
interaction of several genes (e.g. human skin
color, height of humans)
IV. Meiosis
A. Chromosome number
1. Diploid number- means “two sets”.
Represented by symbol 2N. One of each set
from mother/father. Sets called homologous
chromosomes
a. Diploid cells found in body
cells
b. Contains two sets of
chromosomes and two sets of
genes
2. Haploid number- means “one set”.
Represented by N.
a. Gametes (sex cells) all haploid
b. Haploid cells (gametes) produced by
meiosis I
B. Phases of Meiosis (2 stages)
1. Meiosis I- each chromotid arm is
replicated (copied)
a. Similar to mitosis- but chromosomes
line up in pairs- Tetrads in prophase I
b. Exchange of portions of chromatids
takes place while chromosomes exist as
tetrads. Called crossing-over
c. Results in two haploid daughter cells
1.
Meiosis IIa. replication of
chromatids
b. Results in four
haploid daughter cells
C. Gamete formation- in
animals: egg and sperm
Meiosis and fertilization
It’s easy to see how genes located on different
chromosomes assort independently, but what
about genes located on the same
chromosomes? Wouldn’t they generally be
inherited together?
The answer to these questions, Thomas
Hunt Morgan first realized in 1910, is yes!
D. Linkage and Gene Maps
1. Gene Linkage- genes on same
chromosome almost always inherited together
(unless separated by “crossing over” during
meiosis)
a. Experiments by Thomas Hunt Morgan
(1910)- research on fruit flies (Drosophila
melanogaster)
1). Chromosomes big, only 4 pair,
bred quickly
2). Concluded: chromosomes
assort independently, not the
individual genes
b. By luck, 6 of the 7 genes Mendel studied
were on different chromosomes (the two genes
found on the same chromosome were so far
apart that they also assorted independentlydue to crossing over)
2. Gene Maps- rate of “crossing over” used to
map location of genes on chromosomes
a. Alfred Sturtevant- said further apart the
genes were, the more likely they were to be
separated during crossover in meiosis
b. Gathered data and “mapped” location of
genes in Drosophila chromosomes
c. Also used to map human genome
Chapter 11
Introduction to Genetics
Gregor Mendel used pea plants to study
a.
flowering.
b.
gamete formation.
c.
the inheritance of traits.
d.
cross-pollination.
Gregor Mendel used pea plants to study
a.
flowering.
b.
gamete formation.
c.
the inheritance of traits.
d.
cross-pollination.
Offspring that result from crosses between
true-breeding parents with different traits
a.
are true-breeding.
b.
make up the F2 generation.
c.
make up the parental generation.
d.
are called hybrids.
Offspring that result from crosses between
true-breeding parents with different traits
a.
are true-breeding.
b.
make up the F2 generation.
c.
make up the parental generation.
d.
are called hybrids.
What are Mendel’s factors called today?
a.
alleles
b.
traits
c.
genes
d.
characters
What are Mendel’s factors called today?
a.
alleles
b.
traits
c.
genes
d.
characters
Mendel concluded that traits are
a.
not inherited by offspring.
b.
inherited through the passing of factors
from parents to offspring.
c.
determined by dominant factors only.
d.
determined by recessive factors only.
Mendel concluded that traits are
a.
not inherited by offspring.
b.
inherited through the passing of
factors from parents to offspring.
c.
determined by dominant factors only.
d.
determined by recessive factors only.
The principle of dominance states that
a.
all alleles are dominant.
b.
all alleles are recessive.
c.
some alleles are dominant and others are
recessive.
d.
alleles are neither dominant nor recessive.
The principle of dominance states that
a.
all alleles are dominant.
b.
all alleles are recessive.
c.
some alleles are dominant and others
are recessive.
d.
alleles are neither dominant nor recessive.
When Mendel crossed true-breeding tall plants
with true-breeding short plants, all the offspring
were tall because
a.
the allele for tall plants is recessive.
b.
the allele for short plants is dominant.
c.
the allele for tall plants is dominant.
d.
they were true-breeding like their parents.
When Mendel crossed true-breeding tall plants
with true-breeding short plants, all the offspring
were tall because
a.
the allele for tall plants is recessive.
b.
the allele for short plants is dominant.
c.
the allele for tall plants is dominant.
d.
they were true-breeding like their parents.
If a pea plant has a recessive allele for green
peas, it will produce
a.
green peas if it also has a dominant allele
for yellow peas.
b.
both green peas and yellow peas if it also
has a dominant allele for yellow peas.
c.
green peas if it does not also have a
dominant allele for yellow peas.
d.
yellow peas if it does not also have a
dominant allele for green peas.
If a pea plant has a recessive allele for green
peas, it will produce
a.
green peas if it also has a dominant allele
for yellow peas.
b.
both green peas and yellow peas if it also
has a dominant allele for yellow peas.
c.
green peas if it does not also have a
dominant allele for yellow peas.
d.
yellow peas if it does not also have a
dominant allele for green peas.
When you flip a coin, what is the
probability that it will come up tails?
a.
1/2
b.
1/4
c.
1/8
d.
1
When you flip a coin, what is the
probability that it will come up tails?
a.
1/2
b.
1/4
c.
1/8
d.
1
The principles of probability can be used to
a.
predict the traits of the offspring produced
by genetic crosses.
b.
determine the actual outcomes of genetic
crosses.
c.
predict the traits of the parents used in
genetic crosses.
d.
decide which organisms are best to use in
genetic crosses.
The principles of probability can be used to
a.
predict the traits of the offspring
produced by genetic crosses.
b.
determine the actual outcomes of genetic
crosses.
c.
predict the traits of the parents used in
genetic crosses.
d.
decide which organisms are best to use in
genetic crosses.
Organisms that have two identical alleles for a
particular trait are said to be
a.
hybrid.
b.
homozygous.
c.
heterozygous.
d.
dominant.
Organisms that have two identical alleles for a
particular trait are said to be
a.
hybrid.
b.
homozygous.
c.
heterozygous.
d.
dominant.
In the Punnett square shown in Figure 11-1, which of the
following is true about the offspring resulting from the cross?
a.
About half are expected to be short.
b.
All are expected to be short.
c.
About half are expected to be tall.
d.
All are expected to be tall.
In the Punnett square shown in below, which of the following
is true about the offspring resulting from the cross?
a.
About half are expected to be short.
b.
All are expected to be short.
c.
About half are expected to be tall.
d.
All are expected to be tall.
What does a Punnett square NOT show?
a.
all possible results of a genetic cross
b.
the genotypes of the offspring
c.
the alleles in the gametes of each parent
d.
the actual results of a genetic cross
What does a Punnett square NOT show?
a.
all possible results of a genetic cross
b.
the genotypes of the offspring
c.
the alleles in the gametes of each paren
d.
the actual results of a genetic cross
If you made a Punnett square showing Mendel’s
cross between true-breeding tall plants with truebreeding short plants, the square would show
that the offspring had
a.
the genotype of one of the parents.
b.
a phenotype that was different from that of
both parents.
c.
a genotype that was different from that of
both parents.
d.
the genotype of both parents.
If you made a Punnett square showing Mendel’s
cross between true-breeding tall plants with truebreeding short plants, the square would show
that the offspring had
a.
the genotype of one of the parents.
b.
a phenotype that was different from that of
both parents.
c.
a genotype that was different from that
of both parents.
d.
the genotype of both parents.
What principle states that during gamete
formation genes for different traits separate
without influencing each other’s inheritance?
a.
principle of dominance
b.
principle of independent assortment
c.
principle of probabilities
d.
principle of segregation
What principle states that during gamete
formation genes for different traits separate
without influencing each other’s inheritance?
a.
principle of dominance
b.
principle of independent assortment
c.
principle of probabilities
d.
principle of segregation
The Punnett square in Figure above shows that the
gene for pea shape and the gene for pea color
a.
assort independently.
b.
are linked.
c.
have the same alleles.
d.
are always homozygous.
The Punnett square in Figure above shows that the
gene for pea shape and the gene for pea color
a.
assort independently.
b.
are linked.
c.
have the same alleles.
d.
are always homozygous.
How many different allele combinations would
be found in the gametes produced by a pea
plant whose genotype was RrYY?
a.
2
b.
4
c.
8
d.
16
How many different allele combinations would
be found in the gametes produced by a pea
plant whose genotype was RrYY?
a.
2
b.
4
c.
8
d.
16
Situations in which one allele for a gene is not
completely dominant over another allele for that
gene are called
a.
multiple alleles.
b.
incomplete dominance.
c.
polygenic inheritance.
d.
multiple genes.
Situations in which one allele for a gene is not
completely dominant over another allele for that
gene are called
a.
multiple alleles.
b.
incomplete dominance.
c.
polygenic inheritance.
d.
multiple genes.
A cross of a red cow with a white bull produces
all roan offspring. This type of inheritance is
known as
a.
incomplete dominance.
b.
polygenic inheritance.
c.
codominance.
d.
multiple alleles.
A cross of a red cow with a white bull produces
all roan (red ) offspring. This type of inheritance
is known as
a.
incomplete dominance.
b.
polygenic inheritance.
c.
codominance.
d.
multiple alleles.
A cross of a red cow with a white bull produces
all roan (red and white spots) offspring. This
type of inheritance is known as
a.
incomplete dominance.
b.
polygenic inheritance.
c.
codominance.
d.
multiple alleles.
A cross of a red cow with a white bull produces
all roan offspring. This type of inheritance is
known as
a.
incomplete dominance.
b.
polygenic inheritance.
c.
codominance.
d.
multiple alleles.
Mendel’s principles of genetics apply to
a.
plants only.
b.
animals only.
c.
pea plants only.
d.
all organisms.
Mendel’s principles of genetics apply to
a.
plants only.
b.
animals only.
c.
pea plants only.
d.
all organisms.
If an organism’s diploid number is 12, its
haploid number is
a.
12.
b.
6.
c.
24.
d.
3.
If an organism’s diploid number is 12, its
haploid number is
a.
12.
b.
6.
c.
24.
d.
3.
Gametes are produced by the process of
a.
mitosis.
b.
meiosis.
c.
crossing-over.
d.
replication.
Gametes are produced by the process of
a.
mitosis.
b.
meiosis.
c.
crossing-over.
d.
replication.
What is shown in figure above?
a. independent assortment
b. b. anaphase I of meiosis
c. crossing-over
d. replication
What is shown in figure above?
a.
independent assortment
b.
anaphase I of meiosis
c.
crossing-over
d.
replication
Unlike mitosis, meiosis results in the formation of
a.
diploid cells.
b.
haploid cells.
c.
2N daughter cells.
d.
body cells.
Unlike mitosis, meiosis results in the formation of
a.
diploid cells.
b.
haploid cells.
c.
2N daughter cells.
d.
body cells.
Linked genes
a.
are never separated.
b.
assort independently.
c.
are on the same chromosome.
d.
are always recessive.
Linked genes
a.
are never separated.
b.
assort independently.
c.
are on the same chromosome.
d.
are always recessive.
If two genes are on the same chromosome and
rarely assort independently,
a.
crossing-over never occurs between the
genes.
b.
crossing-over always occurs between the
genes.
c.
the genes are probably located far apart
from each other.
d.
the genes are probably located close to
each other.
If two genes are on the same chromosome and
rarely assort independently,
a.
crossing-over never occurs between the
genes.
b.
crossing-over always occurs between the
genes.
c.
the genes are probably located far apart
from each other.
d.
the genes are probably located close to
each other.