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Chapter 11
Introduction
to
Genetics
11-1 The Work of Gregor Mendel
I. Gregor Mendel
A. Studied pea plants
1. Reproduce sexually (have two sex cells = gametes)
2. Uniting of male and female gametes = Fertilization
3. Pollination = Transfer of pollen from male part of plant
to female part of plant
a. Two Types:
Male and female gametes come from
1. Self-pollinate: same plant, offspring are identical to
parents
a. Allows for true breeding: Produce identical offspring to self
2. Cross-pollinate:
Male and female gametes are from
two different plants
II. Laws of Heredity
A. Heredity: Passing on of characteristics from parents
to offspring
B. Genetics: Study of heredity
C. Traits: Characteristics that are inherited
D. Hybrid: Offspring of crosses between parents with different traits
E. Genes: Determines traits
F. Alleles: Forms of a gene
III. Mendel’s Experiment
A. Crossed plants with contrasting traits
1. Studied seven traits
Page 264
Mendel’s F1 Crosses on Pea Plants
D. all plants of intermediate height.
2. First crossed monohybrid (one trait) plants
a. P = parents
b. F1 = first filial generation
c. F2 = second filial generation
Example: P = tall x
short
F1= all tall
Self-pollinate: F1 x F1
F2= ¾ tall, ¼ short  3:1 ratio
B. Three Conclusions:
1. Biological inheritance is determined by factors (genes)
passed from one generation to the next
2. Rule of Dominance:
Some alleles are dominant and others are recessive
3. Law of Segregation:
gametes randomly pair
producing four combinations
of alleles (page 266)
11-2 Probability and Punnett Squares
IV. Probability
A. Likelihood a particular event will occur
B. Can be used to predict the outcomes of genetic crosses
V. Punnett Squares
A. Visual diagram to find all possible genetic variations of
offspring of a cross
B. Phenotype
1. Physical characteristic (looks/behavior/you can see it)
C. Genotype
1. Genetic make-up
2. Made up of alleles
3. Three combinations
a. Homozygous Dominant
TT
b. Homozygous recessive
tt
c. Heterozygous
Tt
D. Example:
Cross: Homozygous Dominant X
Cross:
Heterozygous
X
Homozygous Recessive
Heterozygous
11-3
VI. Dihybrid Cross (2 traits)
A. Round Yellow RRYY
B. F1= RrYy
C. F1 x F1 (self-pollinate)
Page 270
x wrinkled green
rryy
Page 271
D. 9 Round Yellow, 3 Round Green, 3 wrinkled Yellow,
1 wrinkled green
E. Get a 9:3:3:1 Ratio
Genes for different traits are
F. Law of Independent Assortment:
inherited independently from each
other during gamete formation
VII. Modes or Mechanisms (Different Ways) of Inheritance
A. Incomplete Dominance (Page 272 Figure 11-11)
1. Phenotype somewhere between the two alleles
Example: Red (RR) x White (R’R’) = PINK (RR’)
B. Codominance
1. Both alleles contribute to phenotype
Example: Black Rooster (BB)
x White Hen (WW)
= Checkered Chickens (BW)
C. Multiple Alleles (Page 273 Figure 11-12)
1. More than 2 alleles are available
Examples: eye color, rabbit fur color p273, blood type,
pigeon feather color (red, blue or chocolate)
D. Polygenic Traits- “continuous variation”
1. Traits controlled by more than 2 genes
Examples: human skin color, weight, height,
11-4 Meiosis
VIII. Chromosome Number
A. Homologous Chromosomes
1. Paired chromosomes with genes of same traits in same order
2. Not always identical
B. Haploid
1. Gamete cell has one of each kind of
chromosome
2. n
C. Diploid
1. Chromosome appear in pairs
(1 from mom and 1 from dad)
2. 2n
IX. Meiosis
A. Occurs in specialized cells that produce gametes
1. Gamete = sperm/ovum
B. Organisms inherit a single copy of every gene from each parent
C. Produces gametes with only 1 set of genes
D. Two divisions
1. Meiosis I and Meiosis II
2. Diploid (2n) cell at beginning of Meiosis I and 4 haploid
(n) cells at he end of Meiosis II
E. Stages
1. Interphase I
Interphase I
a. DNA replicates
2. Meiosis I
a. Prophase I
Prophase I
1. Chromatin coils, spindle fibers form, homologous
chromosomes pair up (matched gene by gene = TETRAD)
2.Nonsister chromatids overlap and exchange material =
Crossing Over (Page 277)
b. Metaphase I
1. Chromosomes attach to spindle fibers and homologous
chromosomes line up side by side
Metaphase I
c. Anaphase I
1. Homologous chromosomes separate by fibers and move to
opposite ends of the cell
Anaphase I
d. Telophase I and Cytokinesis
1. Nuclear membranes form and cell separates
Telophase I
2. The two cells produced by meiosis I have chromosomes
and alleles that are different from each other and from the
diploid cell that entered meiosis I.
e. The two cells produced by meiosis I now enter a second meiotic
division.
f. Unlike meiosis I, neither cell goes through chromosome (DNA)
replication.
PAGE 276
Meiosis I
Interphase I
Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
and
Cytokinesis
3. Meiosis II
a. Prophase II
1. Spindle fibers forms
Prophase II
Metaphase II
b. Metaphase II
1. Chromosomes line up in the middle of
the cell
c. Anaphase II
1. Centromere splits sister chromatids and
go to opposite ends of the cell
Anaphase II
Telophase II
d. Telophase II and Cytokinesis
1. Nuclei reform, spindle fibers
break down, cytoplasm divides
e. END RESULT: 4 haploid cells (different)
PAGE 277
Meiosis II
Telophase I and
Cytokinesis I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
and
Cytokinesis
X. Gamete Formation
A. In male animals, meiosis results in four equal-sized gametes
called sperm.
Page 278
B. In many female animals, only one egg results from meiosis.
The other three cells, called polar bodies, are usually not
involved in reproduction.
Page 278
XI. Comparing Mitosis and Meiosis
Mitosis
vs
Meiosis
1 division
2 divisions
2 identical diploid cells
4 different haploid cells
Same # of chromosomes as
parent cell
½ the # of chromosomes
as parent cell
Body (somatic) cells
Sex cells (gametes)
Page 280
11-5 Linkage and Gene maps
XII. Gene Linkage
A. Chromosomes are groups of linked genes
B. Chromosomes assort independently not the genes
C. Crossing over sometimes separates genes on
chromosomes = Genetic Diversity increases
XIII. Gene Maps
A. Show distance between genes on chromosomes
B. The closer together two genes are to each other, the
more likely they are to be inherited together.
C. The farther apart two genes are from one another, the less likely
they are to inherited together (due to crossing over).
11-1
Gametes are also known as
A. genes.
B. sex cells.
C. alleles.
D. hybrids.
11-1
The offspring of crosses between parents with
different (contrasting) traits are called
A. alleles.
B. hybrids.
C. gametes.
D. dominant.
11-1
In Mendel’s pea experiments, the male gametes
are found in the
A. eggs.
B. seeds.
C. pollen.
D. sperm.
11-1
In a cross of a true-breeding tall pea plant with a
true-breeding short pea plant, the F1 generation
consists of
A. all short plants.
B. all tall plants.
C. half tall plants and half short plants.
11-1
If a particular form of a trait is always present
when the allele controlling it is present, then the
allele must be
A. mixed.
B. recessive.
C. hybrid.
D. dominant.
11-2
Probability can be used to predict
A. average outcome of many events.
B. precise outcome of any event.
C. how many offspring a cross will produce.
D. which organisms will mate with each other.
11-2
Compared to 4 flips of a coin, 400 flips of the coin is
A. more likely to produce about 50% heads and
50% tails.
B. less likely to produce about 50% heads and 50%
tails.
C. guaranteed to produce exactly 50% heads and
50% tails.
D. equally likely to produce about 50% heads and
50% tails.
11-2
Organisms that have two different alleles for a
particular trait are said to be
A. hybrid.
B. heterozygous.
C. homozygous.
D. recessive.
11-2
Two F1 plants that are homozygous for shortness
are crossed. What percentage of the offspring
will be tall?
A. 100%
B. 50%
C. 0%
D. 25%
11-2
The Punnett square allows you to predict
A. only the phenotypes of the offspring from a
cross.
B. only the genotypes of the offspring from a cross.
C. both the genotypes and the phenotypes from a
cross.
D. neither the genotypes nor the phenotypes from a
cross.
11–3
In a cross involving two pea plant traits, observation of
a 9 : 3 : 3 : 1 ratio in the F2 generation is evidence
for
A. the two traits being inherited together.
B. an outcome that depends on the sex of the parent
plants.
C. the two traits being inherited independently of
each other.
D. multiple genes being responsible for each trait.
11–3
Traits controlled by two or more genes are called
A. multiple-allele traits.
B. polygenic traits.
C. codominant traits.
D. hybrid traits.
11–3
In four o'clock flowers, the alleles for red flowers
and white flowers show incomplete dominance.
Heterozygous four o'clock plants have
A. pink flowers.
B. white flowers.
C. half white flowers and half red flowers.
D. red flowers.
11–3
A white male horse and a tan female horse
produce an offspring that has large areas of
white coat and large areas of tan coat. This is
an example of
A. incomplete dominance.
B. multiple alleles.
C. codominance.
D. a polygenic trait.
11–3
Mendel's principles apply to
A. pea plants only.
B. fruit flies only.
C. all organisms.
D. only plants and animals.
11-4
If the body cells of humans contain 46
chromosomes, a single sperm cell should have
A. 46 chromosomes.
B. 23 chromosomes.
C. 92 chromosomes.
D. between 23 and 46 chromosomes.
11-4
During meiosis, the number of chromosomes per
cell is cut in half through the separation of
A. daughter cells.
B. homologous chromosomes.
C. gametes.
D. chromatids.
11-4
The formation of a tetrad occurs during
A. anaphase I.
B. metaphase II.
C. prophase I.
D. prophase II.
11-4
In many female animals, meiosis results in the
production of
A. only 1 egg.
B. 1 egg and 3 polar bodies.
C. 4 eggs.
D. 1 egg and 2 polar bodies.
11-4
Compared to egg cells formed during meiosis,
daughter cells formed during mitosis are
A. genetically different, while eggs are genetically
identical.
B. genetically different, just as egg cells are.
C. genetically identical, just as egg cells are.
D. genetically identical, while egg cells are
genetically different.
11-5
According to Mendel's principle of independent
assortment, the factors that assort independently
are the
A. genes.
B. chromosomes.
C. chromatids.
D. gametes.
11-5
A chromosome is actually a group of
A. independent genes.
B. linkage groups.
C. crossed-over genes.
D. linked genes.
11-5
Thomas H. Morgan is credited with the discovery
of the principle of
A. segregation.
B. independent assortment.
C. gene linkage.
D. dominance.
11-5
Linkage maps can be produced because the farther
apart two genes are on a chromosome,
A. the less likely they are to assort independently.
B. the more likely they are to be linked.
C. the more likely they are to be separated by a
crossover.
D. the less likely they are to be separated by a
crossover.
11-5
If two genes are close together on the same
chromosome, they are more likely to
A. behave as though they are linked.
B. behave independently.
C. move to different chromosomes.
D. belong to different linkage groups.
Dihybrid Cross
• Parents are heterozygous for both traits.
• Trait- Flower color –Purple dominant over white
•
Height- Tall dominant over short
• List parents, gamete combos, Punnett Square and
Phenotypes with ratios or fractions.