Chapter 10 Sexual Reproduction and Genetics

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Chapter 10Sexual Reproduction and Genetics
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• I. Meiosis produces four haploid sex cells from
  one original diploid (2n) cell.

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A. Eggs are gametes produced by the female.
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B. Sperm are gametes produced by the male.
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C. Diploid cells (2n) are cells with two of each
kind of chromosome.
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D. Gametes are haploid cells (n)cells with one
of each kind of chromosome.
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E. When a sperm fertilizes and egg, the
resulting cell is called a zygote.
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II. Phases of Meiosis I
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A. During Prophase I, each pair of homologous
chromosomes comes together to form a tetrad.
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B. Homologous chromosomes may exchange genetic
material in a process known as crossing over.
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III. Phases of Meiosis II
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IV. Mendels Genetics A. Gregor Mendel
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1. Studied heredity (passing of characteristics
from parent to offspring)
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2. Father of genetics(branch of biology that
studies heredity)
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3. Inherited characteristics are called traits.
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B. Mendels Experiments 1. Used pea
plants because
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Grew fast
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b. reproduced sexually
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Male gamete is pollen
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(2) Female gamete is an ovule
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2. Mendel transferred pollen from one plant to
anotherthis was a cross.
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a. Transfer of pollen to ovule is pollination.
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b. Fertilization occurs when male and female
gametes fuse.
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3. Characteristics or Traits Mendel observed
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4. Phenotype and Genotype
a. Genotype is gene combination (TT)b.
Phenotype is physical appearance expression
of the genotype (tall)
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c. Two organisms can look alike but have
different underlying gene combinations.TTtallTt
tall
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5. Homozygous-two alleles for a trait are the
same (TT or tt)
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6. Heterozygous-two alleles for a trait are
different (Tt)
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C. Mendels Monohybrid Crosses 1. Cross
between two parents that differ only by a
single trait.
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2. Generations a. P1 parent b. F1 filial
(daughter or son) c. F2 2nd filial
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D. Mendels Rule of Unit Factor
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1. Genes exist in alternative forms called
alleles.
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E. Mendels Rule of Dominance 1. Only one trait
is observed (either TALL or short)
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2. The observed trait is dominant.3. The trait
that disappeared is recessive.
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F. Mendels Law of Segregation A parent passes
on at random only one allele for each trait to
its offspring
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G. Punnett Squares
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• Method used to establish the probabilities of the
  results of a genetic cross.

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H. Uses of Punnett Squares in Monohybrid
crosses.
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1. Example 1

• Show the cross between a homozygous tall pea
  plant and a homozygous short pea plant.
• TT X tt

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T
T
Tt
t
Tt
t
Tt
Tt
All offspring will be heterozygous Tall
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2. Example 2

• Show the cross between a homozygous rough coat
  guinea pig and a heterozygous guinea pig.
• Rough is dominant to smooth
• RR X Rr

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R
R
R
RR
RR
r
Rr
Rr
Genotypic Ratio- RR 2 Rr 2 11 Phenotypic
ratio- 100 Rough
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3. Example 3

• Show the cross between two heterozygous Black
  coat rabbits.
• Black is dominate to brown.
• Bb X Bb

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b
B
B
Bb
BB
bb
Bb
b
Genotypic ratio-BB 1 Bb 2 bb 1
Phenotypic ratio- Black 3 Brown 1
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I. Uses of Punnett squares to show Incomplete
dominance and Codominance.


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Incomplete Dominance

• The phenotype of the heterozygotes is a blend of
  the two homozygotes.

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Example of Japanese Four Oclocks

• RedRR
• WhiteRR
• Show the cross between a homozygous red and a
  homozygous white flower.
• RR X RR

R
R


RR
RR
R
R
RR
RR
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Example 2 of Japanese Four Oclocks

• Show the cross between two pink flowered Japanese
  Four Oclocks.

R
R


RR
RR
R
RR
RR
R
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2. Codominance

• The phenotypes of both homozygotes are produced
  in a heterozygote.
• Both alleles are expressed equally.

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Example of Black and White Checked Chickens

• BBBlack
• WWWhite

B
B
B
W




W
BW
BW
BW
BB
B
W
BW
BW
W
BW
WW
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3. Codominance in Humans

• Example Sickle-Cell Anemia (page 303)

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J. Uses of Punnett Squares with Test Crosses
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1. Test Cross

• -the procedure in which an individual of unknown
  genotype is crossed with a homozygous recessive
  individual.

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2. Example of a test cross.

• Biologys rabbit, Buttons (you know the one that
  was spray painted) appears to be Himalayan. I
  need to know her genotype. If she is homozygous
  dominate she is worth about 50. If she is
  heterozygous, she is worth about 5. I can do a
  test cross to determine her genotype and her
  dollar value.

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Buttons genotype HH or Hh?
h
H
H
H




Hh
hh
h
Hh
h
Hh
h
Hh
Hh
hh
h
Hh
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REAL RESULTS

• Button had eight babies 5 Himalayan

• and 3 white.

• SO she is a 5 bunny! (But we love her anyway!)

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K. Uses of Punnett Squares in Dihybrid Crosses.

• A dihybrid cross is a cross involving two
  different traits.
• Example Show the cross between two heterozygous
  tall plants with round seeds.
• TtRr X TtRr

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Rr
Tt
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Combinations of gametes with TtRr X TtRr

• TR
• Tr
• tR
• tr
• Each one of these could become a gamete.

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Tr
tR
TR
tr




TR
TtRR
TTRR
TTRr
TtRr
TtRr
TTRr
TTrr
Ttrr
Tr
TtRr
TtRR
ttRr
ttRR
tR
ttrr
Ttrr
ttRr
TrRr
tr
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L. Simple Dominant Heredity

• 1. Organism needs one dominate allele for
  phenotype to be expressed.
• 2. Human phenotypes include

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a. Hapsburg lip

• The above portrait is of Charles II, who was King
  of Spain from 1665 to 1700, and who displays this
  characteristic trait, a trait that was passed
  down through the Austro-Hungarian monarchy
  through successive inbreeding.  The Hapsburg lip
  deformity affected poor Charles II so badly that
  he could not chew his food.  Years of inbreeding
  had also taken its toll on his intelligence (he
  was retarded) and his powers of procreation (he
  was impotent).

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b. Hitchhikers Thumb
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c. Huntingtons disease
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The Huntington's disease gene was identified in
1993 and is located near the top of the fourth
chromosome.
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M. Simple Recessive Heredity

• 1. Most genetic disorders are caused by
  recessive alleles.
• 2. Human disorders include

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a. Cystic fibrosis
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b. Tay-Sachs Disease
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N. Pedigree-pg. 299 know symbols
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O. Multiple Alleles 1. Multiple phenotypes
result from multiple alleles. 2. Traits
controlled by more than two alleles
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3. Multiple Alleles in Humansa. Blood
TypingKNOW pg. 304!!b. Know why pg. 304 is
important!!
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P. Sex-linked Inheritance 1. Traits controlled
by genes on the sex chromosomes are sex-linked
traits.
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• 2. X and Y are not homologous. 3. Y has no
  corresponding alleles.4. Y-linked traits are
  passed only from male to male.

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5. Sex-linked Traits in Humans

• a. Red-Green Color Blindness caused by the
  inheritance of either of two recessive alleles at
  two gene sites on the X chromosome

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b. Hemophilia

• Males inherit the allele from their carrier
  mother. (Queen Victoria and Royal Hemophilia pg.
  308)
• Females need two recessive alleles.

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Q. Polygenic Inheritance

• 1. Trait is controlled by two or more genes
• 2. May or may not be on the same chromosome
• 3. Represented by upper and lower case letters

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4. Example of Plant Stem Length

• 3 genes A, B, and C
• aabbcc 3 cm tall
• AABBCC 12 cm tall
• AaBbCc 6 cm tall
• each dominant allele 2 cm

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5. Example in Humans Skin Color 3 genes A, B,
C (6 alleles)

• aabbcc very light
• AABBCC very dark
• AaBbCc medium
• all heterozygotes are
• intermediate phenotypes

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R. Changes in Chromosome numbers

• 1. Autosomes with unusual numbers
• Example Trisomy
• three chromosomes
• instead of two
• Downs Syndrome

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2. Sex Chromosomes with unusual numbers

• Example 1 X
• (monosomy)
• Turners
• Syndrome

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Example 2

• XXY or XXX
• or XYY
• Trisomy
• Klinefelter
• Syndrome
• (XXY)