Basic Genetics

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Do Now

• 1. Certain acquired characteristics, such as
  mechanical or mathematical skill may be
  inherited.
• 2. Certain thoughts or experiences of a mother
  mark or alter the hereditary makeup of an unborn
  child.
• 3. Color blindness is more common in males than
  in females.
• 4. A person may transmit characteristics to
  offspring which he/she does not show.
• 5. Certain inherited traits may be altered by the
  stars, planets or moon early in development.
• 6. The total number of male births exceeds female
  births each year.

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Objectives

• To distinguish between heredity and inheritance
• To describe Mendels experiments in heredity
• To compare heterozygous vs. homozygous and
  dominant vs. recessive.

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Genetics

• Chapter 4

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Basic Genetics

The Father of Genetics
Gregor Mendel
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1866- Gregor Mendel

• Austrian Monk
• Worked with Pea Plants
• Pure breeds
• Self-fertilization
• Discovered how traits were inherited in a
  population

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Heredity transmission of traits from parents to
their offspring
Inheritance passing of traits by heredity
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Mendels experiments used pea plants
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Pollination transfer of pollen from anthers to
stigma in flowers

• 1) self pollination occurs within the same
  flower or same plant
• 2) cross pollination occurs between different
  plants

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Mendels Crosses with Pea Plants
X
Pure tall plants
Pure short plants
parental generation
P1
Cross Pollination
All Tall plants
first filial generation
F1
Self Pollination
second filial generation
787 tall plants, 277 short plants
F2
3 to 1 ratio
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Definitions
Genetics study of heredity
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Gene segment of DNA on a chromosome that
codes for a particular protein

• genes occur in pairs

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Allele alternative form of a gene
Dominant capital letter
(shields recessive trait)
T tall
t short
G green pods
g yellow pods
Recessive Lowercase letter (usually hidden)
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Phenotype physical characteristics of an
organism
(Ex Blue eyes or Brown Eyes)
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Genotype genetic makeup of an
organism (genes)
(internal information Ex BB, Bb, bb)
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Where do Phenotypes come from?
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Example of Genotype and Phenotype
Tall
TT
genotype
phenotype
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Homozygous when both alleles
of a pair are the
same
homozygous dominant
TT
homozygous recessive
tt
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Heterozygous when both alleles
of a pair are not
the same
heterozygous (tall)
Tt
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In rabbits, black fur color is dominant over
brown fur color
B black fur
b brown fur
bb
BB
or
Bb
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Think Pair - Share

• If Fred Flintstone is heterozygous for black
  hair.
• (BBlack, bblonde)
• What is Freds genotype?
• What is Freds phenotype?
• Tweety bird is YY. (Y yellow feathers, ybrown
  feathers)
• 1. What is his genotype?
• 2. What is his phenotype?
• 3. Is he heterozygous or homozygous? Explain.

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Homework

• Worksheet on homozygous/heterozygous and dominant
  and recessive.
• Due Tomorrow (or next time I see you!)

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Do Now

• Provide an example of the following terms
• Heterozygous
• Homozygous
• Genotype
• Phenotype
• Dominant
• Recessive
• Allele
• Gene

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Objective

• To describe Mendels 3 laws of inheritance
• Complete a Monohybrid cross
• Take Out your Homework!!!

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1) Law of Dominance

• Each trait is controlled by 2 factors, one factor
  (dominant ) may mask the other factor (recessive
  ) preventing it from having an effect.

F1
F2
P1
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2) Law of Segregation

• Each allele a person has separates into different
  gametes
• Ex. Ww one W goes in one sperm and the other w
  goes into another sperm

W
Sperm
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3) Law of Independent Assortment

• Gene pairs (homologous) will separate randomly
  into gametes (metaphase I of meiosis)

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Monohybrid Cross

• R Can roll your tongue
• r Cant roll your tongue
• Genotype Ratio
• Phenotype Ratio

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Genotypic vs. Phenotypic Ratios

• Phenotype Ratio
• Ratio of different physical traits
• Ex) Brown eyes ¼ or 25
• Genotype Ratio
• Ratio of the different possible alleles
• Ex) Tt ¼ or 25

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Test cross an individual with unknown genotype
is crossed with a homozygous recessive
individual

• used to determine the genotype of any individual
  whose phenotype is dominant

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Lets Try a Test Cross

• Spongebob squarepants doesnt know whether or not
  he is Homozygous Dominant or Heterozygous for his
  yellow color. The recessive trait is a white
  sponge. Lets say that we perform a test cross
  on spongebob (spongebob a white female sponge)
  and all of the baby sponges are yellow. What
  would spongebobs genotype be?

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Lets Try a Monohybrid together!

1. Daffy Duck is heterozygous for black feathers.
   Daisy Duck is homozygous for yellow feathers.
   Set up a punnett square and determine
   probabilities of their potential offspring. (Both
   genotype and phenotype ratios!)
2. B Black b yellow

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Practice!

• Get with a partner and work on the sample
  problems!

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DO NOW

• Sleeping Beauty has freckles. Her prince
  charming is heterozygous for no freckles. What
  are the chances of her children having freckles?
  Please show your work.

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Objectives

• To set up and complete a dihybrid cross.

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What is a dihybrid Cross?

• A dihybrid cross allows us to predict possible
  outcomes of offspring that will have 2 traits
  simultaneously.
• Ex what would you get if you crossed a
  Brown-haired brown-eyed male with a blonde-haired
  blue-eyed female? How many of the children would
  have brown hair and brown eyes? Brown hair and
  blue eyes? Blonde hair and brown eyes? Blonde
  hair and blue eyes?

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Example
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Setting up Dihybrid Crosses

• 1. Determine parent genotypes
• 2. Determine alleles to be passed down
• 3. Set up punnet square
• 4. Determine outcome
• Phenotype Ratio
• Genotype Ratio

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Dihybrid Crosses

• Looking at two different traits
• Ex. Hair color and eye color
• Bbrown eyes
• bblue eyes
• RBrown hair
• rblonde hair
• Mother is heterozygous for both traits
• Father is heterozygous for eye color and
  homozygous dominant for hair color

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What could the phenotypes and genotypes be of
their children?
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More Practice

• Mickey Mouse is heterozygous for Round ears and
  homozygous for Black eyes. Minnie Mouse also is
  homozygous for Floppy ears and heterozygous for
  Black eyes. Determine genotype and phenotype
  ratios. (Bblack, bbrown, Rround, r floppy.)

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Practice!

• Its Harry Potter time!! Get with a partner and
  work on the sample problems involving some of my
  favorite fictional characters!

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DO NOW

• Take out your Harry Potter Homework!
• What is the phenotypic ratio for a dihybrid cross
  where each parent is heterozygous for both traits?

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Objectives

• To define gene linkage and polypoidy.
• To understand pedigrees and figure out how to use
  one.

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10.3 Gene Linkage and Polyploidy

• Several genes on a chromosome
• Gene Linkage
• When two genes are close to each other on the
  same chromosome

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Gene Linkage

• Linked genes on a chromosome results in an
  exception to Mendels law of independent
  assortment
• Linked genes usually do not segregate
  independently

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Drosophila (Fruit Flies)

• First organism with linked genes
• Linked genes typically travel together during
  crossing over

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Chromosome Map

• Crossing over occurs more frequently between
  genes that are far apart
• Map of genes on a chromosomes and frequency of
  crossing over

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Polyploidy

• Occurrence of one or more extra sets of all
  chromosomes in an organism.
• Ex. A triploid organism (3n) - means that it has
  three complete sets of chromosomes.

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True or False Correct false statements

• _______   1. Crossing over occurs more frequently
  between genes that are close together on a
  chromosome.
• _______   2. Gene linkage was first studied by
  using garden peas.
• _______   3. Scientists call a drawing like the
  one shown below a chromosome map.
• _______   4. Chromosome map percentages represent
  actual chromosome distances.

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Matching
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Pedigree

• Shows history of a trait in a family
• Allows researchers to analyze traits within a
  family

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Symbols for Pedigree
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Lets try to figure out their genotypes!
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Dominant or Recessive

• Pedigrees can depict both dominant and recessive
  traits

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Homework

• Pedigree worksheet! Due next class! worth 5
  points!!

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Do Now

• Take out pedigree homework!
• Fill in the genotypes for the following pedigree
• Bbrown eyes
• b blue eyes

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Objectives

• To understand incomplete dominance and be able to
  do incomplete dominance monohybrid crosses.
• To explain codominance, multiple alleles,
  sex-linked traits, and polygenic inheritence.

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Test Cross

• When the genotype of an individual is unknown,
  cross the individual with a homozygous recessive
• The outcome of the cross determines the genotype
  of the unknown

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11.2 Incomplete Dominance

• Heterozygous phenotype is an intermediate
  phenotype between the two homozygous phenotypes.
• Two alleles are blended
• Ex) Four Oclock Flowers
• Red White Pink

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Incomplete Dominance
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Codominance

• Neither trait is dominant instead, both traits
  are shown (No Blending)
• Ex) Roan Cows
• Red White RED AND WHITE

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Sickle Cell Disease

• Affects red blood cells and ability to transport
  oxygen.
• Homozygous recessive alleles
• Heterozygous
• Homozygous dominant alleles

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Sickle Cell and Malaria

• People who are heterozygous for sickle cell, have
  a higher resistance to malaria.

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Multiple alleles 3 or more alleles
that control a trait

• Example blood type (IA,IB,io)

GENOTYPES IAIA IAio RESULTING PHENOTYPES Type A Type A
IBIB IBio Type B Type B
IAIB Type AB
ioio Type O
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Universal Donor?
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Sample Problem

• Determine the possible offspring of the following
  crosses
• 1. AB and O
• 2. AA and BO
• 3. AB and AB

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Coat Color of Rabbits

• Rabbits have a hierarchy of coat color
• 4 alleles (C, cch, ch, and c)
• Dominant C gt cchgt ch gt c Recessive
• C Full color
• cch Chinchilla
• ch Himalayan
• c albino

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Coat Color of Rabbits
Chinchilla
Albino
Full Color
Himalayan
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Lets try a sample problem

• cc x Ccch
• Genotype and phenotype ratios

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What do you see?
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What do you see?
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Sex Linked Traits

• Traits located on the sex chromosomes (X or Y)
• X linked gene is located on the X chromosomes
• Y linked gene is located on the Y chromosome

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What are the chances of having a girl?

• How would you go about solving it?

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Sex-Linked Traits

• A man who is color blind marries a woman that is
  heterozygous for color blindness. What is the
  chance of having a color blind boy?

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Polygenic Traits

• Polygenic traits arise from the interaction of
  multiple pairs of genes.

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Objectives

• To define test cross
• To define incomplete dominance
• To define codominance

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Codominance condition in which both alleles of
a gene are expressed

• example roan coat in horses
• white hair (HW) is codominant with red hair (HR)
• horses with genotype (HRHW) have coats with a
  mixture of red and white hairs (roan)

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Roan Coat
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Objectives

• To predict the results of dihybrid crosses by
  using a Punnett square

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dihybrid cross cross between individuals that
involves two pair of contrasting traits