Final Concepts for Chapter 11 Mendelian Genetics

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Final Concepts for Chapter 11Mendelian Genetics

• Codominance
• Complete dominance
• Dihybrid cross
• Genotype
• Genotypic ratio
• Heterozygous
• Homozygous
• Incomplete dominance
• Monohybrid cross
• Phenotype
• Phenotypic ratio
• Probability
• Punnett square
• Testcross

• Expected/predicted results
• Actual/observed results
• Karyotype
• Amniocentesis
• Linked genes
• Sex-linked disorders
• Autosomal disorders

• Allele
• Dominant
• Recessive
• P-generation
• F1 generation
• F2 generation
• Law of independent assortment
• Law of segregation
• Chromosomes
• Pure breed
• Trait

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Independent Assortment vs. Linked Genes

• Mendel did not know about chromosomes when he
  proposed the Law of Independent Assortment.
• The pea traits he studied happened to be located
  on different chromosomes so they did assort
  independently.

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Independent Assortment vs. Linked Genes

• Question How many traits do you have?
• Question How many chromosomes (per cell) do you
  have?
• Question Is it possible to have only one trait
  per chromosome?
• No, lots of genes are carried or linked together
  on the same chromosome.

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Independent Assortment vs. Linked Genes

• Do the punnett square for the following cross
  assume independent assortment.
• Cross two heterozygous tall, heterozygous red
  flowered plants
• Ttall Rred flower
• t short r white flower

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Independent Assortment vs. Linked Genes
What is the phenotypic ratio?

• TtRr x TtRr

TR
Tr
tR
tr
TR
Tr
tR
tr
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Independent Assortment vs. Linked Genes

• 9331 ratio
• 9 tall and red
• 3 tall and white
• 3 short and red
• 1 short and white

• PROBABILITY
• From this cross, 48 offspring were produced.
• How many offspring would you expect to be tall
  and red?
• How many would expect to be tall and white?
• How many would you expect to be short and white?

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Independent Assortment vs. Linked Genes

• Now, do the following cross BUT the genes for
  tallness and red flowers are linked.

Cross two heterozygous tall, heterozygous red
flowered plants Ttall Rred flower t short r
white flower
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Independent Assortment vs. Linked Genes

• Hint
• T t
• R r

TtRr X TtRr
Is it possible to produce a Tr gamete?
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Independent Assortment vs. Linked Genes
TtRr X TtRr
What is the phenotypic ratio?
tr
TR
31 3 Tall and Red 1 Short and white
TR
tr
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Independent Assortment vs. Linked Genes

• So out of the 48 offspring, if the genes are
  linked, how many would be
• 1. tall and red?
• 2. tall and white?
• 3. short and red?
• 4. short and white?
• Answer
• tall and red 36 tall/white 0
• short and white 12 short/red 0

EXPECTED RESULTS!
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Independent Assortment vs. Linked Genes

• Is it possible for our Actual Results to show any
  flowers that are tall/white or short/red?
• Yes how?
• Crossing over

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Crossing over occurs in meiosis

• Pieces of the chromosomes actual switch places.

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Complete vs Incomplete Dominance
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Codominance the alleles are equally dominant

• Roan Cow Human Blood Type

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Sex-linked Traits

• Traits carried on the X chromosome

Fill in the genotypes on the pedigree.
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Autosomal disorders

• Disorders carried on non-sex chromosomes (first
  22 pairs)
• Some are autosomal dominant
• Huntingtons disease
• Most are autosomal recessive
• Sickle-cell anemia
• Cystic fibrosis

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• Question How do you know if the pure bred dog
  you just paid big bucks for is actually pure?

GG?
Gg?
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Test Cross

• Cross using a homozygous recessive individual
  with a dominant individual to determine if the
  dominant individual is heterozygous or homozygous
  dominant (pure)
• Why use a homozygous recessive individual?

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Test Cross

• Do the punnett squares for each case
• GG x gg Gg x gg

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Test Cross

• All offspring produced should show the dominant
  characteristics if the dominant parent is pure
  (GG) for the trait.

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9-1 Mendels Legacy

• F1 generation are the offspring produced from the
  original parental group whereas

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• The dominant factor gets expressed in the
  individual and the recessive factor can only be
  expressed when the dominant factor is absent.
• Ex. Pure Mendelian traits such as Pea Seed Shape
  S smooth
• s wrinkled

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• 3. An allele is a hereditary factor whereas a
  gene is a segment of DNA that dictates a trait.
  Two alleles for every trait one from mom and one
  from dad

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Multiple Choice

• 1. C
• 2. A
• 3. D
• 4. B

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• SHORT ANSWER
• Strain the body of descendants of a common
  ancestor, genetic crosses show how strains
  display family traits
• Meiosis accounts for both the Law of independent
  assort. and Law of Segregation because the
  chromosomes are pulled apart randomly during
  anaphase 1 and 2 of meiosis

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• 3. F orange and f red, then orange is the
  dominant color
• All flowers in the F1 generation would be orange.

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• 4 Critical Thinking If Mendel studied traits
  that were linked on the same chromosomes his
  observations would have led him to very different
  conclusions. For example, he would not be able
  to conclude that heredity factors are independent
  of one another because some would always be
  displayed together.
• EX round seeds would be produced by red
  flowering plants only

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R r B b
r b
R B
r B
R b
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9-2 Genetic Crosses

• Complete dominance one allele completely masks
  the expression of another
• Incomplete dominance both alleles are partially
  dominant causing an intermediate phenotype (Ex.
  red and white flower produce a pink flower)
• Codominance both alleles are expressed equally
  Ex. blood type AB, both A and B antigens are
  produced

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Multiple Choice

• 1. B
• 2. A 266 short/ total possible of 1,064
• 3. C
• 4. D (test cross)
• 5. C

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Short Answer

• 1. A homozygous individual has two of the same
  alleles for a trait (AA or aa) whereas a
  heterozygous individual has two different alleles
  for a trait (Aa)
• 2. .25 X 80 20 individuals
• 3. AA, Aa are the possible genotypes, 100 of
  offspring will show dominant phenotype

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Critical Thinking

• 4. One offspring is not sufficient enough to
  show if the cow is pure bred or not. The larger
  the sample size the more accurate the conclusion.

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WwRr X WwRr

• 9 dominant for both traits
• 4 will have same genotype as parents
• 1 will be homozygous dominant for both traits
• 1 will be homozygous recessive for both traits

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Gregor Mendel Father of genetics