Final Concepts for Chapter 11 Mendelian Genetics

1
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.

3
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.

4
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

5
Independent Assortment vs. Linked Genes
What is the phenotypic ratio?

• TtRr x TtRr

TR
Tr
tR
tr
TTRR TTRr TtRR TtRr
TTRr TTrr TtRr Ttrr
TtRR TtRr ttRR ttRr
TtRr Ttrr ttRr ttrr
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?

7
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
TTRR TtRr
TtRr ttrr
31 3 Tall and Red 1 Short and white
TR
tr
10
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!
11
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.

13
Complete vs Incomplete Dominance
14
Codominance the alleles are equally dominant

• Roan Cow Human Blood Type

15
Sex-linked Traits

• Traits carried on the X chromosome

Fill in the genotypes on the pedigree.
16
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

17

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

GG?
Gg?
18
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.