Evidence from genetics
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EVIDENCE FROM GENETICS. Can you answer this?. Which represents a monohybrid cross between a homozygous recessive and a heterozygote? A) Tt x Tt B) ttmm x TtMm C) tt x Tt D) ttmm x TTMM. Can you answer this?. In rats, black fur is dominant over white.

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EVIDENCE FROM GENETICS

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Evidence from genetics

EVIDENCE FROM GENETICS


Can you answer this

Can you answer this?

Which represents a monohybrid cross between a homozygous recessive and a heterozygote?

A) Tt x Tt

B) ttmm x TtMm

C) tt x Tt

D) ttmm x TTMM


Can you answer this1

Can you answer this?

In rats, black fur is dominant over white.

If a white rat is crossed with a heterozygous black rat, what is the likely % of the offspring that will be white?

  • 0%

  • 25%

  • 50%

  • 75%


And can you answer this

And can you answer this?

Which of the following pairs of crosses results in the same phenotypic ratios?

  • Aa x Aa and AA x aa

  • AA x aa and AA x Aa

  • AA x Aa and Aa x aa

  • None of the above


Evidence from genetics1

EVIDENCE FROM GENETICS

  • Deduction: If the hypothesis of evolution is correct, then we should see evidence of this in genetics

  • Background:

    Gregor Mendel (1822-1884

    Experiments with the garden pea.

    His paper in 1866 established the field of genetics.


Mendel s garden

MENDEL’S GARDEN


Mendel at work

Mendel at work


Mendel at work1

Mendel at work


Mendel s traits

Mendel’s Traits


Monohybrid crosses breeding experiments involving one trait

Monohybrid Crosses(=Breeding experiments involving one trait)

  • Pea plants

  • P Tall x Tall Short x Short

  • F1 All Tall All Short


Monohybrid crosses breeding experiments involving one trait1

Monohybrid Crosses(=Breeding experiments involving one trait)

  • Pea plants

  • P Tall x Tall Short x Short

  • F1 All Tall All Short

  • F2 All Tall

The tall trait is dominant


Monohybrid crosses breeding experiments involving one trait2

Monohybrid Crosses(=Breeding experiments involving one trait)

  • Pea plants

  • P Tall x Tall Short x Short

  • F1 All Tall All Short

  • F2 F2 x F2

All Tall


Monohybrid crosses breeding experiments involving one trait3

Monohybrid Crosses(=Breeding experiments involving one trait)

  • Pea plants

  • P Tall x Tall Short x Short

  • F1 All Tall All Short

  • F2 F2 x F2

  • F3 75% Tall, 25% Short

All Tall

3:1 Ratio


Mendel s traits1

5474/1850=2.96

6022/2001=3.01

882/299=2.95

428/152=2.82

705/224=3.15

651/207=3.14

787/277=2.84

MENDEL’S TRAITS


Mendel s traits2

5474/1850=2.96

6022/2001=3.01

882/299=2.95

428/152=2.82

705/224=3.15

651/207=3.14

787/277=2.84

MENDEL’S TRAITS

3:1

Ratio


Mendel analyzes the data

Mendel analyzes the data

Traits passed in the gametes

Pollen (sperm) & eggs

Note: ¾ Tall= TT, Tt, tT

¼ Short= tt

3:1 Phenotypic Ratio


Terms and principles

Terms and Principles

  • Dominant (e.g. Tall)

  • Recessive (e.g. Short)

  • Phenotype (visible characteristics)

  • Genotype (genetic characteristics)

  • Particulate theory of inheritance=

    2 particles (factors) determine a trait

Blending hypothesis is wrong!


Using a punnett square

Using a Punnett Square

Alleles= Alternative forms of the same gene (T or t)

T t

T TT Tt

t Tt tt

Suppose Tt X Tt


Using a punnett square1

Using a Punnett Square

Note: 3:1 ratio

Eggs

T t

T TT Tt

Pollen

t Tt tt

Tall

Tall

Short

Tall


Using a punnett square2

Using a Punnett Square

Homozygous condition= both alleles are alike (TT or tt)

T t

T TT Tt

t Tt tt


Using a punnett square3

Using a Punnett Square

Heterozygous condition= both alleles are different (Tt)

T t

T TT Tt

t Tt tt


Clicker question

Clicker Question

  • Blue eyes (b) are recessive to brown (B).Suppose 2 parents had 11 children: 6 with blue and 5 with brown. Which of these statements is most likely to be right?

  • Both parents had blue eyes.

  • One parent had blue & the other was homozygous dominant

  • Both parents had brown eyes.

  • One parent had blue & the other was heterozygous

  • Both parents were heterozygous.


Dihybrid crosses breeding experiments involving two traits

Dihybrid Crosses(=Breeding experiments involving two traits)

Round (R) or Wrinkled (r) seeds

Yellow (Y) or Green (y) seeds

P RRYY x rryy

F1 RrYy Genotype

Round Yellow Phenotype


Dihybrid cross rryy x rryy

Dihybrid Cross RrYy x RrYy

Set up a Punnet Square


Dihybrid cross rryy x rryy1

Dihybrid Cross RrYy x RrYy


Dihybrid cross rryy x rryy2

Dihybrid Cross RrYy x RrYy

Fill in this line first


Dihybrid cross rryy x rryy3

Dihybrid CrossRrYy x RrYy

Now fill in the rest


Clicker question what belongs in the red square

Clicker QuestionWhat belongs in the red square?

  • A) RRYY

  • B) RrYY

  • C rrYy

  • D) rrYY

  • E) rryy


Dihybrid cross rryy x rryy4

Dihybrid CrossRrYy x RrYy


Clicker question how many wrinkled green seeds will there be out of 16 possibilities

Clicker Question:How many wrinkled green seeds will there be out of 16 possibilities?

  • A) All 16

  • B) 9 out of 16

  • C) 50%

  • D) 3 0ut of 16

  • E) 1 out of 16


Clicker question how many wrinkled green seeds will there be out of 16 possibilities1

Clicker Question:How many wrinkled green seeds will there be out of 16 possibilities?

  • A) All 16

  • B) 9 out of 16

  • C) 50%

  • D) 3 0ut of 16

  • E) 1 out of 16


Dihybrid cross rryy x rryy5

Dihybrid CrossRrYy x RrYy

9: 3: 3: 1

Round Round Wrinkled Wrinkled

Yellow Green Yellow Green


Principle of independent assortment

Principle of Independent Assortment

= Factors (genes) sort independently of one another.

i.e. all possible combinations of Y and y and R and r occur

BUT


What if ry are linked together ry are linked together

What ifRY are linked together &ry are linked together ?

Non Independent Assortment


Can you answer this2

Can you answer this?

Which represents a monohybrid cross between a homozygous recessive and a heterozygote?

A) Tt x Tt

B) ttmm x TtMm

C) tt x Tt

D) ttmm x TTMM


Can you answer this3

Can you answer this?

In rats, black fur is dominant over white.

If a white rat is crossed with a heterozygous black rat, what is the likely % of the offspring that will be white?

  • 0%

  • 25%

  • 50%

  • 75%


And can you answer this1

And can you answer this?

Which of the following pairs of crosses results in the same phenotypic ratios?

  • Aa x Aa and AA x aa

  • AA x aa and AA x Aa

  • AA x Aa and Aa x aa

  • None of the above


Evidence from genetics

According to J.K. Rowling wizards & witches can be born from pure bloods or muggles. Suppose the wizard/witch trait is recessive (m)and the muggle trait is dominant (M)

  • Hermione is a witch born of muggle parents. If her parents had another child what are the chances that that one also would be a wizard or witch?

  • 0%

  • 25%

  • 50%

  • 75%

  • 100%

B

E

D

A

C


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