Mechanism of inheritance
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Mechanism of Inheritance. History of Genetics Genetic Terminology Test Crosses Predicting Inheritance. History of Genetics. Father of “modern genetics” His work was published in 1866, but did not become popular until 1900s. Mendel made three major discoveries:

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Mechanism of Inheritance

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Mechanism of inheritance

Mechanism of Inheritance

History of Genetics

Genetic Terminology

Test Crosses

Predicting Inheritance


History of genetics

History of Genetics

  • Father of “modern genetics”

  • His work was published in 1866, but

  • did not become popular until 1900s.

  • Mendel made three major discoveries:

  • a. characters/traits are governed by paired

  • but individual “factors” (genes)

  • b. these “factors” may be dominant or

  • recessive, and

  • c. the “factors” combine to produce

  • characteristic ratios in the later generations

Gregor Mendel

(1822-1884) – an Austrian monk


Mendel s genetics model plant

Mendel’s Genetics Model Plant

  • He worked with PEAS because:

  • They are easyto grow

  • Have many simple traits that distinguish strains of pea plants from each other

  • This includes:

    •  Height - short or TALL

    •  Seed colour – green or YELLOW

    •  Seed shape - wrinkled or ROUND

    •  Seed coat colour - white or GRAY

    •  Pod shape - constricted or SMOOTH

    •  Pod colour - yellow or GREEN

    •  Flower position - terminal or AXIAL

    •  Flower colour – white or PURPLE


Mendel s genetics model plant1

Mendel’s Genetics Model Plant

  • We will focus on these three (3) traits for our discussion

    •  Height - short or TALL

    •  Seed colour – green or YELLOW

    •  Seed shape - wrinkled or ROUND

    •  Seed coat colour- white or GRAY

    •  Pod shape - constricted or SMOOTH

    •  Pod color - yellow or GREEN

    •  Flower position - terminal or AXIAL

    •  Flower colour – white or PURPLE


Genetics terminology

Brown eyes

Brown eyes

Tall

Tall

Brown eyes

Blue eyes

Short

Tall

Genetics Terminology

  • Phenotype – physical characteristics, visible traits that can be identified or compared

  • eg. Facial structures: eye, nose, smile, presence/absence of dimple

  • Genotype – genes we (the offspring) inherit from the parents; constitutes genetic

  • make-up of an individual

  • Allele – variant of a gene (mom’s vs. dad’s)

  • eg. Eye-colour-determining gene; Height gene

  • Homozygous – when the two alleles are identical (eg. BB, yy)

  • Heterozygous – when the two alleles are different (eg. Bb, Vv)


Genetics terminology1

Genetics Terminology

  • Dominant – when the phenotype of an allele is observable in a heterozygous condition

  • Recessive – when the phenotype of an allele is NOT visible in a heterozygous condition

  • Dominant: represented by a CAPITAL letter

  • Recessive: represented by a small letter

  • P generation(parental)

  • F1 generation (first filial): the children of P

  • F2 generation (second filial): the grandchildren of the P generation


Test crosses

Test Crosses

  • Mendel’s experiments with Pea plants required him to pollinate flowers:

  •  this refers to as: crossing (fertilizing the flower’s reproductive organ)


Test crosses1

Test Crosses

  • Mendel’s experiments with Pea plants required him to pollinate flowers:

  •  this refers to as: crossing (fertilizing the flower’s reproductive organ)

  • To make sense of his observations, Mendel would need to know the

  • genotype/allele of the experimental plants (eg. Heterozygousor homozygous)

  • Q: How would you determine if the plant has the following alleles?

  • a) TT (homozygous dominant)

  • b) Tt (heterozygous)

  • c) tt (homozygous recessive)

  •  you cannot rely on the phenotypes alone

  • A: Crossing an individual of unknown genotype with a homozygous recessive individual

  •  Offspring will exhibit certain phenotypes that will allow you to determine if

  • unknown is homozygous or heterozygous dominant

  • Tall

  • Tall

  • short


Test crosses2

Test Crosses

Example:

A test cross is performed on a white ram whose genotype is unknown (WW or Ww) with a black ewe (ww)

X

ww

WW or Ww


Test crosses3

Test Crosses

If any offspring show the recessive trait, then the individual must be heterozygous

  • If all offspring show the dominant trait, then the individual must be homozygous


Predicting inheritance

Predicting Inheritance

For example:

T= the gene for TALL in pea plants

t= the gene for short in pea plants

So:

TT & Tt both result in a TALL plant,

because T is dominant over t. t is recessive.

tt will result in a short plant.

Remember there are two genes for every trait! One from each parent.


Predicting inheritance1

Predicting Inheritance

  • So after you performthe test Cross to make sure of their genotypes

  • Let’s cross a totally dominant tall plant (TT) with a short plant (tt).

  • Each plant will give only one of its’ two genes to the offspring

  • or F1 generation.

  • TT x tt

T

T

t

t

Mendels’ “Law” of Segregation

Each gene (allele) separates from the other so that the offspring get only one gene from each parent for a given trait.


Punnett square

Punnett Square

The genes from one parent go here.

The genes from the other parent go here.


Mechanism of inheritance

Punnett Square

T

T

t

t


Punnett square1

Punnett Square

T

T

t

t

t

t


Punnett square2

Punnett Square

T

T

t

t

t

t

t

t


Punnett square3

Punnett Square

T

T

T

T

t

t

t

t

t

t


Punnett square4

Punnett Square

T

T

T

T

t

t

t

T

t

T

t

t


Punnett square5

Punnett Square

T

T

T

T

t

t

t

F1: Generation

T

t

T

t

t


Punnett square6

Punnett Square

The genotype for all the offspring is Tt.

Thegenotype ratiois:

Tt: 4/4

The phenotype for all the offspring is tall.

Thephenotype ratiois:

Tall: 4/4


Your turn generation ii

Your turn … generation II


Genetics quiz 2 tomorrow

Genetics Quiz #2 -Tomorrow

MCh-10 Q’s

T/F-5 Q’s

Short answer-5Q’s

Cell Cycle

Mitosis-stages

Meiosis- stages, mistakes in meiosis, sources of genetic variation in meiosis

Definitions

Spermatogenesis (formation of male gametes) and Oogenesis (formation of female gametes) and end result for each


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