Hereditary patterns

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•“Wild type” traits are traits most commonly found in nature

HERITABLE VARIATION & PATTERNS OF INHERITANCE

Figure 9.2

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• Various traits exist in organisms

These traits are usually inherited in particular patterns

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Parents:

Figure 9.3

Wild-type Wild-type

Parents:

Wild-type Sky-blue

Offspring:All Wild-type

First- generation offspring:

All wild-type

Matings

Second- generation offspring: 3/4

Wild-type

and 1/4

Sky-blue

(a) Offspring from the mating of two wild-type birds

(b) Two generations of offspring from the mating of a wild-type with a sky-blue bird

X X

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• Gregor Mendel

Was the first to analyze patterns of inheritance

– Deduced the fundamental principles of genetics

Figure 9.4

Mendelian Genetics

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• Mendel studied garden peas

In an Abbey Garden

These plants are easily manipulated

– These plants can self-fertilize

Figure 9.5

Stamen

Carpel

stamen

carpel

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• Mendel carried out some cross-fertilization

Figure 9.6

Removed stamens from purple flower

1

2

3

Transferred pollen from stamens of white flower to carpel of purple flower

4 Planted seeds from pod

Pollinated carpel matured into pod

White

Stamens

Carpel

Parents (P)

Purple

Offspring (F1)

Mendelian Genetics

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Mendelian Genetics

• He also created true-breeding varieties of plants

Mendel then crossed two different true-breeding varieties, creating hybrids

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Mendel’s Principles of Segregation

• Mendel performed many experiments

He tracked several characteristics in pea plants from which he formulated several hypotheses

04/10/23 9Figure 9.7

Dominant Recessive

White

Pod shape Inflated Constricted

Flower position

Pod Color

Dominant Recessive

Flower color Purple

Axial Terminal

Green Yellow

Tall Dwarf

Seed shape Round Wrinkled

Seed color Yellow GreenStem length

Traits in Pea Plants

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• A monohybrid cross is a cross between parent plants that differ in only one characteristic

Monohybrid Crosses

Figure 9.8a

P Generation (true-breeding parents)

All plants have purple flowers

among F1

plants (F1 F1)Fertilization

F2 Generation

3/4 of plants have purple flowers

1/4 of plantsHave whiteflowers

Purple flowers

Whiteflowers

F1 Generation

(a) Mendel’s crosses tracking one characteristic (flower color)

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• Mendel developed four hypotheses from the monohybrid cross:

– 1) There are alternative forms of genes, now called alleles

– 2) For each characteristic, each organism has two genes

– 3) Gametes carry only one allele for each inherited characteristic

– 4) Alleles can be dominant or recessive

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• Including a Punnett square

Figure 9.8b

P plants

Gametes

Genetic makeup (alleles)

PP

p

F1 plants: (hybrids)

Gametes

All Pp

1/2

PP

All P All

P 1/2

P

p

PP

Pp Pp

F2 plants:Eggs Sperm

p

P

Phenotypic ratio 3 purple : 1 white

Genotypic ratio 1 PP : 2 Pp : 1 pp

(b) Explanation of the results in part (a)

p

pp

Mendel’s Results

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• Phenotype

An organism’s physical traits

• Genotype

• An organism’s genetic makeup

Describing Traits:

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Pairs of alleles segregate (separate) during gamete formation; the fusion of gametes at fertilization creates allele pairs again

Mendel’s Principle of Segregation

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• Homologous chromosomes:

Genetic Alleles & Homologous Chromosomes

Have genes at specific loci (locations on the chromosome)

– Have alleles of a gene at the same locus

NCBI Human Ch 21

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Figure 9.9

Homologous chromosomes:

Gene loci

P a bRecessive allele

Genotype:

P a B

Dominant allele

PP aa Bb

Homozygous for the dominant allele

Homozygous for the recessive allele

Heterozygous


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• Homozygous

When an organism has identical alleles for a gene

• Heterozygous

- When an organism has different alleles for a gene


Lifestyle

Hereditary patterns