GeneticsGenetics

VocabularyVocabulary

Genetics: The study of heredity, Genetics: The study of heredity,

Heredity: the passing on of traits Heredity: the passing on of traits from an organism to its offspringfrom an organism to its offspring

Gregor MendelGregor Mendel

An Austrian monk and An Austrian monk and biologistbiologist

Worked during the Worked during the 1860s1860s

Experimented with pea Experimented with pea plantsplants

Called “The Father of Called “The Father of Genetics” for his Genetics” for his discoveries which began discoveries which began the field of geneticsthe field of genetics Public DomainPublic Domain

Mendel did his experiments in Mendel did his experiments in the monastery gardens.the monastery gardens.

Public Domain

Why did Mendel choose to Why did Mendel choose to work with peas?work with peas?

Peas grow and reproduce quickly so he Peas grow and reproduce quickly so he could study many generations.could study many generations.

They had a variety of different traits he They had a variety of different traits he could study at the same time.could study at the same time.

He could easily breed or cross them He could easily breed or cross them through pollination. Peas normally self-through pollination. Peas normally self-pollinate but can be artificially cross-pollinate but can be artificially cross-pollinated by transferring pollen from pollinated by transferring pollen from one plant to another mechanically.one plant to another mechanically.

Experiment 1Experiment 1

Short pea plants X short pea plantsShort pea plants X short pea plants

All short pea plantsAll short pea plants

Short plants are Short plants are true breederstrue breeders – – short plants always have short plants short plants always have short plants

as offspringas offspring

Experiment 2Experiment 2

Tall pea plants X Tall pea plantsTall pea plants X Tall pea plants

Sometimes Sometimes SometimesSometimes

All tall pea plantsAll tall pea plants Mostly tall Mostly tall plants (true breeders)plants (true breeders) with with some short some short plantsplants

Experiment 3

P1 (Parent Generation): True breeding short X

True breeding Tall

Short X Tall P1

Tall F1

75% Tall & 25% Short F2

Mendel concluded each plant must contain two factors for a particular

trait – he called them characters, we call them genes.

Dominant vs. RecessiveDominant vs. Recessive

Genes are the units of heredity.Genes are the units of heredity. A gene may have different forms that A gene may have different forms that

are expressed as different traitsare expressed as different traits They may be They may be dominantdominant (the stronger (the stronger

trait) or trait) or recessiverecessive (the weaker trait) (the weaker trait) If both are present in an organism If both are present in an organism

the dominant trait will be expressed the dominant trait will be expressed and the recessive trait hidden. and the recessive trait hidden.

The different forms are called alleles.The different forms are called alleles.

Seven Traits of Peas that Seven Traits of Peas that Mendel StudiedMendel Studied

1.1. Plant Height - tall or shortPlant Height - tall or short

2.2. Seed Shape – round or wrinkledSeed Shape – round or wrinkled

3.3. Seed Color – yellow or greenSeed Color – yellow or green

4.4. Pod Color – yellow or greenPod Color – yellow or green

5.5. Position of Flowers – axial or terminalPosition of Flowers – axial or terminal

6.6. Pod Shape – inflated or pinchedPod Shape – inflated or pinched

7.7. Flower Color – violet-red or whiteFlower Color – violet-red or white

Dominant vs. RecessiveDominant vs. Recessive

Dominant traits are represented by Dominant traits are represented by capital letters and corresponding capital letters and corresponding recessive traits as the same letter in recessive traits as the same letter in lowercaselowercase

For example: the dominant tall allele For example: the dominant tall allele is T and the recessive short allele is tis T and the recessive short allele is t

Mendel’s Experiment 3 Using Mendel’s Experiment 3 Using Symbols for AllelesSymbols for Alleles

PP11 TT X tt PurebredTT X tt Purebred

FF11 Tt Tt

Tt X Tt HybridTt X Tt Hybrid

FF22 TT Tt Tt tt TT Tt Tt tt

25% 50% 25%25% 50% 25%

By convention, the dominant gene is By convention, the dominant gene is written first in a gene pair no matter written first in a gene pair no matter which parent it comes fromwhich parent it comes from

If an organism has two alike alleles If an organism has two alike alleles (both dominant or both recessive) it (both dominant or both recessive) it is is purebredpurebred for that trait for that trait

If an organism has one dominant If an organism has one dominant allele and one recessive allele it is allele and one recessive allele it is hybridhybrid for that trait for that trait

The Law of SegregationThe Law of Segregation

A law that states that gene pairs A law that states that gene pairs separate during sex cell formationseparate during sex cell formation

This means that each sex cell (egg or This means that each sex cell (egg or sperm) contains only one allele for each sperm) contains only one allele for each genegene

The Law of Independent The Law of Independent AssortmentAssortment

A law that states that each gene pair A law that states that each gene pair for a trait is inherited independently for a trait is inherited independently of the gene pairs for all other traitsof the gene pairs for all other traits

Therefore if you have two hybrid traits, Therefore if you have two hybrid traits, Tt and Rr, the sex cells may have the Tt and Rr, the sex cells may have the following combinations of alleles TR, Tr, following combinations of alleles TR, Tr, tR or trtR or tr

Incomplete DominanceIncomplete Dominance

Discovered by German botanist Discovered by German botanist Karl CorrensKarl Correns

When neither allele in a gene When neither allele in a gene pair masks the other entirely but pair masks the other entirely but their effects blend to produce a their effects blend to produce a result different from the result different from the purebred of either allelepurebred of either allele

Incomplete DominanceIncomplete Dominance

First example:First example: Red Four O'clocks X White Four Red Four O'clocks X White Four

O’clocksO’clocks

(RR)(RR) (WW)(WW)

Pink Four O’clocksPink Four O’clocks

(RW)(RW)

Public Domain: http://en.wikipedia.org/wiki/File:Gul-Abas-4-O%27clock_plant.JPG

Incomplete DominanceIncomplete Dominance

Second example:Second example: Creamy-white Horse X Chestnut-brown Creamy-white Horse X Chestnut-brown

HorseHorse (WW)(WW) (BB)(BB)

Palomino HorsePalomino Horse

(BW)(BW)

A palomino is pale golden-brown A palomino is pale golden-brown

with a white mane and tailwith a white mane and tail

Public Domain: http://en.wikipedia.org/wiki/File:Palomino_Horse.jpg

The Principals of GeneticsThe Principals of Genetics

1.1. Traits, or characteristics, are passed Traits, or characteristics, are passed on from one generation of on from one generation of organisms to the next generation.organisms to the next generation.

2.2. The traits of an organism are The traits of an organism are controlled by genes.controlled by genes.

3.3. Organisms inherit genes in pairs, Organisms inherit genes in pairs, one gene from each parentone gene from each parent

The Principals of GeneticsThe Principals of Genetics

4.4. Some genes are dominant, whereas Some genes are dominant, whereas other genes are recessiveother genes are recessive

5.5. Dominant genes hide recessive Dominant genes hide recessive genes when both are inherited by genes when both are inherited by an organism.an organism.

6.6. Some genes are neither dominant Some genes are neither dominant nor recessive. These genes show nor recessive. These genes show incomplete dominance.incomplete dominance.