Introduction to Genetics

GeneticsThe scientific study of heredity

Gregor MendelFather of Genetics! Austrian Monk - worked

at monastery and taught high schoolGrew peas and became interested in the

traits that were expressed in different generations of peas

True breedingEach and every offspring (produced through self fertilization) have exactly the same traits as the parents – also known as purebred

He was also able to cross breed peas for different traits

Self FertilizationPlants have both male and female parts so

they are able to fertilize themselves

Cross Pollination When male parts from one plant are

dusted with pollen from another plant thus crossing the pollen!

Genes and DominanceMendel studied seven different pea plant traits

Each trait he studied had a contrasting form

Pea Plant Traits

Genes and DominanceThe offspring of crosses between

parents with different traits are called Hybrids

When Mendel crossed plants with different traits he expected them to blend, but that’s not what happened at all.

All of the offspring had the character of only one of the parents

Mendel drew two conclusions1. Inheritance is determined by genes that are passed from generation to generation

Mendel’s 2nd conclusion

2. The Principal of DominanceSome alleles are dominant and some are recessive

AllelesDifferent forms of a gene

Either dominant or recessive

dominantCovers up the recessive form – gene that if present, is always expressed (Capital letter!)

Ex.) T = tall

recessiveGene that gets covered up if there is a dominant allele present (lower case letter)

Ex.) t = short

Mendel wanted to know -Q: Had the recessive alleles disappeared?

To find out, Mendel mated the F1 plants to produce an F2 generation! (grand kids! )

P1 Parental

Tall Short All Tall

F1 F2

3 tall : 1 short

75% tall

25% short

The F1 CrossThe recessive traits reappeared!

Roughly 1/4 of the F2 plants showed a recessive trait (tt)

SegregationRatio 3:1 At some point, the allele for

shortness had been separated from the allele for tallness.

This occurred during the formation of SEX CELLS (when moms egg and dad’s sperm are produced)

Punnett Square VocabIf you do not know the following vocabulary

words you will fail miserably

Punnett SquareDiagram used to determine genetic crosses

ProbabilityThe likelihood that a particular event will occur

Random

HomozygousOrganisms that have 2 identicle alleles for a trait

Ex.) TT , tt

HeterozygousHave two different alleles for a trait

Ex.) Tt

PhenotypePhysical characteristics – The thing you see

WORDSEx.) Tall

GenotypeGenetic make-up LETTERSEx.) Tt, TT, tt

Mendel wondered if alleles segregate during the formation of gametes independently

Does the segregation of one pair of alleles affect the segregation of another pair of alleles?

For example, does the gene that determines whether round or wrinkled in shape have anything to do with the gene for color?

Must a round seed also be yellow?

All heterozygous 9:3:3:1 Ratio

Independent Assortment

Genes that segregate independently do not influence each others inheritance

Incomplete DominanceWhen one allele is not dominant over another

Four o’clock flowersThe heterozygous phenotype is somewhat blended between the two homozygous phenotypes

CodominanceWhen both alleles contribute to the phenotype of an organism

Ex.) Speckled Chickens

Multiple AllelesWhen more than two possible alleles exist in a population

Ex.) blood typeIAIBi

Dominant

Recessive

Human Blood TypesPhenotype Genotype

A

B

AB

O

IAIA or IAi

IBIB or IBi

IAIB

ii

Polygenic TraitsTraits controlled by two or more genes

Ex.) eye color, skin color

Genetics and the Environment

Some characteristics are determined by interactions between genes and the environment

Ex.) genes may affect a plants height but the same characteristic is influenced by climate, soil conditions and availability of water

Do NowHuman hair is inherited by incomplete dominance. Human hair may be curly (CC) or straight (cc). The heterozygous genotype (Cc) produces wavy hair. Show a cross between two parents with wavy hair

Mendel’s principles of genetics require at least 2 things

1. Each organism must inherit a single copy of every gene from each of its parents

2. When an organism produces its own gametes these two sets of genes must be separated from each other so that each gamete contains just one set of genes

HomologousChromosomes that each have a corresponding chromosome from the opposite sex parent