GeneticsGenetics

Heredity Heredity passing down of traits or passing down of traits or characteristics from parents to offspringcharacteristics from parents to offspring

Genetics Genetics study of heredity study of heredity

Gregor Mendel (1822-1884)Gregor Mendel (1822-1884)

Worked with Pea Plants. 2 major traits for each plantPlants were either tall (T) or short (t)Plants were either Purple (P) or white (p)

Mendel’s ExperimentMendel’s Experiment

Male and Female sex organs in pea plants are on the same Male and Female sex organs in pea plants are on the same flower (stamen have pollen and stigma contains the egg)flower (stamen have pollen and stigma contains the egg)

Pure Traits Pure Traits Traits established through self-fertilization Traits established through self-fertilization

StamenStamen StigmaStigma

GeneticsGenetics•Pure white individuals x pure purple individualsPure white individuals x pure purple individuals•F1 F1 All purple offspringAll purple offspring•F1 x F1 F1 x F1 3:1 ratio of purple to white pea plants 3:1 ratio of purple to white pea plants•Out of 1000 plants 750 were purple and 250 were whiteOut of 1000 plants 750 were purple and 250 were white•Results of the Parental cross showed that one trait covered up the other Results of the Parental cross showed that one trait covered up the other traittrait

XX ==

Genetics VocabularyGenetics VocabularyDominant Trait Dominant Trait Trait that masks the recessive Trait that masks the recessive trait trait

Recessive Trait Recessive Trait Trait that is being covered up Trait that is being covered up

In this cross PURPLE color was dominantIn this cross PURPLE color was dominant

Mendel’s HypothesisMendel’s HypothesisGene Gene sequence of DNA on a chromosome sequence of DNA on a chromosome

Each pea plant trait is a combination of 2 genes, Each pea plant trait is a combination of 2 genes, one from mom and one from dad one from mom and one from dad

Each alternative gene is called an alleleEach alternative gene is called an allele

Dominant Gene Dominant Gene shown by a capital letter (P) shown by a capital letter (P)Recessive Gene Recessive Gene shown by a lower case letter (p) shown by a lower case letter (p)

Pure Purple plants Pure Purple plants PP PPPure white plants Pure white plants pppp

PP x pp PP x pp all Pp all Pp

Pp x Pp Pp x Pp PP or Pp or pP or ppPP or Pp or pP or pp

Mendel’s TermsMendel’s Terms

Homozygous Homozygous 2 of the same allele 2 of the same allele (PP or pp)(PP or pp)

Heterozygous Heterozygous 2 different alleles 2 different alleles (Pp)(Pp)

Punnett Square Punnett Square Results of a Results of a cross can be predictedcross can be predicted

Incomplete DominanceIncomplete DominanceSome traits do not have dominant allelesSome traits do not have dominant allelesHeterozygotes appear as a mix between 2 parentsHeterozygotes appear as a mix between 2 parents

1 trait = 3 phenotypes1 trait = 3 phenotypes

4 O’clock Flowers4 O’clock FlowersRr x RrRr x Rr

Ratio of OffspringRatio of Offspring1 Red1 Red2 Pink2 Pink1 white1 white

CodominanceCodominanceNeither allele is dominant. Neither allele is dominant. Multiple alleles Multiple alleles are are expressedexpressed

Presence of heterozygote means both alleles are Presence of heterozygote means both alleles are expressed equallyexpressed equally

Blood type is an exampleBlood type is an example

Sex DeterminationSex DeterminationThomas Morgan discovered that chromosomes differed in males and Thomas Morgan discovered that chromosomes differed in males and femalesfemales

Females- XXFemales- XXMales- XYMales- XY

Called Sex ChromosomesCalled Sex ChromosomesAll other chromosomes are called autosomesAll other chromosomes are called autosomes

Sex-linked InheritanceSex-linked InheritanceMorgan crossed white-eyed male with red-eyed Morgan crossed white-eyed male with red-eyed femalefemale

F1Ratio: All Red EyesF1Ratio: All Red EyesF2 Ratio: 3:1 ratio, but never any white femalesF2 Ratio: 3:1 ratio, but never any white females

Reasoned that there are genes on sex Reasoned that there are genes on sex chromosomeschromosomes

Allele for eye color is on X chromosomeAllele for eye color is on X chromosomeNo gene for eye color on Y chromosomeNo gene for eye color on Y chromosome

Presence of homozygous recessive, or ONLY a Presence of homozygous recessive, or ONLY a recessive allele, yields recessive traitrecessive allele, yields recessive trait

Morgan’s CrossesMorgan’s Crosses

Sex Influenced Traits (Not on test!)

• Sex-influenced traits are autosomal traits that are influenced by sex. If a male has one recessive allele, he will show that trait, but it will take two recessive for the female to show that same trait. One such gene is baldness.

• BB normal male & female• Bb bald male; normal female• bb bald male; bald female

Dihybrid CrossesDihybrid CrossesDihybrid Cross: Cross: Cross of 2 individuals for 2 different traitsDihybrid Cross: Cross: Cross of 2 individuals for 2 different traits

Example:Example:In Pea PlantsIn Pea PlantsTall(T) is dominant to shortTall(T) is dominant to shortPurple(P) is dominant to whitePurple(P) is dominant to white

Crossing homozygous tall, purple plant with a homozygous short, white Crossing homozygous tall, purple plant with a homozygous short, white plantplant

TTPP x ttppTTPP x ttpp

Crossing heterozygous tall, purple plant with a heterozygous tall, purple Crossing heterozygous tall, purple plant with a heterozygous tall, purple plantplantTtPp x TtPpTtPp x TtPp

Genetic DiseasesGenetic Diseases

Autosomal dominant disease Autosomal dominant disease Presence of dominant allele means Presence of dominant allele means that individual will have the diseasethat individual will have the disease

Autosomal recessive disease Autosomal recessive disease Disease only present when BOTH Disease only present when BOTH recessive alleles are presentrecessive alleles are present

Sex-linked Dominant Sex-linked Dominant Disease present when dominant allele is Disease present when dominant allele is present on either sex chromosomepresent on either sex chromosome

Sex-linked Recessive Sex-linked Recessive Disease present when recessive allele is Disease present when recessive allele is present onpresent on either sex chromosomeeither sex chromosome

Common Genetic DiseasesCommon Genetic DiseasesHuntington’s DiseaseHuntington’s Disease Autosomal dominant ; Autosomal dominant ;Neuromuscular disease; degeneration of muscle tissue; onset in early 30’s.Neuromuscular disease; degeneration of muscle tissue; onset in early 30’s.Folk Singer Woody Guthrie had the diseaseFolk Singer Woody Guthrie had the disease

Cystic FibrosisCystic Fibrosis Autosomal Recessive; Defective Protein is made that Autosomal Recessive; Defective Protein is made that creates excess mucus; clogs lungs.creates excess mucus; clogs lungs.

Color BlindnessColor Blindness Sex-linked recessive Sex-linked recessive

Inablity to distinguish colors (8% of male population)Inablity to distinguish colors (8% of male population)

Some Genetics DiseasesSome Genetics DiseasesHemophiliaHemophilia Sex-linked recessive Sex-linked recessive Inablity of blood to clotInablity of blood to clot

Nicholas, Czar of Russia (Mid 1800’s) child was Nicholas, Czar of Russia (Mid 1800’s) child was hemophiliachemophiliac

Muscular DystrophyMuscular Dystrophy Sex-linked recessive Sex-linked recessiveTay-Sach’s Disease Tay-Sach’s Disease Autosomal Recessive Autosomal Recessive

Degeneration of Central Nervous System; infant mortalityDegeneration of Central Nervous System; infant mortality

Changes in Chromosome Number

Nondisjunction – occurs when:

In meiosis I, homologous pair both go into the same daughter cell or

In meiosis II, the sister chromatids both go into the same gamete.

The result:

Trisomy (3 copies of a single chromosome) or

Monosomy (1 copy of a single chromosome)

Nondisjunction in meiosis I

Changes in Chromosome Structure

• Mutation - a permanent genetic change.

• Chromosome mutation - a change in chromosome structure

• Radiation, organic chemicals, or even viruses may cause chromosomes to break, leading to mutations.

• Types of chromosomal mutations: inversion, translocation, deletion, and duplication.

Deletions

Deletions occur when a single break causes a lost end piece, or two breaks result in a loss in the interior.

An individual inherits a normal chromosome from one parent and a chromosome with a deletion from the other parent

No longer has a pair of alleles for each trait

A syndrome can result – type depends on chromosome(s) affected.

Williams Syndrome

• Chromosome 7 loses an end piece

• Children have a pixie look (turned-up noses, wide mouth, small chin, large ears)

• Poor academic skills, good verbal and musical abilities

• Skin ages prematurely from lack of the gene that controls the production of elastin (also affects cardiovascular health).

Duplication

Duplication results in a chromosome segment being repeated in the same chromosome

Produces extra alleles for a trait.

Ex: An inverted duplication in chromosome 15 causes inv dup 15 syndrome

Poor muscle tone, mental retardation, seizures, curved spine, and autistic characteristics

Duplication

• Translocation

Translocation is exchange of chromosomal segments between two, non-homologous chromosomes.

Ex: Alagille syndrome results from a deletion of chromosome 20 or a translocation that disrupts an allele on chromosome 20.

Distinctive face, abnormalities of eyes & internal organs, and severe itching.

Translocation

Inversion• Inversion involves a segment of a chromosome

being turned 180 degrees

• The reverse sequence of alleles can alter gene activity.

• Crossing-over between inverted and normal chromosomes can cause duplications and deletions in resulting chromosomes.

Inversion