Human Human Genetics Genetics

UnitUnit

Creating Genetic DiversityCreating Genetic Diversity

How did you become so How did you become so unique?unique?

1) Sexual reproduction 1) Sexual reproduction

2) Independent assortment of 2) Independent assortment of chromosomes (from mom and chromosomes (from mom and dad)dad)

3) Random fertilization of 3) Random fertilization of gametesgametes

Lets think about thisLets think about this

Egg and Sperm with 2Egg and Sperm with 22323 (or about 8 (or about 8 million) different combinations of million) different combinations of chromosomes are produced through chromosomes are produced through meiosismeiosis

Sexual reproduction involves egg and Sexual reproduction involves egg and spermsperm

A sperm (with 2A sperm (with 22323 different chromosome different chromosome combinations) can fertilize an egg (with combinations) can fertilize an egg (with 222323 different chromosome combinations) different chromosome combinations)

Any sperm can fertilize any egg Any sperm can fertilize any egg

Lets think about thisLets think about this

So what does all that mean?????????So what does all that mean?????????

You are the product of 2You are the product of 223 x23 x 2 22323 (or (or more than 70 trillion) different more than 70 trillion) different combinations of chromosomescombinations of chromosomes

OrOr

You are the outcome of 1 in 70 trillion You are the outcome of 1 in 70 trillion (70,000,000,000,000) different (70,000,000,000,000) different combinations of chromosomes from combinations of chromosomes from mom and dadmom and dad

Creating Genetic DiversityCreating Genetic Diversity (cont)(cont)

4) Crossing over 4) Crossing over

= the exchange of = the exchange of chromosome segments chromosome segments between homologous between homologous chromosomeschromosomes

- occurs during meiosis- occurs during meiosis

1) Two homologous chromosomes pair up with each other during prophase I of meiosis.

2) In this position, some chromatids are very close to each other and segments cross.

3) Some of the segments break off and reattach to other chromosomes

Gene LinkageGene Linkage

= genes located close = genes located close together tend to be together tend to be inherited togetherinherited together

- discovered by American - discovered by American scientist Thomas Hunt scientist Thomas Hunt MorganMorgan

- studied fruit flies- studied fruit flies

Genetic LinkageGenetic Linkage Crossing over is more likely to Crossing over is more likely to

happen between B and C, separating happen between B and C, separating A &B from C & D.A &B from C & D.

Gene LinkageGene Linkage (cont) (cont)

- Morgan’s Conclusions- Morgan’s Conclusions

1) Linked genes are on the 1) Linked genes are on the same chromosomessame chromosomes

2) The farther apart two 2) The farther apart two genes are located, the more genes are located, the more likely they are to be likely they are to be separated by crossing over separated by crossing over (and vice versa)(and vice versa)

Genetic LinkageGenetic Linkage Crossing over is more likely to Crossing over is more likely to

happen between B and C, separating happen between B and C, separating A &B from C & D.A &B from C & D.

Gene LinkageGene Linkage (cont) (cont)

- linkage maps show relative - linkage maps show relative location of genes on a location of genes on a chromosomechromosome

Polygenic TraitsPolygenic Traits

= traits produced by two or = traits produced by two or more genesmore genes

- will show a range of - will show a range of possibilities (ex: skin color, possibilities (ex: skin color, eye color)eye color)

Polygenic TraitsPolygenic Traits (cont) (cont)

- epistasis = when one gene - epistasis = when one gene interferes with the expression interferes with the expression of other genesof other genes

- ex: albinism- ex: albinism

Other Albino AnimalsOther Albino Animals

Environment Influence on Environment Influence on PhenotypePhenotype

- Are identical twins always - Are identical twins always IDENTICAL?IDENTICAL?

NoNo

- nutrition, health care, - nutrition, health care, money, disease, injuriesmoney, disease, injuries

Environmental Influence on Environmental Influence on PhenotypePhenotype (cont)

In animals:- Light – controls the color expression in some insects

Environmental Influence Environmental Influence on Phenotypeon Phenotype (cont)

In animals:- Temperature

- controls the sex of certain types of reptiles

Environmental Influence Environmental Influence on Phenotypeon Phenotype (cont)

In animals:- Temperature

- controls coloration in some mammals

Environmental Influence Environmental Influence on Phenotypeon Phenotype (cont)

- External alteration of phenotype does not affect genotype

- your phenotype is a your phenotype is a mixture of your genes mixture of your genes (genotype) and the (genotype) and the environment you live inenvironment you live in

Sex DeterminationSex Determination

- Male = XY- Male = XY Female = Female = XXXX

- normally, 50% of the - normally, 50% of the offspring of an organism offspring of an organism born are male, 50% are born are male, 50% are femalefemale

Sex Determination (cont)

Genotypic Ratio

Phenotypic Ratio

Sex-Linked TraitsSex-Linked Traits

= traits caused by genes = traits caused by genes located on the sex located on the sex chromosomeschromosomes

- most genes that determine - most genes that determine your phenotype are found your phenotype are found on autosomes, however, on autosomes, however, some are found on sex some are found on sex chromosomeschromosomes

Sex-Linked TraitsSex-Linked Traits (cont) (cont)

- most sex-linked traits are - most sex-linked traits are found on the X chromosomefound on the X chromosome

- males are more likely to show - males are more likely to show a sex-linked trait or disorder a sex-linked trait or disorder than femalesthan females

- Why? Because males only - Why? Because males only have one X chromosomes have one X chromosomes

Sex-Linked TraitsSex-Linked Traits (cont) (cont)

- Example 1: - Example 1:

Red eyes are dominant to Red eyes are dominant to white eyes in fruit flies. Cross white eyes in fruit flies. Cross a homozygous dominant red-a homozygous dominant red-eyed female with a red-eyed eyed female with a red-eyed male. Eye color is a X-linked male. Eye color is a X-linked trait.trait.

Example 1

X Y

X X X X Y

X X X X Y

Genotypic Ratio

2 XRXR: 2 XRY

Phenotypic Ratio

2 red-eyed females: 2 red-eyed males

Sex-Linked TraitsSex-Linked Traits (cont) (cont)

- Example 2: - Example 2:

Red eyes are dominant to Red eyes are dominant to white eyes in fruit flies. Cross white eyes in fruit flies. Cross a heterozygous female with a a heterozygous female with a red eyed male. Eye color is red eyed male. Eye color is an X-linked trait.an X-linked trait.

Example 2

X Y

X X X X Y

X X X X Y

Genotypic Ratio

1 XRXR: 1 XRXr: 1 XRY: 1 XrY

Phenotypic Ratio

2 red-eyed females: 1 red-eyed male: 1 white-eyed male

Sex-Linked TraitsSex-Linked Traits (cont) (cont)

- carrier = does not show a - carrier = does not show a disease/disorder but can disease/disorder but can pass it onto their offspringpass it onto their offspring

- aka: heterozygous- aka: heterozygous

Genetic DisordersGenetic Disorders

1) Single allele disorders = 1) Single allele disorders = controlled by a single allele controlled by a single allele (letter) of a gene, either (letter) of a gene, either dominant or recessivedominant or recessive

- genetic marker = a short - genetic marker = a short section of DNA that is known to section of DNA that is known to have a close association with a have a close association with a particular gene located nearbyparticular gene located nearby

Cystic Fibrosis - RecessiveCystic Fibrosis - Recessive

Huntington’s Disease - Huntington’s Disease - DominantDominant

Genetic DisordersGenetic Disorders (cont) (cont)

2) monosomy = a zygote 2) monosomy = a zygote with 45 chromosomeswith 45 chromosomes

- has only one copy of a - has only one copy of a particular chromosomeparticular chromosome

Genetic DisordersGenetic Disorders (cont) (cont)

3) trisomy = a zygote with 47 3) trisomy = a zygote with 47 chromosomeschromosomes

- has three copies of a particular - has three copies of a particular chromosomechromosome

- most common example is down - most common example is down syndrome (aka: trisomy 21)syndrome (aka: trisomy 21)

- has an extra copy of - has an extra copy of chromosome 21chromosome 21

Genetic Disorders with the Genetic Disorders with the Sex Chromosomes Sex Chromosomes

- XO = Turner’s Syndrome- XO = Turner’s Syndrome

- XXY = Klinefelter Syndrome- XXY = Klinefelter Syndrome

- XXX = Triple X Females- XXX = Triple X Females

- XYY = Jacob Syndrome- XYY = Jacob Syndrome

- YO = Does not exist…need an - YO = Does not exist…need an X chromosome to liveX chromosome to live

What about hermaphrodites?What about hermaphrodites?