Genetics Why are some of us so alike, and others so different?

GeneticsWhy are some of us so alike, and others so different?

Genetics TermsGenetics TermsChromosome:

A long strand of DNA that contains many genes.

Gene:A specific location on a chromosome that codes for a specific trait. Ex: the gene for having/not having Ear Pits!

Allele:

Two “versions” of the same gene. Ex: Dominant for not blue eyes, or recessive for blue eyes.

More Genetics More Genetics Terms…Terms…

Loci:

The exact location of a gene on a chromosome.

Write this down Write this down 100,000 times:100,000 times:

You have TWO You have TWO genes for every genes for every ONE trait.ONE trait.

Still More Genetics Still More Genetics Terms…Terms…

Dominant:

A version of the allele that is expressed if one gene of that type is present. Represented by a capital letter.

Recessive:

A version of the allele that is shown only if BOTH genes for that trait have that allele. Represented by a lower case letter.

If you locked these two girls in a room….who is getting her way?

Genes basically work in the same way.

And More Genetics Terms… yee And More Genetics Terms… yee ha!ha!

Genotype:The combination of genes a person has.

The possible combinations are..?Homozygous Dominant RRHeterozygous RrHomozygous Recessive rr

What’s your

genotype, baby?

Phenotype:

The physical expression of a trait.

Ex: showing the dominant trait of non-red hair, or showing the recessive trait of red hair.

dominantrecessive

Mendel:Mendel: The first guy The first guy with a clue.with a clue.

Mendel was a mathematician who started to see mathematical trends when breeding plants.

Prior to Mendel, people thought sperm were actually tiny little people that just grew inside the woman!! weird.

Mendel’s work wasn’t recognized as correct (or brilliant) until after his death in 1884!

(the princess and the) (the princess and the) PeaPeaokay..no princess, just peasokay..no princess, just peas

The first cross was the P generation. They were either homozygous dominant or homozygous recessive.

The F1 generation were all ____________heterozygous

The F2 generation showed:

Homozygous Dominant ____%25

Heterozygous ____%50

Homozygous Recessive ____%25

Mendel’s LawsMendel’s LawsRule #1: No eating my peas!

Mendel created “Laws” of genetics that still apply today. Each can be proven with a specific punnett square.

1. The Law of Dominance

2. The Law of Segregation

The Law of Recombination

3. The Law of Independent Assortment

TT x tt

Tt x Tt

TTRR x ttrr

Law of Dominance: P=polydactyl, p=5 digits

P P

p

p

Pp Pp

Pp

Pp

Genotype Ratio: 100% heterozygousPhenotype Ratio: 100% polydactyl

Dominance: Only one copy is needed for

expression!

Law of Segregation/Recombinati

on: U=uncombable hair, u=combable hair

U u

U

u

UU Uu

Uu uu

Genotypic ratio: 25% hom.dom. 50% het. 25% hom.rec.Phenotypic ratio: 75% uncombable hair 25% combable hair

There are 2 “factors” for each trait that separate in gametes and randomly rejoin in offspring making variations.

Law of Independent Assortment: Dihybrid Cross If genes for different traits are located on separate

chromosomes they will segregate independently. Therefore they can be inherited separately and all combinations can occur resulting in a phenotypic ratio of 9:3:3:1Linkage: If genes

for different traits are on the same chromosome. they must be inherited together like lights and eye size of the deep sea viper fish.

Punnett Squares for Punnett Squares for Mendel’s Laws!Mendel’s Laws!

Law

of

Dom

inan

ce

Laws of Segregation & Recombination

Law of Independent Assortment

1 in 18 people has a third nipple! Like this guy!

Other really cool DOMINANT traits!

Check this out!

Hapsburg jaw

nevus flammeus

Michelin Tire Baby Syndrome

cleft chin

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Test Cross: To determine the genotype of a dominant phenotype. Must mate with a

homozygous recessiveZ=brown,

z=zebarooalope

ZZ or Zz?

ZzZz zzzz

ZzZz zzzz

ZzZz ZzZz

ZzZz ZzZz zz

Z z

Z Z

z

z

z

z

Sex-Linked genes:

What? More naughty bits? Haven’t you

people caused enough trouble

already?

Alleles found on the X or Y chromosome

European Royal Family with hemophilia

Hematoma caused by platelet malfunction.

XhY is the genotype

How do Sex-Linked Genes How do Sex-Linked Genes work?work?

Certain traits are found on the 23Certain traits are found on the 23rdrd pair of pair of chromosomes (the “sex” chromosomes)chromosomes (the “sex” chromosomes)

Males are XY in the 23rd position. Females Males are XY in the 23rd position. Females are XX. The Y chromosome is very small, are XX. The Y chromosome is very small, having fewer genes.having fewer genes.

•Therefore, if a male has one copy of a Therefore, if a male has one copy of a recessive trait (found on his one X recessive trait (found on his one X chromosome), he will have the trait.chromosome), he will have the trait.EX: Colorblindness – much more common in EX: Colorblindness – much more common in males. Why??males. Why??

What do you see?

Colorblindness is a recessive X-linked gene. Found more often in .

Now remember, your toothbrush is the green one and mine is the blue one.

males

Genotype XcY

Multiple Alleles: More than two alleles exist in the gene pool for a given trait, however the loci only holds two. Why?

Blood genes: IA, IB, i

Fruit size and coat color in Italian greyhounds.

Mult

iple

A

llele

s!

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bbEEbbEEbbEebbEe

BBeeBBeeBbeeBbee

How is this possible?Most traits are controlled by more than one set of genes.In fact, most DNA on genes codes for the production of

for metabolism! Not physical characteristics.

enzymes

Incomplete dominance: When both alleles for a trait are dominant and the heterozygous conditions blends them together to produce a third phenotype.

+ =

So what’s going on So what’s going on here?here?

Codominance: Codominance: When both When both genes are dominant and in the genes are dominant and in the

heterozygous condition both are heterozygous condition both are expressed separately showing two expressed separately showing two

distinct phenotypes on one distinct phenotypes on one organism.organism.

A red cow crossed with a white bull A red cow crossed with a white bull produces roan calves, which have a red produces roan calves, which have a red coat and white blotches.coat and white blotches.

Pedigree:

A representation of the transmission of a hereditary condition through a family tree.

This shows an autosomal recessive trait.Autosomal= found on a chromosome that is not #23

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