Genetics is the study of inheritance – the passing of traits from parent to offspring

What is Genetics?

Austrian Monk - Bred pea plants• cross-pollinated true breeding parents (P)

P = parental generation• raised offspring & then observed traits (F1 )

F = filial gen. (offspring)• allowed F1 offspring to self-pollinate & observed traits in next generation (F2)

F2generation

3:175%purple-flower peas

25%white-flower peas

P

100%F1generation(hybrids)

100%purple-flower peas

Xtrue-breeding

purple-flower peastrue-breeding

white-flower peas

self-pollinate

Traits come in alternate versions: called alleles• purple flower and white flower color• alleles – different version of same gene.

• different alleles vary in the sequence of nucleotides (building blocks of DNA)

For each characteristic, an organism inherits 2 alleles, 1 from each parent◦diploid organism inherits 2 sets of chromosomes, 1 from

each parent homologous chromosomes like using 2 different websites for

research Wikipedia About.com

What is the advantage of being diploid???

Paired genes separate during the formation of reproductive cells and the gamete only receives one gene from the pair

During meiosis, alleles segregate When homologous chromosomes separate During anaphase I

◦ each allele for a trait is packaged into a separate gamete

Genes for different characteristics are distributed (sorted) to gametes independently.

This means that traits produced by dominant genes are not necessarily shown together.

Does red hair ALWAYS sort with green eyes?

Genes are only inherited together if they appear on the same chromosome.

Some traits “mask” others ◦ purple & white flower colors are separate traits that

do not blend purple x white ≠ light purple purple masked white

◦ dominant allele Directs the formation of a

functioning protein Creates the characteristic

masks other alleles ◦ recessive allele

Has directions for a malfunctioning protein – wrong shape (doesn’t work) Does not affect characteristic

allele producingfunctional protein

mutant allele malfunctioning

protein

homologouschromosomes

Indicate the two alleles that an individual inherited for a specific trait. ◦ One allele on each homologous chromosome◦ Two allele conditions:

Homozygous (2 of same allele) Must specify if they are dominant or recessive alleles

Heterozygous (2 different alleles)

◦ For peas: 3 possible genotypes for flower color Homozygous dominant (PP) Homozygous recessive (pp) Heterozygous (Pp)

Physical appearance of the trait.

Depends on the genotype

Recessive phenotype only present if genotype is homozygous recessive (pp) = white flower

Dominant phenotypes: ◦ Homozyous dominant (PP) = purple flower◦ Heterozygous (Pp) = purple flower

Show the possible genotypic outcomes from crossing the parents (fertilization). ◦ Gives probability of offspring genotypes

Now lets assume that Black-haired rabbits are dominant to white haired rabbits

B = black hair b = white hair

Probability of phenotype:75% black25% white

Heterozygous black rabbit with a white rabbit

What are the offspring phenotypes?

The End - Genetics Part 1

2006-2007

Beyond Mendel’s Laws:Other Patterns of Inheritance

Heterozygote shows an intermediate, blended phenotype◦ example:

RR = red flowers rr = white flowers Rr = pink flowers

R is not completely dominant – so does not make enough color (pigment) to completely cover “white”

RR Rr rr

R Wmale / sperm

R

Wfem

ale

/ egg

s RR

RW WW

RW

25%

1:2:1

25%

50%

25%

1:2:1

%genotype

%phenotype

RR

RW

RW

WW

25%

50%

RW x RW

2 alleles are both equally dominant◦ affect the phenotype equally & separately

not blended phenotype◦ Example: ABO blood groups◦ 3 alleles

IA, IB, i IA & IB alleles are co-dominant to

each other both cell markers (proteins) are

produced both IA & IB are dominant to i allele

◦ Cell surface markers act as ID cards

Both red and white hairs are expressed in the phenotype – not pink hairs!

Also exhibits Multiple Alleleswhen there are more than two possible alleles for a trait

Three alleles lead to four blood types; A, B, AB and OBlood type A is represented by IAIA or IAiBlood type B is represented by IBIB or IBiBlood type AB is represented by IAIB

Blood type O is represented by ii

Some phenotypes are determined by 2 or more genes ◦ phenotypes exist as a continuum

many more than 2 possibilities◦ human traits include:

skin color height weight eye color intelligence Hair color

autosomal

chromosomes

sexchromosomes

The sex of the offspring is determined by the presence or absence of the Y chromosome◦ If the offspring is XX, it is a female, if it is XY, it is a male

Not all genes on the X chromosome are “gender” traits◦ Some are for other traits that both males and females

have Traits on the X chromosome are inherited in a

different pattern than those traits on the autosomes

Examples of traits that are sex-linked include baldness and red-green color blindness

Sex-linked genes are always on the X chromosome

Lets assume that the colorblindness allele is recessive (Xa)

How many children will be colorblind?