genetics is the study of inheritance – the passing of traits from parent to offspring what is...
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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?