Download - 5. genetics
GENETICS
I. GREGOR MENDEL (1822-1884)
General
Monk
Worked with pea plants
Self-fertilization
Simple traits
Used Statistics
Looked at 1 trait at a time
A. Experiment – example
Parents purple flower x white flower
F1 100% purple
F2 75% purple 25% white
WHAT HAPPENED?
II. MENDELIAN GENETICSA. . DEFINITIONS
Gene – a segment of DNA that codes for a specific trait. It is found at a specific locus (location) on a chromosome
Chromosome – A condensed structure made of one or two DNA molecules with genes.
Allele – A form of a gene.
2 chromatids 1 chromatid
T or t
Dominant – Allele that is expressed when present.
Recessive – Allele expressed when the dominant is not present.
T
t
Co-dominant – Alleles for the same gene that both express themselves when present.
Incomplete dominance – The heterozygous
genotype results in a phenotype between the two homozygous genotypes.
ABO Blood
RR Rr rr
Red Pink White
Genotype – The alleles an organism/cell has.
Phenotype – The physical expression of a gene.
TT Tt tt
Tall Tall Short
Homozygous – The homologous pair has the same alleles for the same gene.
Heterozygous – The homologous pair has different alleles for the same gene.
TT or tt
Tt
Diagram
Gene – Coat Color
Chromosome
Allele
Dominant
Recessive
Genotype Bb
Phenotype black
B. Monohybrid Cross –
Look at one gene at a time
1. Principle of SegregationEvery individual (diploid) has 2 copies
(alleles) of a gene (one from the female and one from the male) for every trait.
In the production of gametes (by Meiosis) these alleles are separated randomly and come back together in the formation of a zygote (fertilization).
2. Example – Coat Color in Labrador
B = black (dominant) b = brown (recessive)
Phenotype: Black Black Brown
Parent Genotype: BB Bb bb
Parent gametes: B B B b b b
Example of the cross
Male Female
Bb Bb
B b B b gametes
BB Bb
Bb bb
Punnett square
B b
B
b
Genotype
1BB:2Bb:1bb
Phenotype
3black:1brown
C. DIHYBRID CROSS – When look at two genes at a time.
Linked genes are when genes are on the same chromosome.
Example
1. PRINCIPLE OF INDEPENDENT ASSORTMENT
Genes on different chromosomes (so are not linked)
randomly assort into gametes during Meiosis and have an
equal chance for any combination.
Meiosis I or Meiosis I
2. Example Gene Alleles
ear lobes E=free e=attached
freckles F=have f=none
Parent Genotypes EeFf EeFf
Gametes EF Ef eF ef EF Ef eF ef
EACH GAMETE MUST CONTAIN ONE COPY OF EACH GENE (in
this case each must have an E/e and a F/f)
EEFF EEFf EeFF EeFf
EEFf EEff EeFf Eeff
EeFF EeFf eeFF eeFf
EeFf Eeff eeFf eeff
EF Ef eF ef
EF
Ef
eF
ef
Free earlobes, freckles
Free earlobe, none
Attached, freckles
Attached, none
SEX-LINKED
• Gene is on the X chromosome (usually).
Male XY
Ex. Recessive trait - XHY or XhY
Female XX
Ex. Recessive trait – XHXH or XHXh or XhXh
Co-dominant
When more than one allele for any given gene are
both dominant and express themselves if present.
Example:ABO Blood
Phenotype Genotype
A blood IAIA or IAiB blood IBIB or IBi
AB blood IAIB
O blood ii
ABO are sugar antigens on the surface of
the red blood cells (rbc)
Rh factors are proteins on the surface of rbc.
Incomplete dominance
The heterozygote has a phenotype between
the two homozygous genotypes
GENOTYPES RR RR’R’R’
PHENOTYPES red pink white
III. PedigreeA tool used to track a genetic history. Used
for a family for some specific trait.
without trait with trait
Female
Male
mated
offspring
GENETIC PROBLEMS
MONOHYBRIDIn silkworms yellow cocoon is dominant to white cocoon.
Two silkworms are mated (one heterozygous and the
other homozygous recessive).
Find the: parent genotype and phenotypegametes producedPunnett SquareOffspring genotypeOffspring phenotype
Albinism is inherited as a recessive trait.
a. A heterozygous female has children by a homozygous normal male. What % of their offspring will be carriers for albinism?
b. A normally pigmented man whose mother was albino marries a homozygous normal woman. What % of their offspring will be homozygous normal?
c. A heterozygous male marries an albino female. What percentage of their offspring will be albino?
DIHYBRIDIn hogs, a gene that produces a white belt around the
animal’s body is dominant over its allele for a uniformly
colored body. Another independent gene produces fusion
of the two hooves on each foot (an instance of syndactyly).
It is dominant over its allele, which produces normal
hooves.
Supposed a uniformly colored male hog homozygous for syndactyly is mated with anormal-footed female hog homozygous for thebelted character.
CO-DOMINANCEIn cattle, red is not dominant to white. When the
two colors are crossed, the claves have both red
and white hairs, called roan.
A rancher mates a red bull and white cow.
Show Punnett Square and label phenotypes.
INCOMPLETE DOMINANCEIn four o’ clock flowers there are red, white and
pink petal colors. Pink petals is a heterozygous condition resulting from a cross of red and white.
Cross two pink plants
BLOOD TYPE AND SEX-LINKED
A normal visioned female has type A blood.
Her father was colorblind with type O blood
and her mother had AB blood. She marries
a man who is colorblind and has type B
blood (whose mother had normal vision and
O blood and whose father had normal vision
and B blood).