Transcript genetics_4

Genetics
Genetics
• Is the science of heredity.
• Heredity is the transmission of genetic
or physical traits from parent to
offspring.
Gregor Mendel
• Austrian Monk
• Considered the “Father of Heredity”
• He conducted plant breeding
experiments in their monastery
garden.
• In 1865 he made his work public, units
of inheritance.
What makes us unique?
• Each of the 100 Trillion cells in our
body except the red blood cells
contains the entire human genome, in
the nucleus of every cell is the genetic
information “blueprint” to construct
the individual.
• It is the Deoxyribonucleic acid (DNA)
• Function of DNA
– Genetic code for almost every organism.
– Provide template for protein synthesis.
Chromosomes
• The DNA in every cell is located in
rod like segments called chromosomes
• Chromosomes occurs in pairs in every
cell of our body except in the sperm
and ovum.
• Chromosomes numbers are the same
for each specie.
Chromosome Numbers
Specie
Cattle
Swine
Sheep
Horse
Human
Chicken
Goat
Donkey
Diploid #
60
38
54
64
46
78
60
62
Haploid #
30
19
27
32
23
39
30
31
Chromosomes
• There are 2 sex chromosomes included
in the diploid number of the
chromosomes.
• All of the other chromosomes are
referred to as autosomes.
• In mammals if the sex chromosomes
are alike, XX it results in a female.
• If the sex chromosomes are different,
XY it results in a male.
Sex Determination
• Female can contribute only a X chromosome
towards the sex of their offspring.
• Male can contribute an X or a Y
chromosome toward the sex of their
offspring.
• Absence of an Y chromosome results in a
the embryo developing into a female.
• Presence of an Y chromosome results in the
embryo developing into a male.
Tell me what I am ?????
Tell me what I am ?????
Genes
• Chromosomes contains several units
of inheritance “genes”.
• Genes usually occurs in pairs, one
from each parent.
• Some traits are inherited directly from
one set of genes.
• Some traits are inherited through
several sets of genes.
Terms to know
• Homozygous- contains 2 identical genes for
the same trait, AA, BB, cc
• Heterozygous- contains 2 different genes
for the same trait, Aa, bB, Cc
• Phenotype- Outward appearance of a trait,
coat color, polled, horned.
• Genotype- Genetic classification of a gene,
AA, Aa, aa.
• Allele- Location of a gene on the
chromosome.
• F-one = First cross mating.
• F-two = Second cross mating.
What are dominant genes?
• The gene that express itself, the powerful
and dominant gene.
• It has the power to overshadow the
recessive gene when there is complete
dominance.
• Some examples are:
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–
White faced in cattle
Droopy ears in swine
Polled in cattle
Black coat color in Angus cattle
What are Recessive Genes?
• The gene that is overshadowed by a
dominant gene
• Recessive genes can only express
themselves in the absence of the
dominant gene
• Polled vs Horned (Pp) (pp)
• Black wool vs white (Ww) (ww)
• Dwarfism vs normal size (dd)
• Albino
Punnet Square
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Angus- Black coat color is dominant.
BB = Homozygous Dominant and Black
Bb = Heterozygous and is black
bb = Homozygous recessive and red
A heterozygous bull is mated to 50
homozygous recessive cows.
• How many calves are black?
• How many calves are red?
• What is the genotypic and phenotypic
ratios?
Punnet Square
B
b
b
Bb
bb
b
Bb
bb
Results
• 2 heterozygous =
Bb
• 2 Homozygous
Recessive bb
• 25 Black, 25 Red
• Genotypic ratio =
0:2:2
• Phenotypic ratio =
2 Black: 2 Red
What are Sex Linked Genes?
• Some recessive genes are attached to
the X and Y chromosomes
• Humans: Colorblindness and
Baldness are on the X chromosomes
• In Men, traits expressed anytime
present
• In Women, must have two recessives
to show trait
• Children get baldness from mothers
What is Incomplete
Dominance?
• If both genes express themselves
• Shorthorn Cattle: Red male mated to a
White female = Roan calf
• RR crossed rr = Rr
What is a Mutation?
• Dramatically different from what is
expected genetically
• Horned calf from polled parents
• Loss of some or extra body parts
• Lethal Mutation: causes death at birth
• Sublethal Mutation: limits animals
ability to grow to maturity
• Beneficial Mutation: loss of tail in
lambs
Monohybrid Crosses
• Cross 1 character – Flower Color
• Purple Flowers are dominant – P
• White Flowers are recessive – p
• Cross a Heterozygous with a
Cross:
homozygous recessive
 Genotype Ratio:
2 Pp; 2 pp
 Phenotype Ratio:
2 Purple
2 White
 Probabilities:
Being Purple:
Pp X
pp
P
p
p
p
P
p
P p
p
p
p
p
Pedigrees
• A family history that shows how a
trait is inherited over several
generations
• Helps to track down the carriers
(heterozygotes) of recessive disorders.
Reading Pedigrees
A shaded box
–
affected male …………
A shaded circle -
affected female……….
A clear box
normal male…………..
-
Pedigree Practice
I
II
III
IV
Legend:
Hemophilic Male: ………
Hemophilic Female: …...
Normal Female: ………
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Codominance
Case in which both forms of the character are
displayed.
Ex. The ABO blood groups
Neither IA nor IB are dominant is dominant over the
other.
Both are dominant over i (Type O).
When both IA and IB are present they are codominant
and the individual is type AB
Blood Typing
Blood Types
IA
IB
i
A
AB
B
IA
IB
i
O
IA IA
IA IB
IA i
IA IB
IB IB
IB i
IA i
IB i
ii