Transcript Genetics Mendel - Oceanside Moodle

Foundations of
Genetics
Genetics
• Alleles- different forms of a gene
– Ex: Genes for eye color can be brown or
blue.
– You can have alleles that are homozygous
for a trait or heterozygous for a trait
• Homozygous- the
organism has the same
alleles for the trait.
– EX: BB or bb
• Heterozygous/Hybridthe organism has
different alleles for a trait.
– EX: Bb or Yy
Genotype vs. Phenotype
• Genotype- is the
actual genetic make
up of an organism.
What is not seen.
• Phenotype- is the
actual PHYSICAL
appearance of the
organism. What is
seen.
Dominant vs. Recessive
• Dominant Traits- are the traits that
are expressed
• Recessive Traits- are only expressed
when no dominant allele is present.
Genetics
• Genetics- is the branch of
biology that studies how
hereditary material is passed
from parent to offspring
– Gregor Mendel- Austrian monk
who began to genetically
investigate pea plants.
Mendel’s Law of Dominance
Mendel’s first law
It states that when an
organism is homozygous
dominant and another is
homozygous recessive
then the dominant trait is
always seen.
T
T
t
Tt
Tt
t
Tt
Tt
Law of Segregation and
Recombination
• 2nd Law Alleles
separate during
gametogenesis and
recombine during
fertilization.
**He used offspring from
law of dominance**
Types of Dominance
• There are four types of dominance:
– Incomplete dominance
– Co dominance
– Multiple Alleles
– Polygenic traits
Incomplete Dominance
• When one allele is not completely
dominant over the other.
– Ex. Japanese Snapdragon flowers
W
R
R
RW
RW
KE Y
RR Red
WW White
W
RW
RW
RW Pink
Co-dominance
• When both alleles contribute to the
phenotype.
– Ex. Seen in cattle
CR
CR
CW
CRCW
CRCW
KE Y
CRCR RED
CWCW WHITE
CW
CRCW
CRCW
CRCW ROAN
Multiple Alleles
• When genes have more than two alleles
for a trait
•
•
•
•
•
Blood Types are an example
A
I
A– IAIA (Homozygous) or IA i (Heterozygous)
Ai
I
B– I BIB or IB i
i
AB– IAI B
O– i i (recessive)
i
IA i
IA
IA i
IA i
•
Sex Determination &
Chromosomes
Sex Chromosomes
Diploid cells have one pair of
chromosomes that are not alike
• Human Sex Chromosome– Human cells contain 22 pairs of autosomal (body
cells) chromosomes and 1 pair of sex
chromosomes
• Males are XY
Female XX
• Egg Cells always carry an X
• Sperm Cells can carry a X or Y
Karyotype
Sex Linkage
• The “X” chromosome carries many alleles that
the Y does not.
• The expression of the gene is affected by the
sex of the individual.
• Ex: Lorenzo’s Oil (ALD)
• Females are “XX”. In order for the trait to be
expressed it must be on both X’s. Males only
have one X so if it lands on the X it will be
expressed.
• For Example: Colorblindness and
hemophilia are sex linked traits.
Carrier Female
Affected boy
XX-
X-X-
X
X-X
25% Affected Female
25% Carrier Female
25% Affected Male
Y
X-Y
XY
25 % Normal Male
Genetic Disorders
• Phenylketonuria- inability of the body to make an
enzyme needed to break down a certain amino acid.
– Diet products like: Diet Coke, Equal, Splenda
• Have this amino acid in it and people with this disease can’t
consume these products
• Tay Sachs- Deterioration of nerve tissue due to the
accumulation of fatty material
• Down’s Syndrome- Chromosomal disorder resulting in
an extra number 21 chromosome. (Caused by nondisjunction during meiosis)