Mendelian genetics
By : Sif elwakil
Genetics
-the scientific study of inheritance
inheritance- the process in which genetic
material is passed from parents to their
offspring
Gregor Mendel
• Austrian monk-studied
pea plants
• Mathematical basis for
experiments
• Kept careful records of
numbers
• Studied simple traits
(seed color, shape, flower
color, height, etc.)
Monohybrid Cross
• A cross between two parents that are
identical in all but one characteristic.
• Example: cross a short pea plant
and a tall pea plant
• P is parent generation,
• F1 is first filial generation,
• F2 is second filial generation
• Result of cross: F1-all tall, F2-3
tall:1 short
Modern Genetics
• Allele: Alternate forms of the same gene. Each trait has
two alleles:
• Dominant: masks the effects of the recessive (ex. T)
• Recessive: is masked by the dominant (ex. t)
Modern Genetics cont’d
• Gene Locus: the place on a homologous
pair of chromosomes where the alleles
occur, one on each chromosome.
• Homozygous (true-breeding): Both copies
of the allele are identical (TT or tt)
• Heterozygous: Each copy of the allele is
unique (Tt)
Genotype vs. Phenotype
•
Genotype: the alleles an individual receives at fertilization. TT
is homozygous dominant, tt is homozygous recessive, and Tt is
heterozygous.
•
Phenotype: refers to the physical characteristics of an
individual. Homozygous dominant and heterozygous individuals both
show the dominant phenotype (tall), while homozygous recessive shows the
recessive phenotype (short).
Classes of chromosomes
autosomal
chromosomes
sex
chromosomes
of Sex
• In humans Genetics
& other mammals,
there are 2 sex
chromosomes: X & Y
• 2 X chromosomes
• develop as a female: XX
• an X & Y chromosome
• develop as a male: XY
50% female : 50% male
X
Y
X
XX
XY
X
XX
XY
Sex-Linked Traits
• Sex-linked traits are produced by genes only on the X chromosome.
• They can be Dominant or Recessive.
• A = dominant a = recessive
• What would be the genotypes of a male and female that have a Sex-linked
Dominant trait and do not express the trait?
• Expresses Trait:
Male - XA Y
Female - XA XA or XA Xa
• No Expression:
Male - Xa Y Female - Xa Xa
• What would be the genotypes of a male and female that have a Sex-linked
Recessive trait and do not express the trait?
• Expresses Trait:
Male - Xa Y Female - Xa Xa
• No Expression:
Male - XA Y
Female - XA XA or XA Xa
(Carrier)
• Most Sex-linked traits are Recessive!
Dihybrid Cross
• A cross between two
individuals that differ from
each other in regards to two
traits.
• Ex: pod color and pea color:
GGYY and ggyy.
• F1 generation will be GgYy.
Environmental Effects
• Phenotype is controlled by both
environment & genes
Human skin color is influenced
by both genetics &
environmental conditions
Coat color in arctic
fox influenced by
heat sensitive alleles
Color of Hydrangea flowers
is influenced by soil pH
Biotechnology
• -any procedure or methodology that uses biological systems or
living organisms to develop or modify either products or processes
for specific use.
• Genetic engineering- a technology that includes the process of
manipulating or altering the genetic material of a cell resulting in
desirable functions or outcomes that would not occur naturally.
• genetically modified organism- an organism whose genetic material has
been altered through some genetic engineering technology or technique.
• gene therapy- the intentional insertion, alteration, or deletion of genes within an individual’s
cells and tissues for the purpose of treating a disease.
• gene splicing- a type of gene recombination in which the DNA is intentionally broken and
recombined using laboratory techniques
• Cloning- a process in which a cell, cell product, or organism is copied from an original
source
• DNA cloning- making exact copy of a DNA fragment
• Reproductive cloning- transfer of genetic material from the nucleus of a donor adult
cell to an egg that has had its nucleus removed ; the embryo is an exact genetic copy of
the donor organism.
• Therapeutic cloning- using STEM cells for use in research
•
STEM cells- undifferentiated cells; have not decided “what they want to be” when they “grow up”