Genetics

Fundamentals of Genetics
Patterns of Inheritance
The History of Genetics
Genetics – scientific study of heredity
Trait – characteristic that can be passed from parents to offspring
Father of Genetics
Gregor Mendel (born 1822)
Austrian Monk
Studied 7 different pea plant traits that are true-breeding
Produce offspring identical to themselves
Mendel’s 1st Conclusion
Biological inheritance is passed from one generation to the next- Genes
Alleles- different forms of a gene
Parental Cross
Cross-pollinated flowers with opposite traits (tall, short)
P generation
Plants from the first cross were all tall- hybrids.
F1 generation
F1 Cross
Allowed plants from P cross to self-fertilize
The recessive trait had reappeared!!
About 25% of the offspring (F2 generation) were short.
Mendel’s 2nd Conclusion
Principle of Dominance
Some alleles are dominant
Capital Letter -R,D
This trait will be always be seen
Some alleles are recessive
Lower case Letter –r,d
This trait will only be seen when a dominant allele is NOT present
Mendel’s 3rd Conclusion
Principle of Segregation
Alleles separate from each other during formation of sex cells, or gametes.
Purebred – organism receives the same genetic traits form both of its parents
Homozygous – AA or aa

Hybrid – organism receives different forms of a genetic trait
Heterozygous - Aa
Important Terms
Genes – sections of a chromosome that code for a trait
Allele – distinct form of a gene
Dominant Allele – expressed when two different alleles are present; represented with capital letter
Recessive Allele – form of gene that is not expressed when paired with a dominant allele; represented with lower case letter
Genes Represent Traits
Genotype – genes that make up an organism
Includes both genes in a homologous pair
Phenotype – outward expression of the trait
Homozygous – two alleles are identical (AA or aa)
Heterozygous – two alleles are different (Aa)
Also known as a hybrid organism
Genetics and Prediction
Predictions for One Trait
Probability – predict likelihood of an event or outcome
Punnett square – grid for organizing genetic information
Can be used to make predictions about a cross between two organsims
Monohybrid Cross – cross between two parents and one trait
Monohybrid Cross
Predictions for Two Traits
Dihybrid Cross – cross between two parents and two traits
Use a 4 x 4 Punnett square
Sixteen possible outcomes
Incomplete Dominance
Heterozygous offspring show a phenotype that is in-between the phenotypes of the two homozygous parents
Blending of traits
Color in snapdragons;
instead of white or red,
color is pink
Codominance
Both alleles are expressed
Example: Blood type
IA, IB, i(O), or IAIB blood type
Both A and B are dominant so they are both expressed in the IAIB blood type
Polygenic Trait
Trait controlled by more than one gene
Example: eye color
Pleiotropy
Single gene affects more than one trait
Example: sickle cell anemia
Effects include blood cell shape, anemia, weakness, brain damage, spleen damage, and heart damage
Environmental Effects
Phenotype is a combination of genetic and environmental influences
Example: Himalayan rabbit – fur color depends on body temperature
Human Genetics
Difficulties in Studying
Human Heredity
Controlled experiments are not possible
Small numbers of offspring per generation
Long periods between generations
Sex Determination
Autosomes – body chromosomes – first 22 pair
Same in both male and female
Sex Chromosomes – 1 pair, last pair
XX – Female
XY - Male
XX = 50%
XY = 50%
You always have a 50% chance of having
a girl and a 50% chance of having a boy!
Sex Linked Traits
Traits controlled by recessive genes located on sex chromosomes (normally associated with the X chromosome)
Hemophilia – blood clotting enzyme
is absent
Queen Victoria’s family affected
Sex Linked Traits
Red – Green Colorblindness – individuals cannot distinguish between these two colors
Sex Linked Traits
Duchene Muscular Dystrophy – wasting away of skeletal muscle
Females
XRXR = normal
XRXr = carrier
XrXr = disease

Males
XRY = normal
XrY = disease

Sex – Limited Traits
Controlled by genes located in the autosomes
Only expressed in the presence of sex hormone
Only expressed in one gender
First seen at puberty (hormones produced in large enough quantities
Sex – Limited Traits
Examples:
Male bird’s colorful plumage
Beard growth in males
Milk production in females
Sex Influenced Traits
Traits that are caused by a gene whose expression differs in males and females
Also located on autosomes
Expressed in the presence of male or female hormones
Example: male pattern baldness
BB = normal
Bb = males bald, females normal
bb = males and females bald
Hereditary Disorders
Techniques for detecting genetic disorders
Amniocentesis – technique used that removes and studies amniotic fluid
during pregnancy;
identifies only
chromosomal disorders
Hereditary Disorders
Karyotyping – an enlarged photo of the chromosome pairs (map) to identify any abnormalities in the chromosomes
Chromosomal Disorders
Chromosomes fail to separate during meiosis

Nondisjuction-abnormal numbers of chromosomes enter gametes
Pedigree Charts
Chart which shows how a trait and the genes that control it are inherited within a family
Identifies the presence or absence of particular trait in members of each generation
Pedigree Charts
Males =
Females =
Generations = Roman Numerals
Individuals = Numbered sequentially
Trait Expressed = Filled in
Non Carriers = Empty
Carrier (not ill) = Half filled
Individual who carries a recessive allele that is not expressed