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GENETICS
The Basics
Genetics
Genetics is the study of heredity or the patterns of inheritance of specific traits, relating to genes and genetic information.
Heredity is the passing of genetic information (DNA) from parent to offspring during sexual reproduction. Each sex cell (egg or sperm) of the parent organism (plant or animal) contains one-half of the genetic information or chromosomes needed to create a new organism.
Chromosomes are structures found in the nucleus of a cell. Chromosomes contain strands of genetic information or DNA. DNA stands for deoxyribonucleic acid. DNA strands are coiled to form a double helix or spiral ladder shape. Segments of a DNA strand code for specific traits. These segments are called genes. Genes typically come in pairs. One gene from the pair is called an allele.
STRUCTURAL ORGANIZATION
Human Chromosome Chart
The 23rd pair, the sex chromosomes, differ between males and females. Females have two copies of the X chromosome, while males have one X and one Y chromosome. Therefore, males determine the sex of the next generation. Can you calculate the probability for the sex of four children born to the same Dad and Mom?
DNA
deoxyribonucleic acid
[ dee-ok-si-rahy-boh-noo-klee-ik ]
Lab: Extracting DNA
Mendel Researched Heredity Using Pea Plants
- Mendel planted seeds from purebred "parent" plants.
- He observed how some traits where visible generation to generation.
- He observed how some traits were not visible generation to generation.
- Mendel kept very accurate records for hundreds of individual plants.
- He used statistical analysis (MATH) to study the traits of different generations.
- Through his findings, he proposed that the traits were passed by parents.
- He said the traits that were visible generation to generation were dominant.
- He said the traits that were less visible or rarely visible were recessive.
dominant - a trait that is expressed if present
recessive - a trait is that is expressed if there is not a dominant trait
Traits That Mendel Observed
trait = seed color
variation = the seed color is either yellow or green
Why Pea Plants?
- easy to grow
- grow quickly
- can be cross pollinated
- few traits
- two variations for traits
Mendel Conducted Monohybrid Experiments.
- one trait at a time was followed
- data was recorded on the variations generation to generation
- a total of seven traits were followed and recorded
- the data showed that some trait variations were more likely to show up
- some trait variations were hidden
The Data Results
- He called the trait variations that showed up dominant
- He called the trait variations that were hidden recessive
- He proposed that traits were controlled by two alleles
- One allele came from the father and one came from the mother
- The trait variation were passed down randomly as alleles
Mendel's Research
Test Crosses & Pedigress
Taste Receptors Are Inherited - Passing DNA
2. In general, girls have more tastebuds than boys.
3. Taste is the weakest of the five senses.
4. Insects have the most highly developed sense of taste.
5. Some insects have taste organs on their feet, antennae, and mouth.
5. Fish can taste with their fins, tail, and mouth.
What We Think We Know About Inherited Traits
Complete Dominance
- form of dominance in heterozygous condition wherein the allele that is regarded as dominant completely masks the effect of the allele that is recessive.
Incomplete Dominance
- traits are simultaneously blended together resulting in a new phenotype
- RW = a pink carnation is expressed or a new phenotype occurs
Codominance
- both traits are independently expressed within one organism
Multiple Alleles = Variety
POLYGENICS = EYE COLOR & SKIN TONE
Skin Tone & Multiple Genes
Consider the punnett square that follows.