Gregor Mendel

Genetics- the scientific study of heredity Mendel was an Austrian monk who wanted to understand genetics. Mendel studied pea plants to improve his understanding of how traits are passed from parents to offspring. Mendel Video

Self-Pollinating-Sperm cells in pollen fertilize the egg cells in the same flower Pea flowers are self-pollinating The seeds that are produced by self-pollination inherit all of their characteristics from the single plant that bore them.

The Experiment: True-Breeding- occurs when plants produce offspring identical to themselves after self- pollination Mendel’s pea plants were true-breeding as a result of self-pollination. Cross-Pollination- when pollen from one flower is delivered to a flower from a different plant. Mendel used cross-pollination to produce seeds that had two different parents.

He cut away the pollen-bearing male parts of the plant and dusted the plant’s flower with pollen from another plant.

The original parents are represented by P (parental) The offspring of the original parents are called the F 1 generation (1 st filial) The offspring of the F 1 generation are called F 2 generation (2 nd filial)

Hybrid- The offspring of crosses between parents with different traits Ex: the offspring of a cross b/w a red rose & white rose. The term “crossing” means mating

Punnett Square- A tool used to determine the gene combinations that might result from a genetic cross A capital letter is used to represent the dominant allele A lower case letter is used to represent the recessive allele Allele- alternative forms of genes Ex: Gene for flower color; the alleles are red, purple, and yellow color.

Mendel’s Hypotheses If there are two or more alleles for a gene, some of the alleles may be dominant and others may be recessive A sperm cell has only one allele for each trait An egg cell has only one allele for each trait Dominant allele- always expressed Recessive allele- only expressed in the absence of the dominant allele

Homozygous- Organisms that have two identical alleles for a particular trait organisms are true-breeding for a particular trait. Two alleles for black fur Heterozygous- Organisms that have two different alleles for the same trait organisms are hybrid for a particular trait. One allele for black fur and one allele for white fur

Genotype- genetic make up of the organism Ex: genes for black fur and white fur Ex: Tall (T) allele and short (t) allele Phenotype- the physical characteristics or what the organisms looks like. Ex: the mouse has black fur. Ex: all plants appear tall

After Mendel’s experiments he formulated the principle of segregation Principle of Segregation- Pairs of genes separate (segregate) when gametes are formed.

Alleles for a gene are at the same locus (location) on homologous chromosomes

Independent Assortment- Genes that segregate (separately) independently do not influence each other's inheritance. The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes

Mendel did a dihybrid (two trait) cross to see if the separation of one pair of alleles affects the separation of another pair of alleles. Instead of crossing a yellow seed with a green seed; he observed seed color and seed shape together Seeds that are round (R) and yellow (Y) are dominant to seeds that are wrinkled (r) & green (y)

True-breeding round & yellow (RRYY)seeds were crossed with true breeding wrinkled and green seeds (rryy) The result: All individuals in the F 1 generation were round & yellow

Dihybrid Cross: F2 Heterozygous F1 plants (RrYy) were crossed with each other to determine if the alleles would segregate from each other in the F2 generation. RrYy × RrYy

The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F2 generation 9 round & yellow: 3 round & green: 3 wrinkled & yellow: 1 wrinkled & green

The results of the experiment: some seeds were round and yellow some seeds were wrinkled and green some seeds were round and green some seeds were wrinkled and yellow Mendel had discovered the principle of independent assortment Independent Assortment explains the variation observed in plants, animals, and other organisms

Probability can be used to predict the results of genetic crosses. Probability- the likelihood that something is going to happen. In genetics expressed as a ratio or percentage. Ex: the probability that it will snow in March is 50:50

Probability of Blue vs. Green Beetle

Probabilities predict the average outcome of a large number of events. Probability cannot predict the exact outcome of an individual event In genetics, the larger the number of offspring, the closer the resulting numbers will get to the expected values.

Geneticis who study humans triats study matings that have already occurred. Pedigree charts- shows relationships w/i a family of traits controlled by a single gene and not by environmental influences. Ex: ability to taste PTC (a bitter taste) Colorblindness Albinism (lack of pigment in skin, hair, & eyes)

People who are heterozygous for a trait are called carriers Ex: DD (normal hearing) Dd (carrier/heterozygous) dd (deaf)

There are two types of inherited disorders in humans; recessive & dominant Recessive Disorders Most human disorders are recessive Cystic Fibrosis is common in the U.S. Excessive mucus secretion clogs the lungs Few black people have the disease (1/17,000) More white people have the disease (1/1,800)

Dominant Disorders Only copy of allele needs to present for the disordered to have the disease

Most genetic disorders can be detected before the birth Test done between weeks 14 and 20 of the pregnancy can determine genetic disorders Amniocentesis- taking a sample of the amniotic fluid and testing it Chorionic villus sampling (CVS)-small amount of fetal tissue is suctioned from the placenta; karyotyping is performed & chemical analysis Ultrasound Imaging- an image of the fetus is used to determine anatomical deformities