Transcript File
Mendelian Genetics Mendel laid the groundwork for genetics. Genetics is the study of biological inheritance patterns and variation. Gregor Mendel showed that traits are inherited as discrete units. Traits are distinguishing characteristics that are inherited. Many in Mendel’s day thought traits were blended. How did he do this? Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. Purple x purple = purple offspring White x white = white offspring Then he crossed one white and one purple from these offspring. Purple crossed with white = all purple How is this possible??? He then let the purple offspring self-pollinate…. 3 purple flowers : 1 white flower Mendel observed patterns in the first and second generations of his crosses. Mendel drew three important conclusions. Traits are inherited as discrete units, that we call genes. Organisms inherit two copies of each purple gene, one from each parent. The two copies segregate during gamete formation. (The last two conclusions are called the law of segregation.) white Now we know more about our genes…. Both parents have 2 alleles for each gene An allele is a variation, or form of a gene, and is located on the same spot on homologous chromosomes. Meiosis: chromosomes & alleles are separated. Each gamete gets one of the alleles. Each parent contributes only 1 allele to their offspring. There is a 50% chance of receiving either allele from either parent. Genotype vs. Phenotype Genotype: actual alleles from parents (letters) Phenotype: physical appearance of organism (no letters: What does it look like? What traits does it have?) If 2 alleles differ, one is dominant over the other (this trait will be expressed). The other one is recessive. (it will be masked by the dominant allele) What would have to happen in order to see a recessive trait expressed??? Genetic Crosses Capital letters = dominant alleles Lowercase letters = recessive alleles Use the SAME letter to represent both alleles! Example: Flower color: purple = P white = p Seed color: green = G yellow = g freckles: F no freckles= f Both alleles are same = homozygous Both alleles are different = heterozygous Try this: Let’s use freckles. Having freckles is dominant= F No freckles = f How would you show an individuals genotype if they were: Homozygous dominant for freckles? Homozygous recessive for freckles? Heterozygous for freckles? Brown eyes = B Blue eyes = b Write the genotype for an individual that is: Blue eyed:________________________ Homozygous dominant for eye color:____________ Heterozygous for eye color:___________________ Homozygous recessive for eye color:________ What genotypes can a person have if they have brown eyes?_____________ Only 1 allele from each parent is in each box. Each box ends up with 2 total alleles, one from the mother and one from the father. Monohybrid Cross Cross involving one contrasting trait Use a Punnett square to predict probabilities… (let’s use F) Cross a heterozygous purple flower with a homozygous recessive white flower. __________X__________