Genetics Notes PDF: Mendel, Genes, and Traits for Study
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Uploaded by SweepingOrientalism3484
University of St. La Salle
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These genetics notes, from the University of St. La Salle, cover key concepts in genetics including Mendel's work, genes, traits, and the principles of inheritance. They include explanations of genotypes, phenotypes, and Punnett squares. The notes are designed to help students understand the basics of biology. Some information about the education level is undergraduate and high-school.
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From the Works of Mendel… Genetics Notes “Father of Genetics” Who is Gregor Mendel? Principle of Independent Assortment – Inheritance of one trait has no effect on the inheritance of another trait Traits Genetics – study of how traits are passed from...
From the Works of Mendel… Genetics Notes “Father of Genetics” Who is Gregor Mendel? Principle of Independent Assortment – Inheritance of one trait has no effect on the inheritance of another trait Traits Genetics – study of how traits are passed from parent to offspring Traits are determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait. Chromosomes come in homologous pairs, thus genes come in pairs. Homologous pairs – matching genes – one from female parent and one from male parent Example: Humans have 46 chromosomes or 23 pairs. One set from dad – 23 in sperm One set from mom – 23 in egg One pair of Homologous Chromosomes: Gene for eye color (blue eyes) Homologous pair of chromosomes Gene for eye color (brown eyes) Alleles – different genes (possibilities) for the same trait – ex: blue eyes or brown eyes Dominant and Recessive Genes Gene that prevents the other gene from “showing” – dominant Gene that does NOT “show” even though it is present – recessive Symbol – Dominant gene – upper case letter – T Recessive gene – lower case letter – t Recessive Dominant color color Example: Straight thumb is dominant to hitchhiker thumb T = straight thumb t = hitchhikers thumb (Always use the same letter for the same alleles— No S = straight, h = hitchhiker’s) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt * Must have 2 recessive alleles for a recessive trait to “show” Both genes of a pair are the same – homozygous or purebred TT – homozygous dominant tt – homozygous recessive One dominant and one recessive gene – heterozygous or hybrid Tt – heterozygous BB – Black Bb – Black w/ bb – White white gene Genotype and Phenotype Combination of genes an organism has (actual gene makeup) – genotype Ex: TT, Tt, tt Physical appearance resulting from gene make-up – phenotype Ex: hitchhiker’s thumb or straight thumb Punnett Square and Probability Used to predict the possible gene makeup of offspring – Punnett Square Example: Black fur (B) is dominant to white fur (b) in mice 1. Cross a heterozygous male with a homozygous recessive female. Black fur (B) White fur (b) Heterozygous Homozygous male recessive female White fur (b) White fur (b) Male = Bb X Female = bb Female gametes – N (One gene in egg) b b Possible offspring – 2N Male gametes - N B Bb Bb (One gene in sperm) b bb bb Write the ratios in the following orders: Genotypic ratio = 2 Bb : 2 bb Genotypic ratio 50% Bb : 50% bb homozygous : heterozygous : homozygous Phenotypic ratio = 2 black : 2 white dominant recessive 50% black : 50% white Phenotypic ratio dominant : recessive Cross 2 hybrid mice and give the genotypic ratio and phenotypic ratio. B b Bb X Bb B BB Bb b Bb bb Genotypic ratio = 1 BB : 2 Bb : 1 bb 25% BB : 50% Bb : 25% bb Phenotypic ratio = 3 black : 1 white 75% black : 25% white Example: A man and woman, both with brown eyes (B) marry and have a blue eyed (b) child. What are the genotypes of the man, woman and child? Bb X Bb Man = Bb B b Woman = Bb B BB Bb b Bb bb
