Ch. 11 Introduction to Genetics Unit 4 Genetics Ch. 11 Introduction to Genetics

The Work of Gregor Mendel Genetics - the scientific study of heredity Mendel is considered the “Father” of genetics

Gregor Mendel’s Peas Mendel was an Austrian monk, that worked on pea plants His experiments with pea plants laid the foundation of the science of genetics

Gregor Mendel’s Peas Fertilization - when male & female sex cells join together Pea flowers are normally self-pollinating, meaning the sperm cells in the pollen fertilize the egg cells in the same flower

Gregor Mendel’s Peas Seeds produced by self-pollination inherit all of their characteristics from the single plant that bore them True-breeding - if plants were allowed to self-pollinate, they would produce offspring identical to themselves

Gregor Mendel’s Peas Mendel wanted to produce seeds by joining male & female sex cells from 2 different plants He cut off the pollen (male) parts of a plant, & dusted pollen from another plant onto the flower (female)

Gregor Mendel’s Peas Cross-pollination - produces seeds that had 2 different parent plants

Genes & Dominance P - parent generation F1 - First generation (first generation of offspring) F2 - Second generation (offspring from the F1 generation)

Genes & Dominance Trait - a specific characteristic Ex.) seed color, plant height Hybrids - offspring of crosses between parents with different traits Ex.) cross between plant with yellow seed color & plant with green seed color

Genes & Dominance Mendel concluded that biological inheritance is determined by factors that are passed from 1 generation to the next Genes - chemical factors that determine traits

Genes & Dominance Alleles - different forms of a gene Ex.) gene for plant height occurs in 1 form that produces tall plants & in another form that produces short plants Mendel’s 2nd conclusion is the principle of dominance

Genes & Dominance The principle of dominance states that some alleles are dominant & others are recessive Dominant allele for a trait will always be exhibited (expressed or shown) Recessive allele will only be expressed when a dominant allele is not present

Mendel’s Seven F1 Crosses on Pea Plants

Segregation Gametes - sex cells (sperm or egg) Segregation - during gamete formation, alleles segregate (separate) from each other so each gamete only carries a single copy of each gene

Segregation Therefore, each F1 plant produces 2 types of gametes, those with the allele for tallness & those with the allele for shortness

Punnett Squares Punnett square - a diagram that might result from a genetic cross Punnett squares can be used to predict & compare the genetic variations that will result from a cross

Punnett Squares Homozygous - organisms that have 2 identical alleles for a particular trait Ex.) TT or tt Heterozygous - organism that has 2 different alleles for the same trait Ex.) Tt

Punnett Squares Phenotype - physical characteristics Ex.) Tall plants Genotype - genetic makeup Ex.) TT

Independent Assortment Independent assortment - genes for different traits can segregate (separate) independently during gamete formation Independent assortment increases genetic variation (genetic diversity, helps create genetically different organisms)

A Summary of Mendel’s Principles 1. The inheritance of biological characteristics is determined by individual units - genes Genes are passed from parents to their offspring

A Summary of Mendel’s Principles 2. In cases where 2 or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant & others may be recessive

A Summary of Mendel’s Principles 3. In most sexually producing organisms, each adult has 2 copies of each gene (1 from each parent) These genes are segregated (separated) from each other when gametes are formed

A Summary of Mendel’s Principles 4. The alleles for different genes usually segregate (separate) independently of 1 another

Beyond Dominant & Recessive Alleles Some alleles are neither dominant nor recessive, & many traits are controlled by multiple alleles or multiple genes

Beyond Dominant & Recessive Alleles Incomplete dominance - when 1 allele is not completely dominant over another The heterozygous phenotype is somewhere in between the 2 homozygous phenotypes

Beyond Dominant & Recessive Alleles Codominance - where both alleles contribute to the phenotype Flowers would not be pink, (a blend of red & white), but both red & white speckled

Beyond Dominant & Recessive Alleles Multiple alleles - when genes have more than 2 alleles It does not mean that an individual can have more than 2 alleles It only means that more than 2 possible alleles exist in a population

Multiple Alleles

Beyond Dominant & Recessive Alleles Polygenic traits - traits controlled by 2 or more genes Ex.) at least 3 genes are responsible for making the reddish-brown pigment in the eyes of fruit flies

Genetics & the Environment The characteristics of any organism are not determined solely by the genes it inherits Characteristics are determined by interaction between genes & the environment

Genetics & the Environment Ex.) genes may affect a sunflower plant’s height & the color of its flowers However, these conditions are also influenced by climate, soil conditions, & the availability of water Ex.) Rabbit fur color in winter & summer

Chromosome Number All cells of an organism (except for sex cells, gametes) have the same # of chromosomes Each body cell has 2 sets of chromosomes Homologous chromosomes - the same chromosomes, 1 set from each parent

Homologous Chromosomes

Chromosome Number Diploid - (2n) - a cell that has both sets of homologous chromosomes Haploid - (n) - a cell that has half the normal set of chromosomes, or 1 set (only sex cells are haploid)

Phases of Meiosis Meiosis - process of reduction division, where the # of chromosomes per cell is cut in 1/2, through the separation of homologous chromosomes in a diploid cell

Phases of Meiosis During meiosis 1, crossing-over may occur Crossing-over - when chromosomes exchange portions of their chromatids

Phases of Meiosis Crossing-over results in the exchange of alleles between homologous chromosomes & produces new combinations of alleles Crossing-over increases genetic variation (genetic diversity, helps create genetically different organisms)

Phases of Meiosis Meiosis II, begins with 2 genetically different haploid (n) cells, & results in 4 (n) genetically different haploid cells Therefore, Meiosis II is a mitotic division

Meiosis I

Meiosis II

Gamete Formation In males, the haploid gametes are sperm In females, the haploid gametes are eggs

Comparing Mitosis & Meiosis Mitosis results in the production of 2 genetically identical diploid (2n) cells Mitosis produces all cells of the body, except sex cells Meiosis produces 4 (n) genetically different haploid cells Meiosis produces ONLY sex cells (gametes)

Gene Linkage Each chromosome is a group of linked genes It is the chromosomes, however, that line up independently, not individual genes (Principle of Independent Assortment)