Chapter 11: Introduction to Genetics Mendel and Meiosis

11.1: Mendel’s Laws of Heredity Gregor Mendel – Father of Genetics genetics = branch of biology that studies heredity traits = characteristics that are inherited Mendel cross pollinated plants, studied one trait at a time transferred gametes

Mendel’s Monohybrid Crosses tall pea plant x short pea plant  tall plant what happened to “shortness?” tall offspring x tall offspring  ¾ tall, ¼ short

Mendel concluded that each organism has 2 factors for each of its traits these are genes, located on chromosomes different forms of genes = alleles ex: plant may have 2 alleles for tallness alleles are located on different copies of chromosomes – one from each parent

Principle of Dominance dominant alleles – expressed whenever present recessive alleles – only expressed if dominant is not present

Law of Segregation alleles for each trait separate when gametes are formed During fertilization, gametes randomly pair together

Phenotypes & Genotypes phenotype = physical characteristics (observable) genotypes = gene combination homozygous – alleles are the same ex: TT or tt heterozygous – alleles are different ex: Tt

Punnett Squares used to predict the possible genotypes of offspring Assign letters (dominant = upper case, recessive = lower case) Write out cross Fill in Punnett square Answer any questions

Mendels’s Dihybrid Crosses dihybrid involves two traits Mendel concluded that different traits are inherited independently of each other = law of independent assortment See Figure 11-8, pg 316

11.4: Meiosis genes are found on chromosomes 1000+ genes on each chromosome

Diploid & Haploid Cells number of chromosomes varies with each organism; is not related to complexity of organism diploid – (2n): cell has 2 kinds of each chromosome haploid – (n): cell with one of each chromosome

Homologous chromosomes = paired chromosomes have genes for the same traits arranged in same order not identical to each other – can have different allele for same gene see pg 324-325

Meiosis meiosis produces cells with ½ the number of chromosomes as the parent 1 diploid (2n) cell  4 haploid (n) cells haploid cells are gametes male = sperm female = eggs combining egg & sperm  zygote

Phases of Meiosis