Biology Chap10 Notes

Destiny Cobb Biology Unit 4, Chapter 10 Mendel and Meiosis pgs.258-285

Main Idea Section 10.1 Mendel’s Laws of Heredity

Section 10.2 Meiosis

Notes/Vocabulary • Genes are located on chromosomes and exist in alternative forms called alleles. A dominant allele can mask the expression of a recessive allele. • When Mendel crossed pea plants differing in one trait, one form of the trait disappeared until the second generation of offspring. To explain his results, Mendel formulated the law of segregation. • Mendel formulated the law of independent assortment to explain that 2 traits are inherited independently • Events in genetics are governed by the laws of probability. Heredity- passing on of characteristics from parents to offspring Genetics- branch of biology that studies heredity Trait- characteristic that is inherited; can be either dominant or recessive Gamete- male and female sex cells; sperm and egg Pollination- transfer of male pollen grains to the pistil of a flower Fertilization- fusion of male and female gametes Hybrid- offspring formed by parents having different forms of a trait Allele- alternative forms of a gene for each variation of a trait of an organism Dominant- observed trait of an organism that masks the recessive form of a trait Recessive- trait of an organism that can be masked by the dominant form of a trait Law of Segregation- Mendelian principle explaining that because each plant has two different alleles, it can produce two different types of gametes. During fertilization, male and female gametes randomly pair to produce 4 combinations of alleles Phenotype- outward appearance of an organism, regardless of its genes Genotype- combination of genes in an organism Homozygous- paired chromosomes with genes for the same traits arranged in the same order Heterozygous- when there are 2 different alleles for a trait Law of Independent Assortment- Mendelian principle stating that genes for different traits are inherited independently of each other • In meiosis, one diploid(2n) cell produces 4 haploid (n)cells, providing a way for offspring to have the same number of chromosomes as their parents • Mendel’s results can be explained by the distribution of chromosomes during meiosis • Random assortment and crossing over during meiosis provide for genetic variation among the members of a species • Mistakes in meiosis may result from nondisjunction, the failure of chromosomes to separate properly during cell division Diploid- cell with 2 of each kind of chromosome; is said to contain a

Destiny Cobb Biology Unit 4, Chapter 10 Mendel and Meiosis pgs.258-285

diploid, or 2n, numbers of chromosomes Haploid- cell with 1 of each kind of chromosomes; is said to contain a haploid of n, number of chromosomes Homologous Chromosome- paired chromosomes with genes for the same traits arranged in the same order Meiosis- type of cell division where one body cell produces 4 gametes, each containing half the number of chromosomes as a parent’s body cell Sperm- haploid male sex cells produced by meiosis Egg- haploid female sex cells produced by meiosis Zygote- diploid cell formed when a sperm fertilizes an egg Sexual reproduction- pattern of reproduction that involves the production and subsequent fusion of haploid sex cells Crossing Over- exchange of genetic material between nonsister chromatids from homologous chromosomes during prophase 1 of meiosis; results in new allele combinations Genetic Recombination- major source of genetic variation among organisms caused by reassortment or crossing over during meiosis Nondisjunction- failure of homologous chromosomes to separate properly during meiosis; results in gametes with to many or to few chromosomes