Ch 10 Sexual Reproduction Genetics 10 1 Meiosis

Ch. 10 – Sexual Reproduction & Genetics 10. 1 – Meiosis Genetics the scientific study of heredity and variability The transition of traits from one generation to the next Shows offspring differ in appearance from parents and siblings

Ch. 10 – Sexual Reproduction & Genetics Genes units of heredity segments of DNA found at a specific locus on the chromosomes 10. 1 – Meiosis

Ch. 10 – Sexual Reproduction & Genetics 10. 1 – Meiosis Humans have 23 pairs of chromosomes One set of chromosomes is inherited from each parent Both chromosomes in a pair carry genes controlling the same characteristics

Ch. 10 – Sexual Reproduction & Genetics 10. 1 – Meiosis Reproductive cells (gametes) have only one set of chromosomes. They are called haploid cells (n) Fertilization occurs when two gametes combine As a result of fertilization the new cell will now contain a total of 2 n chromosomes and is called diploid

Ch. 10 – Sexual Reproduction & Genetics 10. 1 – Meiosis Reproductive cells (gametes) have only one set of chromosomes. They are called haploid cells (n) Fertilization occurs when two gametes combine As a result of fertilization the new cell will now contain a total of 2 n chromosomes and is called diploid

Ch. 10 – Sexual Reproduction & Genetics Meiosis reduces the number of chromosomes from diploid to haploid It takes place in 2 sets of cell divisions Meiosis I separates homologous pairs Meiosis II separates sister chromatids Resulting in 4 unique daughter cells 10. 1 – Meiosis

Ch. 10 – Sexual Reproduction & Genetics Meiosis reduces the number of chromosomes from diploid to haploid It takes place in 2 sets of cell divisions Meiosis I separates homologous pairs Meiosis II separates sister chromatids Resulting in 4 unique daughter cells 10. 1 – Meiosis

Ch. 10 – Sexual Reproduction & Genetics 10. 1 – Meiosis Crossing Over During meiosis I segments of chromosomes are randomly exchanged between homologous pairs

Ch. 10 – Sexual Reproduction & Genetics 10. 1 – Meiosis

Ch. 10 – Sexual Reproduction & Genetics 10. 1 – Meiosis

Ch. 10 – Sexual Reproduction & Genetics Gregor Mendel and the gene idea 10. 2 – Mendelian Genetics

Ch. 10 – Sexual Reproduction & Genetics 10. 2 – Mendelian Genetics P Generation Purebred X parental plants X X F 1 Generation - 1 st generation of plants produced by cross pollination

Ch. 10 – Sexual Reproduction & Genetics 10. 2 – Mendelian Genetics F 1 X 787 277 F 2 Generation - Offspring of F 1 crosses

Ch. 10 – Sexual Reproduction & Genetics 10. 2 – Mendelian Genetics ~ 3: 1 ratio for the F 2 generation of all of these traits

10. 2 – Mendelian Genetics These findings lead Mendel to propose the following: • Traits are controlled by alternate “heritable factors” (genes). Ch. 10 – Sexual Reproduction & Genetics • For each trait an organism inherits 2 alleles (one from each parent) • If both allele exist in an individual, then one trait will be dominant over the other. • The two alleles for a heritable trait separate during gamete formation and end up in different gametes. The Law of Segregation

10. 2 – Mendelian Genetics Ch. 10 – Sexual Reproduction & Genetics TT X TT TT X Tt Tt Tt Gametes T Tt X t tt tt Tt Tt tt P F 1 Tt T t Segregation Seperation of alleles Fertilization TT X Tt tt F 2

10. 2 – Mendelian Genetics Ch. 10 – Sexual Reproduction & Genetics TT X TT TT X Tt Tt Tt Gametes T TT Tt X t Tt tt tt Tt X tt P F 1 Tt T Tt t tt Segregation Seperation of alleles F 2

Ch. 10 – Sexual Reproduction & Genetics T TT t Tt T Tt t tt 10. 2 – Mendelian Genetics Punnett Square T t T TT Tt tt

Ch. 10 – Sexual Reproduction & Genetics TT Tt 10. 2 – Mendelian Genetics Tt Homozygous Dominant tt Homozygous Recessive Heterozygous

Ch. 10 – Sexual Reproduction & Genetics TT Tt 10. 2 – Mendelian Genetics Tt tt Phenotype The physical characteristics Genotype The genetic makeup How many different phenotypes are there above? 2 – Tall & Short How many different genotypes are there above? 3 – TT, Tt & tt

Ch. 10 – Sexual Reproduction & Genetics The Test Cross Developed by Mendel to reveal the genotype for an organism 10. 2 – Mendelian Genetics

Ch. 10 – Sexual Reproduction & Genetics 10. 2 – Mendelian Genetics The Dihybrid cross Mendel also crossed pea plants that were true-breeding for two traits Not just one trait which would be called a monohybrid cross He was curious to see if traits got passed on together in a “package”

Ch. 10 – Sexual Reproduction & Genetics 10. 2 – Mendelian Genetics Examination of this Yy. Rr x Yy. Rr information lead Mendel to his Law of independent Assortment which states: Genes (on separate chromosomes) sort independently during meiosis

10. 2 – Mendelian Genetics Ch. 10 – Sexual Reproduction & Genetics What is the phenotypic ratio of the following cross? 4: 4: 4: 4 or 1: 1: 1: 1 Yyrr x yy. Rr Yy. Rr x Yy. Rr y. R Yr Yr yr yr Yy. Rr yy. Rr Yyrr yyrr yr y. R yr

Ch. 10 – Sexual Reproduction & Genetics 10. 3 – Gene Linkage & Polyploidy Offspring with a phenotype matching one of the parental phenotypes are called parental types Offspring with nonparental phenotypes (new combinations of traits) are called recombinant types, or recombinants A 50% frequency of recombination is observed for any two genes on different chromosomes • A linkage map is a genetic map of a chromosome based on recombination frequencies