Genetics BISC120 PDF

Figure 17.04b_3 Figure 17.5 Nuclear envelope TRANSCRIPTION RNA PROCESSING NUCLEUS DNA Pre-mRNA mRNA CYTOPLASM TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell Figure 17.6 Figure 17.5 Genetics BISC120 1. Understand how offspring acquire genes from parents by inheriting chromosome...

Figure 17.04b_3 Figure 17.5 Nuclear envelope TRANSCRIPTION RNA PROCESSING NUCLEUS DNA Pre-mRNA mRNA CYTOPLASM TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell Figure 17.6 Figure 17.5 Genetics BISC120 1. Understand how offspring acquire genes from parents by inheriting chromosomes. Learning Objectives 2. Understand how meiosis and fertilization bridge one generation to the next (life cycle). 3. Understand how meiosis reduces the number of chromosome sets from diploid to haploid (overview of stages of meiosis). Heredity and Genetics • The transmission of traits from one generation to the next is called inheritance, or heredity • Sons and daughters are not identical copies of either parent or of their siblings • Along with inherited similarity, there is variation • The study of heredity and inherited variation is called genetics https://www.illumina.com/ Genes and Chromosomes (review?) • Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs) • Most DNA is packaged into chromosomes – Humans have 46 chromosomes in the nuclei of their somatic cells – A gene’s specific position along a chromosome is called its locus Figure 13.3 Figure 13.3 Chromosomes and Inheritance • Although genes are very important, they make up only a small percentage of all of the DNA in the genome. • Each gene has a specific location on one of our 23 chromosomes and is inherited, or passed down, from generation to generation as a unit. • We have two copies of each chromosome and, thus, two copies of each gene. Figure 13.3 Broad Picture View of Meiosis and Fertilization Figure 13.1 1. Understand how offspring acquire genes from parents by inheriting chromosomes. Learning Objectives 2. Understand how meiosis and fertilization bridge one generation to the next (life cycle). 3. Understand how meiosis reduces the number of chromosome sets from diploid to haploid (overview of stages of meiosis). Life Cycle • A life cycle is the generation-togeneration sequence of stages in the reproductive history of an organism • The behavior of chromosomes is related to the human lifecycle and other types of sexual life cycles Figure 13.5 Gamete (n) • A gamete (sperm or egg) contains a single set of chromosomes and is thus a haploid cell (n) – In humans n=23 • Each set of 23 consists of 22 autosomes and a single sex chromosome • In an unfertilized egg (ovum), the sex chromosome is X • In a sperm cell, the sex chromosome may be either X or Y Figure 13.5 Gamete (n) • The ovaries and testes produce haploid (n) gametes by meiosis – Contains a single set of chromosomes, in humans n=23 • Each set of 23 consists of 22 autosomes and a single sex chromosome • In an unfertilized egg (ovum), the sex chromosome is X • In a sperm cell, the sex chromosome may be either X or Y Figure 13.5 Zygote (2n) • Fertilization is the union of gametes (the sperm and the egg) • The fertilized egg is called a zygote (2n = 46) and has one set of chromosomes from each parent • The zygote produces somatic cells by mitosis and develops into an adult Figure 13.5 1. Understand how offspring acquire genes from parents by inheriting chromosomes. Learning Objectives 2. Understand how meiosis and fertilization bridge one generation to the next (life cycle). 3. Understand how meiosis reduces the number of chromosome sets from diploid to haploid (overview of stages of meiosis). Meiosis • Meiosis takes place in two consecutive cell divisions, called meiosis I and meiosis II • The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis • Each daughter cell has only half as many chromosomes as the parent cell Figure 13.7 Meiosis (IPMAT x2) • Meiosis I separates homologous chromosomes – What does this mean? • Meiosis II separates sister chromatids – What does this mean? Figure 13.7 Meiosis I - Prophase I • Centrosome movement, spindle formation, and nuclear envelope breakdown • The mitotic spindle is a structure made of microtubules that controls chromosome movement • Assembly of spindle microtubules begins in the centrosome, a type of microtubuleorganizing center • Chromosomes condense progressively throughout prophase I Figure 13.8 Meiosis I - Prophase I • In early prophase I, each chromosome pairs with its homolog and crossing over occurs • Crossing over is the exchange of genes between two chromosomes, resulting in nonidentical chromatids that comprise the genetic material of gametes. • X-shaped regions called chiasmata are sites of crossovers Figure 13. Meiosis I - Metaphase I • In metaphase I, pairs of homologs line up at the metaphase plate (an imaginary plane midway between the spindle’s two poles), with one chromosome facing each pole • Microtubules from one pole are attached to the kinetochore of one chromosome of each pair • Microtubules from the other pole are attached to the kinetochore of the other chromosome Figure 13.8 Meiosis I - Anaphase I • Breakdown of proteins allow homologous pairs of chromosomes to separate • Homologs move toward opposite poles guided by spindle apparatus. • Sister chromatid cohesions persists at the centromere – Enables each the two chromatids of each chromosome to move as a unit towards the same pole. Figure 13.8 “Pulling” Chromosomes – At which end to kinetochore microtubules shorten? Figure 12.9 Meiosis I – Telophase I and Cytokinesis • In the beginning of telophase I, each half of the cell has a haploid set of duplicated chromosomes • Each chromosome still consists of two sister chromatids • Cytokinesis usually occurs simultaneously, forming two haploid daughter cells Figure 13.8 Meiosis I Overview Figure 13.8