Chapter 13: Genetic Inheritance and Variation in Sexual Reproduction PDF

Independent assortment of chromosomes during meiosis I contributes to genetic varia- tion. Crossing over during meiosis I creates new combinations of alleles. Sources of Genetic...

Independent assortment of chromosomes during meiosis I contributes to genetic varia- tion. Crossing over during meiosis I creates new combinations of alleles. Sources of Genetic Variation Each gene in an organism's DNA is located at a specific locus on a chromosome. Random fertilization of egg cells by sperm further increases genetic diversity. In asexual reproduction, a single parent produces genetically identical offspring Genetic variation is essential for evolution by mitosis. natural selection. Mechanisms of Genetic Inheritance through Genetic Variation Produced in Sexual reproduction involves the combina- Mutations are the original source of genetic Sexual Life Cycles Contributes to variation. of genes from two parents, resulting in tion Role of Genetic Variation in Evolution Evolution genetically diverse offspring. Offspring Acquire Genes from Recombination of variant genes generates Parents by Inheriting Chromo- Human offspring resemble their parents due additional diversity, allowing populations adapt to to changing environments. somes the to inheritance of genes. Independent assortment, crossing over, They are not identical to their parents because random fertilization generate significant they inherit a unique combination of genes and from both parents. genetic variation. Human Offspring Resemblance to Paren… These processes ensure that each offspring Genetic recombination during sexual has a unique genetic makeup. reproduction contributes to this varia- Processes Unique to Sexual Reproduction tion. Genetic diversity is crucial for the survival and Mutations and environmental factors also adaptation of species in diverse environmen- a role in differences. play ts. Meiosis consists of two cell divisions: meiosis I Normal human somatic cells are diploid, and meiosis II. containing 46 chromosomes in two sets of 23. Meiosis I reduces the chromosome sets from diploid to haploid. Overview of Meiosis Chapter 13: Genetic Human Somatic and Gamete Cells One set of chromosomes is inherited from each parent. Inheritance and Variation in Sexual Meiosis II separates sister chromatids, Human diploid cells include 22 pairs of resulting in four haploid daughter cel- autosomes and one pair of sex chromosomes, determining sex (XX for females, XY for males). ls. Homologous chromosomes pair up and Reproduction undergo synapsis and crossing over dur- Ovaries and testes produce haploid gametes prophase ing I. through meiosis, each containing 23 chromosomes. Fertilization and Meiosis Alternate in Chiasmata hold homologs together un- Sexual Life Cycles anaphase til I. Meiosis Reduces the Number of Chromosome Sets During fertilization, an egg and sperm unite Production of Haploid Gametes form to a diploid zygote with 46 chromosomes. Unique Events in Meiosis I from Diploid to Haploid Cohesins are cleaved along the arms at anaphase I, allowing homologs to sepa- The zygote develops into a multicellular rate. organism through mitosis. At anaphase II, cohesins at the centromeres are cleaved, releasing sister chromatids. Sexual life cycles vary in the timing of meiosis relative to fertilization. Synapsis and crossing over occur during prophase I, not prophase II. The point at which a multicellular organism is Differences in Sexual Life Cycles produced by mitosis differs among species. These processes involve the exchange of genetic material between homologous These variations influence the genetic diver- chromosomes. and sity evolutionary adaptations of organisms. Synapsis and Crossing Over Crossing over contributes to genetic varia- by tioncreating new combinations of alleles.