Chapter 7 Genes 02 20 2014 Heredity passing characteristics from parents to offspring by genes Mistaken belief Tiny humans in every sperm cell 1600 1800 Gergor Mendel 1860 s worked on the science of inheritance o Experimented without knowledge of modern genetics Mendel died in 1866 work not discovered until early 1900 s Single gene traits traits determined by one gene Attached unattached ear lobes Widow s peak Dimples Great experiment 1 Ideal study organism pea plant 2 Focused on easily categorized traits 3 Established distinct populations o True breeding always produces offspring with the same type of trait as the parents Genotype alleles an organism has for a particular trait Allele alternative version of a gene Phenotype Physical expression of a genotype Homozygous genotype with same alleles Heterozygous genotype with different alleles Dominant allele masks recessive allele 3 Important Ideas 1 Each parent puts into every egg and sperm a single set of instructions for building a trait 2 Offspring receive 2 copies of instructions for each trait one from mom and one from dad 3 The trait observed in an individual depends on the 2 copies of the gene it inherits from its parents Punnett Square tool to determine possible outcome of crosses between 2 individuals Figure out ratios of phenotypes and genotypes for offspring Albinism condition in which your body can not produce melain skin color Recessive trait must have two copies of recessive allele Phenotype albinism Genotype aa A dominant a recessive Dominant Disorders Rare Selected against Achondroplasia Huntington s Disease o Usually don t see symptoms until later in life after already reproducing CHAPTER 7 Continued Charles II of Spain Last Habsburg ruler The Bewitched Died in 1700 Not all patterns of inheritance deal with 1 gene and 2 alleles Incomplete Dominance o The phenotype of a heterozygote is intermediate between the phenotypes of the 2 homozygotes Co dominance heterozygote displays characteristics of both homozygotes in other words all alleles are expressed Polygenetic trait is influenced by many different genes o EX Height skin color eye color autism Pleiotropic 1 gene affects many traits o Sickle cell anemia Red blood cell are sickle shaped Unable to transport oxygen effectively o Hemoglobin molecule and susceptibility to malaria Multiple Allelism a single gene has more than 2 alleles o An individual will ONLY have 2 alleles but more than 2 alleles present in the population o BLOOD TYPE 3 Alleles possible A dominant to O and co dominant to B B dominant to O and co dominant to A O recessive to A and B 6 Genotypes possible A A B B O O A O B O A B 4 phenotypes Type A Type B Type AB Type O Mother A B AB O A A or O A or B or O AB or A or B A or O B AB A B or O B or O AB or A or B B or O AB AB or A or O AB or A or B AB or A or B A or B O A or O B or O A or B O Father Red Green colorblindness On X chromosome gene involved in producing proteins in eye that allow you to see red and green If an individual has 1 functioning allele she he will see green and red Reproduction Humans 46 Chromosomes 02 20 2014 Each chromosome has a homolog Homologous chromosomes contain the same type of genetic information Humans are diploids 2n organisms we have two copies of each chromosomes One from father and one from mother Sexual Reproduction Eggs o Female gamete o Haploid Sperm o Male gamete o Haploid Gamete Haploid n 23 Gamete haploid n 23 Zygote Diploid n 46 Haploid n o The haploid number n is the number of chromosomes in a gamete sex cell egg sperm o The n number is the number unique chromosomes an organism has Diploid 2n o Twice the haploid number two copies of a unique chromosome Zygote diploid cell formed by the union of sperm and egg the product of fertilization that develops into an organism Mitosis cell duplicates its genome and divides into two genetically alike daughter cells Meiosis cells divide and reduce the genome by half Male Reproductive Structure Semen Production o Seminal vesicle o Prostate gland o Bulbourethral gland Sperm production o Vas deferens o Epididymis o Seminiferous Tubules At ejaculation approximately 300 million sperm cells are expelled as part of fluid called semen o Average ejaculation is 3 4 mL 2 5 of semen volume is sperm Structure of Sperm o Head contains the nucleus with DNA o Body contains mitochondria to generate energy o Tail flagellum propels the sperm Female Reproductive Structure Uterus thick walled muscular organ where an embryo develops during pregnancy Endometrium lining of the uterus where the fertilized egg is implanted and nourished by a rich supply of blood vessels Cervix opening to uterus Vagina function receive the penis during sexual intercourse serves as birth canal and exit for menstrual flow Ovary produces the egg Fallopian tube oviduct connects the ovaries to the uterus and is the site of fertilization Fimbriae small fingerlike projections at the end of the fallopian tubes connect to the ovary Females are born with a set amount of follicles immature eggs Since oocytes are present at birth they age as the woman ages Only a small number of follicles about 400 ever mature because females produce only one egg per month during her reproductive years Reproduction Cont 02 20 2014 Hormones regulate both the ovarian and menstrual cycles Day 0 14 Pituitary gland releases FSH stimulating follicle growth Follicles produce estrogen high levels of estrogen trigger a burst of luteinizing hormone LH causing the follicle to expel the egg ovulation Day 14 28 Empty follicle becomes corpus luteum which produces progesterone Progesterone causes the body to prepare for gestation or carrying of an embryo Thus the endometrium or lining of the uterus becomes increasingly thick and rich with blood vessels that can nourish a developing embryo Two Possible Fates of an egg 1 If the egg is not fertilized o The corpus luteum degenerates o Progesterone level decrease o The endometrium sloughs off and is shed along with the egg as menstruation begins 2 If the egg is fertilized o The zygote secretes hCG preserving the corpus luteum o Progesterone levels remain high o Endometrium thickens in preparation for implantation Fertilization occurs in the fallopian tubes 1 PENETRATION A sperm pushes its way through the granulosa cells and enzymes within its acrosome digest the zona pellucida 2 ACTIVATION The plasma membrane of the sperm and egg fuse making it impossible for other sperm to fuse with the egg 3 NUCLEI FUSION The