Download Gregor Mendel

Gregor Mendel •  Discovered many of the principles of modern gene5cs •  Mendel studied the inheritance of traits using pea plants •  Principles of basic inheritance are called Mendelian gene-cs Genes •  Genes are segments of chromosomes that determine the traits of an organism (ex. Eye color, height, ) •  There may be several hundred to several thousand genes on a chromosome (we have a total of 20,000 – 25,000 genes) •  We inherit 50% of our genes from our mothers and 50% from our fathers Human Karyotype
(picture of all 46 chromosomes) Each pair is called a homologous pair Homologous Chromosomes •  Chromosomes that are very similar (size, shape, same type of genes) except that they come from two different individuals (see diagram) From Mother From Father A pair of homologous chromosomes from one individual Meiosis •  Forma5on of gametes (sex cells ‐ sperm and egg) •  Happens in testes (males) and ovaries (females) •  Produces haploid cells (cells with half the normal number of chromosomes) •  Meiosis produces 4 gene5cally different cells from the original cell Why are the cells produced in meiosis different? •  When gametes are made, they randomly receive only one chromosome from each homologous pair •  This results in different combina5ons of chromosomes in each gamete •  The inheritance of one chromosome is not affected by the inheritance of other chromosomes (known as the independent assortment) Gene5c recombina5on and muta5ons also produce gene5c varia5on •  Gene-c recombina-on (crossing over) ‐ homologous chromosomes exchange gene5c informa5on forming new combina5ons of genes (see diagram) •  Muta-ons ‐ a change in the DNA of an organism ‐ muta-ons in gametes are passed on to offspring Crossing over during prophase I of meiosis Meiosis in males and females •  Spermatogenesis ‐ sperm produc5on •  Oogenesis ‐ egg produc5on Oogenesis ‐ egg produc5on Alleles •  Every gene comes in different varia5ons called alleles •  Most genes have two different alleles while some have more than two •  One person can have no more than two different alleles for the same gene (we get one from each parent) Three people with different alleles for a gene involved in eye color Dominant vs. Recessive Alleles •  Alleles interact to produce traits (eye color, shape of skeleton, blood type, etc.) •  Dominant alleles “overpower” recessive alleles (see diagram) Brown eyes Brown eyes Blue eyes Heterozygous & Homozygous •  Homozygous ‐ having the same alleles for a given trait •  Heterozygous ‐ having different alleles for a trait Genotype vs. Phenotype •  Genotype is the gene5c make‐up of an organism (its genes) •  Phenotype refers to the actual physical traits an organism has as a result of its genes •  The genotype determines the phenotype (see picture) The genes of the fly give it its unique characteris5cs Mendel’s Law of Segrega5on •  Alleles for the same trait separate from each other during the forma5on of gametes (see Punne< square diagram) Mendel’s Law of Independent Assortment •  Alleles for different traits are randomly distributed to gametes (unless they are located on the same chromosome)
Pa4erns of Inheritance •  Complete dominance •  Incomplete dominance •  Codominance •  Polygenic Inheritance •  Sex‐linked inheritance Incomplete Dominance •  Neither allele of a pair is dominant over the other •  A blend of both traits results •  Results in 3 dis5nct phenotypes Genotypes and phenotypes of flowers showing incomplete dominance for petal color (R= red and W=white) What type of offspring will two pink flowers produce? R W R RR RW W RW WW 25% red: 50% pink: 25% white Codominance •  Both alleles are dominant causing both traits to be expressed in the phenotype of the organism •  Examples: 1. Roan coat color in some mammals 2. Blood type in humans Example of roan coat showing codominance – Has both red AND white hairs Polygenic Traits •  A trait that is determined by the combined ac5on of many genes •  Show a wide range of phenotypes (lots of different possibili5es (see diagram) •  Many traits are polygenic: Skin color, hair color, eye color, height, risk for heart disease, etc. Varia5on in skin color Sex‐linked traits •  Any trait that is carried on the X or Y chromosome •  If allele is on the X chromosome, females will have two copies (XX) but males only one (XY) •  Men are more likely to get a sex‐linked trait since they have only 1 X chromosome Independent assortment of sex chromosomes