Human Evolution Dr Chiu Lecture Feb 6 2012 Topic Brief overview of mitosis and meiosis Reading Chapter 3 pp 49 53 60 64 pdf article about inherited traits see handout on the course website Web link http www nature com scitable topicpage gregor mendel and the principles of inheritance 593 Topic Mendelian Genetics Reading Chapter 4 pp 80 85 Chapter 5 pp 105 112 Web link http www nature com scitable topicpage evolutionary adaptation in the human lineage 12397 Meiosis Mitosis Mendelian Inheritance 1 a Genes and alleles Remember our entire DNA genome is 3 2 billion bases long and each cell in our body contains one genome in the nucleus packaged tightly into chromosomes Humans are diploid meaning we have genetic information from both parents paternal and maternal Diploid is referred to as 2n see below We have 23 pairs of homologous chromosomes 22 pairs of autosomes chr 1 22 and one pair of sex chromosomes XX female XY male A karyotype Figure 3 10 in your text shows the 46 total chromosomes in an individual You should be able to read a karyotype and tell me if it is of a male or a female There are two types of cells in our body Somatic and gamete sex i e egg or sperm Prior to cell division DNA replicates b d c e Human Evolution Dr Chiu Lecture Feb 6 2012 1 2 Mitosis produces two daughter cells that are each identical to the parent cell Mitosis occurs in somatic cells e g skin cells a b c Parent cell is 2n each daughter cell is 2n Parent cell is diploid each daughter cell is diploid Parent cell has 23 pairs of chromosomes each daugher cell has 23 pairs of chromosomes Meiosis produces two daughter cells that each have half the chromosomes of the parent cell The daughter cells are NOT identical to the parent or to each other due to recombination crossing over a b c Parent cell is 2n each daughter cell is n Parent cell is diploid each daughter cell is haploid Parent cell has 23 pairs of chromosomes each daughter has 23 chromosomes Mendel s Laws are based on meiosis d Mendelian Inheritance One of the most important take home messages is to be able to distinguish genotype the pair of alleles see below from phenotype the physical appearance A second important take home message is the difference between dominant and recessive A third take home message is the diference between homozygous two identical alleles and heterozygous two different alleles Mendelian Inheritance only applies to traits that are caused by a single gene Human diseases caused by mutations in a single gene include cystic fibrosis sickle cell anemia and Huntington s Disease Traits that are caused by a single gene include freckles a cleft chin and dimples the presence of these is dominant However the majority of human disease and traits are due to more than one gene i e polygenic and can also be influenced by the environmental e g nutrition hormones Therefore the inheritance of most human diseases and traits cannot be tracked using Mendelian rules In class we ll go over Mendel s two laws Law of Segregation and Law of Independent Assortment In class we ll go over how to use a Punnett square for calculating probabilities of inheriting single gene traits 3 a b c d e f
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