Anthro 101: Human Biological Evolution Lecture 3: Genetics & Inheritance Prof. Kenneth Feldmeier feldmekj@lavc.edu feldmekj.weebly.com
What is Genetics??? Genetics is the scientific study of heredity. Heredity is what makes each species unique.
Reminders Quiz 1 week from today Most of content is based upon the reading 3
Who was the man when it came to genetics? http://www.youtube.com/watch? v=nwqgzunjday 4
Mendel s Work Mendel used true-breeding plants which means if they were left to breed with themselves they would produce offspring identical to themselves. Mendel studied 7 different traits in pea plants. A trait is a specific characteristic that varies from one individual to another.
Mendel showed simple genetic principles Segregation Traits determined jointly by pairs of alleles Either allele can end up in a gamete Zygotes get 1 allele from mom, 1 allele from dad Dominance Sometimes, two different alleles at a gene loci (heterozygous) only one is expressed
More on Mendel s Work Hybrids are offspring from parents with different traits. Genes are the chemical factors that determine a trait. The different forms of a gene are called alleles.
Lets get down to the basics Somatic cells & Gametes both contain DNA nucleus mitochondria DNA in nucleus, mtdna in mitochondria
DNA Basics 99.99% of all DNA in the nucleus of a cell DNA long strands of biochemical information (legos or beads) Sections of DNA form functional units = genes Genes are recipes for proteins Proteins serve functions in the body = traits
Genotype / Phenotype Phenotype: observable traits The proteins that are built using the recipe. Genotype: the alleles you carry The recipe in your DNA.
Universal Genetic Code All living organisms have DNA made of the same material that serves similar functions The universality of the genetic code implies a common ancestry for all life on the planet Organisms differ in the amount of DNA BUT the most important differences are in the arrangement of the DNA. Different order of nucleotides à different proteins
What the heck is DNA? http://www.youtube.com/watch?v=8kk2zwjrv0m 12
Where we at? Quiz 1 Thursday/Tuesday 13
Chromosomes = packages of DNA Cells have 2 versions of each chromosome we have 23 homologous pairs, 46 total Homologous Chromosomes
Genes are segments on chromosomes Genes on chromosomes like beads on a string Each gene has a specific location = locus Gene loci There can be different versions of the same kind of gene: these are called alleles Homologous alleles work together to produce phenotype
Homozygous vs. Heterozygous Genotypes Homozygous: the same allele at the same locus on both versions of the chromosome Heterozygous: a different allele at a particular locus on each chromosome
Dominant & recessive alleles 2 different alleles (heterozygous) = Aa Sometimes one of the alleles overrides the effects of other: this is called dominance = A > a Aa A dominant allele overrides the effects of a recessive allele AA or aa
I. Introduction to Mendelian Genetics a. Who is considered to be the father of modern genetics? c. Brie3ly de3ine the following key terms: i. Mendelian Traits= ii. Principle of Segregation = iii. Principle of Independent Assortment = iv. Gene = v. Allele= vi. Phenotype = vii. Genotype= 18
Cell Division: Sharing the recipe DNA replicates before cell division Two types of replication: Mitosis: makes a new somatic (body) cell Meiosis: makes gametes (sex cells, sperm and eggs) used in sexual reproduction
Mitosis: replication of somatic cells When somatic cells divide chromosomes are doubled Doubles are split between two daughter cells Each daughter cell has an identical set of chromosomes to the original cell
Meiosis: production of gametes Gametes (eggs and sperm) have only 1 copy of each chromosome Chromosome pairs duplicate and divide into singles, distributed between 4 gametes When gametes fuse during sexual reproduction, they create a zygote with full set of chromosomes
To make a new organism Parents make gametes Gametes from two parents fuse to form offspring For each chromosome, offspring carry two copies: one from each parent
Punnett Square Method a A Aa A Aa Genotypes 4 Aa a Aa Aa Phenotypes 4 Yellow
Punnett Square Method A A AA a Aa Genotypes 1 AA 2 Aa 1 aa a Aa aa Phenotypes 3 Yellow 1 Green
Practice Problem # 1: In humans, the allele for free hanging ear lobes (E) is dominant over the allele for attached earlobes (e). Two heterozygote individuals are crossed. What are the resulting genotypic and phenotypic ratios for their offspring (Generation I)? Genotypic Ratio: Phenotypic Ratio: 25
Recombination is important for evolution Recombination shuffling of alleles during meiosis = unique gametes Independent assortment of alleles at different gene loci Mixing of alleles during sexual reproduction = unique offspring The fate of a new mutation is unrelated to other traits New traits can spread independently in a population Novel combinations of traits can appear in offspring This provides new phenotypes for natural selection to act upon
Mendel studied discontinuous (discrete) traits Darwin observed continuous variation Before Selectio h Beak Depth
MOST traits vary along a continuum Continuous Traits Height Weight Skin color Discontinuous Traits Finger number Litter size Rolling tongue
Simple Mendelian inheritance is rare (discontinuous traits) Lots of traits are linked and so get inherited as a package deal Linked (same chromosome) Lots of alleles for a gene aren t clearly dominant/recessive Codominance: Sickle-cell anemia Complex dominance: ABO blood type Lots of single genes controls multiple traits Pleiotropy Lots of genes work together to affect the same trait = Polygenic inheritance
Linked traits are inherited together
Codominance: Two alleles, three phenotypes Sickle-cell anemia Normal hemoglobin (A) allele Sickling hemoglobin (S) allele Three genotypes and three phenotypes: AA = normal blood cells SS = sickled blood cells AS = slightly impaired blood cells, greater defense against malaria
Complex Dominance: ABO Blood Type Three alleles: A, B & O Genotype Phenotype Compatibility O recessive to A & B A & B co-dominant AA AO Type A Rec.: A or O Don.: A or AB AB Type AB Universal recipient BB BO Type B Rec.: B or O Don.: B or AB OO Type O Universal donor
Pleiotropy: One gene controls two traits In Darwin s finches, beak traits are correlated Depth & width vary together Deeper & wider Shallow & narrow Correlations arise when one gene affects multiple traits
Polygenic Traits: Many genes, continuous variation Many genes affect each trait Each one has small effect Generates a continuous range of variation in the trait Height So far approx 10 genes Affect about 30% of variation in height
All this variation! Where does it come from? Mutation Meiosis Recombination of alleles into unique gametes increases genetic variation at a faster rate than mutation Sexual Reproduction Recombination of alleles from unique gametes into unique offspring New phenotypes for NS to act upon Complex genetic inheritance Polygenic traits Environment interacts with genotype
Polygenic Traits + Environment: Beak Depth Multiple genes interact to determine the actual beak phenotype Environmental effects blur across genetic differences producing a range of phenotypes
Polygenic Traits shaped by many genes + environment Phenotypes are almost ALWAYS the product of genes & environment interacting Adjusted Mean Intelligence Test Scores Across 5 Categories of Breastfeeding Duration 41 106 IQ Score 40 39 38 104.3 102.5 100.8 37 <=1 2 to 3 4 to 6 7 to 9 > 9 Duration of Breastfeeding WAIS Verbal IQ BPP Test 99
Variation is maintained in the DNA Intermediate types common, but genetic variation is maintained MOST individuals have some + and some alleles for height Recessive alleles hidden by dominant alleles Still passed into gametes & remain in population Much of the variation is hidden from selection If a trait is affected by genes at many loci Many different genotypes may have similar selective fate Some variation is protected Neutral mutations can be hidden Variation is essential for Natural Selection without differences in traits, nothing to select & survival is random
What is the nature of variation? Variation is (usually) continuous Continuous traits are generated via many genes and environmental effects to produce the phenotype + Variation is generated and extended by: + Mutation Meiosis Sexual reproduction Hidden alleles Polygenic inheritance + environment