Gene Linkage and Polyploidy Chapter 10 Section 3 Gene Linkage and Polyploidy

Genetic Recombination The new combination of genes after crossing over (prophase I) and independent assortment (metaphase I) occur in meiosis Independent assortment calculated by 2n n= # of pairs of chromosomes Humans n= 23, so 2n= 46 for male and female 2n= 246= ~ 70 trillion different recombinations

Gene Linkage One exception of Mendel’s Law of Independent Assortment Chromosomes have multiple genes that code for proteins, said to be linked to one another on the same chromosome and thus usually travel together during meiosis Drosophila melanogaster- fruit fly study confirmed this Chromosome maps show the sequence of genes on chromosomes using data

Polyploidy Occurrence of one or more extra sets of all chromosomes in an organism (most are diploid organisms) Triploid= 3n (3 complete sets of chromosomes) Earthworms, goldfish, flowering plants Others Bread Wheat (6n) Oats (6n) Sugar Cane (8n)

Basic Patterns of Human Inheritance

Recessive Genetic Disorders Dominant Genetic Disorders MUST BE HOMOZYGOUS RECESSIVE Can be a heterozygous carrier and not have the disorder Cystic Fibrosis Albinism Tay-Sachs Disease Glactosemia Dominant Genetic Disorders CAUSED BY DOMINANT ALLELE Must be homozygous dominant or heterozygous to have disorder Huntington’s Disease Acondroplasia

Pedigrees A diagram that traces the inheritance of a particular trait through several generations. Take note: Male= Square, Female= circle Colored in shape= expresses trait, or half way colored in is a carrier of trait

Dominant Disorder Pedigree Recessive Disorder Pedigree

Genetics – Types of Inheritance

Test Cross Tt tt Tt Tt Tt tt Tt Tt t t t This is done to determine if an organism with a dominant trait is homozygous or heterozygous Cross the unknown with a __________________. If any of the offspring are recessive, the unknown must have been __________________. T T? T t? t t t Tt tt Tt Tt Tt tt Tt Tt

Incomplete Dominance Produces a phenotype that is an intermediate (a blend) of the dominant trait and the recessive trait in a heterozygote. Example: In four o’clock flowers, the alleles for red flowers (CR) and white flowers (CW) both influence the phenotype CRCR = red CWCW = white CRCW = pink

Codominance Occurs when both alleles for a gene are expressed Example: Roan horses are a combination of white and red horses Human example: AB blood type - Type A proteins & type B proteins both show up on blood cells

Sickle-cell disease: common of African descent Chronic pain Affects RBC and ability to transport oxygen b/c they block circulation in small blood vessel. Changes in the blood cell shape from round to a “c” shape (sickle) Heterozygous for trait have BOTH normal and sickle cell shapes, can live a normal life

Multiple Alleles Some traits are determined by more than two alleles. These are multiple allele traits. Example: Human blood type Alleles: IA, IB, i Rh factors (blood protein) + is dominant - is recessive Blood Type Possible Genotypes A IAIA or IAi B IBIB or IBi AB IAIB (codominant) O ii O is the absence of A and B markers and is recessive to A and B ABO blood group is an example of multiple alleles and codominance

Rabbits 4 allele codes for coat color: C, cch, ch, and c C > cch > ch > c Can have many different combinations: more alleles equals more possible phenotypes and genotypes Produces 10 possible genotypes and 4 possible phenotypes C= dominance homozygous recessive= cc

Epistasis Variety resulting from one allele hiding the effects of another allele Labrador retrievers: yellow-black E= dark e= light B= how dark b= how light EEbb or Eebb= chocolate lab eebb or eeBb or eeBB= yellow lab WHY? Because the “e” masks the effects of the dominant B allele

Chromosomes in Humans Each cell in our body has 46 chromosomes, besides sex cells which have 23 Humans have 23 pairs of chromosomes 22 pairs of autosomes 1 pair of sex chromosomes Contain genes that determine gender XX = female, XY = male Sex-Determination 50% chance for male 50% chance for female Who determines gender?

Dosage Compensation Females= 22 pairs of autosomes and 1 pair of X chromosomes Males= 22 pairs of autosomes and one X and one Y chromosome Do females have more dosages? no, randomly one of the X chromosomes stop working in each cell of female’s body (dosage compensation) Calico Cats- orange fur spots Barr Bodies- dark stain on cells DIFFERENT SIZES X chromosomes help development of M and F Y chromosome help development of just male

Sex Linked Traits Genes located on the X chromosome are X-linked genes. Genes located on the Y chromosome are Y-linked genes. Sex-linked traits are coded for by an allele on a sex chromosome. More on X chromosome because it’s larger Because males only have one X chromosome, if they carry a recessive allele on the X chromosome, they exhibit the trait. Examples: color-blindness, hemophilia

Red-green color blindness Recessive X-linked trait 8% of males in US dad= not a carrier b/c he does not have the “b” allele mom=carrier b/c has recessive allele (b) Only possible offspring that can have red-green colorblindness is MALE

Hemophilia- delayed blood clotting

Polygenic Traits Many phenotypic traits come from the interaction of multiple pairs of genes skin color, height, eye color, finger prints Bell curve shows that the more the dominant allele occurs, the less the extreme phenotypes will occur

Environmental Influences Can effect the appearance of organisms: Sunlight Water Temperature

Twin Studies Identical twins= genetically the same If a trait is inherited, the both will have it Concordance Rate If a trait is cause by environmental factors, they may not both have it

Chromosomes and Human Heredity Chapter 11 Section 3

Karyotype Studies The study of whole chromosomes by using images of chromosomes stained during metaphase. Stains= identify marks on homologous chromosomes Placed in decreasing size to produce a micrograph (karyotype) 22 autosomes matched together 1 pair of nonmatching sex chromosomes

Telomeres Protective protein end capping chromosomes Possibly linked to aging and cancer

Nondisjunction Down’s Syndrome -Trisomy 21 Cell division during which sister chromatids fail to separate properly

During meiosis cells do not get the right number of chromosomes and when they divided the resulting cells do not get the correct number either Can be extra sets or lack of sets of chromosomes 3 sets= trisomy 1 set= monosomy

Trisomy- Down Syndrome Extra chromosome 21 (“Trisomy 21”) 1/800 Americans 60% chance if mom is 45+ Characteristics distinct facial features short stature heart defects mental disabilities

Nondisjunction Sex Chromosomes Occurs in both autosomes and sex chromosomes

Fetal Testing

Mutations Germ-cell mutations occur in gametes Affect offspring only Somatic-cell mutations occur in body cells Affect the organism only, not inherited Lethal mutations cause death, often before birth Some mutations are beneficial and give an organism an evolutionary advantage.

Chromosome Mutations Deletion – loss of a piece due to breakage Inversion – a piece breaks off, flips, and reattaches Translocation – a piece breaks off and reattaches to a nonhomologous chromosome

Chromosome Mutations Nondisjunction – a chromosome fails to separate from its homologue during meiosis One gamete gets an extra copy, the other gets no copies Example: Down’s syndrome is caused by 3 copies of the 21st chromosome

Gene Mutations Point Mutation – A mutation in a single nucleotide Substitution – one nucleotide changed for another C = A instead of C = G Frameshift Mutation – Results when all of the codons are changed due to an addition or deletion of a nucleotide Addition – one nucleotide added Deletion – one nucleotide removed