Chapter 12 Inheritance Patterns & Human Genetics
Bellwork: Complete with your partner on the white boardThe synthesis of polypeptides from the genetic information encoded in mRNA isA. TranscriptionB.TranslationC. TransposonD. DNA MethylationAt the end of DNA replication, each of the daughter molecules has one old strand and one new strand. This explains why DNA replication is described as _____________.
Chromosomes & InheritanceThomas Hunt Morgan- early 1900s-experiments with fruit flies-observed 4 pairs of chromosomes -noticed that 3 pairs were the same in males & females but that 1 pair was different. - called these sex chromosomes.
Autosomes & Sex Chromosomes
Sex chromosomes- contain genes that determine the gender of an individual.Autosomes- the remaining pairs of chromosomes that do not directly determine sex. In mammals - 2 X chromosomes= FEMALE (XX) - 1 X + 1 Y is a MALE (XY)
In mammals, males determine the sex of the offspring-each sperm has an equal chance of having an X or a Y-however- the only option for eggs is to receive an X chromosome.1:1 male to female ratio
Karyotype with an extra chromosome
Linked & Sex-Linked Genes
A. Linked genesGenes which are close together on same chromosome.Inherited together Linked genes do not exhibit Mendels law of independent assortment
Chromosome MappingThe farther apart two genes are located on a chromosome, the more likely a cross-over will occur.Researchers use recombinant percentages to construct chromosome maps showing relative gene positions.
Sex-Linked traitsare traits that are coded for by alleles on a sex chromosome.Genes found on the X chromosome are X-linked genesSince the X chromosome is larger- there are more X-linked than Y- linked traits.NOTE: Since males have only 1 X- a male who carries the recessive allele will show the X-linked trait.
Sex Linked Traits
MutationsMutation -a change in the nucleotide-base sequence of a gene or DNA - Germ cell- occurs in gametes - can affect offspring- Somatic Cell-occur in organisms body cells - may affect the organism (ex-cancer) - does NOT affect offspring
Mutations- Lethal Mutations-cause death, often before birth- Beneficial Mutations- result in phenotypes that are beneficial .
Types of Chromosome Mutations1. Deletion- loss of a piece of chromosome due to breakage.2. Inversion a chromosome piece breaks off, flips around backwards & reattaches3. Translocation a piece of chromosome breaks off & attaches to a non-homologous chromosomeNon-Disjunction a chromosomes fails to separate from its homologue during meiosis.
On your white board, with your partner, explain why your assigned answer is either correct or incorrect.Your assigned answer is the letter on your whiteboard!
Types of Chromosome Mutations
Types of Chromosome Mutations
An example of a human disorder with a deletion error:Cri du chat syndrome- missing part of chromosome 5- cry of infants is similar to that of a meowing kitten, due to problems with the larynx and nervous system. About 1/3 of children lose the cry by age 2.
Types of nondisjunction:Trisomy- an extra chromosome leads to an individual with an extra chromosome in every cell of his/her body.Monosomy- is a deficiency in number of chromosomes and is defined as only one copy of a chromosome that is normally present in two copies. When fertilized, the outcome is 45 chromosomes in total. Monosomies are less likely to survive when compared to trisomies.
What causes non-disjunction?cause of non-disjunction is unknown. non-disjunction occurs more frequently in the eggs of women as they get older.
Non- Disjunction Disorders with an extra chromosome(these folks have 47 instead of the normal 46 chromosomes in people):Down syndrome- extra 21Edwards Syndrome- extra 18Patau syndrome extra 13
Examples Non disjunction:Extra #21= Downs Syndrome
Extra #18= (most dont live beyond 1st 7 months) This girl is now 6.)
Sex-chromosome abnormalities may also be caused by non-disjunction. Klinefelters Syndrome- XXY ( extra X)Turners Syndrome only 1 X- missing a second X (XO)Super males XYYAny combination (up to XXXXY) produces maleness. Males with more than one X are usually underdeveloped and sterile. XXX and XO women are usually sterile
Gene Mutationschanges in one or more of the nucleotides in a gene.
Types of Gene Mutation1. Point Mutation- the substitution, addition or removal of a single nucleotide, occurs within a single gene or segment of DNA2. Substitiution- one nucleotide replaces another3. Frameshift Mutation- if some nucleotides are deleted- whole segment moves4. Insertion Mutation one or more nucleotides added- also causes a frameshift
Which type of gene mutation do you think would cause the most serious errors?
Example: substitution errorJust 1 Amino Acid is a Substitution ERROR in Sickle Cell Hemoglobin
Causes Hb to be sickle shaped instead of round- cant fit into red blood cells & changes their shape too.
On your white board, with your partner, explain why your assigned answer is either correct or incorrect.
ObjectiveCheck3210.4.3 Apply data to complete and interpret a genetic pedigree.SPI 3210.4.5 Apply pedigree data to interpret various modes of genetic inheritance.
Inheritance of Traits
Pedigree - a diagram that shows how a trait is inherited over several generations
Creating the foldable
Reading a pedigreemales are represented by squares females by circles.
An individual who exhibits the trait , (for example, someone who suffers from Marfan syndrome), is represented by a filled symbol.
A horizontal line between two symbols is a mating
Reading a PedigreeThe offspring:are connected to each other by a horizontal line above the symbols and to the parents by vertical lines.
Example pedigree:Is the mom or dad in generation I affected by a trait?How many offspring are shown in generation II?How many daughters & sons in generation II?How many have the trait?How many offspring does daughter #1 have? How many have the trait?
Dominant traits are passed on to a son or daughter EVEN if only one parent has it. Every affected individual has at least one affected parent Affected individuals who mate with unaffected individuals have a 50% chance of transmitting trait to each childTwo affected parents may have unaffected children.
Where did the trait seen in generation III come from?Traits can be passed on to children if both parents, even if they may seem "normal, are carriers of the recessive trait.Recessive Pedigree
Recessive pedigree:If individuals 2 + 3 in generation 3 have more children- will they be affected?Can Individual #8 in gen. 3 have any unaffected children?Can individual #9 in gen 3 have affected children?
Example pedigree of cystic fibrosis www.cfscreening.com.au/.../CF/CFInherited.shtml
Objective3210.4.4 Compare different modes of inheritance: sex linkage, co-dominance, incomplete dominance, multiple alleles and polygenic traits3210.1.6 Describe the connection between mutations and human genetic disorders3210.4.7 Assess the scientific and ethical ramifications of emerging genetic technologies
Polygenic Inheritance- traits influenced by several genes (most human characteristics) example- skin color is additive effect of 6 genes
Complex Characterstraits influenced by both genes & environment Example- height
3. Multiple Alleles-genes with 3 or more alleles. Example- human blood type. IA, IB, i3 alleles- both IA & IB are dominate over i, Codes for sugars that are on blood cell surface. four different blood types- A, B, AB, O
What are the 2 genotypes for type B?Which blood type can donate to all the others? (universal donor?)Which blood type makes antibodies (will clot against) both A & B blood types?
Incomplete Dominancethere is an intermediate phenotypeHuman example- wavy hair is the intermediate between straight & curly hair
(remember chapter 9 plant example: - pink 4 oclock flowers,In between red & white flowers)
X-linked TraitsTraits that are on the X chromosome. Since males only have one X chromosome- they are affected more than femalesFemales have 2 chances to get a good copy of the gene but males only get 1 chance.
Examples of human X-linked traits
Hemophilia- blood clotting disorder- boys may bleed to death Duchene muscular dystrophy -affects cardiac and skeletal muscle, as well as some mental functions. Fragile-X syndrome- part of X chromosome has errors- most common cause of mental retardation in malesRed-green color blindness- males cannot see these 2 colors.
Sex- Influenced Traitsmales & females show different phenotypes with same genotype- example- male pattern baldness
7. Single Allele Traitstrait controlled by 1 allele- Dominant or RecessiveDominant Examples: Achondroplastic dwarfism- dwarf size Polydactly is the presence of a sixth digit.Huntington's disease (also called Woody Guthrie's disease)-progressive destruction of brain cells after age 30Marfans Syndrome- progressive connective tissue disord