INHERITANCE PATTERNS AND HUMAN GENETICS
Quick reviewGenetics is the field of biology devoted to understanding how characteristics are transmitted form parents to offspring.
The DOMINANT factor/gene masks the effect of the other factor in the F1 generation. Use CAPS ex. T for tallThe RECESSIVE factor/genes effect can only be seen in the P generation or F2 generation when the DOMINANT gene is absent. Use lower case ex. t for short
Generations:P Tall x ShortF1 Tall (tall is dominant)F2 3 Tall : 1 short
MENDELS 2 LAWS:#1 LAW OF SEGREGATION:A pair of factors is segregated, or separated, during the formation of gametes.
Factors for different characteristics are distributed to gametes independently.
#2 LAW OF INDEPENDENT ASSORTMENT:
GENOTYPE is the genetic makeup of the organism.TT = homozygous dominantTt = heterozygoustt = homozygous recessivePHENOTYPE is the physical appearance of that organism.Ex. Tall or shortMENDELIAN INHERITANCE- DOMINANCE. 2 phenotypes only.
If someone has the dominant phenotype but you arent sure of Their genotype use a pedigree (humans) or do a test cross.
Other Patterns of Inheritance:Incomplete Dominance- blending seen in heterozygote (ex. pink flowers, brown hair)Codominance- both dominant and recessive phenotypes seen in heterozygote. (ex. type AB blood, roan horse fur color)Polygenic- more than 1 gene determines the phenotype. (Ex. Eye color, Hair color aabbcc)Multiple alleles- more than just 2 alleles (Ex. Blood type = A allele, B allele, O allele is recessive.)
EX. Polygenic Inheritance- when the trait is controlled by multiple genes so many phenotypes are possible.
AaBbCc x AaBbCc
Huge variety in possible Phenotypes of the offspring
- skin, hair, eye color- foot size- nose length- height
Multiple alleles- trait controlled by three or more alleles.
-Ex. ABO blood groups: - TYPE A - TYPE B - TYPE AB Shows Codominance! - TYPE O
The process of using phenotypes to deduce genotypesWhen someone has the DOMINANT phenotype you are uncertain of their genotype.
TT or TtWhen someone has the recessive phenotype you can be sure of their genotype.
DIRECTIONS:For each of the following single gene/ Mendelian traits, write your phenotype on the line.Write as much of your genotype as you can be certain. - both alleles if RECESSIVE (rr)- one allele if DOMINANT (R __)Repeat the process by studying two blood relatives (parents work the best)Use a pedigree.
1. HAIR TYPEvery curly or straightTT, Tt tt
2. Hair ColorDark or LightDD, Dd dd
3. Hair LineContinuous or Widows PeakWW, Ww ww
4. Iris ColorPigmented or BlueEE, Ee ee
5. Lens of EyeAstigmatism or NormalAA, Aa aa
6. Nose ShapeRoman (convex) or ConcaveNN, Nnnn
7. Ear LobeFree/Long or AttachedLL, Llll
8. P.T.C. TasterTasteror NontasterRR, Rrrr
9. Tongue CurlingCan curlor Can not curlCC, Cc cc
10. Point of chinDimpled or NO dimpleII, Iiii
11. Number of FingersPolydactylism or Normal #PP, Pp pp
12. Little FingerBent or StraightFF, Ff ff
13. Hypermobility of ThumbLoose Jointed or Not soHH, Hhhh
14. Thumb ExtensionHitchhikers Thumb or Not HH, Hh hh
15. Middigital HairPresent or AbsentMM, Mm mm
16. Palmar MuscleNormal (2) or Long (3)UU, Uu uu
17. AllergiesTendency Or No tendencyAA, Aa aa
18. VeinsVaricoseorNormalVV, Vvvv
19. White Skin SpottingFreckles or No frecklesSS, Ssss
20. White Forelock
LIST OF STRANGE MENDELIAN TRAITSEar wigglingMisshapen toes or teethInability to smell musk or skunkLack or teeth, eyebrows, nasal bones or thumbnailsWhorl in the eyebrowTone DeafnessHairs that are triangular in cross-section or that have multiple hues (colors)Hairy knuckles, palms, soles, or elbowsEgg-shaped pupilsMagenta urine after eating beetsSneezing fits in bright sunlight.
DNA in chromosomes contain information to make proteins.
Geneticists use their knowledge of DNA and the way chromosomes behave to study how traits are inherited and expressed.
The parents genotype can be agene pair of either:- TT homozygous dominant- tt homozygous recessive- Tt heterozygous
The parent can make gametes (sperm or eggs), through the process of MEIOSIS, that have either one or the other of the gene pair in it.
SEX DETERMINATIONMORGANs Fruit fly (Drosophila)breeding experiments ofthe 1900s revealed theidentity of sex chromosomes.
In males they were differentXY; in females they were thesame XX.
The other chromosomes (22 in humans) are AUTOSOMES.
The male determines the sex of the offspring
SEX LINKAGE traits caused by genes found on a sex chromosomeX-LINKED GENES:Genes located on the X chromosome.Women can be carriers.Ex. gene for ALD (Lorenzos Oil)
Y-LINKED GENES:Genes located on the Y chromosome.Only males show these traits.Ex. SRY- triggers male development of testis.
Males exhibit X-linked traits more often than women because they only have ONE X chromosome.Females have two XBXb or sex linked genes.Females can be carriers of the bad gene yet not show the disease..Males only have one X or sex linked gene since they are XbY. Males have a higher chance of having the condition than if it were on an autosome. THERE IS NO HETEROZYGOUS for men.
Eye color in DrosophilaRed-green colorblindnessMale Pattern BaldnessHemophiliaDuchenne Muscular DystrophyALD (adreno leuko dystrophy)
What do you see in the circle?
Do your bruises look like this?
If a carrier (woman) for hemophilia marries a normal man, what are the chances of having kids who are hemophiliacs? Who are not?What if the man is a hemophiliac???????
LINKAGE GROUPSGenes located on the same chromosome are said to be linked.
Linked genes tend to be inherited together.
Examples: Hair color and intelligence are linked in humans. fur color and deafness in cats are linked.
Im kidding about intelligence and hair color being linked.But if they were linked
What would the phenotype(s) be of children of a dumb,blonde & smart,brunette
smart,brunetteIf that smart,brunette had kids w/ a dumb,blonde
What kinds of kids could they have? What is the probability of each?
Parental Phenotypes:Smart, brunetteDumb, blondeRecombinant Phenotypes:Smart, blondeDumb, brunette
Linked genes result in traits that tend to be inherited together
If the intelligence and hair color genes were linked, wed only see smart-brunettes and dumb-blondes. (HA HA)
So, since there are smart blondes- are these genes on separate chromosomes or on the same chromosome yet separated by crossing over????? If you do a test cross of your Heterozygote you can see if the genes Are linked (5:5:1:1) or not (1:1:1:1).
Chromosome maps can be created by conducting breeding experiments.Linked genes that separate by crossing over X% of the time are X map units apart.
Compare 4 phenotype inheritance to 2 phenotype inheritance.
Genes can now be placed on a chromosome in some order.
Genes W and Z separate by crossing over 20% of the time. Genes W and X separate by crossing over 5% of the time, and genes Z and X are separated by crossing over 25% of the time. CONSTRUCT A CHROMOSOME MAP.Z W XI----20-------I--5--I
Mutations, Disease, & Human Mendelian TraitsWhere they occur/ significance.Types: Chromosome or GeneDiseases & Inheritance Patterns.Using Phenotypes to deduce Genotypes
Germ cell mutationoccurs in the gametesdoes not effect the organismmay be passed on to offspring if fertilized
Somatic mutationoccurs in the organisms body cells & can affect the organismex. Skin cancer & leukemiaare not passed on to offspring
Lethal mutationcauses death (often before birth)is not passed on if death occurs before reproduction
Beneficial mutationresult in phenotypes that are beneficial.beneficial phenotypes lead to increased reproduction.
Mutation: a change in the DNA sequence.A) chromosome mutations (affects many genes)B) gene mutations (one gene)
A) Chromosome mutations:Cross over errors:Deletion- loss of a piece due to breakage.Inversion- a piece is attached upside down.Translocation- a piece reattaches to a non-homologous chromosome.Segregation Error:Nondisjunction- failure of homologous chromosomes to separate during meiosis. ex. Down Syndrome = Trisomy 21 (egg usually has 2 of #21)
B) Gene mutations/ point mutations- are nucleotide differences.Substitution- one nucleotide is switched for another.- ex. sickle cell anemiaFrame shift mutations- occur when nucleotides are added or removed either more or fewer than 3 nucleotides at a time. - addition- deletion
GENE MUTATION: SUBSTITUTION ex. Sickle Cell Gene- Hemoglobin
INHERITANCE OF GENETIC DISEASES follow different Patterns of InheritanceSingle allele DominantSingle allele recessiveX-linked Sex influenced
PEDIGREE ANALYSISHumans have about 100,000 genes.
Most studies are of disease-causing genes.- easy to track through generations..
A pedigree is a family record that shows how a trait is inherited over several generations.
Single allele DOMINANT- need only one gene to have the disease.- huntingtons disease (1/10,000) Hh- dwarfism Dd- cataracts Cc- polydactyly Pp
PATTERN: effected individuals in every generation of both male and female sex.
Single allele recessive- The individual needs two genes to have the disease.Albinism aaCystic fibrosis (1/200 whites) ccPhenylketonuria (1/1800) ppHereditary deafness ddSickle cell anemia (1/500 African-Americans) sc scTay-Sachs disease (1/1600 European Jews) ttPattern: 2 healthy parents have effected child of either sex.
X-Linked- women need two genes, men need only one gene.- colorblindness XcXc XcY-hemophilia (1/7000) XhXh XhY-muscular dystrophy (1/10,000) XdXd XdY-Icthyosis simplex-ALD
Pattern: more common in males, Can kip generations.