Theoretical Genetics Mrs. Ragsdale Bio SL

A Lil Vocab Genotype – the actual genes (alleles) Each gene has two alleles Example: Aa, AA, aa Phenotype – the physical characteristic expressed Blue eyes vs green eyes Dominant – the allele that is always expressed if its present Recessive – an allele that is only expressed when a dominant allele isn’t around

Some More Vocab… Homozygous – when both alleles are the same AA or aa Both dominant or both recessive Heterozygous – when one allele is dominant, the other recessive Aa Locus – the location of a gene on a chromosome

GREGOR MENDEL “FATHER OF MODERN GENETICS” STUDIED PEA PLANTS GENETICS – THE STUDY OF HUMAN HEREDITY STUDIES HOW TRAITS ARE PASSED FROM PARENT TO OFFSPRING

Law of Segregation GAMETES – SEXUAL REPRODUCTIVE CELLS EGG AND SPERM LAW OF SEGREGATION – EACH PARENT PASSES ON ONE OF THEIR ALLELES FOR A GENE TO THEIR OFFSPRING

LAW OF INDEPENDENT ASSORTMENT GENES FOR DIFFERENT TRAITS CAN SEPARATE DURING GAMETE FORMATION They separate and assort themselves independently of each other ALL OF YOUR MOM’S DNA DOES NOT END UP IN ONE GAMETE AND ALL OF YOUR DAD’S IN A DIFFERENT GAMETE EACH OF YOUR GAMETES WILL BE A MIXTURE OF YOUR MOM AND DAD’S GAMETES

GENETIC PROBABILITY PUNNETT SQUARES DOMINANT ALLELES – CAPITAL LETTERS RECESSIVE ALLELES – LOWER CASE

Punnett Example Two heterozygous blue flowering pea plants are crossed. Blue is dominant over white What is the probability of a white flowering pea plant being produced?

B b Bb bb Punnett Example 2 A heterozygous blue flower is crossed with a homozygous white flower. What are the possibilities of the offspring and to what predicted probability? B b Bb bb

Dihybrid Crosses T=tall, t=short, R=red, r=white Tall white x short red Ttrr x ttRr Phenotypes: Tall red, Tall white, short red, short white tR tr Tr TtRr Ttrr ttRr ttrr

INCOMPLETE DOMINANCE SOMETIMES ONE ALLELE IS NOT COMPLETELY DOMINATE OVER ANOTHER INCOMPLETE DOMINANCE IS A BLEND OR A MIXTURE OF TWO ALLELES ONLY CAPITAL LETTERS ARE USED

Test Cross Let’s say you have a flower that is dominant when red and recessive when white If you have a red flower, how can you know if it is homozygous dominant or heterozygous? Test cross – in order to test if something is AA or Aa, cross the unknown with a homozygous recessive aa. If the subject was AA the offspring will all be Aa If the subject was AA the offspring will be 50/50 Aa and aa

INCOMPLETE DOMINANCE THE OFFSPRING OF A CROSS BETWEEN DOMINATE RED AND DOMINATE WHITE IS A BLENDED PINK

CODOMINANCE BOTH ALLELES ARE SHOWN IN A PHENOTYPE

MULTIPLE ALLELES WHEN A GENE HAS MORE THAN 2 DIFFERENT ALLELES THAT CONTROL IT’S PHENOTYPE Ex: Rabbit color C = full color cch = gray ch = white with some brown c = albino

Blood Groups: ABO Human blood inheritance is a perfect example of both a multiple allele and codominance situation Three alleles all based on the letter I IA and IB are codominant to each other. Both these alleles are dominant to i The Allele hierarchy is IA = IB and both are > i

Punnett Squares Revisited IA IB IA i i IAi IBi IAIA IAi ii IA i

POLYGENIC TRAITS CHARACTERISTICS CONTROLLED BY MORE THAN ONE GENE EXAMPLES: HUMAN SKIN AND EYE COLOR

Polygenic Inheritance -skin color   ABC   ABc   AbC Abc  aBC   aBc   abC  abc ABC 6 5 4 3 ABc 2 AbC Abc 1 aBC aBc abC

Polygenic Inheritance Height Eye color Continuous variation Continuous variation Different amounts of melanin Polygenic Inheritance

Two Main Types of Chromosomes: Sex Chromosomes Chromosomes that determine the sex of the individual In humans – X and Y Females have XX Eggs always donates X Males have XY Sperm donates either X or Y Autosomes Every other chromosome is an autosome

Human Sex Determination Females XX Males XY Always a 50/50 chance of male or female at birth

Karyotyping Photographic display of human chromosomes arranged in homologous pairs Paired based on size, centromere location and banding

Sex Linkage Sometimes, certain diseases and disorders only affect you based on your sex These alleles are typically found on the sex chromosomes X or Y For recessive alleles, women become carriers while men display the phenotype (the actual disease). Examples: Hemophilia Color Blindness

Hemophilia: Recessive Sex-Linked Disease Carried by women, expressed by males The hemophiliac allele (Xh)is recessive to the normal allele (XH) Females can be either homozygous or heterozygous for sex linked diseases **Heterozygous females are called carriers because they have the allele but don’t express it

Pedigree Charts Modified family tree Shows relationships within a family

Example Pedigree

Royal Pedigree http://www.sciencecases.org/hemo/hemo.asp