Mendelian Genetics How Genes Work

Who Are You? Phenotype – Expressed genes – PHysical appearance/ – traits that are “seen” Genotype – Your genetic makeup; the alleles your GENEs code for

Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants Father of Genetics Figure 9.2A, B Stamen Carpel

Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation parental (P) to offspring (Filial – F1, F2) Figure 9.2C This illustration shows his technique for cross- fertilization 1 Removed stamens from purple flower White Stamens Carpel Purple PARENTS (P) OFF- SPRING (F 1 ) 2 Transferred pollen from stamens of white flower to carpel of purple flower 3 Pollinated carpel matured into pod 4 Planted seeds from pod Flowers are reproductive organs pistil stamen

Mendel ‘s basic ideas Dominance vs. Recessiveness Law of Segregation Law of Independent Assortment

Genetics Basics Chromosomes occur in pairs, one from MOM, one from DAD (homologues) Genes code for a trait or characteristic (I.e. hair color) Alternate forms of that trait are called ALLELES (ie. Blond, brown, redhead, etc) Alleles can be dominant or recessive – Homozygous vs. heterozygous

Meiosis and separation of alleles on chromosomes

The chromosomal basis of Mendel’s principles Figure 9.17

How did Walter Sutton’s Theory of Chromosomal Inheritance match up with Mendel’s Laws? Sutton Gametes contribute to heredity via nuclear material (chromosomes) Homologues segregate during meiosis Homologues separate independently of other homologous pairs – i.e. traits are not necessarily inherited together Mendel Law of Segregation Law of Independent Assortment

Punnett Square Visual representation or model of – what alleles can be present in gametes – how those alleles can recombine in offspring Used to determine the probability of offspring’s genetic makeup

Monohybrid Cross One gene – 2 alleles considered (one from mom, one from dad

Dihybrid Cross 2 genes – 4 alleles considered

How can we determine Homo- vs. heterozygous individuals? Test Cross – Must use homo recessive to conduct cross in order to “see” the questionable allele

What Mendel Didn’t See Multiple alleles Codominance Epistasis Polygenic traits Pleiotropy Incomplete Dominance Environmental Effects Sex linked and sex influenced traits Linked traits

CoDominance – Both alleles expressed at the same time; both dominant

Incomplete dominance: neither allele is fully dominant (blended inheritance) Figure 9.12Ax

Epistasis Sequential action of genes – Product of one gene influences another one gene gives “permission” for another allele to work – Gene action acts as a biochemical pathway & feedback inhibition Ex: Indian corn coloration

Pleiotropy – One allele may have multiple effects on phenotype Normal and sickle red blood cells Figure 9.14x1

Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickle cells Breakdown of red blood cells Clumping of cells and clogging of small blood vessels Accumulation of sickled cells in spleen Anemia Heart failure Pain and fever Brain damage Damage to other organs Spleen damage Kidney failure Rheumatism Pneumonia and other infections Paralysis Impaired mental function Physical weakness

Continuous Variation or Polygenic Traits Multiple genes acting to influence a characteristic – Produces gradual changes, not distinct “borders” Ie. Height, weight, nose length, skin pigment

Figure 9.16 P GENERATION F 1 GENERATION F 2 GENERATION aabbcc (very light) AABBCC (very dark) AaBbCc Sperm Fraction of population Skin pigmentation

Environmental Influence Example = color change of fur in arctic animals

Same eyes, different lighting

Multiple Alleles More than one allele per gene – Blood groups 3 alleles – A, B, O to determine 4 phenotypes –A, B, AB, O

A, B and O arae glycoproteins (sugar name tags or antigens) mark cells Non-recognition of the correct “name tag” for blood type can cause agglutination

Landsteiner Blood Groups Type A – galactosamine – AA (homo) or AO (hetero) Type B – galactose – BB or BO Type AB – galactosamine + galactose (codominant) Type O – no sugar marker - OO

Blood Donor Facts Universal Donor Universal Recipient

Rh factor Rh factor can be + or – + dominant - recessive Rh- moms that have Rh+ babies are subject to spontaneous abortions – Erythroblastosis fetalis – Controlled with an injectionof RhoGam to “hide” babies cells

Sex Linked “Sex on the X” trait/disorder is found ON sex chromosome, usually the X Usually recessive traits Disorder shows up more often in males than females Ex: color blindness, hemophilia

Sex influenced Hormones influence our gene expression i.e. baldness baldness is dominant in males (homo or hetero show trait) and recessive in females (for a female to be bald, she has to be homo recessive.

Barr Body inactivation In females (XX), both X chromosomes are not metabolically active Random inactivation of one X chromosome may influence traits expressed