DO NOW: Pass it on! How are the members of this family different? How are they the same? Do children ever look exactly the same?

Mendelian Genetics Genetics –Branch of biology dealing with heredity and variation of organisms Heredity –Passing of traits from parent to offspring Chromosomes –Carry the hereditary information (genes) Gene –Arrangement of nucleotides in DNA –DNA --> RNA --> proteins

Genetics Gene (trait) Hair color Eye color Height Skin color Allele –Different forms of a gene

Different forms of a gene –found at the same position on homologous chromosomes Example: –Dark purple = brown eyes –Light purple = blue eyes Allele

Homologous Chromosomes Chromosomes (w/genes) occur in pairs Colors represent different alleles *Sister chromatids are identical, *homologous chromosomes are not

Locus –Fixed location on DNA where gene is found –Found at same location on chromosome NEED TO KNOW: Terminology

Gregor Mendel (Father of genetics) “pure” lines of peas Studied one trait through several generations Used probability

Past: Inherited traits thought to be a “dilution” or “blend” of parental traits Mendel predicted –Genes “factors” occur in pairs –One gene of each pair is present in gametes

Mendel’s Peas Looked at seven traits of peas

To study one trait Mendel… –Crossed two plants with different alleles of that one trait Height: tall x short –Found that the offspring looked like either parents Offspring: He found dominant and recessive traits

Homozygous –Having identical genes for a certain trait (one from each parent) Homozygous dominant (TT) Homozygous recessive (tt) Heterozygous –Having two different genes for a certain trait (Tt) NEED TO KNOW: Terminology

Dark blue (BB)- brown eyes Light blue (bb)- blue eyes During sexual reproduction, crossing over occurs and makes new combinations of genes (BB, Bb, bb)

What heights would your plants be if you… Crossed two pea plants that differ only in height (one tall and one short) –Parent pea plant 1: Tall (T) –Parent pea plant 2: Short (t)

T = allele for tall t = allele for short TT = homozygous tall plant Tt = heterozygous tall plant tt = homozygous short plant Monohybrid Cross (one trait difference)

Dominant –Allele of a gene that masks the expression of an alternate allele –Appears in homozygous dominant –Appears in heterozygote Recessive –Allele that is masked by dominant allele –Does not appear in heterozygote (Bb) (It’s carried) –Only appears in homozygous recessive NEED TO KNOW: Terminology

Genotype –Genetic makeup of an organism –BB, Bb, bb Phenotype –Physical appearance of an organism –Description (brown eyes, blue eyes) NEED TO KNOW: Terminology

Punnett Square Tool to do genetic crosses For monohybrid crosses use a square with four boxes Used to predict genotypes and phenotypes of offspring

Using a Punnett Square steps: 1. Determine genotypes of parents 2. Choose letters to represent genotypes 3. Write down your cross using those letters 4. Draw the Punnett Square 5. “split” the letters of the genotype and put them outside the square

Let’s do one! Monohybrid cross Parental generation Cross a homozygous tall plant with a homozygous recessive plant TT x tt T t t T Tt

TT x tt P = ? –True breeding homozygous (TT) –Homozygous recessive (tt) F 1 = ? –ALL heterozygous (Tt)

Generations P = parental F 1 = first filial offspring of parental cross F 2 = second filial offspring of F 1 generation cross

Now an F 1 generation cross Cross the offspring of your F 1 generation T T t t TTTt tt

Results: F 2 generation Genotypes –1 TT = Tall –2 Tt = Tall –1 tt = short Phenotypes –3 Tall –1 short T T t t TTTt tt Genotypic ratio = 1:2:1 Phenotypic ratio = 3:1

Practice Problems! Worksheets! –In-class and homework!

Mendelian Principles Dominance –One allele masks another Segregation –When gametes are formed, the pairs of genes get separated –Each gamete receives only one of each gene Happens when sister chromatids seperate

Segregation

Independent Assortment –Genes of individual characteristics are not connected Depends how chromos line up in metaphase Brown eyes not always inherited with long hair Can have brown eyes with short hair –Advantage of sexual reproduction Mendelian Principles

Independent Assortment

Dihybrid crosses Matings involving parents that differ in two genes (two independent traits)

Chalkboard Dihybrid crosses Learn short cut

Test Cross! Individual with an unknown genotype crossed with a homozygous recessive individual Ex: You have a black guinea pig –Is it BB or Bb? –Need to know offspring to figure out parents

Test Cross Practice problems…

Non-Mendelian Genetics Covers genes that do not follow Mendel’s inheritance patterns –1. Incomplete dominance –2. Codominance –3. Multiple Alleles

Incomplete dominance Neither allele shows complete dominance The heterozygote is an intermediate phenotype Japanese four-o’clock flowers

1:2:1 C R C R : C R C W : C W C W Red : pink : white Incomplete Dominance

Codominance Both alleles are equally dominant Both alleles are expressed in heterozygote Example: Roan coat in cattle –Homozygous red x homozygous white

Codominance Roan coat –Each hair is neither all red or all white

How to represent Incomplete or Codominance Capital letters with superscripts –C R = red coat –C W = white coat –Homozygous red = C R C R –Heterozygous = C R C W (roan) –Homozygous white = C W C W

Multiple Alleles So far we have studied patterns of heredity in which each trait has two alleles –Pod color Green (G) Yellow (g) Multiple alleles- traits controlled by more than two alleles

Multiple alleles ABO blood groups I A = allele for type A I B = allele for type B i = allele for type O Blood is also an example of…?

Antigen- molecule that binds specifically to an antibodyantibody Antibody- used to identify and combat foreign objects

Modern Genetics 1. Polygenic (multiple gene) inheritance 2. Sex-linked traits

Polygenic Inheritance More than one set of alleles Example: –Skin color is controlled by a two allele sets –Eye color also

Polygenic Inheritance If skin color was controlled by 3 gene pairs… –Dominant A, B, C produced pigment –But A, B, C are incompletely dominant to a, b, c

Polygenic Inheritance The quantity of dominant genes determines how much pigment –AABBCC = lots of pigment –aabbcc = very little pigment –AaBbCc = middle range of pigment –So 2 heterozygotes (AaBbCc) could produce a child with any pigment range

Polygenic Inheritance

Sex-linked traits There are alleles on the sex chromosomes Called sex-linked traits –Y-linked –X-linked

Y-linked If gene is on the Y chromosome –Sons will inherit it from dad Hairy ears –Not very common –Females cannot get Y- linked traits Why not?

X-linked If gene is on X chromosome –Can be inherited from mom or dad –Son will ALWAYS inherit it from mom Why? Examples: –Colorblindness –Hemophilia –Severe Combined Immunodeficiency (SCID) (Boy in the Bubble Disease)

Hemophilia X H X H = normal female X H X h = female carrier X h X h = female with hemophilia X H Y = normal male X h Y = male with hemophilia

Pleiotrophy 1 gene affects 2 characteristics Sickle cell Anemia –Affects ability of blood to carry oxygen –Disease only present in homozygous recessive –Affects ability of malaria to affect blood cells –Have allele for sickle cell you can’t get malaria

Sickle Cell Anemia S = normal alleles = sickle allele SS = normal (dies from malaria) Ss = sickle cell trait (protected) ss = sickle cell anemia (dies from sickle cell anemia)

Epistasis Two genes affect 1 trait (masking) Labrador fur –B = blackb = brown –E = enzymee = no enzyme

BBEE = BlackBbee = yellowBBEe = Black BbEE = BlackBbee = yellowBbEe = black bbEE = brownbbee = yellowbbEe = brown

Linked genes Two genes for two different traits on the same chromosome Normally inherited together –Light hair/light eyes –Red hair/freckles

Linked genes The closer the two traits are on the chromosome, the more likely they will be passed on together When they are far apart and become separated this is called… CROSSING OVER

Crossing over During Meiosis when sister chromosomes are lined up they exchange genetic information

Importance… Sex-cell mutations –Important! –If mutation is present in gamete, when fertilization occurs, the embryo has mutation

Why is learning about mutations important? Lead to recessive/dominant, autosomal/sex-linked disorders! –Hemophilia –Cystic fibrosis –Down syndrome –Tay-Sachs disease –Huntington disease –Sickle Cell

Testing for genetic disorders Karyotyping Amniocentesis Chorionic villus sampling Ultrasound Fetoscope

Jumping genes Sometimes genes “jump” to new locations on the same chromosome Can cause inactivation of gene Important sources of variation between species