Genetics Part I: Mendel and Basics Unit 7

How does this happen?

The answer?...GENETICS! Genetics: The study of genes and heredity. Heredity: passing traits from parents to offspring.

The Father of Genetics Gregor Mendel, 1822 – 1884 Austrian monk Performed crosses with the garden peas at his monastery Made laws of heredity based on analysis of how traits are inherited

Genetics Terms Trait: any observable characteristic Gene: DNA that holds information for a trait Allele: one version of that trait – Diploid organisms (like humans) have two copies of each gene. Ex) Trait: flower color, Alleles: purple/white Trait: pea shape, Alleles: round/wrinkled Trait: height, What would be alleles?

Dominant and Recessive When one allele masks the effect of another, that allele is called dominant and the other recessive. – Dominant allele = capital letter (R) – Recessive allele = lowercase letter (r) Exceptions to recessive/dominance Incomplete dominance – alleles blend Co-Dominance – alleles show up together Unless it says differently, assume traits show normal dominant/recessive

x = Incomplete Dominance in Snapdragons Co-Dominance in Chickens x=

Genetics Terms 2 Humans are diploid (2 copies of each chromosome) so genes occur in pairs. Genotype – gene combination for a trait (RR, Rr, or rr) – Homozygous – two of the same alleles (RR, rr) – Heterozygous – two different alleles (Rr) Phenotype – the physical feature resulting from the genotype (eg. red, white)

Writing Genotypes Each allele is written as a letter – the letter is usually from the dominant allele. Dominant is UPPERCASE. Recessive is lowercase. Ex) Flower color – Red is dominant over white so choose letter – R to show red and r to show white. Genotype (Words)Genotype (Letters)Phenotype Homozygous dominant Heterozygous Homozygous recessive

How did we figure all this out? Mendel’s Breeding Experiments: Parental P 1 Generation = the parental generation in a breeding experiment. F 1 generation = the first-generation offspring in a breeding experiment. F 2 generation = the second-generation offspring in a breeding experiment. – Come from breeding individuals from the F 1 generation

705 purple: 221 white What did Mendel observe? Crossed those flowers. What do you think the next generation looked like? Crossed parental generation pure purple x pure white. What do you think the next generation looked like?

Following the Generations Cross 2 Pure Plants TT x tt Results in all Hybrids (Tt) Cross 2 Hybrids get 3 Tall & 1 Short (TT, Tt, tt)

Mendel’s Laws 1.Law of Segregation: You only pass on 1 copy of your genes to your offspring. Child gets second copy from other parent. 2.Law of Independent Assortment The allele you pass on of one trait doesn’t affect what alleles get passed on for a different trait in a gamete. Ex) purple allele for flowers doesn’t affect whether pea will pass on short or tall height 3.Law of Dominance Alleles that are recessive are masked by dominant alleles when they are both present.

Polygenic Traits Polygenic: “many genes”, when several genes influence a trait Ex) Eye color, height, weight, hair & skin color All these characteristics show a range of traits and are harder to study than single-gene traits At least 3 known genes control eye color Outcomes for 3 genes for skin color

Genetics Part II: Genetic Crosses Unit 7

Punnett Squares Predicts the expected outcomes of a genetic cross by finding all possible combinations of gametes. Punnett Squares show probable frequencies of offspring – not the actual offspring you will get. Genotypic ratio = frequencies of each genotype for a trait Phenotypic ratio = frequencies of each phenotype for a trait

Steps to Solving Punnett Square Problems Step 1: Write out the genotypes, if not already given. Step 2: Draw the Punnett Square Step 3: Always write the first organism’s genotype across the top of the box; write the second organism’s genotype down the left side of the box Step 4: For each box, write the allele from the top and the side. – Always write capital letters before lowercase letters. Step 5: Write the genotypic and phenotypic ratios of the offspring from the cross

Punnett Square #1 Cross a homozygous dominant red flowered plant with a homozygous recessive white flowered plant.

Punnett Square #2 In cats, long hair is dominant to short hair. Cross a heterozygous long haired cat with a short haired cat. Write the genotypic and phenotypic ratios.

Human Traits Lab Trait# Dominant# Recessive Tongue Rolling225 Ear Lobes176 Dimples108 Freckles513 Chin419 Thumb Folding157 Hairline118 Ear Wiggling715 PTC Paper213

Genetics Part III: Dihybrid Crosses Unit 7

Punnett Square #3 – Test Cross Test Cross: Cross between an unknown and a homozygous recessive to figure out unknown. Ex) We want to find out if a dominant red flower is RR or Rr. When crossed with a white flower (rr), 50% of the offspring are red and 50% are white.

Dihybrid Crosses Dihybrid Crosses: a cross between individuals that involves two traits (e.g., pod color and plant height) Tall = H, Short = h…. Green = G, Yellow = g Example: 1) Parent 1: HHGG  Tall, Green 2) Parent 2: hhgg  Short, Yellow

Finding the Gametes for Dihybrid Crosses Each gamete must have ONE COPY of the two genes To find gametes for each parent, FOIL Parent 1: H H G G Parent 2: h h g g Possible Gametes: hg Possible Gametes: HG

Parent Genotypes: HHGG x hhgg Offspring Ratios -Genotype: 100% HhGg -Phenotype: 100% Tall + Green Homozygous x Homozygous HGHGHGHGHGHGHGHG hghg hghg hghg hghg HhGg

Another Example: Heterozygous x Heterozygous Parent 1: H h G g Parent 2: H h G g Possible Gametes: HG Hg hG hg Possible Gametes: HGHG HgHg hGhG hghg

Heterozygous x Heterozygous Parent Genotypes: HhGg x HhGg Offspring Ratios -Genotype: too complicated! -Phenotype: Next Slide! HGHG HgHghGhG hghg HGHG HgHg hGhG hghg HhGg HHGG HHGgHhGG HHGgHHggHhGg Hhgg HhGGHhGghhGGhhGg HhgghhGghhgg HGHG HgHg hGhG hghg Possible Gametes:

Heterozygous x Heterozygous Parent Genotypes: HhGg x HhGg Phenotype: 9: 3: 3: 1 9 Tall, Green 3 Tall, Yellow 3 Short, Green 1 Short, Yellow HGHG HgHghGhG hghg HGHG HgHg hGhG hghg HhGg HHGG HHGgHhGG HHGgHHggHhGg Hhgg HhGGHhGghhGGhhGg HhgghhGghhgg

Genetics Part IV: Blood Type Crosses Unit 7

Multiple Alleles Multiple Alleles: Genes with more than two alleles that could code for a trait. There are three or more possible alleles in the population, BUT an individual can still only carry two alleles for each trait.

Human Blood Types Three different possible alleles: I A, I B, and i. I A and I B are dominant over i, but are codominant with one another. Four different blood types: – Type A - I A I A or I A i – Type B - I B I B or I B i – Type AB - I A I B – Type O - ii

Simpler Way to Write Blood Genotypes Type AAA, Ao Type BBB, Bo Type ABAB Type Ooo

Blood Type Problem A and B are co-dominant O is recessive. Mother with type AB blood type says that John Doe is the father of a baby with type AB. His blood type is O – could he be? AB o o Possible blood types: A or B Bo AoBo Ao AB is impossible – NOT the father.

Blood Types Blood Type% of Americans with this blood type Who can receive this type O+37%O+, A+, B+, AB+ O-6%All blood types A+34%A+, AB+ A-6%A+, A-, AB+, AB- B+10%B+, AB+ B-2%B+, B-, AB+, AB- AB+4%AB+ AB-1%AB+, AB-

Genetics Part V: Sex-linked Crosses Unit 7

Sex linked genes You have two copies of almost all genes What two chromosomes do not have all the same genes?

Sex-linked Genes = genes found on the X chromosome Males are XY so they only have 1 copy of genes on the X chromosome Females are XX so they have two copies of genes on the X chromosome Recessive genes on X chromosome show up more in males.

Heterozygous Red-Eyed Female x Red-Eyed Male Genotypes: Phenotype Ratio: 50% Red-eyed females 25% Red-eyed males 25% White-eyed males XRXR XrXr XRXR Y XRXRXRXR XRXrXRXr XRYXRY XrYXrY X R X r x X R Y Question: Can a father pass on an x-linked trait to son?

Human Examples of Sex Linkage Hemophilia is a disorder that causes blood to clot incorrectly  patient bleeds out after minor cut – Common in royal families because of inbreeding Red-green color blind Male pattern baldness …Can identify patterns using pedigrees

Genetics Part VI: Human Inheritance Unit 7

Pedigree: shows how a trait is passed down in a family Unaffected Affected Carrier Female Male Carrier = individual who has ONE copy of a recessive allele (doesn’t have disease) These aren’t always shown on pedigrees!

If the disease is more common in males, the gene is likely sex-linked. If it is even between male and female, it is autosomal (not sex-linked).

Dominant or Recessive? If a person can have the disease and neither parent had the disease, it must be recessive. If carriers are shown, it’s a recessive trait.

Recessive or dominant?

Autosomal or Sex-Linked?

Recessive or dominant? Female Male Albino Individuals

Many inherited diseases are usually recessive – why do you think that is?

What type of inheritance?