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 Ex) Trait: flower color, Alleles: purple/white Trait: pea shape, Alleles: round/wrinkled Trait: height,_________________________

Dominant and Recessive Diploid organisms (like humans) have two copies of each gene on homologous chromosomes (one from mom and one from dad). 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)

Dominant and Recessive 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 – Blue is dominant over white so choose letter – B for blue allele and b for white allele. 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 combinations of all possible gametes from each parent. Punnett Squares show probable frequencies of offspring – not the actual offspring you will get. Genotypic ratio = frequencies of each genotype for a trait Ex) 50% RR and 50% Rr Phenotypic ratio = frequencies of each phenotype for a trait Ex) 75% blue and 25% white

Steps to Solving Punnett Square Problems Step 1: Write out the genotypes, if not already given. Step 2: Write gametes for parents on each side of the square. Step 3: Fill in the boxes of the square by looking at alleles on the top and left of the box. – Always write capital letters before lowercase letters. Step 4: Write the genotypic and phenotypic ratios of the offspring from the cross - Each box represents ¼ or 25% of the offspring

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 Rolling Ear Lobes Dimples Freckles Chin Thumb Folding Hairline Ear Wiggling PTC Paper

Punnett Square #3 – Test Cross Test Cross: Cross between an unknown individual with dominant phenotype and a individual that is recessive to figure out the genotype of the unknown individual. 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.

Genetics Part III: Dihybrid Crosses Unit 7

Dihybrid Crosses A cross between individuals that involves two traits Example: pea pod color and plant height Tall = HGreen = G Short = hYellow = g Ex #1) Parent 1 is homozygous dominant for tall and green Genotype: __________________ Parent 2 is homozygous recessive for short and yellow Genotype: __________________

Finding the Gametes for Dihybrid Crosses Each gamete must have ONE COPY of the two genes. Gametes will be combinations of the two letters, NOT HH or gg. Parent 1: HHGG Parent 2: hhgg Gametes:

Parent Genotypes: HHGG x hhgg Phenotypic Ratio: Homozygous x Homozygous

Ex #2) Heterozygous x Heterozygous Parent 1: __________ Parent 2: __________ Possible Gametes:

Heterozygous x Heterozygous Parent Genotypes: HhGg x HhGg Phenotypic Ratio:

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: A, B, and o. A and B are dominant over o, but are codominant with one another. Four different blood types: – Type A - AA or Ao – Type B - BB or Bo – Type AB - AB – Type O - oo *Notes: The alleles are sometimes written: A allele = I A B allele = I B o allele = i Be able to recognize these if you see them.

Blood Type Problem Remember: A and B are co-dominant o is recessive. Mother with type AB blood type mother says that John Doe is the father of a baby with type AB. His blood type is type O – could he be?

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 Sex-linked genes are 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 sex-linked genes show up more often in males.

Heterozygous Red-Eyed Female x Red-Eyed Male Genotypes: Genotypic Ratio: Phenotypic Ratio:

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

Application Question Can a father pass a sex-linked trait down to his son?

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 two unaffected parents can produce an affected child, 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 recessive – why do you think that is?

What type of inheritance?