ACADEMIC BIOLOGY GENETICS I Gregor Mendel 1842 Who

ACADEMIC BIOLOGY GENETICS

I. Gregor Mendel 1842 Who was he? - Austrian monk whose task was tending the garden in his monastery. - Known as the “Father of Genetics. ” - Studied 7 characteristics of pea plants. (Height, Seed color & shape, Flower color, Pod color & shape & Flower position)

II. GENETICS TERMS A. What is Genetics? - The study of heredity B. Heredity - The passing on of traits from parent to offspring. Ex. You have your father’s eyes. C. Trait - A physical or genetic characteristic.

D. What is a Purebred? - An organism that always produces an offspring with the same physical / genetic characteristic(s). 1. P Generation – Parents 2. F 1 Generation – Offspring from parents 3. F 2 Generation – Offspring from F 1

III. GENES & ALLELES A. What is a “Gene? ” - Portion of DNA that codes for a specific protein(s). B. What is an “Allele? ” - An alternative form of a gene found on a specific chromosome. - You have 2 alleles for each gene: one from mommy & one from daddy. (Remember: Half from mom & half from dad. )

IV. PATTERNS OF INHERITANCE A. Law of Dominance - An allele can be either dominant or recessive. - When present, a dominant allele will ALWAYS express its trait. (Exceptions apply!) - Recessive traits get hidden behind dominant - A dominant allele is represented as a Capital Letter while a recessive allele will be a lowercase letter.

B. LAW OF SEGREGATION - Each gamete only donates one allele for each gene. C. LAW OF INDEPENDENT ASSORTMENT - Traits are inherited separately of one another (No 2 genes are linked!) Ex. Just b/c you have blonde hair doesn’t mean you have to have blue eyes.

V. Probability - The likelihood an event will or will not occur. Ex. What is the probability of flipping heads? Ex. What is the probability of pulling an ace out of a deck of cards? The prior occurances have no effect on future results – it is all chance and it starts over each time

VI. PHENOTYPES & GENOTYPES A. Phenotype - Refers to an organisms physical trait(s). Ex: Height & Eye Color B. Genotype - Refers to an organisms genetic make-up, or allele combination for a trait(s). Ex: Hh for height.

1. Types of Genotypes: a. Homozygous - When an organism has two of the same allele for a trait. - Can be either dominant or recessive. b. Heterozygous - When an organism has both a dominant and recessive allele for a trait.

VII. PUNNETT SQUARES A. What are they? - A chart that shows all possible allele combinations. 1. Monohybrid Crosses - A cross involving only one trait. - Create a table with 2 columns & 2 rows. - Put the Male gametes on left and female gametes on top - Record ratio like this: Genotypic: Homo. Dom : Hetero: Homo Rec. Ex: 1 : 2 : 1 Phenotypic: Dominant: Recessive Ex: 3 : 1

Example: Being tall is dominant to being short. If a homozygous tall man marries a homozygous short woman, what are their chances of having a short child? Genotypic ratio- : : TT: Tt : tt Phenotypic ratio- : D : r

Example 2: Brown eyes are dominant to blue eyes. If a mother, heterozygous for brown eyes, marries a man homozygous for blue eyes. What are their chances of having a child with brown eyes? Blue eyes? Genotypic ratio: : : Phenotypic ratio-

2. Dihybrid Crosses - A cross involving two traits. - Create a table with 4 columns & rows. Example 1: Black hair is dominant to blonde hair. Being tall is dominant to being short. What would be the possible phenotypes of a cross between a heterozygous black-haired, tall female with a male who is homozygous for having black hair and being short? Parent Genotypes?

Dihybrid Cross: Use FOIL! - To get the proper segregation of alleles for the parents in a dihybrid cross, use the FOIL method: First, Outer, Inner, Last (Bb)(Tt) BT, Bt, b. T, bt - Because there a lot of genotypes, we only record the phenotypic ratio like this: Dom, Dom: Dom, Rec: Rec, Dom: Rec, Rec 9: 3: 3: 1 (It needs to add to 16!)

Example 2: Round peas are dominant to wrinkled peas. Yellow peas are dominant to green peas. What would be the possible phenotypes of a cross between a homozygous round, yellow pea plant with a homozygous wrinkled, heterozygous yellow peas plant? Parent Genotypes?

VIII. Exceptions to the Law of Dominance A. Incomplete Dominance - When alleles of a heterozygote blend together. - One allele is not fully dominant over the other. - Write the more dominant allele as a capital letter and the more recessive allele as a capital followed by an apostrophe.

• Incomplete Dominance: • Think of it as neither trait being strong, so when they are both present, no trait will dominate. • They blend together • You can think of them being kind of “wimpy” because neither stands out

Example 1: Red flowers are incompletely dominant over white flowers. What would be the offspring phenotypes of a cross between a red flower with a white flower? (Use R = red, R’ =white)

Example 2: Two snapdragon flowers are crossed. All of their offspring were pink. What were the genotypes of the parents? Prove your answer using a Punnett square.

B. Co. Dominance - When alleles of a heterozygote show “equal” dominance. - You will see both traits, not a blending. - Write each allele similar to the following example: Black is codominant to White

Example: We have two cute fuzzy bunnies in the back of the classroom. One has black and white fur, the other is pure white. What are the genotypes of these two bunnies? What would be the phenotypic ratio of their offspring?

C. Multiple Alleles - When there are more than two possible alleles for a gene. - Along with having multiple alleles, a gene may also show incomplete or codominance. EXAMPLE: Blood Types Possible Alleles: (IA, IB, i) IA = Type A (IAIA or IAi) IB = Type B (IBIB or IBi) i = Type O (ii) IAIB = Type AB

Example: What possible blood type(s) could a child have from the result of a cross between a mother who is heterozygous Type A blood and a father who is homozygous Type B blood.

D. BLOOD TYPE NOTES

Karyotype • Picture of homologous chromosomes that are arranged in order of size • A normal human Karyotype has 44 autosomal chromosomes and 2 sex chromosomes

Karyotypes • Karyotypes can help determine chromosomal abnormalities – Do you remember this?

Chromosomal Disorders • Nondisjunction – means “not coming apart” – results in abnormal numbers of chromosomes in gametes • Monosomy – when there is a chromosome missing • Trisomy- when there is an extra chromosome

E. POLYGENIC TRAITS - A trait controlled by two or more genes. Examples: Height, Eye Color & Skin Color Example Genotype: Ee. Bb. Yy = Hazel Eyes

IX. HUMAN SEX INHERITANCE A. Chromosomes & Sex Determination - We have 22 pairs of chromosomes called Autosomes. - We have 1 chromosome pair that are our Sex Chromosomes. - XX for a girl and XY for a male. Problem: Chances of having a boy or girl?

B. Sex-Linked Inheritance - Sex-linked genes are found on the X chromosome - Because males have only one X chromosome, males are more likely than females to receive & express a recessive trait. - A person is a carrier if they have one recessive allele “and” one dominant allele for a trait.

How Does This All Work With Inheritance? Example: Red-Green colorblindness is an X-linked recessive trait. Males are affected more often than females. If a normal male marries a woman who is a carrier for redgreen colorblindness, what are their chance of having a child with red-green colorblindness? A boy who is colorblind?

Example: Being as intelligent, good-looking and athletic as Mr. D is a sex-linked recessive trait. If Mr. D marries a phenotypically normal woman, whose father was also intelligent, etc…, what are their chances of having a boy who is intelligent, etc. ? A girl who is intelligent, etc. ?

C. Autosomal Inheritance - Traits not located on the sex chromosomes. 1. Autosomal Recessive - Equal numbers of males & females affected. - Can skip generations. i. e. Cystic Fibrosis & Sickle Cell Anemia Problem: A female homozygous dominant for C. F. marries a man who is a carrier for C. F. What are their chances of having a child with C. F. ?

2. Autosomal Dominant / Lethal Alleles - One dominant allele leads to death. - Seen in every generation. i. e. Huntington’s Disease Problem: A female heterozygous for Huntington’s disease marries a man who does not have the disorder. What are the chances their child will have Huntington’s disease?

X. PEDIGREES A. Chart that helps track which members of a family express a trait. B. Symbols used in a pedigree: Male = Square Female = Circle Carrier = Half-shaded circle or square Affected = Fully-shaded circle or square Married = Line connecting two individuals

C. Interpreting Pedigrees STEPS: 1. Determine if its Autosomal or Sex-Linked? - If “most” affected individuals are male, then it is most likely X-Linked. - If there is a 50: 50 ratio of affected males to females, than it is most likely Autosomal. 2. Is it dominant or recessive? - If dominant, one parent must have the trait and it will be seen in every generation. - If recessive, neither parent has to have it and it can skip generations.