INHERITANCE Chapter 5

Review What is the process that makes somatic cells? What is the process that makes gametes? How many chromosomes in a somatic cell? How many in a gamete?

Review What is the process that makes somatic cells? mitosis What is the process that makes gametes? meiosis How many chromosomes in a somatic cell? 46 How many in a gamete? 23

MENDELIAN GENETICS Genetics was unknown in Darwin’s time Gregor Mendel bred pea plants and discovered the laws of inheritance He was successful partly because the traits he observed were simple traits, controlled by only one gene These are now called Mendelian traits Examples: black fur or white fur Right-handed or left-handed

MENDELIAL GENETICS Mendel’s laws of inheritance: 1. Principle of Segregation: chromosomes inherited from mom and dad stay separated 2. Principle of Independent Assortment: you have an equal chance of inheriting each gene from each parent

MENDELIAL GENETICS A gene is a segment of a chromosome’s DNA that codes for specific functions or traits Genotype is the 2 alleles at a given locus. They are represented by letters. (ex. Aa or AA) If an individual inherits two alleles that code for the same form of a trait they are homozygous. If they have different forms they are heterozygous.

MENDELIAL GENETICS If an allele is always expressed when present, it is dominant. If it is masked, it is recessive. The only time recessive traits are expressed is if they are both recessive, or homozygous recessive. Homozygous dominant: 2 dominant forms (AA) Homozygous recessive: 2 recessive forms (aa) Heterozygous: one of each (Aa) Dominant does not mean better, healthier, or more common

MENDELIAL GENETICS The physical expression of a trait is the phenotype So, the genotype is the actual genes and the phenotype is the observable form of the genes Genotype: BB, phenotype: B blood type If a specific trait is coded for by a gene on a chromosome pair numbered 1-22 it is an autosomal trait If it is on the 23rd pair it is a sex-linked trait Important for Extra Credit Assignment

AUTOSOMAL TRAITS We will deal with discrete traits: there are clear categories Continuous traits are not measurable and have an unlimited number of possibilities (we won’t use these)

TRANSMISSION OF TRAITS: ONE AT A TIME Let’s look at albinism Recessive autosomal gene AA and Aa would result in normal melanin and no albinism aa is the only form that would result in albinism To predict probability of a trait in offspring: List genotype of mother and father Figure out what alleles for this trait will be carried by gametes of mother and father Set up a Punnett Square Fill it in List the possible genotypes and phenotypes and the probability of each List the ratio of phenotypes and genotypes

TRANSMISSION OF TRAITS: ONE AT A TIME Let’s do the example on page 86-87

ASSIGNMENT Lab 5 Handout Genetics Practice WS

BLOOD TYPING Each different blood type is coded for by genes at different loci on our chromosomes Blood type is determined by the kind of antigen on the red blood cell Each person has antibodies against foreign blood antigens. You can test for blood type by adding antigens and seeing the reaction If antibodies attack antigens, the result is the clumping of blood, or agglutination

BLOOD TYPING The ABO blood group is a unique trait Alleles called A, B, or O determine the type of antigen on the cell Genotypes are: AA, AO, AB, BO, BB, or OO A and B alleles are both dominant over O A and B are codominant So, OO is the only way to get type O blood AB is the codominant form Chart on page 93 summarizes this

BLOOD TYPING Blood types for the ABO blood group must match if blood from a donor is used for a recipient Type O blood does not provoke agglutination with A, B, or AB so it is the universal donor Type AB has neither anti-A nor anti-B antibodies so it is the universal recipient

RH BLOOD GROUP Blood type associated with the Rh blood group are Rh+ and Rh- Homozygous dominant form is Rh+ Homozygous recessive form is Rh- A person with Rh+ has antigens on the surface of red blood cells that provoke production of antibodies for Rh- Rh incompatibility can occur between a mother and her fetus, which can result in anemia

ASSIGNMENT Blood Type Lab Put answers on Handout

SEX-LINKED TRAITS Sex-linked traits can be on X or Y chromosome Most are X-linked An example is red/green colorblindness. Most are males because this trait is transmitted by a recessive gene on the X chromosome A female has a better chance of getting a dominant X that will mask the gene, but males only have 1 X, so the trait will show Males are hemizygous

EXAMPLE, PAGE 97 A man with normal vision and a woman who is a carrier for colorblindness are having a child 1. list genotypes of each parent 2. set up Punnett Square 3. fill it in 4. list possible genotypes and phenotypes

PEDIGREES Search for patterns of transmission of traits from one generation to the next We do this by constructing a pedigree There are 5 modes of inheritance. We focus on 3: 1. autosomal recessive: 2 unaffected parents and affected child. Child’s trait is “hidden” 2. autosomal dominant: 2 affected parents have unaffected offspring 3. X-linked: males get it more often

Work on Self-tests 5.1 #1, #2(a & b), #4, #7 5.2 All