Warm-Up   List all of the possible gametes produced by organisms with the following genotypes. Separate the gametes with a comma: AA, bb, AABb, aaBb   What are the genotypic ratios of the offspring for the following cross? Ff x ff

Beyond dominant and recessive alleles  There are some exceptions to Mendel’s principles.  CodominanaceIncomplete Dominance

Multiple Alleles  When more than 2 alleles for the same trait exist within a population.  Each individual organism can only contain 2 alleles (one from mom and one from dad) although, more than 2 alleles may exist within the population.

Polygenic Traits  Traits that are determined by alleles from more than one gene; these traits usually have a range of phenotypes.  Ex. Skin color in humans & height in humans.

Incomplete Dominance  Cases in which there is no dominant allele. A heterozygous phenotype is somewhere in between the two homozygous phenotypes.

Codominance  Both alleles contribute to the phenotype and can be observed in the offspring.

Sex Determination  There are two types of chromosomes.  Autosomes: Of the 46 chromosomes, 44 of them (22 pairs of chromosomes) are called autosomes (non-sex chromosomes).  Sex chromosomes: The last two chromosomes are called the sex chromosomes because they determine the sex of the person. Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).

Sex Linked Traits  Traits that are determined by alleles that are found on the X or Y chromosome.  The Y chromosome is shorter and does not carry all the same alleles are the X chromosome.

Sex Linked Traits  Females are XX and males are XY.  Females can be homozygous or heterozygous for a trait carried on the X chromosome, but males (only having 1 X chromosome) are hemizygous.

Sex Linked Traits  If they inherit a defective gene from the parent, then they will exhibit the trait because they cannot inherit a second gene to mask it.  Conversely, a healthy male cannot be “hiding” a bad recessive allele because they only have one X chromosome.

Example of a sex-linked Punnett square: X B X b (heterozygous female with normal vision) crossed to X B Y (hemizygous male with normal vision) X B X b (heterozygous female with normal vision) crossed to X B Y (hemizygous male with normal vision) XBYXBY XBYXBY XbYXbY X B X B X b Y XBXB XBXB XbXb

Sex Linked Traits

 Scientists can analyze an individual’s chromosomes by taking a picture of cells during mitosis.  It is easiest to view chromosomes during mitosis because they are condensed.  Scientists will cut and paste to arrange the chromosomes in pairs to form a karyotype.  They are arranged from largest (pair #1) to smallest (pair #22). The last pair (#23) is the sex chromosomes. Karyotypes

Karyotype XY Is this karyotype for a male or female?

X Y X X Male or Female? MaleFemale

 Genetic disorders can be identified by looking at an individual’s karyotype.  Ex: Down Syndrome can be confirmed in an individual when 3 chromosome 21s are present in a karyotype. Karyotypes

Pedigree  A pedigree, similar to a family tree, is used to demonstrate how traits are passed from one generation to another.  Genetic counselors use pedigrees to follow how genetic disorders are inherited.  People who are heterozygous for a recessive genetic disorder (they are unaffected) are called carriers.  Sometimes, carriers of traits may be represented as a half-shaded shape or a shape with a dot in the middle.

female male marriage parents children

Add to your notes: Sometimes, but not always, carriers of traits (heterozygotes) may be represented as a half-shaded shape or a shape with a dot in the middle.

Blood Typing  In humans, blood type is determined by the Rh blood group and the ABO blood group.  The Rh blood group determines if your blood is positive or negative.  There are two Rh alleles: the Rh + allele is dominant and the Rh - allele is recessive.  Your blood is positive if you are Rh + /Rh + or Rh + /Rh -.  Your blood is negative if you are Rh - /Rh -

 When determining the ABO blood group there are three alleles: I A, I B, and i.  The I A and I B alleles are codominant. The I A and I B alleles cause expression of carbohydrate chains called antigens on surface of red blood cells. They help your body identify the cells.  The i allele is recessive to the I A and I B alleles. The i allele produces O blood because it does not produce any antigens.

 If the blood recipient has never been exposed to an antigen (A or B) and that antigen enters the body, it will cause an immune reaction. This can cause death. Blood Transfusions

 In emergency rooms, if there is not enough time to figure out the blood type of the patient, which type of blood will the patient receive Type O blood. This is because these blood cells have no A or B antigens. People with Type O blood are called universal donors. Blood Transfusions

 People with AB blood can receive any blood type.  They are considered to be the universal recipient. Blood Transfusions

Genetics and the Environment  Characteristics are determined by both genes and the environment.  External: While genes will influence the height of a plant, the amount of water, sun, and other climate conditions will also affect the height.

Genetics and the Environment  Internal: There are recent findings that proteins involved with DNA can turn genes on or off based on environmental factors.  Certain chemical exposure can turn genes on or off (make the traits show up or not) for generations after exposure, but there are no changes to the DNA (no mutations).  This new understanding of how genes are expressed is called epigenetics.