Complex Patterns of Heredity Chapter 12

Sometimes Heredity Follows Different Rules Dominant allele patterns Incomplete Dominance: Appearance of a third phenotype Codominance: Expression of both alleles Multiple phenotypes from multiple alleles Sex determination Sex-linked inheritance Polygenic Inheritance Environmental Effects

Use the textbook to find out information about the following genetic patterns Dominant Genetic disorders (pg 298) Incomplete Dominance (pg 302) Codominance (pg 302) Multiple Alleles (pg 304) Use two columns – fold paper in half lengthwise right side – notes left side - examples

Incomplete Dominance With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits.  RED Flower x WHITE Flower ---> PINK Flower The allele for red is not completely dominant over the allele for white

Codominance The genetic gist to codominance is pretty much the same as incomplete dominance.  A hybrid organism shows a third phenotype --- not the usual "dominant" one & not the "recessive" one ... but a third, different phenotype.  In COdominance, there are basically two “dominant” traits which appear together in the phenotype of hybrid organisms.

Codominance Cont R = allele for red flowers W = allele for white flowers red x white ---> red and white spotted RR x WW ---> 100% RW

Codominance Example red x white ---> red & white spotted With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.

Examples of Codominance A very common phenotype used in questions about codominance is roan fur in cattle.  Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together).  Another example of codominance is human blood type AB, in which two types of protein ("A" & "B") appear together on the surface of blood cells.

Multiple Alleles When a trait is controlled by Multiple Alleles Controlled by 3 or more alleles of the same gene that code for a single trait Ex. Blood types A & B are codominant – both are expressed when together; and both are dominant to O. A person can only have type O blood if they receive the “O” allele from both parents.

Multiple Phenotypes from Multiple Alleles Although each trait that we have studied so far only has two alleles, it is common for more that two alleles to control a trait in a population For instance, Pigeons – three colors possible (red, blue, chocolate) However, each pigeon can have only two of these alleles

Blood Types Codominance and Multiple Alleles Human blood is separated into different classifications because of the varying proteins on the surface of blood cells. These proteins are there to identify whether or not the blood in the individual's body is it's own and not something the immunity system should destroy.

ABO Blood type and genetics Codominance and Multiple Alleles The proteins (antigens) that are present on the surface of the cells are controlled by three alleles A, B, o The individual's blood type is determined by which combination of alleles he/she has. Type A – AA or Ao Type B – BB or Bo Type AB – AB Type O - oo Blood types A and B are codominant alleles. AB – both antigens present O is the recessive allele No antigens present

Human Blood Types

Human Blood Types

Blood type practice Use a Punnett Square! A woman has type A blood. Her father has type O blood. The woman marries a man with type O blood. What is the chance that they will have a child with type A blood? What is the chance that the couple from question 1 will have a child with type AB blood? *Show me your answers when you are finished. Keep these in your notes!

Simple Dominant Heredity Traits controlled by a Single Allele More than 200 human traits are determined by a single dominant allele Ex. Huntington’s Disease More than 250 other traits are determined by homozygous recessive alleles Both parents must have this allele in order for their offspring to have the disease. Ex. Cystic Fibrosis & Sickle cell anemia

Comparison Inheritance Patterns Recessive Allele Inheritance Patterns Unaffected parents can have affected offspring The phenotype can skip a generation Carriers - Individuals with no signs of the trait but carry the allele (Tt) Dominant Allele Inheritance Patterns Affected offspring must have at least one affected parent, there are no carriers for the trait. The phenotype appears in every generation without skipping Two unaffected parents have no affected offspring

Polygenic traits A trait that is controlled by a groups of genes. Polygenic traits are controlled by two or more genes at different locations on different chromosomes. Examples are height, skin color and weight. Polygenes allow a wide range of physical traits. For instance, height is regulated by several genes so that there will be a wide range of heights in a population.

Eye Color Activity http://www.athro.com/evo/gen/genefr2.html

Sex determination Remember that in humans the diploid number of chromosomes is 46, or 23 pairs. There are 22 matching pairs of homologous chromosomes called autosomes. The 23rd pair differs in males and females, they determine the sex of an individual (sex chromosomes) X females (XX) Y males (XY) Complete a punnett square to determine the expected ratio of males to females produced given their possible gamete contribution

Sex-linked inheritance Traits controlled by genes located on sex chromosomes are called sex-linked traits Thomas Hunt Morgan discovered this pattern of inheritance

Patterns of Inheritance Sex-Linked Traits Are found only on the X chromosome Ex. Colorblindness (recessive) Ex. Hemophilia (recessive)

Pedigrees Pedigree – a family record that shows how a trait is inherited over several generations. Scientists often study disease causing genes because they can easily be traced

Patterns of Inheritance Sex-Influenced Traits Influenced by male or female sex hormones Ex. Patterned Baldness Homozygous baldness-both will lose hair Heterozygous-men will lose hair but women will not

Pedigrees Cont. Square = Male Circle = Female No shading = normal Shaded = displays trait Half/Half = Carrier Carriers – Heterozygous; they do not express the recessive allele, but they pass it along to their offspring.

A Pedigree of Hemophilia in the Royal Families of Europe

Human Karyotype

Things to look for in pedigrees Autosomal recessive disorders (rr) males and females have the disorder equally and can be carriers can skip generations Autosomal dominant disorders (Hh) males and females could have the disorder equally, no carriers will appear in every generation Sex-linked recessive disorders (X CXc XCY) males are more likely to have disorder only female carriers

Environmental Effects Genes are inherited from parents, but sometimes their expression is modified by environmental factors. An example is the snowshoe hare we discussed earlier in the year-these hares have dark fur in the summer and white fur in the winter.

Epigenetics Watch the video and record a few notes on what epigenetics is.

Snowshoe Hare What causes the change in coat color in these rabbits?

Nondisjunction Nondisjunction is the failure of homologous chromosome pairs to separate properly during meiosis. The result of this error is a cell with an abnormal (too few or too many) number of chromosomes.

Nondisjunction

Patterns of Inheritance Disorders due to Nondisjunction Monosomy (45 Chromosomes) Trisomy (47 Chromosomes) Trisomy-21 (Down’s Syndrome) Klinefelter’s (XXY)-male w/ some female traits Turner’s (XO)-female appearance Single Y chromosome do not survive

Detecting Human Genetic Disorders Genetic Screening – examination of genetic makeup Karyotype: a picture of chromosomes grouped in pairs and arranged in sequence. Screening of Blood: look for certain proteins Genetic Counseling-medical guidance informing of problems that could affect their offspring.

Human Karyotype

Detecting Human Genetic Disorders Amniocentesis: removal of small amount of amnionic fluid surrounding the fetus Chorionic Villi Sampling: tissue that grows between the mother’s uterus and the placenta (between the 8th and 10th week) Screening Immediately after Birth: Ex PKU (Phenylketonuria)-body cannot metabolize the amino acid phenylalanine Special diet lacking phenylalanine

Karyotyping http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping2.html