Patterns of Heredity and Human Genetics When Heredity Follows Different Rules

Incomplete Dominance The phenotype of the heterozygous is intermediate between those of the two homozygous individuals. Neither allele is completely dominant.

Incomplete dominance

Incomplete Dominance In humans, curly hair (HH) is incompletely dominant to straight hair (H’H’).  The heterozygous individual has wavy hair (HH’).  Cross a person with curly hair with a person who has wavy hair. __________    X   _________            

Codominance The phenotypes of both homozygous individuals are visible in heterozygous individuals. Both alleles are expressed equally. EX: Red horse (RR) crossed with a white horse (WW) results in roan (RW)

In chickens, black feather color (BB) is codominant to white feather color (WW).  Both feather colors show up in a checkered pattern in the heterozygous individual (BW). Cross a checkered chicken with a checkered chicken.  __________      X      ________  

Codominance

Codominance in Humans Sickle cell carriers Heterozygous individuals have normal and sickle shaped cells. Carry sickle cell trait and can pass on to offspring.

Multiple Allelic Traits controlled by more than two alleles EX: blood type (A-B-O)

RESULTING PHENOTYPES Type A Type A GENOTYPES IAIA IAi RESULTING PHENOTYPES Type A Type A IBIB IBi Type B Type B IAIB Type AB ii Type O

1. A woman with Type O blood and a man who is Type AB have are expecting a child.  What are the possible blood types of the kid? So our cross is: ii x IAIB.  The proper p-square would look like this:   on to #2                                    As you can see, our results are as follows: 50% of kids will be heterozygous with blood Type A 50% will be heterozygous with blood Type B

2. What are the possible blood types of a child who's parents are both heterozygous for "B" blood type?                                       There is a 75% (3 of 4) chance that the child will be Type B, and a 25% (1 of 4) chance that the child will inherit Type O (ii).  

Jill is blood Type O.  She has two older brothers (who tease her like crazy) with blood types A & B.  What are the genotypes of her parents with respect to this trait? With some careful thinking we don't even need to do the p-square thing.  Jill is Type O, meaning her genotype is "ii".  This means that her parents each have at least one "i" in their genotype (since she inherited one from each parent). Since one brother is Type B, one of the parents must have the IB allele, making that parent IBi.  And since the other brother is Type A, the other parent must have the IA allele & have a genotype of IAi.  There you have it.  Jill's parents are IAi & IB , and her brothers shouldn't be so mean. on to #6

Multiple Alleles in Humans Blood type Importance: Mixing incompatible blood causes clumping resulting in death. Determining parentage

Sex-Linked Inheritance Traits controlled by genes located on sex chromosomes are sex-linked traits. The alleles for sex-linked traits are written as superscripts (XRY, XRXr) Traits carried on Y chromosomes are only passed from a father to his son. X-linked traits can be passed to a son or daughter.

X-linked traits EXAMPLE: Drosophilia In males fruit flies, eye color is carried on the X chromosome. Red eyes (R) is dominant to white (r). If a male inherits a single recessive allele (r ) he will have white eyes. If a female inherits a single recessive allele (r ) she will have red eyes. Male XrY white eyes Female XRXr –red Female XRXR - red Male XRY red eyes Female XrXr -white

Sex-linked traits in Humans Red/green color blindness X-linked disorder. Can’t differentiate b/w red and green. Trouble identify red and green traffic lights. Hemophilia X-linked disorder Inability to clot. Males inherit from carrier mothers. Females need two recessive alleles. Treated with transfusions, injecting blood clotting enzyme.

Polygenic Inheritance The inheritance of a trait that is controlled by two or more genes that may or may not be on the same gene. All heterozygous individuals have an intermediate phenotype.

Polygenic Inheritance in Humans Skin color When a light and dark-skinned person mate, children are intermediate color. Eye color Height stature, hair color, and body shape

Environmental Influences The genetic makeup (GENOTYPE) determines an organisms potential to develop and function. Many factors can influence how a gene is expressed. External influences Internal Influences

Environmental Influences External Temperature Nutrition Light Chemicals Infectious agents Internal Hormones Structural differences Age

Human gender differences in facial hair                                     Human gender differences in facial hair

Pictures and examples are taken from various websites.