11.3 Other Patterns of Inheritance Genes can act in various ways Dominant vs. Recessive – one allele completely covers another allele. Incomplete Dominance Definition : one allele is not completely dominant over another Ex: flowers – white x red flowers = pink flowers

Beyond Dominant and Recessive 3. Codominance Definition: both alleles contribute to the phenotype of the organism Ex: chicken feather – black and white alleles = black and white feathers Colors don’t blend like incomplete dominance

blood-type donors and recipients Multiple Alleles Definition: more than two alleles (more than 2 alleles exist in a population not an individual) Ex: rabbit’s coat color Ex: human’s blood type blood-type donors and recipients

Polygenic Traits Definition: traits that are controlled by 2 or more genes Ex: fruit fly red eyes - 3 genes involved in making pigment Diff. combo of genes produce different eye colors Ex: Human skin color – more than 4 different genes

Genetics and the Environment Does the environment have a role in how genes determine traits? - YES 1. Phenotype is only partly determined by genotype 2. Environmental conditions affect gene expression and influence genetic traits Ex. Butterfly color is temperature dependent Hydrangea flowers blue or pink depending on soil pH.

11.5 Gene Linkage Thomas Hunt Morgan noticed in fruit flies that genes for certain traits seemed to be inherited together The reason: these genes are on the same chromosome (linked) It is the chromosomes that assort independently, not the genes.

14.1 Human Chromosomes Karyotype –photograph of chromosomes taken during mitosis, then arranged in decreasing size Where did these chromosomes come from? 23 from mom 23 from dad 5,000

14.1 Human Chromosomes Chromosome pairs 1 - 22 = autosomes Chromosome pair 23 = sex chromosomes (XX or XY) Females are written as 46XX; males are written as 46XY.

Sex Chromosomes Males and females born in 50:50 ratio X chromosome carries about 1,200 genes. Y carries only about 140.

Sex-Linked Genes Sex-linked Genes – genes located on the X chromosome More than 100 sex-linked genetic disorders have been linked to the X chromosome Y chromosome is much smaller and contains only a few genes Males have only 1 X chromosome All alleles on the X chromosome are expressed in males, even if they are recessive

X Chromosome Disorder Colorblindness 3 genes associated with colorblindness are found on the X chromosome 1/10 males are colorblind 1/100 females are colorblind Why is colorblindness more common in males? Males need only one allele to be colorblind. Females need two alleles to be colorblind.

Chromosomal Disorders Nondisjunction – homologous chromosomes fail to separate during meiosis Abnormal number of chromosomes find their way into gametes

Chromosomal Disorder Trisomy – having three copies of a chromosome Trisomy in chromosome 21 – Down Syndrome 1/800 births, causes mild to severe mental retardation

Chromosomal Disorder Turner Syndrome Females are born with only one X chromosome Females are sterile because sex organs do not develop at puberty. Klinefelter’s Syndrome Males born with an extra X chromosome Male is sterile

Human Traits How does one trace an inherited trait through generations? How does one predict who in the next generation will show that trait? The Pedigree Chart – show the relationships within a family

Human Traits Circle represent female Square represents male Horizontal line represents marriage Vertical line represents children

Human Traits Unshaded circle or square indicates that the person does not express the trait Half shaded circle or square indicates the person is a carrier for the trait. Completely shaded circle or square indicates that the person expresses the trait. How many generations are shown? 3