11.3 Other Patterns of Inheritance

• Genes can act in various ways

1. Dominant vs. Recessive – one allele completely covers another allele.

2. Incomplete Dominance1. 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

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 genesEx: 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? - YES1. Phenotype is only partly determined by genotype2. 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 5,00

0

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 TraitsUnshaded 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