Cell division

When one cell divides into 2 identical clones.

How then are we different?

Types of cell division

• Mitosis one mother cell into 2 daughter cells– In growth, replacement, are identical to one another

• Meiosis one mother cell into 4 daughter cells– Production of sperm (4) and egg (1+ 3 polar bodies)

– Will result in different individuals with differences.

Observable Patterns of Inheritance

What you are is a result of genetic expression

How Simple Traits Are Passed to the Next Generation

Genetic Terms:

• Genes: carry encoded information about specific traits

• Locus: the position of a gene on a chromosome

• Homologous chromosome: two chromosomes that contain the same genes in diploid cells

More genetic terms

• Alleles: various molecular forms of a gene for some trait. (same yet different)

• Homozygous: both alleles are the same

• Heterozygous: the alleles differ

• Dominant: (A) allele that shows the phenotype

• Recessive: (a) allele that is masked

More gene words

• Homozygous dominant: AA

• Heterozygous: Aa

• Homozygous recessive: aa

• Genotype: is the sum of all genes

• Phenotype: genes that are expressed

Mendels three basic rules

• Inheritance is controlled by discrete units (genes)• Each diploid organism has two units for each trait

(one from mom and one from dad)• In parents different units assort independently into

gametes (law of segregtion)– if dad is heterozygous you have 50% probability of

getting one or the other allele

The Pedigree

• Circles are females

• Boxes are males

• Empty boxes are normal (average)

• Filled boxes have the trait of interest

• A horizontal line indicates a mating or a brother sister relationship

The Punnett Square

• Provides a simple way to view patters of inheritance for a single pair of alleles

The Monohybrid cross

• Mating of two individuals with contrasting forms of one trait

• one of these traits will not show in the first generation

Possible Male gametes

Pos

sibl

e F

emal

e ga

met

es

The testcross

• The old way to determine if someone is a heterozygote

Homozygous recessive

Heterozygote

Independent assortment

• When 2 different traits assort they do so without any affect on one another

• 16 possible allele combinations exist 9:3:3:1 ratio in a dihybrid cross

Variations on Mendelian Genetics

• Codominance: both alleles are expressed in heterozygotes like blood type

• Multiple effects: one gene may have many phenotypes, cystic fibrosis, osteogenesis imperfecta

• Penetrance: phenotype depends on other genes• Polygenic traits: result from 2 or more genes skin

color, eye color, behavior, IQ

Height controlled by

3 genes

Chromosome variations

The chromosomal basis of inheritance

• Gene: unit of a heritable trait

• genes are located on chromosomes (locus)

• genes of different chromosomes are inherited independently

• genes on the same chromosome travel together

Autosomes and sex chromosomes

• Autosomes consistently 44 chromosomes of the same quantity and type

• Sex chromosomes: determine gender

• females XX• males XY• all have 22 other

chromosomes that are alike

Karyotype:

• Is a visualization of the chromosomes where the chromosomes are lined up by size.

• Is used to determine if an abnormality occurred.

The sex chromosomes

• One of the few genes on the Y chromosome is the sry “make determining gene”

• Only one copy of the X chromosome is required by the cells, the extra copy in females is stored in a condensed form

• females are genetic mosaics because cell may express different X chromosomes

Sex determination

• Gender is determined by the father’s sperm

• X bearing sperm fertilizes an egg, a female results

• Y bearing sperm fertilizes an egg, a male results– Y has the male determining gene

X chromosome inactivation in females

• Most or all of one X chromosome is switched off in early development of the female

• the female body is a mosaic of cells in which one or the other X chromosome is inactivated

Chromosome Linkage

• What chromosome a gene is located on

• Chromosome #7 has CF

• X is hemophilia• Y is TV clicker gene

Mutations

• Are a change in the sequence of a gene (DNA is altered)

• can be– Neutral - no change in the information– beneficial - makes and organism better– harmful - can kill the organism

Genetic testing before birth

Human Genetic analysis

• The pedigree, be able to write one out• abnormal: genetic condition that is a

deviation from the usual or average and is not life threatening

• genetic disorder: conditions that cause medical problems

• genetic counseling: determining the probabilities and risks of having children

Patterns Autosomal Inheritance

Most of your genes have nothing to do with sex

Autosomal Recessive

• Both parents must be a carrier

• only homozygous children are affected

• 3:1 ratio of normal to affected children

• Phenylketonuria: mental retardation

• Cystic fibrosis: build up of mucus in lungs

• Tay-Sachs disease: lipid buildup in brain

Autosomal dominant Inheritance

• Allele is expressed in each generation

• Dwarfism: 4 feet in height

• Progeria: rapid aging dies at age 10

• Huntington’s disease: degeneration of nervous system after age 40.

Patterns of X linked inheritance

• X linked recessive occurs more in males than females– Hemophilia A, Duchenne muscular dystrophy,

Color blindness

• Testicular feminizing syndrome– mutation in the X chromosome on male results

in defective receptors for the male sex hormones

– embryo develops into an apparent female

Chromosomes can be abnormal

• Deletion

• Duplication

• Insertion

• Translocation

• A woman with cystic fibrosis comes into your Genetic counseling clinic. She is going to marry her first cousin. What she wants to know that if they have children what is the probability that they will have a child with cystic fibrosis. Use your knowledge of genetics to give her an idea of the different probabilities.

• What does the filled figure mean? What figure represents mails, which females. In what generation are the woman’s grandparents. Now that you know this information , what is the woman’s possibility of having a child with Cystic fibrosis? Using this example, explain why it is not a good idea for closely related individuals to have children together?

• The widow’s peak is a feature where the hairline dips down the forehead in a v like pattern. Look at 3 generations of your family Draw a pedigree and give the names of all the members of your family. Indicate weather they have a widows pear or if they have a straight hairline. Indicate weather you think the widows peak is dominant or recessive give your reasoning. If your family is all straight or widows peak describe what type of results you would need in order to determine if a trait is dominant or recessive.