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

Figure: 20-01 Title: Important terms in genetics. Caption:

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

Table: 20-T01 Title: Common terms in genetics. Caption:

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

Figure: 20-03 Title: Gamete formation and freckles. Caption: Gamete formation by a female who is homozygous dominant for freckles (FF) and a male who is homozygous recessive for no freckles (ff) and the heterozygous (Ff) individual resulting from the union of these gametes.

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

Figure: 20-07 Title: The inheritance of cystic fibrosis is shown in this pedigree. Caption: A pedigree is constructed so that each generation occupies a different horizontal line, numbered from top to bottom with the most ancestral at the top. Males are indicated as squares, and females as circles. A horizontal line connects the partners in a marriage. An affected individual is indicated with a solid black symbol.

The Punnett Square Provides a simple way to view patters of inheritance for a single pair of alleles

The Monohybrid cross A A A A A A A A A a a a Mating of two individuals with contrasting forms of one trait one of these traits will not show in the first generation Possible Male gametes A A A A A Possible Female gametes A A a a a

The testcross Homozygous recessive a a A A a A a a a ? ? ? The old way to determine if someone is a heterozygote A A a A a a a Heterozygote ? ? ?

Figure: 20-05b Title: Heterozygous parents and freckles. Caption: (b) A Punnett square showing the probable outcome of a mating between two people who are heterozygous for the freckle trait (Ff).

Figure: 20-05a Title: Heterozygous parents and freckles. Caption: (a) Gamete formation by a person who is heterozygous for the freckle trait (Ff).

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 Figure: 20-10a Title: Human height varies in a continuous manner. Caption: (a) One reason is that height is determined by more than one gene (polygenic inheritance). This figure shows the distribution of alleles for tallness in children of two parents of medium height, assuming that three genes are involved in the determination of height. The top line shows the parental genotypes, and the second line indicates the possible genotypes of the offspring. Alleles for tallness are indicated with dark squares.

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

Figure: 20-11 Title: X-linked genes. Caption: Genes that are X linked have a different pattern of inheritance than do genes on autosomes, as seen in this cross between a carrier mother and a father who is normal for the trait. The recessive allele is indicated in red.

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 Figure: 20-14 Title: Amniocentesis and chorionic villi sampling. Caption: Amniocentesis and chorionic villi sampling (CVS) are procedures available for prenatal genetic testing.

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 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.

Generation A B C T

What does the filled figure mean 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.