NOTES GENETICS Biology Mendels Laws of Heredity Gregor

NOTES GENETICS Biology

Mendel’s Laws of Heredity Gregor Mendel – 1843, an Australian monk who developed three principles of inheritance. Conducted many genetic studies on plants.

Vocabulary: Heredity: is the transmission of traits from parents to their offspring Pure: offspring that are pure for a specific trait Strain: all plants that are pure for a specific trait

Pollination is the transfer of pollen from anthers to stigma of a flower Self-pollinated is a reproductive process in which fertilization occurs within a single plant

P 1 Generation is a parent trait F 1 Generation is the first filial (Latin for son or daughter) generation F 2 Generation is the second filial generation

Gene is a segment of DNA on a chromosome that controls a particular hereditary trait. Genes occur in pairs. Each part of the gene “pair” is called an allele

Dominant the allele that masks a hidden trait Recessive the allele that is masked or hidden by a dominant allele

Genotype the genetic make up of an organism Phenotype the way an organism looks

Mendel’s 3 Principles of Genetic Inheritance 1. The principle of Dominance and Recessiveness: One factor in a pair of alleles may mask or hide another factor preventing it from having an effect.

2. The principle of segregation: The two factors for a characteristic segregate or separate during the formation of sperm and eggs

3. The principle of independent assortment: Factors of different characteristics are distributed to the reproductive cells (sperm and eggs) independently

How are Alleles Written? Dominant alleles are shown with capital letters: T Dominant alleles are written first: Tt or TT NOT t. T Recessive alleles are shown with small letters: t

Homozygous = the gene pair of alleles are identical. This can be shown as TT or tt Heterozygous = the gene pair of alleles are opposite. This can be shown as Tt

Probability = is the likelihood that a specific event will occur. P = Number of one kind of event Number of all events Test cross = cross of an individual of unknown genotypes with an individual of known genotype

Punnett Square (Reginald Punnett) Monohybrid cross – cross between individuals that involves only one pair or trait

1. Homozygous x Homozygous Dominant recessive R=red, r=white

2. Homozygous x Heterozygous dominant

3. Heterozygous x Heterozygous

Dihybrid cross-a cross that involves 2 or more alleles

Rr. Ii heterozygous x rrii homozygous recessive R=red r=white I=inflated pod i=constricted pod

NOTES COMPLEX PATTERNS OF INHERITANCE, GENETICS PART 2 Biology

Many inheritance patterns are more complex that those studied by Mendel. Not all traits are simply dominant or recessive.

1. Incomplete Dominance – Appearance of 3 rd phenotype. Occurs when the phenotype of the heterozygous is intermediate between those of the two homozygous Ex: homozygous red flowered snapdragon plant (RR) is crossed with a homozygous white flowered snapdragon plant (R’R’) all of the F 1 offspring will have pink flowers.

1. Incomplete dominance P 1=RR x R’R’ G= P= R’ R’

1. Incomplete dominance P 1=RR’ x RR’ R’ R’ G= P= RR’ R R R’ R’ R’

2. Co dominance-Expression of both alleles Causes the phenotype of both homozygotes to be produced in heterozygous individuals. In co dominance, both alleles are expressed equally.

Ex: In chickens, black-feathered and whitefeathered birds are homozygous for the CB and CW alleles respectively. Two different uppercase letters are used to represent the alleles in co dominance inheritance. The heterozygote produced is neither black nor gray. Instead, all offspring are checkered; some feathers are black others are white.

2. Codominance P 1=GG x WW G= P= In horses, gray horses (GG) are codominant to white horses (WW). The heterozygous horses(GW) is an appaloosa horse (a white horse with gray spots on the rump and loins). Cross a white horse with an appaloosa horse.

In horses, gray horses (GG) are codominant to white horses (WW). The heterozygous horses(GW) is an appaloosa horse (a white horse with gray spots on the rump and loins). Cross a white horse with an appaloosa horse. 2. Codominance P 1=GW x GW G= P=

3. Multiple Phenotypes form multiple alleles. Occurs when traits are controlled by more than two alleles. The number of alleles for any particular trait is not limited to three. A new allele can be formed any time a mutation occurs in a nitrogen base somewhere within a gene Ex: In pigeons, a single gene that controls feather color has three alleles: B (black), Bh (chocolate), and b (white) alleles.

Simple Recessive Heredity, genetics part 3

Most genetic disorders are caused by recessive alleles; a few are common to certain ethnic groups

Examples are: 1. Cystic fibrosis common Treatmentamong Caucasian physical (white) Americans therapy, special (1/20 carry the recessive diets. allele); due to defective proteins in the plasma membrane and results in the formation of thick mucus in the

2. Tay-Sachs Disease common among Amish people and some Jews(E. Europe); disorder of the Central Nervous System and results in the absence of an enzyme that breaks down a lipid produced and stored in tissues; causes the lipid to accumulate in

3. Phenylketuria (PKU) most common in people whose ancestors came from Norway or Sweden results from the absence of an enzyme that converts one amino acid to another thus accumulating in the body and resulting in severe damage to the CNS(babies appear normal at first). Treatment- infants are now given a test and a given a diet low in phenylanine until

Simple Dominant Heredity in Humans Disorders inherited just by Mendel’s rule of dominance. Ex: Tongue rollers, Hitchhikers thumb, Hapsburg lip, Free earlobes, Almond-shaped eyes, Thick lips, etc.

1. Huntington’s Disease is a lethal genetic disorder cause by a rare dominant allele; it is a breakdown of certain areas of the brain; usually occurs between ages 30 -50; no effective treatments genetic test done to allow carriers to decide if they want to risk passing the trait to their children.

Polydactyly More than 5 digits

Pedigree page 342 Graphic representation of genetic info often used by a Geneticists Looks similar to a family tree Made up of set of symbols that identify males and females affected by the trait being studied and family relationships

Autosomal dominant

Autosomal recessive

MEIOSIS, GENES, , AND MISTAKES Genetics part 4

CELLS In the body cells of animals and most plants, chromosomes occur in pairs; one from the male parent and one from the female parent.

Diploid cells – is a cell with each kind of chromosome (2 n) Haploid cells – is a cell with one of each kind of chromosome (1 n) The chromosome number of a species is not related to the complexity of the organism.

CHROMOSOME are paired chromosomes; each of the pair having genes for the same trait, arranged in the same order (however they are not always identical to each because there are different alleles for the same gene)

? When cells divide by Mitosis, the new cells have exactly the same number of chromosomes as the original cell. In Meiosis cell division produces gametes containing half the

REPRODUCTION involves the production and fusion of haploid sex cells or gametes Sperm-are male gametes 23 Eggs- are female gametes 23 Zygote- formed when sperm fertilizing an egg,

SEX DETERMINATION In humans the diploid number of chromosomes is 46, or 23 pairs Autosomes- are 22 pairs of matching homologous chromosomes

Sex chromosomesrd 23 pair, which determines the sex of an individual and differs in males (X, Y) and female(X, X) Any individual with at least one Y is a male; any without a

PHASES OF MEIOSIS: CONSISTS OF 2 SEPARATE DIVISIONS: Meiosis I, which begins with 1 diploid (2 n) cell. Prophase I, Metaphase I, Anaphase I, Telophase I.

Meiosis II, by the end there haploid (n) cells or gametes. Prophase. II, Metaphase II, Anaphase II, Telophase. II

MISTAKES IN MEIOSIS Non-disjunction- is the failure of homologous chromosomes to separate properly during meiosis.

Examples are: Trisomy- condition that occurs when a gamete with an extra chromosome is fertilized by a normal gamete. Ex. Down syndrome (having an extra 21 st chromosome)

Monosomy- condition that occurs when a gamete with a missing chromosome fuses with a normal gamete during fertilization. Ex. Turners syndrome(missing an X) chromosome from the 23 rd pair).

1: 5000 live births; the only viable monosomy in humans - women with Turner's have only 45 chromosomes!!! XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)

Polyploidy- occurs in organisms with more than the usual number of chromosomes sets. It is rare in animals and almost lethal. It occurs frequently in plants; they are usually larger and healthier than normal. Ex. Triploid and Tetraploid.

CHANGES IN CHROMOSOME NUMBERS? Karyotype- is a chart of chromosomes that is valuable in pinpointing unusual chromosome numbers in cells. Metaphase chromosomes are photographed, enlarged, cut apart, and arranged in pairs on a chart according to length and location of the centromere.

Amniocentesis a procedure that allows genetic analysis of fetal cells.

Sex Determination genetics part 6

In humans the diploid number of chromosomes is 46 or 23 pairs. Autosomes- are 22 pairs of matching homologous chromosomes. Sex chromosomes- 23 rd pair ; which determine the sex of an individual and differs in males(XY); and females(XX). Any individual with at least one Y is a male; any without a Y is a female.

Sex-linked Inheritance Sex-linked traits are those controlled by genes located on sex chromosomes

Thomas Hunt Morgan (1910)- discovered traits linked to sex chromosomes by studying Drosophilia- fruit flies. He discovered that the gene for eye color is carried on the X chromosome & that the Y has no allele for eye color. Ex. Crossed P 1 white eyed x red eyed; then crossed 2 F 1 and found a 3: 1 ratio in the F 2.

Most of the human traits carried on the sex chromosomes are also located on the X chromosome. 2 examples are: Color blindness- those affected can not differentiate between red- green colors; it is caused by the inheritance of either of 2 recessive alleles at 2 gene sites on the X chromosome tat affect red green receptors in the cells of eyes.

Hemophilia causes blood not to clot; and affects more males than females treated with blood fusion & injections of Factor VIII- blood clotting enzyme lacking in those affected.

Polygenic Inheritance pattern of a trait controlled by 2 or more genes on either the same or different chromosomes (upper cased and lower cased letters are based but all heterozygotes are intermediate in phenotype.

Many human traits are determined by polygenic inheritance: (example) eye & skin color. Internal and external environmental factors can affect all inheritance patterns. Ex. Temperature, nutrition, light, chemicals and infectious agents.

Multiple alleles in Humans Genetics part 5

(Example): ABO Blood Group A. Traits that are governed by more than two alleles of genes have multiple alleles.

The gene has 3 alleles IA , IB, i, Io 1) Human blood types are determined by the presence or absence of certain molecules (proteins) on the surface of RBC as the determinant of blood types A, B, AB, and O.

Importance? 1. 2. Necessary before a person can receive a blood transfusion RBC of incompatible blood types could clump together, causing death. Also helpful in cases of disputed parentage Ex. Child with type AB blood whose Mother has type A blood could not have a dad with type O.

ABO Blood Group- how it works? Each allele codes for a different protein IA dominant to i IB dominant to i IA IB is dominant to Io or i.

Possible Genotypes A A A O = Type A I I or I I B B B O = Type B I I or I I A B = Type AB I I ii = I O = Type O

Codominance in Humans In codominance, the phenotypes of both homozygotes are produced in the heterozygotes. example: SC SC x SS = SCS (trait).

Sickle Cell Anemia is a major health problem in black Americans whose families originated in Africa & whites whose families originated in countries surrounding the Mediterranean Sea.

Cause- oxygen carrying protein (hemoglobin) differs by one amino acid from normal hemoglobin; which causes the hemoglobin to form crystal-like structures that change the shape of the RBC (sickle or half-moon shape); slowing blood flow and blocking vessels resulting in tissue damage and pain.

Sickle cells have shorter life than normal RBC and leads to anemia.

C S S = Trait (carriers) are more resistant to Malaria. C C S S = sickle- anemia

Sample Punnett with Blood types A woman with Type A blood is claiming that a man with Type AB blood is the father of the child who is also AB. Could this man be the father of the child?