Study of Genes And Inheritance Austrian Monk studied pea plants to explain How characteristics are passed from one generation to another Genetics Study of Genes And Inheritance Gregor Mendel (Founder of Genetics)

The Work of Gregor Mendel Section Outline The Work of Gregor Mendel Genes (genotype/phenotype) Gregor Mendel’s “Laws” Dominance verses Recessive Monohybrid Cross Dihybrid Cross Co dominance (Blood Groups) Incomplete Dominance (4 O'clock flowers) Gene Linkage (Autosomal linkage) Sex Linkage (genes linked to sex chromosome) Pedigrees (Family Trees) Go to Section:

Analyzing Inheritance Offspring resemble their parents Offspring inherit genes for characteristics from their parents. Recall: Each parent contributes 23 chromosomes (containing many genes) to their offspring.

Genes Have “addresses” or Loci A gene locus – the location of a particular gene on a chromosome Genes come in alternate forms called alleles.

Genotype verses Phenotype Genotype refers to the total number of genes we inherit (all the genes on our chromosomes) Phenotype – represents the genes that are actually used and expressed For example: If you inherit a blue eye allele (b) and a brown eye allele (B) Genotype Bb However, your phenotype (actual eye color) would be brown eyes

Pure genotype When we inherit the same allele for a particular trait, we are HOMOZYGOUS for that trait. For Example: If you inherit a blue eye allele from both mom and dad your genotype will be bb and your phenotype will be blue eyes. If you inherit a brown eye allele from both your genotype = BB brown eyes

Hybrid Genotype When we inherit different alleles for a particular genetic trait, we are HETEROZYGOUS for that trait. For example: If we inherit a blue eye allele from one parent (b) and a brown eye allele from the other parent (B), then your genotype = Bb, and you are heterozygous brown eyed

Mendel’s Laws of Inheritance Gregor Mendel experimented with concluded that Pea plants “Factors” determine traits Some alleles are dominant, and some alleles are recessive Alleles are separated during gamete formation Mendel referred to Genes as “factors” which is called the which is called the Law of Dominance Segregation Dominant alleles Overpower recessive alleles (always expressed) Describe how homologous chromosomes separate during meiosis

The characteristics that Mendel studied Were easy-to-observe, contrasting traits Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Section 11-1 Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall P = Parent (pure) F1 = First generation offspring Go to Section:

Principles of Dominance Unlike humans, height in pea plants is determined only by two genes T= tall and short (t) Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short When Mendel crossed a homozygous Tall plant (TT) with a homozygous Short plant (tt), all offspring were heterozygous tall (Tt) When the heterozygous plants Were crossed , there were 3 Tall and one short plant What are their Genotypes?? Go to Section:

Probability and Punnett Squares Section Outline Probability and Punnett Squares A. Genetics and Probability B. Punnett Squares C. Probability and Segregation D. Probabilities Predict Averages Go to Section:

Punnett Square Monohybrid Cross The Punnett square show the possible Alleles that enter gametes And, how the alleles then recombine In the offspring Heterozygous tall parent Heterozygous Tall parent

Dihybrid Cross: Predicting offspring genotypes Figure 11-10 Independent Assortment in Peas Dihybrid Cross: Predicting offspring genotypes And phenotypes of two different genetic traits Section 11-3 R= dominant Smooth seed coat r= recessive rough seed coat Y= dominant yellow color y= recessive green color Represent possible gene combinations in gametes Go to Section:

Homozygous white parent Incomplete Dominance in Four O’Clock Flowers Incomplete dominance does not follow Mendel’s law of Dominance because Here when homozygous parent plants Produce offspring, the color produced Is different from both parents. “Blending of colors” Homozygous Red parent Homozygous white parent Go to Section:

Co dominance: both alleles have equal dominance In some cases both alleles of a genetic trait are of equal strength Both are expressed ABO blood groups and fur color in some animals are good examples of co dominance Red Blood Cells carry two antigens, A and B antigens are molecules the immune system can recognize

A and B Alleles are of Equal Strength (Codominant) Group O individuals Have NEITHER A or B Alleles; missing a gene at the Loci where A / B would be (denoted as ii). Blood Transfusions Blood Group Phenotype Possible Genotype Antigen on RBC To From Complete ABO punnett square

Alleles for Normal and Sickle Hemoglobin also Co dominant N = Allele for normal hemoglobin S = Allele for Sickle hemoglobin NN = Homozygous for Normal hemoglobin NS = Heterozygous; both Normal and Sickle hemoglobin – Resistance to Malaria SS = Homozygous for Sickle (Disease/ Fatal)

Sickled cells Sickled cells do not move through the capillaries and block blood flow, depriving cells of oxygen and nutrients. Painful

Human Karyotype 23 Pairs of Chromosomes A Karyotype is a picture of a cell’s Chromosomes grouped in homologous pairs

A Family Tree Section 14-1 To understand how traits are passed on from generation to generation, a pedigree, or a diagram that shows the relationships within a family, is used. a circle represents a female a square represents a male. The horizontal line that connects a circle and a square represents a marriage. Vertical lines show Children of that couple A filled-in circle or square shows that the individual has the trait being studied. Go to Section:

Human Pedigree Other pedigree typical symbols to know

Human Chromosomes 22 pairs of Autosomes; 1 pair of Sex chromosomes Humans have 23 pairs of chromosomes 22 exist as homologous pairs called AUTOSOMES Genes located on autosomes called Autosomal 1 pair exist as Sex chromosomes Genes located on sex chromosomes are called sex-linked

Hypercholesterolemia Disorders located on Autosomal Genes: Concept Map Section 14-1 Autosomal Disorders caused by Dominant Alleles Recessive alleles Co dominant alleles include include include Albinism Galactosemia Tay-Sachs disease Huntington’s disease Sickle cell disease Cystic fibrosis Phenylketonuria Achondroplasia Hypercholesterolemia Go to Section:

Cystic fibrosis – autosomal recessive disorder- “affected” Individual receives defective allele from both carrier parents Section 14-1 Chromosome # 7 CFTR gene The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

Autosomal Dominant Genetic Disorders Only one dominant gene is needed to express the trait (disorder) Achondroplasia -dwarfism Huntington’s Disease- Mental deterioration and uncontrollable movements; middle age Hypercholesterolemia – excess cholesterol and heart disease

Sex-linked = Genes found on the X and Y chromosomes If a gene is found on the X or the Y chromosome, it is said to be a sex-linked trait. Because the X chromosome is much larger than the y Sex-linked genes are generally found on the X chromosome More than 100 sex-linked genetic disorders have Been linked to the X chromosome If the

Sex Linked Genes Males have just one X chromosome, thus all X-linked alleles are expressed in males, even if They are recessive

Examples of Sex-linked Traits Stats in US: Red-green colorblindness (1out 10 males) Male Pattern Baldness – Premature hair loss Hemophilia- missing blood clotting factor(s) (1 out of 10,0000 males) Duchenne Muscular Dystrophy – progressive weakening and loss of skeletal muscle (1 out of 3000 males)

Colorblind – sex-linked traits always expressed Figure 14-13 Colorblindness Colorblind – sex-linked traits always expressed In males (they have no other gene to mask it) Section 14-2 Father (normal vision) Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind) Females need to have two copies of the defective allele to be Colorblind; so colorblind females are more rare Go to Section:

Red-Green Colorblindness What do you see?

Hemophilia sex-linked recessive

Homologous chromosomes fail to separate Other Genetic Disorders: Nondisjunction Section 14-2 Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II Nondisjunction of Homologous chromosomes during meiosis of gametogenesis Go to Section:

Nondisjunction RECALL: If nondisjunction occurs, abnormal numbers of chromosomes may enter gametes Downs Syndrome – autosomal nondisjunction of chromosome #21 - individuals having 47 chromosomes instead of 46 Turner’s and Kleinefelter’s Syndrome – nondisjunction of sex chromosomes

Phenotype determined by more than one pair of alleles Height in pea plants is controlled by one pair of alleles. The allele for a tall plant is the dominant allele (T) The allele for a short plant is the recessive one (t). What about people? Are the factors that determine height more complicated in humans?

Many Human phenotypes are Polygenic Often genetic traits in humans are determined by more than one pair of alleles Called Polygenic traits Height, pigmentation, intelligence are three examples of such traits Phenotypes are expressed in “ranges”, rather than “either/ Or”

Generic Bell Curve for Polygenic Trait Section 16-1 AKA: “Normal” Curve Frequency of Phenotype Phenotype (height)