traits phenotype genotype alleles meiosis fertilization Punnet squares

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1 Paper Bag Project 1. Make Paper Bag according to guidelines for traits 2. Fill in phenotype column of table 3. Fill in genotype column of table 4. Fill in alleles on chromosomes 5. Act out meiosis to create gametes 6. Mate animals (fertilization) 7. Use Punnet squares to predict traits of baby 8. Give birth and decorate baby to match inherited genotype

2 Paper Bag Project Genetic Traits inherited characteristics of a living organism (examples: hair color, number of limbs, ability to make insulin) Phenotype the observable version of a trait expressed (examples: brown hair, four limbs, diabetic) Allele the genetic sequence that codes for each distinct possible phenotype for a trait (examples: the alleles for hair color are brown, black, red, and blonde; the alleles for insulin would be all of the different variations of insulin that exist in the human genome, some of which have mutations that make it not work as well or at all) Genotype in humans, the pair of alleles that determine each trait, because humans get one set of genes from mom and one set from dad with the exception of the genes on the X and Y chromosomes (example: if you have black hair, your genotype may include the black allele from one parent and a brown allele from the other parent) Dominant Allele the allele that is expressed as the phenotype of an organism when paired with a competing allele (in the example above, black is dominant over brown) Recessive Allele the allele that is NOT expressed as the phenotype of an organism when paired with a competing allele that is dominant over it (in the example above, brown is recessive to black)

3 Inheritance Gregor Mendel Father of Genetics Did experiments with pea plants in mid-late 1800 s to show basic patterns of inheritance Genetic Traits inherited characteristics of a living organism Allele the genetic sequence that codes for each distinct possible phenotype for a trait Seed Shape (round or wrinkled) Seed Color (yellow or green) Seed Coat color (gray or white) Pod Shape (smooth or constricted) Pod Color (green or yellow) Flower Position (axial or terminal) Plant Height (tall or short) Traits Alleles (genes)

4 Inheritance Gregor Mendel Father of Genetics Phenotype the observable version of a trait expressed Found that when two plants with different alleles are crossed, the offspring look like one of the parents, rather than a blending of both parents Principle of Dominance: Some alleles are dominant and others are recessive Seed Shape (round or wrinkled) round wrinkled Seed Color (yellow or green) yellow green Seed Coat color (gray or white) gray white Pod Shape (smooth or constricted) smooth constricted Pod Color (green or yellow) green yellow Flower Position (axial or terminal) axial terminal Plant Height (tall or short) tall short Traits Alleles (genes) Dominant Alleles Recessive Alleles Phenotypes Homozygous dominant or Heterozygous Homozygous recessive genotypes

5 Inheritance Gregor Mendel Father of Genetics Phenotype - The observable physical characteristic of a trait Genotype - The genetic combination of alleles for a trait Letters are used to represent the alleles (usually correspond to the dominant phenotype Example: P for purple if purple flowers are dominant over white) Upper Case Letters = Dominant Allele Lower Case Letters = Recessive Allele traits alleles genotypes = phenotypes homozygous homozygous dominant recessive heterozygous Seed Shape: round (R) or wrinkled (r) RR = round rr = wrinkled Rr = round Seed Color: yellow (Y) or green (y) YY = yy = Yy = Pod Shape: smooth (S) or constricted (s) SS = ss = Ss = Pod Color: green (G) or yellow (g) GG = gg = Gg = Plant Height tall (T) or short (t) TT = tt = Tt =

6 Practice Questions 1. Which of the following are genotypes and which are phenotypes: Brown hair Heterozygous Bb Webbed Fingers Homozygous recessive Down Syndrome For each statement below, underline any genotypes and put a box around any phenotypes. 2. Robert and his wife are both carriers for Tay Sach s disease. 3. Maria inherited an allele for brown hair from her mother and an allele for black hair from her father; and now she has black hair. 4. My mother has brown hair and I had blonde hair until I was ten. 5. Ron s parents both have brown eyes, but they are both heterozygous for eye color. As a result, Ron has blue eyes. 6. If you have a widow s peak, you are homozygous recessive for this trait.

7 Practice Questions

8 Inheritance Paper Bag Project Which of the following are traits and which are alleles? Gender Eye Shape Eye Color Hair Color Eyelashes (X-linked) Traits male (XY) or female (XX) oval (E) or slit (e) brown (B), blue (b), green (g), yellow (y) black (H), brown (h), Alleles yellow(y) present (L), not present (l) Tail (Y-linked) present (T), not present (t) Ear Shape round (R), pointed (r) Nose Shape triangle (N), circle (n) Most Dominant Most Recessive Genotype EE Ee Bg bg nn hy ly LY Xt Phenotype

9 Meiosis Cell division that results in production of gametes (sex cells) Eggs (females) occurs in ovaries Sperm (males) occurs in testes (singular = testis) Fertilization (enables mixing of genes from two different individuals which helps create genetic variation among individuals)

10 Meiosis Meiosis is similar to mitosis, but results in the formation of gametes: four cells each having only one set of chromosomes (a total of 23 chromosomes) Recall that normal cells are diploid, they have two sets of 23 chromosomes (one set from mom, one set from dad) for a total of 46 chromosomes Gametes are haploid, they have one copy of each chromosome either from mom or dad (the other copy ended up in the sister gamete) These cells have two sets of 3 chromosomes, humans have 2 sets of 23 chromosomes These cells have one set of 3 chromosomes, human gametes have one set of 23 chromosomes

11 Meiosis Homologous chromatids or homologous chromosomes have the same genes but are not identical Sister chromatids are exact copies of one another homologous chromatids homologous chromosomes sister chromatids

12 Review of Mitosis 1. Prophase Chromatin condenses to form chromosomes Mitotic spindle begins to form 2. Metaphase Mitotic spindle attaches to chromatid pairs and pulls them into alignment at center of cell 3. Anaphase Centromeres replicate Mitotic spindle pulls chromatids apart to opposite sides of cell 4. Telophase The cell membrane invaginates and pinches off between the two daughter cells Interphase DNA Replication

13 Meiosis Similar to mitosis, but results in four cells each having only one copy of each chromosome (a total of 23 chromosomes) Recall that normal cells have 23 sets of chromosomes (one from mom, one from dad) for a total of 46 chromosomes 1. DNA replication during interphase 2. DNA condenses to form 92 chromatids 3. Homologous chromatids from mom and dad pair up and crossing over occurs homologous chromatid pairs line up at center of cell 5. Homologous chromatid pairs are separated into two halves of cell (random assortment) 6. Cytokinesis divides cell into two cells (each daughter cell gets 23 pairs, 46 chromatids total, each chromatid pair is either derived from mom or dad)

14 Meiosis Similar to mitosis, but results in four cells each having only one copy of each chromosome (a total of 23 chromosomes) Recall that normal cells have 23 sets of chromosomes (one from mom, one from dad) for a total of 46 chromosomes DNA replication during interphase 2. DNA condenses to form 92 chromatids 3. Homologous chromatids from mom and dad pair up and crossing over occurs homologous chromatid pairs line up at center of cell 5. Homologous chromatid pairs are separated into two halves of cell (random assortment) 6. Cytokinesis divides cell into two cells (each daughter cell gets 23 pairs, 46 chromatids total, each chromatid pair is either derived from mom or dad) chromatid pairs line up at center of each daughter cell (46 chromatids total) 8. Centromeres divide and 46 chromosomes are separated into two halves of cell 9. Cytokinesis divides two cells into four cells (each gamete gets 23 chromosomes)

15 Mitosis vs. Meiosis Mitosis results in two daughter cells that are both genetically identical to the original cell Meiosis results in four gamete cells that are each genetically identical due to crossing over and random assortment 46 chromosomes (one set of 23 from each parent) 92 chromatids 46 chromosomes Diploid cells (identical to original cell) 46 chromosomes 92 chromatids (crossing over occurs between homologous chromosomes) 46 chromosomes (random assortment divides mom and dad chromosomes) 23 chromosomes (haploid cells = gametes)

16 Meiosis Genetic variation comes from Mutations Crossing Over Random Assortment Results in four genetically unique haploid cells (gametes)

17 Predicting Inheritance Gregor Mendel Father of Genetics Found that alleles show up in predictable patterns and that some alleles show up more often than others Punnett Square tool used to predict probability of a particular phenotype Phenotype: White Genotype: pp (homozygous recessive) Phenotype: Purple Genotype: PP (homozygous dominant) Mr. Anderson: Mendelian Genetics WqgZUnJdAY Learn Biology: How to Draw a Punnett Square:

18 Predicting Inheritance Homozygous (Pure-Breeds) - both alleles are the same Pure-Breed Dominant Crosses result in: 100% chance dominant phenotype Pure-Breed Recessive Crosses result in: 100% chance recessive phenotype

19 Predicting Inheritance Heterozygous (Hybrids) - both alleles are different Carriers heterozygous for a recessive trait Both parents have the dominant phenotype but are carriers for the recessive allele Hybrid Crosses result in: 75% chance dominant phenotype 25% chance recessive phenotype

20 Inheritance Gregor Mendel Father of Genetics Found that alleles can be tracked through multiple generations and probabilities determined First Generation: 100% chance dominant phenotype Second Generation: 75% chance dominant phenotype Third Generation: 63% chance dominant phenotype 100% chance 75% chance 75% chance 0% chance

21 Summary of Mendel s Principles Gregor Mendel s work forms the basis of modern genetics: Genes are passed from parent to offspring Some forms of genes (alleles) are dominant while others are recessive Genes randomly segregate (random assortment) when gametes are formed = Law of Segregation The alleles for different genes usually segregate independently of one another = Law of Independent Assortment Linked genes (genes that occur very close to one another on a chromosome) are the exception (for example, freckles and the gene for red hair are close together on the same chromosome)

22 Solving Punnett Squares If a round pea plant (AA) is crossed with a wrinkled pea plant (aa), what percent of the offspring will be: Round? Wrinkled? If two heterozygous round pea plants are crossed, what percent of the offspring will be: Round? Wrinkled? If a heterozygous round pea plant is crossed with a homozygous wrinkled pea plant, what percent of the offspring will be: Round? Wrinkled?

23 Solving Punnett Squares Honors Predicting phenotype gets more complicated when you look at more than one trait at a time Parents Depending on how the chromosomes independently assort determines the genotype, and thus phenotype, of the resulting progeny (offspring) Offspring

24 Solving Punnett Squares Honors If a round, yellow pea plant (AABB) is crossed with a wrinkled, green pea plant (aabb), what percent of the offspring will be: Round and yellow? Round and green? Wrinkled and yellow? Wrinkled and green?

25 Other Types of Inheritance Complete Dominance (what we have been studying): Homozygous dominant genotype dominant phenotype Heterozygous genotype dominant phenotype Homozygous recessive genotype recessive phenotype

26 Other Types of Inheritance Complete Dominance Codominance Homozygous genotype one phenotype Heterozygous genotype both phenotypes R R W RW RW W RW RW R1 R1 R2 R1R2 R1R2 R2 R1R2 R1R2

27 Other Types of Inheritance Complete Dominance Codominance Homozygous genotype one phenotype Heterozygous genotype both phenotypes

28 Other Types of Inheritance Complete Dominance Codominance Incomplete Dominance Homozygous genotype one phenotype Heterozygous genotype new phenotype (usually an intermediary between both) C C C = curly CS = wavy S = straight S CS CS S CS CS

29 Other Types of Inheritance Complete Dominance Codominance Incomplete Dominance Homozygous genotype one phenotype Heterozygous genotype new phenotype (usually an intermediary between both) Pink = new genotype

30 Complete Dominance Codominance Incomplete Dominance Sex-Linked Other Types of Inheritance X-linked: gene lies on X chromosome (males only have one copy of the gene) Y-linked: gene lies on Y chromosome (only males have the gene) Contributes to slightly younger mortality rate in males males are more likely to have a genetic disease Hemophilia

31 Phenotypic Expression Varies Complete Dominance Codominance Incomplete Dominance Sex-Linked X-linked: gene lies on X chromosome (males only have one copy of the gene) Y-linked: gene lies on Y chromosome (only males have the gene) Contributes to slightly younger mortality rate in males males are more likely to have a genetic disease Hemophilia

32 Phenotypic Expression Varies Complete Dominance Codominance Incomplete Dominance Sex-Linked X-inactivation disables one x-chromosome in each cell (females and males each only use one x-chromosome) can lead to unique phenotypes in females

33 Phenotypic Expression Varies Polygenic Traits Controlled by more than one gene Most common type of expression There are three known gene pairs that control eye color. The bey 2 gene on chromosome 15 contains a brown and blue allele, the bey 1 gene on chromosome 15 contains a brown gene, and the gey gene on chromosome 19 contains a green allele and a blue allele. All four alleles must be blue to produce a blue eyed person. There are two layers to the iris, the anterior and the external, or front and back layers. To produce blue eyes, there is no pigment found in the front layer. The brown pigment melanin is deposited in the back layer only. It appears blue because of reflection and diffraction of light. In green eyes, a small amount of melanin is deposited in the front layer of the iris along with the melanin found in the back layer. The additional pigment to the amount needed for blue eyes, causes the eye to appear green. To produce gray eyes, the dark pigment is distributed in the front layer of the iris and over the blue background it appears gray. In brown eyes there is so much pigment in the front layer, that the blue behind is completely covered up. Some people have so much pigment in the front layer that their eyes appear very dark brown or black. Hazel, blue-green, gray-blue eye colors are produced by different amounts of pigmentation and the pattern in which the pigment is placed. Albino eyes are have no pigment at all in either layer of the iris. The iris appears pink or red because of the reflection of blood vessels in the back of the eye. The pattern in which the pigment is deposited is also determined by genetics. The pigment may be deposited in rings, clouds, radial stripes, or spread over the entire iris. (from

34 Sources of Genetic Diversity During Interphase (DNA Replication) Mutations create new alleles During Meiosis Random Assortment (law of segregation) mixes up chromosomes inherited from mother and father Crossing Over mixes up genes that occur on the same chromosome ( Linked genes occur adjacent or very close to one another on the same chromosome and so are almost always inherited together) During Sex Fertilization mixes up genes from two different partners

35 Genetic Disorders Inherited (from mom or dad or both) New Mutations ( De Novo ) (new point mutations or chromosomal) Complete Dominance Incomplete Dominance Codominance Sex-Linked Polygenic Traits meiosis Gametes (egg / sperm) Tay Sachs (one wrong letter) How do mutations during meiosis affect an organism differently than mutations during mitosis?

36 Pedigrees Graphically shows the lineage of a disorder in a particular family Be able to tell if disorder is dominant, recessive, or sex-linked from a pedigree Be able to predict the chance that an indicated couple will have a child with the disorder Autosomal Dominant Pedigree How can we tell? Autosomal Recessive Pedigree How can we tell?

37 Pedigrees Honors Sex-Linked Pedigrees How can we tell? Which is X-linked and which is Y-linked? Is the X-linked dominant or recessive?

38 Practice Problems 1. What are gametes? Where are they made in the body? How are they made? 2. What are the eight phases of meiosis? What occurs during each phase? How does meiosis differ from mitosis? 3. How do crossing over and random assortment mix up genes so that children are genetically different from their parents? 4. At each step of meiosis, is the cell haploid or diploid? 5. If an allele is dominant and two heterozygous individuals mate, what is the chance that their child will have the dominant phenotype? 6. If two alleles are codominant and two heterozygous individuals mate, what is the chance that their child will have both phenotypes? 7. If two individuals mate and their child has a phenotype completely different from both parents, what was the genotype of the parents? 8. If a disorder is X-linked and a normal man mates with a woman who is a carrier, what is the chance that they will have a boy with the disorder? What is the chance that they will have a girl with the disorder?