Introduction to Genetics Meiosis Vocabulary Terms Homologous each
Introduction to Genetics Meiosis
Vocabulary Terms • Homologous: each chromosome from the male parent has a corresponding chromosome from the female parent (a match!) ▫ Not identical, but similar in shape and the genes they code for! • Diploid: cell with full set of homologous chromosomes ▫ Represented by the symbol 2 N ▫ Human diploid number is 46 • Haploid: cell with a half set of homologous chromosomes ▫ Represented by the symbol N ▫ Human haploid number is 23
Diploid
Meiosis ▫ Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell �Meiosis involves two divisions: �Meiosis I + Meiosis II �By the end of meiosis II, the diploid cell has become 4 haploid cells known as gametes �Gametes = sex cells (sperm/egg)
Phases of Meiosis I ▫ Meiosis I Interphase I Meiosis I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis
Prophase I (Meiosis I) • Just like the prophase we know and love, with a few changes ▫ Nuclear membrane dissolves, spindle forms • Chromosomes form tetrads ▫ Tetrad – formed when a chromosome pairs with its homologous chromosome �There are 4 chromatids in a tetrad.
�When homologous chromosomes form tetrads in meiosis I, they swap portions of their chromatids in a process called crossing-over. �Crossing-over produces new combinations of alleles.
Metaphase I • Spindle fibers attach to the chromosomes, which are lined up in the middle of the cell • Important: There is not a set order for how these chromosomes line up, they just do!
Anaphase I • The fibers pull the homologous chromosomes toward opposite ends of the cell.
• Nuclear membranes reforms • The cell separates into two cells End result of Meiosis I: two cells that have chromosomes and alleles different from each other
�The two cells produced by meiosis I now enter a second phase of division. �Important: Unlike meiosis I, neither cell goes through chromosome replication.
Phases of Meiosis II • Meiosis II Telophase I and Cytokinesis I Meiosis II Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis
Prophase II • Nuclear membrane dissolves • Spindle forms Just like old times!
• The chromosomes line up in the center of cell.
Anaphase II • The sister chromatids separate and move toward opposite ends of the cell.
� Nuclear membrane reforms, cell begins to separate into new cells End Result of Meiosis II results in four haploid (N) daughter cells.
Gamete Formation ▫ Meiosis produces 4 genetically different haploid cells ▫ In male animals, meiosis results in four equal-sized gametes called sperm.
• In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.
Comparing Mitosis vs. Meiosis Mitosis Meiosis �Cells produced by mitosis have the same number of chromosomes as the original cell �Cells produced by meiosis have half the number of chromosomes as the parent cell �Mitosis allows an organism to grow and replace cells �Some organisms reproduce asexually by mitosis. �These cells are genetically different �Meiosis is how sexually reproducing organisms produce gametes (sperm �Diploid! �Haploid and egg)
Mitosis results in the production of two genetically identical diploid cells. Meiosis produces four genetically different haploid cells.
1. 2. 3. 4. 5. 6. 7. 8. What does the symbol 2 N represent? What is our haploid number? How many cells does meiosis result in? Are the cells produced through the process of meiosis haploid or diploid cells? What are the female haploid cells created during meiosis? What are the male haploid cells created during meiosis? During what specific phase of meiosis do tetrads form? What process during meiosis creates genetic variance across generations?
Genetics Day 2
Gregor Mendel • Austrian monk who carried out work with various plants that contributed to the understanding of genetics ▫ Most notable of the plants was his work with pea plants �Worked in the monastery's almost 5 acres of experimental garden ▫ Now referred to as the “father of modern genetics”
Pea Plant Traits • Mendel studied seven different pea plant traits ▫ Trait: specific characteristic (seed color, height, etc. ) that varies from one individual to another • Mendel crossed seven contrasting traits and studied the results • Mendel cross-pollinated the pea plants by removing the male reproductive parts and dusting pollen from another plant onto the flower ▫ This produced seeds with two different parents
• While studying the appearance of the varying traits, Mendel coined the terms “recessive” and “dominant” in reference to certain traits. ▫ For example, green peas are recessive and yellow peas are dominant. • He published his work in 1866, demonstrating the actions of invisible “factors”— now called genes —in providing for visible traits in predictable ways.
Mendel’s 3 Laws • Law of Dominance – some alleles are dominant and others are recessive ▫ ▫ Alleles: different forms of a gene A recessive allele will only be evident when a dominant allele is not present • Law of Independent Assortment – Alleles on different chromosomes are distributed randomly to individual gametes during meiosis ▫ Homologous chromosomes lining up for metaphase varies from cell to cell because there’s NO SET WAY they have to arrange • Law of Segregation – allele pairs separate or segregate during gamete formation, and randomly unite at fertilization ▫ Gametes have one set of alleles
Generations… Parent F 1 F 2 • Parent (P) generation = the first 2 individuals that mate in a genetic cross • F 1 generation = first offspring from a cross between the (P) generation • F 2 generation = offspring from crosses among individuals of the F 1 generation
Terms • Genotype: A set of alleles that determines the expression of a particular characteristic or trait (MMRr) • Phenotype: physical characteristics (tall, freckles, green, brown hair, etc. ) • Homozygous dominant: MM (two capital); dominant trait expressed • Heterozygous dominant: Mm (one capital, one lowercase); dominant trait expressed • Homozygous recessive: mm (two lowercase); recessive trait expressed
• Eye color: ▫ Brown = dominant BB, Bb ▫ Blue, green, hazel = recessive bb • Facial Features: ▫ ▫ Freckles = dominant FF, Ff No freckles = recessive ff Dimples = dominant DD, Dd No dimples = dd • Hair Color: ▫ Dark hair = dominant HH, Hh ▫ Blonde hair = recessive hh
• • Trait Lab Widows Peak Bent Little Finger Hitchhiker’s thumb Tongue Rolling Tongue Folding Dimple Chin Long Eyelashes Free Ear Lobe
Genetics Day 3
Genotype Punnett Squares • Diagram that shows the result of a genetic cross ▫ Simple Punnett Square – one trait examined ▫ Two generations shown ▫ Letters represent alleles (genotype) Parent Generation F 1 Generation
• Breakdown of cross results • Let’s cross two of the offspring from the F 1 generation
▫ genes that segregate independently do not influence each other’s inheritance • Dihybrid Cross • Cross between 2 heterozygous dominant individuals crossed • 2 traits crossed • 16 box square • The phenotype ratio predicted for dihybrid cross is ratio 9: 3: 3: 1. ▫ 9 offspring that exhibit both dominant traits ▫ 3 offspring that have one dominant, one recessive trait ▫ 3 offspring that have one dominant, one recessive (opposite of last) ▫ 1 offspring that is recessive for both traits
• Rr(Yy) take the first R and multiply it out with the two Y’s Ry RY • Rr(Yy) r. Y ry now focus on the next r and multiply it out by the two Y’s
• Set up the cross with the allele combinations from the FOIL method. • Begin to cross the parents to create the predicted offspring
Another one… • Rr. YY and Rryy ▫ Allele combinations: �RY, r. Y �Ry, ry, ry RY RY r. Y Ry RRYy Rr. Yy ry Rr. Yy rr. Yy
Analyze the Results: • RRYy – round, yellow (4) • Rr. Yy – round, yellow (8) • rr. Yy – wrinkled, yellow (4) 12: 4 ratio… simplified to: 3: 1 RY RY r. Y Ry RRYy Rr. Yy ry Rr. Yy rr. Yy
Tricks of the Trade • If one parent is homozygous recessive, and other parent is homozygous dominant = F 1 will be heterozygous dominant • If crossing two heterozygous dominant, ratio will always be • Break down genotype into
If you HAVE taken your exam! • Please sit on the left side of the room • Grab a textbook • Grab a pre-unit review and get started If you have NOT taken your exam • Please sit on the right side of the room • Grab a scantron • Get out your study guide and labeling sheets • Get a pencil!
• Ratio of a trihybrid cross ▫ 27 : 9 : 9 : 3 : 3 : 1 � 27 = all dominant � 9 = 2 dominant, 1 recessive � 3 = 1 dominant, 2 recessive � 1 = recessive
POP QUIZ! Get something to write with! Once you’re finished – turn your quiz into the tray and grab the notes in front of the A-day tray!
Genetics Day 4
Beyond dominant and recessive alleles heterozygous phenotype is somewhere in between the two homozygous phenotypes • Example: red, white, and pink flowers
• Codominance: situation in which both alleles contribute to the phenotype ▫ Example: black and white chicken feathers “erminette” ▫ Appear separately, not as a “blend” • Multiple alleles: genes that have more than two alleles ▫ Example: blood type ▫ DOES NOT MEAN the individual can have more than two alleles (hh, AA, Aa)
• • Type A – has the A antigen on red cells Type B – has the B antigen on red cells Type AB – has both A and B antigens on red cells Type O – has neither A nor B antigens on red cells
• Rh (rhesus) is a protein found on the surface of red blood cells. is a single gene with two alleles, “+” and “-” • Rh+ is dominant • Rh- is recessive • Named after the monkeys used to study the blood types
Caucasians African American Hispanic Asian O + 37% 47% 53% 39% O - 8% 4% 4% 1% A + 33% 24% 29% 27% A - 7% 2% 2% 0. 5% B + 9% 18% 9% 25% B - 2% 1% 1% 0. 4% AB + 3% 4% 2% 7% AB - 1% 0. 3% 0. 2% 0. 1%
• To prevent this condition, she can take a drug that keeps her from developing the antibodies to the Rh+ blood group
• Range of eye color caused by particular combinations of alleles • Locus (plural loci) is the specific location of a gene • Eye color is found on different loci • Alleles B/b and G/g • Come together and give eye color
• Two eye colors ▫ Heterochromia ▫ Considered abnormal and may be pathological ▫ Born with two different colored eyes congenital heterochromia • Height • # of Fingers (d) • Poison ivy susceptibility (R)
Karyotype • Karyotype: set of photographs of chromosomes grouped in homologous pairs • Used to analyze chromosomes • 46 (diploid) chromosomes in humans • Sperm (haploid) = 23 chromosomes • Egg (haploid) = 23 chromosomes Pairs 1 through 22 = Autosomes 23 rd pair = Sex Chromosomes
• Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. ▫ Different from autosomal trait inheritance, where both sexes have the same probability of inheritance. • In mammals: ▫ female is the homogametic sex, with two X chromosomes ▫ male is heterogametic, with one X and one Y chromosome
X-Linked Traits • A male or female child of a heterozygous mother affected with an X-Linked dominant trait has a chance of inheriting the mutation • children of an affected father will inherit the affected X chromosome (daughters possess their fathers' X-chromosome). • children of an affected father will be affected (sons do not inherit their fathers' Xchromosome).
• Because the Y-chromosome is small and does not contain many genes, few traits are Y-linked, and Y-linked diseases are rare • Since the only humans who have a Y chromosome are males, Y-linked traits are passed only from father to son
• X-Linked Genes ▫ Linked to the (no kidding? ) ▫ No male will get an X-linked trait from his father, only from his mom ▫ Mom’s have 2 X’s to donate 50% probability of inheritance for males and females • Y-Linked Genes ▫ Linked to the ▫ Small chromosome, not many traits ▫ Passed from father to son
Examples of X and Y Linked Traits • X-linked ▫ Hemophilia ▫ Rickets (dominant) bone deformity ▫ Rett Syndrome growth failure, small hands, feet, head ▫ Male pattern baldness (recessive) ▫ Colorblindness • Y-linked ▫ Retinitis pigmentosa damaged retina, vision impairment ▫ Azoospermia immobility of the sperm or inability to produce sperm
• RECESSIVE TRAIT
Polygenic Traits • Polygenic traits are controlled by two or more than two genes at different loci on different chromosomes. ▫ These genes are described as polygenes “poly” means many! ▫ Examples are human height, weight, skin color ▫ Eye color is a polygenic trait with multiple alleles.
Probability and Mendelian Genetics • Probability is the likelihood that an event will occur ▫ When using Punnett Squares, you are showing the probability (likelihood) of certain traits appearing in offspring with 2 parents are crossed ▫ Punnett Squares don’t show actual results – they show possible results. �If enough is known about the family genetics, then Punnett Squares are much more accurate.
Pedigrees Day 5
PEDIGREE • Chart that shows the relationships within a family • Family tree! ▫ Used to determine genotypes of family members for certain traits
Interpreting a Pedigree Chart
Determine if the pedigree chart shows an autosomal or X-linked disease: • If mostly males in the pedigree are affected the disorder is X-linked because males have only one X and therefore cannot be a carrier ▫ No dominant allele to cover up the recessive! • If it is roughly a 50/50 ratio between men and women the disorder is autosomal. ▫ Meaning that the trait is carried on chromosomes 1 -22 (freckles, dimples, etc. )
Is it Autosomal or X-linked? Autosomal – roughly 50/50 male and female X-linked Trait – males seen with it
Interpreting a Pedigree Determine whether the disorder is dominant or recessive: • If the disorder is dominant, one of the parents must have the disorder AND the disorder will be seen across all the generations • If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous AND the trait will likely NOT be seen across all generations
Dominant – all generations Recessive – skips generation
II 1 III 5
Today’s Agenda • EOC Bell Ringer #3 ▫ Keep at your desk, we will be going over it! • Pedigree worksheet – help each other answers the questions! ▫ Mr. Martin and I will be around to help! • Last half of class = makeup work! ▫ Check your grade sheet printout for missing assignments or low scoring assignments ▫ Use this time to submit missing work and/or correct previous assignments/quizzes
BACK TO THE BASICS…
• Meiosis: 1 diploid cell 4 haploid cells 1 cell with 46 chromosomes 2 cells with 46 chromosomes 4 cells with 23 chromosomes ▫ 2 DIVISIONS! (meiosis I and meiosis II) • Mitosis: 1 diploid cell 2 diploid cells ▫ 1 cell with 46 chromosomes 2 cells with 46 chromosomes
Male and Female Gametes 23
methemoglobinemia
Questions! (Page 278) • 1. 4 haploid cells genetically different from one another and the original cell • 2. Mitosis produces two genetically identical diploid cells; meiosis produce for genetically different haploid cells • 3. Diploid: two sets of chromosomes ▫ Haploid: one set of chromosomes • 4. Homologous chromosomes pair up and form tetrads, which may exchange portions of their chromatids results in the exchange of alleles between the homologous chromosomes • 5. Both sperm and egg cells have 23 chromosomes because they are gametes, which are haploid cells. A white blood cells has 46 chromosomes because it is a diploid body cell
Questions! (page 266) • 1. Dominant: form of an allele who trait always shows up if it is present. Recessive: form of an allele whose trait shows up only when the dominant allele is not present • 2. Separation of paired alleles ▫ Alleles are separated during gamete formation with the result that each gamete carries only a single allele from the original pair • 3. Factors that are passed from one generation to the next • 4. Mendel cut away the male parts of one flower; then dusted it with pollen from another flower • 5. Only ¼ of the possible gamete formations did not have a dominant allele • 6. True-breeding pea plants have two identical alleles for one gene, so in a genetic cross each parent contributed only one form of a gene, making inheritance patterns more detectable
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