Chapter 11: Introduction to Genetics

Meiosis QUESTIONS/EXAMPLES TITLE: Mitosis produces cells with exactly the same amount of chromosomes as the original cell. If this was the only means of cell division, offspring would end up with twice as many chromosomes as the parents. Why Meiosis? Egg (14 chrom.) + Sperm (14 chrom) Offspring (28 chrom) F1 Egg (28) + F1 Sperm (28) F2 Offspring (56)

To produce haploid gametes, organisms under go meiosis QUESTIONS/EXAMPLES TITLE: Haploid: cell with one of each kind of chromosome (n) Organisms produce gametes that are haploid…egg and sperm EX: Diploid: cell with two of each kind of chromosome (2n) Body cells (somatic cells) of animals/plants have chromosomes that occur in pairs…one from each parent EX: To produce haploid gametes, organisms under go meiosis How do organisms produce haploid gametes?

Meiosis QUESTIONS/EXAMPLES TITLE: Meiosis has 2 separate divisions…Meiosis I and Meiosis II Meiosis I begins with a Diploid cell…2n has 46 chromosomes Meiosis II finishes with 4 Haploid cells (1n) These 4 Haploid cells are Gametes (Egg or Sperm) Meiosis I = 2n Meiosis II = 1n

Meiosis QUESTIONS/EXAMPLES TITLE: How many chromosomes does a human sperm contain? -23 chromosomes How many chromosomes does a human egg contain? With Fertilization, Sperm (23) and Egg (23).. Haploid…come together to produce a Zygote (46)..Diploid What happens during Sexual Reproduction? -Haploid gametes (egg and sperm) combine. This pattern of reproduction that involves the combining (fusion) of haploid gametes is called Sexual Reproduction How many chromosomes does a human skin cell contain? -46 (diploid)

Meiosis QUESTIONS/EXAMPLES TITLE: Homologous Chromosomes: Paired chromosomes, each with genes for the same traits. These exist in Diploid cells and are what determine how an individual looks (traits) Where do you find homologous chromosomes? in Diploid Cells Ex: Mom’s chromosomes for hair color Dad’s chromosomes for hair color

Phases of Meiosis

What happens within the cell during Interphase of Meiosis? Questions/ Examples Phases of Meiosis TITLE: Interphase What happens within the cell during Interphase of Meiosis? -DNA is replicated. DNA Replication

Meiosis I

- Crossing Over can occur Questions/ Examples Phases of Meiosis TITLE: Prophase I Example of a TETRAD Each pair of homologous chromosomes come together to form a four-part structure called a Tetrad Example of CROSSING OVER - Crossing Over can occur

Phases of Meiosis Metaphase I Questions/ Examples TITLE: Example of Metaphase I Metaphase I In Meiosis I, the Tetrad of homologous chromosomes lines up down the middle What lines up down the middle of the cell during Metaphase I of Meiosis? -Homologous pairs

What gets separated during Anaphase I of Meiosis? Questions/ Examples Phases of Meiosis TITLE: Anaphase I Example of Anaphase I Spindle fibers pull homologous chromosomes toward opposite ends of the cell What gets separated during Anaphase I of Meiosis? -Homologous pairs

Telophase I - the cells begin to separate into two cells. Questions/ Examples Phases of Meiosis TITLE: Example of Telophase I Telophase I - the cells begin to separate into two cells. Are the two cells identical? -No, they have different sets of chromosomes At the end of Meiosis I the two new cells are Haploid and have different sets of chromosomes

Meiosis I

Meiosis II

Do chromosomes replicate during Prophase II of Meiosis? Questions/ Examples Phases of Meiosis TITLE: Prophase II Example of Prophase II Nuclear Membrane breaks down, chromosomes condense Meiosis II is identical to Mitosis Do chromosomes replicate during Prophase II of Meiosis? -NO!

Phases of Meiosis Metaphase II Chromosomes Questions/ Examples Phases of Meiosis TITLE: Example of Metaphase II Metaphase II Chromosomes (sister chromatids) line up down the center of the cell

What gets separated during Anaphase II of Meiosis? Questions/ Examples Phases of Meiosis TITLE: Example of Anaphase II Anaphase II - Sister chromatids separate towards opposite ends of each cell What gets separated during Anaphase II of Meiosis? -Sister chromatids

Phases of Meiosis Telophase II Questions/ Examples TITLE: Telophase II Example of Telophase II 4 A nuclear membrane forms around each set of chromosomes and cytokinesis occurs, producing four daughter cells At the end of Telophase II of Meiosis II, how many chromosomes are found within each daughter cell? -One chromosome from each homologous pair from Meiosis I How many and what type of cells are produced at the end of Cytokinesis? - 4 Haploid cells that are genetically different Produces 4 Haploid Cells that are genetically different

Meiosis II

Examples of Differences Mitosis vs. Meiosis 2 genetically identical daughter cells Diploid (46) chromosomes Somatic cells 4 genetically different cells Haploid (23) chromosomes Gametes (eggs) (sperm)

Questions/ Examples Genetic Variation TITLE: Why are offspring not identical to their parents/why does genetic variation exist? -Because Meiosis randomly shuffles chromosomes Meiosis “shuffles” chromosomes = offspring are not identical to the parents - Principle of Independent Assortment: genes for different traits separate INDEPENDENTLY during meiosis, as long as they are on separate chromosomes What principle describes how genes for different traits separate independently during Meiosis? - Principle of Independent Assortment HOW do genes for different traits separate independently? -By homologous chromosomes lining up randomly during meiosis - homologous pairs line up completely random during Metaphase I…

Questions/ Examples Genetic Variation TITLE: Example of Crossing Over Crossing Over -an exchange of genetic material between homologous chromosomes Occurs randomly anywhere on the chromosome. **What does crossing over and independent assortment create?** -Genetic Variation/offspring that are different from their parents Genetic Recombination= reassortment of chromosomes and genetic information they carry, either by crossing over or independent segregation of homologous chromosomes How does genetic recombination occur? -By independent segregation/assortment or crossing over

Genetic PROBLEMS Questions/ Examples Title: What occurs when both chromosomes from a homologous pair are pulled to the same pole of the cell? -Nondisjunction/ extra or missing chromosome Nondisjunction: When chromosomes fail to separate correctly during meiosis Both chromosomes from a homologous pair move to the same pole of the cell Trisomy: (nondisjunction) where a zygote has an extra chromosome -Ex: Trisomy 21 What is one example of Nondisjunction? -Trisomy: having an extra chromosome

Genetic Problems Questions/ Examples Title: What occurs when a zygote is missing one chromosome? -Monosomy Monosomy: (nondisjuction) when the zygote is missing one chromosome In humans, most zygotes/organisms with monosomy do not survive Ex: (non lethal) Turner Syndrome= Human females with only one X chromosome Do most organisms that are missing a chromosome survive? -No What is one example of Monosomy where organisms can survive? - Turner Syndrome: having only one X chromosome

Nondisjuction of homologous chromosomes Questions/ Examples Genetic Problems Title: Nondisjuction of homologous chromosomes - Complete Diploid set of chromosomes is passed to gamete Offspring has 3 sets of that chromosome after fertilization Called: Triploid What happens when homologous chromosomes do not separate? -Offspring has more than two sets of chromosomes (3 sets) When an organism has 3 sets of chromosomes what is this called? - Triploidy What does polyploidy usually cause in animals? death - Death Polyploids: Organisms with more than 2 sets of chromosomes - Rare in animals and usually causes death - Occurs frequently in plants Flowers/fruits are larger and usually healthier Example of Polyploidy in plants

Gene Linkage Questions/ Examples Title: Genes close on a chromosome are less likely to separate These genes are usually inherited together It is the chromosomes that separate independently not genes Example of Gene Linkage Blonde hair and blue eyes, fruit fly with reddish-orange eyes and miniature wings When are genes less likely to separate ? -When they are close together on a chromosome.

The Work of Gregor Mendel QUESTIONS/ EXAMPLES TITLE: Genetics: study of Heredity What is the study of heredity? Heredity: the passing of characteristics from parents to offspring. Ex of Traits: -hair color -eye color -height Traits: Inherited characteristics. http://www.writing.ucsb.edu/faculty/samuels/dna.jpg

The Work of Gregor Mendel QUESTIONS/ EXAMPLES TITLE: What Austrian monk was curious about the passing of traits so he studied pea plants? Gregor Mendel (1822-1884): An Austrian monk Wanted to know how traits were passed from parent to child. Studied pea plants

The Work of Gregor Mendel QUESTIONS/ EXAMPLES TITLE: What type of pea plants did Mendel choose for his first cross? Started with pea plants that only produced tall offspring and pea plants that only produced short offspring. Mated short plants with tall plants. All the offspring were tall!! What was going on??? http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ge/m2/s2/assets/images/gem2s2_1.jpg

The Work of Gregor Mendel QUESTIONS/ EXAMPLES TITLE: (Background info. on cross terminology) Example: Parental generation = P1 generation First generation of offspring = F1 generation Second generation of offspring = F2 generation (F means Filial) http://www.fastplants.org/graphics/genetics/parent_F2.jpg

The Work of Gregor Mendel QUESTIONS/ EXAMPLES TITLE: He let the new tall offspring (F1 plants) self-pollinate and observed the second generation (F2 Plants). Draw a picture representing what happened. The resulting F2 plants were tall ¾ of the time, and short ¼ of the time! What was the result of the F1 plants self pollinating? http://www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/graphics/02Q.gif

SUMMARY OF WHAT MENDLE DID/SAW P1 TT x tt Forced Mating Tall x Short   F1 All Tt Self-pollinate All Tall F2 TT Tt Tt tt Count 3 Tall:1 Short

Example of Mendel letting the F1 generation self-pollinate Tall Short Tall Tall Tall Tall Tall Short

The Work of Gregor Mendel QUESTIONS/ EXAMPLES TITLE: 1st: Mendel Determined: Trait inheritance is determined by factors that are passed from generation to generation What did Mendel conclude about trait inheritance? Genes: Factors that determine traits Some Examples of Alleles Ex. Gene = height, the allele could be tall or short. Gene = eye color, the allele could be light or dark. Alleles: A particular form of a gene, one comes from the mother, one from the father. http://ghs.gresham.k12.or.us/science/ps/sci/soph/genetics/alleles.gif

When is a recessive allele seen/expressed? Rule of Dominance QUESTIONS/ EXAMPLES TITLE: If there are two alleles, and only one observed trait, which allele is dominant? A dominant allele is always expressed. A recessive allele not expressed when in the presence of a dominant allele. is expressed when paired with another recessive allele. When is a recessive allele seen/expressed? http://wellspring.isinj.com/bio/principlesI/Images/segregation.jpg

Rule of Dominance QUESTIONS/ EXAMPLES TITLE: (Don’t write this down, just listen): Remember, Mendel said there were two alleles, one from the female and one from the male for every trait, or gene- these get passed from generation to generation. Example of alleles and the traits they show: How many Tall plants are there, how many short? For the pea height gene, the allele T=Tall and the allele t=Short. T = dominant to t = recessive (Know because most of the plants were tall) http://web.grcc.edu/biosci/revhand/genetic/~wp0002.jpg

Rule of Dominance QUESTIONS/ EXAMPLES TITLE: If T is dominant, then: TT=Tall, Tt=Tall, and tt=Short. Write an example of a genotype. The allele combo/gene combo: (TT, Tt, or tt): = genotype of the trait. Write an example of a phenotype. Phenotype: The expression of the gene/the way you look. Blue eyes, straight hair, smooth pea, wrinkled pea are all phenotypes. http://web.grcc.edu/biosci/revhand/genetic/~wp0002.jpg

What is the genotypic ratio? Phenotypic ratio? QUESTIONS/ EXAMPLES TITLE: LAW OF SEGREGATION (Remember: All plants/animals have two alleles for each gene: different alleles = two different types of gametes: pair randomly during fertilization (independent assortment!)) Segregation = Separation of alleles during gamete formation Segregation + Independent assortment = four possible combinations of alleles. Example: F1 (Tt) X F1 (Tt) F2: TT Tt Tt tt Each F1 has a tall and short allele (for the gene for height) that it can pass on to its offspring (F2) What is the genotypic ratio? Phenotypic ratio?

A diagram used to show what might result from a genetic cross Punnett Squares QUESTIONS/ EXAMPLES TITLE: Tt Male T T Female t t A diagram used to show what might result from a genetic cross -Used to predict/compare genetic variations

Punnett Squares Monohybrid cross= one gene QUESTIONS/ EXAMPLES TITLE: How many alleles does each parent donate in a monohybrid cross? Monohybrid cross= one gene Each parent donates one allele to the offspring

Punnett Squares Homozygous: Two of the same allele for a trait. QUESTIONS/ EXAMPLES TITLE: Homozygous: Two of the same allele for a trait. Homozygous Ex. TT or tt. Heterozygous: Two different alleles for one trait. Heterozygous Ex. Tt. TT is homozygous dominant. tt is homozygous recessive. Tt is heterozygous.

Dihybrid Crosses QUESTIONS/ EXAMPLES TITLE: So far we have only looked at single or lone traits like height. The crossing of these plants when only looking at one gene or trait is called a monohybrid cross. What would happen if we looked at two traits and their alleles at the same time? Crossing 2 traits at the same time: This is called a dihybrid cross. Ex. Wrinkled and yellow peas or round and green peas How many traits are crossed in a dihybrid cross?

Ex. Wrinkled and green peas or round and yellow peas Dihybrid Crosses QUESTIONS/ EXAMPLES TITLE: Ex. Wrinkled and green peas or round and yellow peas Each parent donates two alleles to the offspring

Phenotypes – Dihybrid Cross P1 Round Yellow x Wrinkled Green F1 All Round and Yellow F2 Round Yellow (9): Round Green (3): Wrinkled Yellow (3): Wrinkled Green (1) 4 Possibilities http://campus.queens.edu/faculty/jannr/Genetics/images/dihybridtestcross.gif

Example: Cross red (RR) flower + white (WW) flower = pink (RW) Incomplete Dominance QUESTIONS/ EXAMPLES TITLE: Example: Cross red (RR) flower + white (WW) flower = pink (RW) One allele is not completely dominant over the other.

Codominance Both alleles contribute to the phenotype QUESTIONS/ EXAMPLES TITLE: Example: A red cow crossed with a white cow results red cows with white blotches. Both alleles contribute to the phenotype

Multiple Alleles Example: various hair colors in mice. QUESTIONS/ EXAMPLES TITLE: Example: various hair colors in mice. When genes have more than 2 alleles that contribute to the phenotype. The result = various expressions of the gene.