Ch. 10 Sexual Reproduction and Genetics p. 270 -
10.1 Meiosis p. 270-276
Essential Question
Main Idea! Meiosis produces haploid gametes
Where are the instructions for each trait located in a cell?! On the DNA inside the nucleus
! DNA segments Genes! Genes are segments of DNA on a chromosome in the nucleus of a cell
How many chromosomes do! 46 human body cells have?
! 23 How many do each parent contribute?
Homologous Chromosomes! Chromosomes that make up a pair, one chromosome from each parent
Gametes! Sex cells (egg and sperm)! Contain ½ the number of chromosomes
How many chromosomes do! 23 or n human gametes have?
Haploid! A cell with ½ the number of chromosomes of a diploid cell! Sex cells are haploid! Represented by n
Fertilization! When a haploid gamete joins with another haploid gamete
How many chromosomes does! 46 or 2n a fertilized cell have?
Diploid! Having 2 copies of each chromosome
Meiosis! Formation of gametes! Cell division that reduces the number of chromosomes by separating homologous chromosomes! Involves 2 stages; Meiosis I and Meiosis II
Meiosis I - Interphase! Chromosomes replicate! Chromatin condenses
Meiosis I Prophase I! Pairing of homologous chromosomes! Each chromosome consists of two chromatids! Nuclear envelope breaks down! Spindles form
Meiosis I Prophase I! Crossing over segments of chromosomes are exchanged between a pair of homologous chromosomes! The results of crossing over are new kinds of genes
Meiosis I Metaphase I! Chromosome centromeres attach to spindle fibers! Homologous chromosomes line up at the equator
Meiosis I Anaphase I! Homologous chromosomes separate and move to opposite poles of the cell
Meiosis I Telophase I! Spindles break down! Chromosomes uncoil and form two nuclei! Cell divides
End of 10.1 I
Meiosis II Prophase II! A second set of phases begins as the spindle apparatus forms and the chromosomes condense
Meiosis II Metaphase II! A haploid number of chromosomes line up at the equator
Meiosis II Anaphase II! Sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell
Meiosis II Telophase II! Chromosomes reach the poles and the nuclear membrane and nuclei reform
Meiosis II - Cytokinesis! Results in four haploid cells, each with n number of chromosomes
Mitosis vs. Meioisis! One division! Two identical cells formed! Daughter cells genetically identical! Occurs only in body cells! Involved in growth and repair! 2 sets of divisions! 4 haploid cells formed! Daughter cells NOT genetically identical! Occurs in reproductive cells! Involved in production of gametes
How does meiosis provide variation? 1. Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result 2. Crossing over
Where does an asexual organism get its chromosomes?! The organism inherits all of its chromosomes from a single parent
Why is sexual reproduction beneficial?! Beneficial genes multiply faster over time than they do when reproduction occurs asexually.
10.2 Mendelian Genetics p. 277-282
Essential Question
Main Idea! Mendel explained how a dominant allele can mask the presence of a recessive allele
What is heredity?! The passing of traits to the next generation! Also called inheritance
How did Mendel perform cross pollination in pea plants?! By transferring a male gamete from the flower of one pea plant to the female reproductive organ in a flower of another pea plant
Genetics! The science of heredity
What is the P generation?! The parent generation! Yellow seeds (YY) crossed with green seeds (yy)
What is the F 1 generation?! The offspring of the P cross! All appeared yellow (Yy)
What is the F 2 generation?! The offspring from the F 1 cross! Most (3/4) appeared yellow (YY or Yy) and some (1/4) appeared green (yy)
What did Mendel conclude?! That there must be two forms of the seed trait in pea plants yellow and green
allele! An alternative form of a single gene passed from generation to generation! Example: pea color (yellow or green), pea shape (round or wrinkled)
Dominant! A trait that appears! Denoted by an uppercase letter
Recessive! A trait that is masked! Denoted by a lowercase letter
Example:! If yellow (Y) is dominant and green (y) is recessive, what color will the pea be? 1. YY 2. Yy 3. yy
Homozygous! An organism with two of he same alleles for a particular trait! YY! yy
Heterozygous! An organism with two different alleles for a particular trait! Yy
Genotype! An organism s allele pairs! YY, Yy, or yy
Phenotype! The observable characteristic! Yellow or green
Law of Segregation! The two alleles for each trait separate during meiosis! During fertilization, two alleles for that trait unite
Hybrids! A heterozygous organism! Yy
Monohybrid cross! A cross that involves hybrids for a single trait! Three possible genotypes: YY, Yy, yy! Genotypic ratio is 1:2:1! Phenotypic ratio is 3:1
Dihybrid cross! The simultaneous inheritance of two or more traits in the same plant! They are heterozygous for both traits! 4 types of alleles: Y_R_, yyr_, Y_rr, yyrr! Phenotypic ration (9:3:3:1)
Law of independent assortment! Random distribution of alleles occurs during gamete formation! Genes on separate chromosomes sort independently
Punnett Squares! Used to predict the possible offspring of a cross between two known genotypes
Main Idea! The crossing over of linked genes is a source of genetic variation
Genetic Recombination! The new combination of genes produced by crossing over and independent assortment
Polyploidy! Is the occurrence of one or more extra sets of all chromosomes in an organism! 1 in 3 plants are polyploid! Helps with vigor and size
End of Ch. 10