Homework: For tomorrow: Read 6.1 do FAQ # 2 Read 6.2 do FAQ # 4

Genetics Unit 3 Ch. 6-9

Sexual Reproduction and Meiosis Ch. 6.1 – 6.2

Lesson Objectives At the end of this lesson, students will be able to… Explain the difference between somatic cells and gametes in terms of genetics and function Compare and contrast mitosis and meiosis in terms of the process, genetics, and products

Asexual vs. Sexual Reproduction We have already learned that cell division by mitosis results in cells that are identical to the parent – Asexual reproduction also results in organisms identical to the parent In order to create UNIQUE individuals, organisms use a process called meiosis and sexual reproduction

Meiosis Meiosis – this process is very similar to mitosis but it requires two rounds of division and results in gametes containing only half the chromosomes of the parent Remember: Meiosis makes gametes

Vocabulary Somatic cells – these are the cells that make up everything in our body, they reproduce by mitosis Diploid cells – these are cells that contain a double set of chromosomes (in humans this would be 46 since n = 23), the short hand for this is 2n, somatic cells are diploid

Vocabulary Gametes – these are sperm and egg cells, also called sex cells, they contain half of each parent’s chromosomes, they are produced by meiosis Haploid cells – these cells only contain half the chromosomes of the parent cells, gametes are haploid, the shorthand for this is 1n

Vocabulary Gametogenesis – “making gametes,” gametogenesis is the process that matures haploid cells made by meiosis into gametes

Mitosis vs. Meiosis During mitosis, a cell simply grows and divides to create an exact copy of itself During meiosis, the cells created are genetically different from the parent cells due to a mixing and shuffling of chromosomes during division

Mitosis Vs. Meiosis Mitosis Meiosis DNA Replication Rounds of Division During interphase before mitosis starts During interphase before meiosis starts Rounds of Division One Two Number of Daughter Cells Four Genetic Composition 2n (diploid) 1n (haploid) Role in the Animal Body Somatic cells, makes up tissues and organs Gametes, sex cells (eggs and sperm)

Meiosis: Making Gametes Gametes are produced from cells called germ cells located in the gonads of sexually reproducing organisms. The first round of division separates homologous chromosomes

Vocabulary Homologous Chromosomes – homologous means “matching” – we get half of our chromosomes from each parent so we end up with 2 copies of each chromosome (2n). The matching copies are the homologous chromosomes.

(During S Phase)

Are homologous chromosomes identical to each other? Discuss: Are homologous chromosomes identical to each other? Explain. No, they are very similar in size and type of genes but since they were inherited from different parents, they carry different versions of genes.

How does meiosis make gametes? It takes two rounds of division to produce haploid gametes Meiosis I – homologous pairs of chromosomes separate and are put into two different cells Meiosis II – the sister chromatids of the chromosomes separated in meiosis I are separated and put into different cells The final result is 4 daughter cells containing 1 sister chromatid from each of the original chromosomes Because DNA gets shuffled, each daughter cell has a different genetic combination

Gametes

Meiosis Video Things that are similar to mitosis Things that are different from mitosis

Paperclip Meiosis!! Use packet to start

Why are gametes important? When most animals reproduce, it requires a male and female Each parent donates a gamete carrying half of their chromosomes These gametes fuse (fertilization) and the two half sets of DNA combine to form a diploid cell That diploid cell then divides, multiplies, differentiates and eventually becomes a baby

Meiosis: Making Gametes After homologous chromosomes have been separated into 2 daughter cells, the next round of division can start During the second round, sister chromatids are separated – This results in FOUR HAPLOID cells These haploid cells are gametes – sperm or eggs

Why is it important that gametes are haploid cells? Discuss: Why is it important that gametes are haploid cells?

Why are gametes important? We get 22 regular chromosomes from each parent – these are called autosomes We also get 1 sex chromosome from each parent – and X or a Y – this determines if we will be male or female XX = girl XY = boy This results in a total of 46 chromosomes (in humans)

Page 162: Data Analysis Working on your own or with a neighbor, look at the graphs and answer 1 - 3

Meiosis I and II Meiosis Using fig 2.3 on pg. 164 or the link above, make a Venn Diagram to compare meiosis I and II

Homework: Catch up: For tomorrow: Read 6.1 do FAQ # 2

Heredity, Traits, Genes, and Alleles Ch. 6.3 – 6.4

Lesson Objectives At the end of this lesson, students will be able to… Explain how genes are expressed in terms of genotype and phenotype, homozygous, heterozygous Explain the difference between dominant and recessive alleles in terms of how this affects phenotype

Why are chromosomes important? They carry instructions called genes - The specific set of genes that a chromosome carries is called the genotype Genes determine the physical appearance and function of an organism – the physical expression of the genotype is called the phenotype. Traits are physical characteristics expressed in the phenotype (eye color, size, etc)

Gregor Mendel Austrian monk – mid 1800s He worked in the gardens of the monastery paying special attention to the traits of pea plants At this time no one knew about DNA or how it worked, they could only observe phenotypes

Mendel Flowering plants contain both male and female parts – this means they can self pollinate or cross pollinate

Gregor Mendel Mendel bred thousands of pea plants and recorded every outcome He noticed that there seemed to be a pattern of traits in his data

Pea Traits

Gregor Mendel At the time it was thought that offspring were always an even blend of parent characteristics Mendel observed that traits seemed to be “either-or” and not a blend at all This observation allowed him for correctly predict genetic inheritance decades before it could be proven

Gregor Mendel One of the patterns he saw was that each trait seemed to have a common and rare form The common form showed up about 3 times more often in F2 than the rare trait In other words, the ratio of common to rare versions of a certain trait was 3:1 Fig 3.4

Pea Phenotypes

Gregor Mendel These more commonly seen traits are called dominant Dominant does NOT mean better or stronger The less common traits are called recessive Recessive does NOT mean worse or weaker Remember: Mendel is in control of breeding, when left to nature, dominant isn’t always more common

Discuss: Looking at figure 3.3 on page 168: Would you say that purple flowers are dominant or recessive? Why?

Pea Genotypes Note that each parent has 2 of the same and each F1 has 1 of each

Gregor Mendel Mendel was well educated, but his success was partly luck He just happened to make 3 key choices that worked in his favor: He had control over breeding Used purebred plants And observed “either-or” traits

Gregor Mendel See pages 168-169 After selectively crossing the plants Mendel observed the presentation of 7 traits (fig 3.4) His findings would later go on to support the Law of Segregation which says: Organisms inherit 2 copies of each gene, one from each parent The organisms then donates one copy of each gene to their own gametes so the 2 copies become separated

Homework: Catch up: For tomorrow: 6.1 # 2 6.2 # 4 6.3 # 4 Read 6.4 ***DEFINE: gene, allele, homozygous, heterozygous, dominant, and recessive*** This will be DUE first thing tomorrow

Do you have a genetic twin?? At your desk: Fill out your predictions and your own traits Then: get up and fill in traits for 5 other people and see if you can find a “genetic twin!” Once you have 5 people sit in your seat

Same gene, many versions Genes are sections of DNA that contain instructions to produce certain traits or necessary cell parts Since we get half of our DNA from one parent and half from the other, there is a possibility that we will inherit different versions of that gene

Same gene, many versions The version of a gene that we inherit from each parent is called an ALLELE In peas we talked about dominant and recessive traits, this was caused by dominant and recessive alleles Yellow = Dominant, Green = Recessive

Pea Phenotypes

Same gene, many versions When both parents donate the SAME version of a gene (allele), we say the offspring is HOMOZYGOUS for that particular gene “Homo” = the same GG When each parent donates a DIFFERENT allele, we say the offspring is HETEROZYGOUS for that particular gene “Hetero” = different Gg See page 170 “Visual Vocab”

Genotype and Phenotype The GENOME is ALL of the genetic material an organism has The GENOTYPE of an organism is the specific combination of genes it has The PHENOTYPE is the way that the genotype is physically expressed – in other words, the set of traits or characteristics an organism has

Dominant and Recessive With most genes there is a dominant and recessive allele Remember, this isn’t talking about better or worse – just which allele will mask the other one Dominant alleles will overpower recessive alleles so the dominant phenotype shows up A recessive phenotype will only show up if the alleles are homozygous recessive (see pg. 171 “visual vocab”)

Dominant and Recessive When we are talking about dominant and recessive alleles we use upper and lower case letters to symbolize them Uppercase is dominant Lowercase is recessive

Practice: Dominant and Recessive Pretend a mouse’s coat color is determined by an allele on a particular chromosome. Black hair is dominant (C) and white hair is recessive (c). What are the possible genotypes for a black mouse? What are the possible genotypes for a white mouse?

Homework Catch up: For tomorrow: 6.1 # 2 6.2 # 4 6.3 # 4 6.4 Definitions For tomorrow: Read 6.5 # 5