1 Chapter 5 Key Terms Gene Punnett Square

1 Chapter 5 Key Terms Gene Punnett Square Diploid Cell cycle Ovum Meiosis Phenotype Chromosome Carrier Haploid Gamete Sperm Allele Genotype

2 Biology Chapter 5 GENETICS

3 Characteristics Species characteristics Characteristics 2 eyes, 2 ears, liver, stomach… Individual Characteristics Hair A that every member of a species possesses that make a person unique color, eye color, skin color… person is made of species characteristics and individual characteristics

4 Mechanism of Heredity Genetics Study of heredity History Aristotle’s particulate theory of reproduction Believed that particles of parent’s blood mixed to form the offspring This is where “pure blood” and “blood relative” come from Gregor Mendel (1800 s) Performed many experiments that helped advance our understanding of genetics Experimented on peas and their characteristics

5 Mechanism of Heredity Mendel proposed there are pairs of factors in organisms that affect the offspring 1953, Watson and Crick discovered DNA Found This that the “factors” Mendel talked about were located on DNA opened the way to modern genetics

6 Genes Defined as “a section of DNA that produces a particular polypeptide chain of amino acids that causes a particular trait” Coiled DNA from all cells in person’s body would fit in 1 in. cube from one cell would stretch out to be 2 yards long Information pages contained in DNA of one cell would fill 600, 000

7 Chromosomes In an inactive cell, the chromosomes exist in the nucleus as chromatin material A tangled mass of chromosomes Chromosomes with do not look like what we normally associate them

8 Chromosomes Histones Provide support and protection for DNA strand Help maintain shape of chromosomes Chromatids Two identical halves of duplicated chromosome Centromere Constricted chromatids area that joins sister

9 Review

10 Chromosomes The number of chromosomes in a cell is a species characteristic Horse Cat = 64 chromosomes = 38 chromosomes Humans have 46 chromosomes (23 pair) in cell nuclei Karyotype Picture of chromosomes arranged in pairs according to length and centromere location each

11 Chromosomes The pairs of chromosomes are called homologous chromosomes Each member of the pair is called a homologue Haploid One cell set of unpaired chromosomes (n) Diploid cell Homologous pairs of chromosomes (2 n)

12 Cell Cycle The repeating cycle of events in the life of a cell Divided into 3 parts Interphase, mitosis, cytokinesis Interphase Longest portion of the cell cycle Divided into 3 stages: G 1, S, G 2 phases G 1 = cell grows, makes new organelles, proteins and other molecules S = DNA is replicated, centrosome divides into centrioles G 2 = cell produces proteins and molecules needed for mitosis

13 Cell Division Mitosis Division of nuclear material to ensure each new nucleus contains identical copies of genetic information from mother cell 4 phases Prophase Metaphase Anaphase Telophase

14 Mitosis Prophase Chromosomes Centrosomes shorten and become visible migrate to the poles and form spindle fibers Metaphase Chromosomes line up in the middle look like X’s because the sister chromatids appear to repel each other

15 Mitosis Anaphase Chromatids separate into daughter chromosomes Spindle fibers pull chromosomes toward poles of cell Telophase Chromosomes reach end of spindle Two nuclei form around daughter chromosomes Chromosomes uncoil into chromatin Spindle disappears leaving the centrosome Mitosis is complete when nuclear membrane has reformed around the nucleus

16 Cell Division Purpose of mitosis To ensure that both daughter cells get an exact copy of the same information the parent cell contained Is not important to have equal amounts of cytoplasm and organelles Is important to have correct and complete set of genes/chromosomes

17 Cell Division Cytokinesis Division of the cytoplasmic content (organelles, proteins…) Cell completely divides Different process in plants than in human and animal cells Once cytokinesis is complete, the cell cycle begins all over again

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19 Meiosis Edouard van Beneden Discovered meiosis in 1883 when he noticed the reproductive cells of a worm only contained half the chromosomes the normal cells contained Proposed some process occurred to reduce the chromosomes in gametes As gametes form, the chromosome number is reduced to the haploid number (23 in humans) Zygote forms when two gametes (sperm and egg) unite Each gamete must have 1 of every homologous pair Meiosis is the reduction of a cell’s chromosomes from diploid to haploid by two consecutive cell divisions (Meiosis I and Meiosis II)

20 Meiosis I Prophase I Chromosomes Then coil, spindles begin to form duplicated homologous chromosomes pair up, form a tetrad Chromatids are very close together and sometimes exchange genetic material Metaphase Tetrads I line up on equatorial plane

21 Meiosis I Anaphase I Homologous of spindle Telophase pairs separate and move toward end I Chromosomes arrive at poles of cell, but chromosomes do NOT uncoil Cytokinesis Cells completely divide and go directly into Meiosis II

22 Meiosis II Prophase Mitotic II spindles reform and move chromosomes toward equatorial plane Metaphase II Chromosomes Anaphase Sister II chromatids separate and move to opposite sides of cell Telophase Nuclei align in middle of cell II and cytokinesis reform and each of the four new cells are haploid

Telophase I Prophase II Metaphase II Anaphase II Telophase II Cytokinesis 23

24 Comparing Mitosis and Meiosis Functions: Mitosis – produce 2 new cells with same number of chromosomes as parent cell (diploid) Meiosis Both All – produces four haploid cells go through interphase events unique to meiosis occur during meiosis I

Meiosis I Review 25

Meiosis II Review 26

27 Genetics Study Gregor of heredity Mendel Father of Modern Genetics Experimented 1865 with how pea plants passed on traits – published paper on Mendelian Genetics Mendel’s work on heredity is important to understanding modern genetic theories

28 Genetics Mendel Tall studied traits of the pea plants that had two variations or short plants; green or yellow pods, green or yellow peas Self-Pollination Pollen (male gamete) fertilizes the pistil (contains the female gamete) of the same plant Cross-Pollination Fertilizing the pistil of one plant with the pollen from another

29 Genetics P 1 = Parent plants/generation One F 1 = First filial generation All F 2 tall parent, one short parent plants were tall = Second filial generation Out of 1064 offspring, 787 (74%) plants were tall, 277 (26%) plants were short

30 Genetics Mendel 1. The concept of unit characteristics 2. proposed several concepts An organism’s characteristics are caused by units he called factors (we call genes) The concept of dominant and recessive Dominant: expressed trait when two different genes are present Recessive: masked trait

31 Genetics 3. The concept of segregation Each The gamete contains only 1 gene for each characteristic gamete would pass on that gene and work with the gene from the other gamete

32 Genetic Terminology Genotype: the specific genes an organism contains Phenotype: Locus: Allele: the physical expression of an organism’s genes specific site on chromosome where gene is located alternate form of a gene that occupies the same locus on homologous chromosomes

33 Genetic Terminology Homozygous: both alleles are the same (TT or tt) Heterozygous: alleles are different (Tt) Monohybrid cross: cross between individuals that deals with only one set of alleles Punnett Squares: determine the probability of the offspring’s genotype and phenotype

34 Punnett Squares Purpose: Visualize Predict genetic crosses probability of genotype or phenotype of offspring Rules Female Male along top of square along side of square Dominant Allele written first

35 Practice A father is homozygous for unattached earlobes (dominant) while the mother is homozygous for attached earlobes (recessive). What will the genotypes and phenotypes of the offspring be? (F is dominant, f is recessive)

36 Practice Now, two individuals who are heterozygous for earlobe attachment cross. What are the possible genotypes and phenotypes of the offspring?

37 Punnett Squares Test cross Mating an organism with dominant phenotype but unknown genotype with plant that is homozygous recessive phenotype If all offspring have dominant phenotype, parent was homozygous Pedigree Chart used to trace presence or absence of a trait through a number of generations Used to predict possibilities of certain traits in offspring

38 Variations of Mendelian Genetics Incomplete Occurs Dominance when two alleles are both expressed Phenotype Ex. of offspring is blend or mixture of two parent traits flower color

39 Practice A cross between a blue bird and a white bird produce silver offspring. The color is determined by two alleles. A) What are the genotypes of the parents in the original cross? B) What are the genotypes of the silver offspring? C) What would the phenotypic ratios of offspring produced by two silver birds?

40 Variations of Mendelian Genetics Codominance Both alleles for a trait are expressed Colors are not blended but are both present

41 Variations of Mendelian Genetics Multiple alleles More than two alleles can be present at a locus Only two possible alleles on the homologous chromosomes Ex. ABO blood type A = IAIA or Iai B = IBIB or IBi AB O = I AI B = ii

42 Dihybrid Cross A cross of two pairs of contrasting traits at the same time Color Pod of the pod is one pair of genes characteristics is another pair Green is dominant, yellow is recessive Inflated is dominant, constricted is recessive

43 Dihybrid Cross Independent Assortment Segregation of one set of alleles during meiosis is not affected by the presence or segregation of other sets of alleles Polygenetic When genes inheritance a trait is affected by multiple

44 Sex-Linked Inheritance Normal people have 22 pairs of autosomes and 1 pairs of sex chromosomes Males = XY Females = XX Sex-linked inheritance deals with genes found mostly on the X chromosome Sex-linked traits Colorblindness and hemophilia

45 Colorblindness The gene for colorblindness is on the X chromosome and is recessive If a male receives the colorblindness gene, he will be colorblind If a female receives the colorblindness gene, she may not express it, depending on the gene of the other X chromosome

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