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Mitosis & Meiosis What’s the difference? Write down these terms: • • • • • Mitosis Meiosis Diploid Haploid Sex chromosomes in a Male? • Sex chromosomes in a Female? • Number of chromosomes in a person? • • • • • • • • • Karyotype Allele Genotype Phenotype Dominant Recessive Homozygous Heterozygous Pedigree Mitosis • Mitosis is the process where one cell divides into 2 identical cells • This is how we go from 1 cell (the fertilized egg) to millions of cells! • It is also HOW we grow & repair our bodies. • What has to happen BEFORE mitosis can occur? • Answer: The DNA has to replicate ( be copied!) • All 46 chromosomes (yes, MOST human cells have 46 chromosomes) have to be copied so both DAUGHTER cells get the same 46 chromosomes that were in the parent cell. Parent cell Chromosomes are copied and double in number (sister chromatids are attached at by the centromere Chromosomes now split 2 daughter cells identical to original What is a Chromosome? • The structure that the DNA forms in our cells • The DNA is associated with proteins that compact it so it fits and is organized inside the nucleus! • Animation of mitosis: • http://www.cellsalive.com/mitosis.htm • So, we’ve got 46 chromosomes. • How many different PAIRS of chromosomes do we have? – Are ALL the pairs the same? • 23 pairs of chromosomes – Yes & No- 2 copies of chrom 1, 2 copies chrom 2……, except for the sex chromosomes (X & Y) in MEN ( XY) & Women (XX) CHROMOSOME NUMBER • Number of chromosomes in body cells of a species is diploid = 2n (n is the number of different chromosomes; 2n = 2 copies of each different chromosome) • The number of chromosomes in egg and sperm cells (gametes) is haploid which is “n”, or 1 copy of each different chromosome What are diploid and haploid for us? Answer: • Diploid= 46chromosomes =2 copies of 23 different chromosomes (1-22 + XX or XY) • Haploid = 1 copy of 23 different chromosomes (1-22 + X or Y) • Where does each chromosome of the pair come from? (Ex. You’ve got 2 copies of chr 1- where did each copy come from?) • One chromosome comes from MOM, and one chromosome comes from Dad So, who determines the sex of the baby???? DAD- He is the ONLY parent that can contribute the Y chromosome that makes the fetus male. • • • How do the gametes (sex cells) end up with only 23 chromosomes? THINK MEIOSIS!! • WHY do they need to be haploid (only 1 copy of each chromosome or 23 total chromosomes)? MEIOSIS IT’S ALL ABOUT SEXUAL REPRODUCTION… MEIOSIS • A type of cell division where the number of chromosomes is reduced by half • ONLY occurs in gonads (ovaries or testes) during formation of gametes (egg or sperm) • Human body cells have 46 chromosomes; human sperm and egg cells each have 23 chromosomes Gametes are haploid for SEXUAL REPRODUCTION! • When egg and sperm combine during fertilization, each brings half the total number of chromosomes for that species • Half + half = whole • In humans, 23 chromosomes (from Dad) + 23 chromosomes (from Mom) = 46 chromosomes (child) !!! FERTILIZATION egg + sperm = zygote 23 n Haploid + + 23 n = 46 2n haploid = diploid Summary of Meiosis • Type of cell division used to form the gametes (egg & sperm) where chromosome number is reduced to haploid (n). • It involves 2 rounds of cell division, NOT 1 like in mitosis. • Results in 4 HAPLOID daughter cells! Animation of Meiosis • http://www.cellsalive.com/meiosis.htm MORE ABOUT CHROMOSOMES • In humans, there are 22 different “regular” chromosomes (numbered 1 to 22 by size & shape) and 2 different sex chromosomes • The sex chromosomes are X and Y • Which sex chromosomes are in a girl? XX • Which are in a boy? XY Karyotype • A photograph of all of an organisms chromosomes. • Scientists freeze cells at the metaphase of mitosis. At this stage, chromosomes are easy to isolate and stain. Why perform a karyotype? • Verify chromosome number (some genetic diseases are caused by MORE copies of a chrom.) • Confirm chromosome shape, structure and size. Down’s Syndrome Karyotype (Trisomy 21) ALL HUMANS HAVE THE SAME GENES ON THE SAME CHROMOSOMES! • If mom’s chromosome #1 carries the genes for eye color, hair color, and height, then dad’s chromosome #1 also carries the genes for eye color, hair color, and height • Each chromosome of the pair contains an ALLELE (or copy) of every gene. Different versions of the same Gene are known as Alleles!!) CHROMOSOME PAIR #1 BLUE EYES BLUE EYES BROWN HAIR BLOND HAIR TALL SHORT = A GENE (allele) ON A CHROMOSOME • What is Phenotype? – Outward expression of an allele (how it looks- PHYSICAL) – Ex.: Blue or Brown eyes, Tall or short, Artistic, Athletic • What is Genotype? – Genetic makeup (the GENES) of an organism – Ex. Ff, FF, ff DOMINANCE • Some genes are “stronger” than others; they are called dominant • The weaker gene is recessive • EXAMPLES: – BROWN EYES ARE DOMINANT OVER BLUE EYES- A person may have BOTH genes, but we ONLY see the Brown eyes – Tall is dominant over short • In many cases, one gene is NOT stronger than the other. • This is called Incomplete Dominance • This can cause a MIXED phenotype– For Ex.: Incomplete dominance of the gene for red and white flower color will result in PINK flowers. Combinations of alleles • FF and ff are Homozygous for the genes and traits – FF= homozygous dominant; phenotype is DOMINANT trait – ff = homozygous recessive; phenotype is RECESSIVE trait Combinations of alleles • Ff is Heterozygous for the genes (genotype). – If F is dominant, a person who is Ff will look the SAME as someone who is FF (different genotype, same phenotype!) How do we PREDICT which traits an offspring will inherit? • A Punnett square!!! • Put MOM’s 2 genes (alleles) on the top; Dad’s 2 genes (alleles) on the side • Match up the possibilities in every square. • For 1 trait, there are 4 possible offspring! Example: • F= dominant= fuzzy seed & • f= recessive= smooth seed • What are the genotype and phenotype for homozygous dominant? • What are the genotype and phenotype for homozygous recessive? • What are the genotype and phenotype for heterozygous? • Cross Ff x Ff (Punnett Square)- what are the POSSIBLE genotypes and phenotypes of offspring? Answers: • Homozygous dominant= FF= fuzzy • Homozygous recessive= ff= smooth • HETEROZYGOUS= Ff= fuzzy • Have you ever noticed that certain traits run in families? Like musical ability, athletic, mechanical ability, more intellectual, etc. • Our genes determine a LOT of who we are (but NOT everything) – What we are good at- sports, music, schoolwork – Our height, eye color, hair color – personality traits Do Chromosomes ever change? • YES! Changes can occur in the chromosome (a BIG change- deletion, repeat, extra copy) or in the sequence of the DNA (LITTLE change- switch the nucleotide base (letter); delete 1 or more bases; insert extra 1 or more bases). • Both these types of changes are called MUTATIONS. What MAY happen when there is a mutation in the DNA or chromosome? • The offspring may develop a GENETIC DISEASE. • How is a GENETIC DISEASE (like cystic fibrosis) different from an INFECTIOUS DISEASE (strep throat)?