welcome to the unit five summary video for heredity this recap is going to briefly review all of the unit 5 topics according to the College Board curriculum which accounts for 8 to 11% of the AP exam here are the time stamps for each subtopic if you prefer to skip around don't forget that you can always download the podcast and watch our YouTube channel for more help you printed the UniFi study guide already right good let's zoom out living things are currently classified into one of three domains of life ARA bacteria and ukaria and in order for all living things to continue on well living the secret code of life has to be stored in DNA and RNA and passed on from one generation to the next we see this as the process of heredity occurring throughout all three domains and they have a ton of other things in common too like the presence of ribosomes genetic code and even the same metabolic pathways each of these cross overs provides evidence that all organisms are linked through shared common ancestry let's zoom in a human cotype is organized into 23 homologous pairs these homologous chromosomes are a similar size and carry similar but not identical information the chromosomes you have in each of your cells right now came from your parents gametes with homologous chromosomes from egg and sperm pairing back up during random fertilization even though genetic are from the same gene pool random fertilization contributes to genetic variation following the same logic the process of cell division by meiosis is to separate homologous pairs into separate gametes meiosis occurs in sex organs such as testes and ovaries and includes the familiar steps of prophase metaphase anaphase and telophase however in order to reduce the chromosome number the cells will need to go through pmat twice and since it would be difficult for me to draw meiosis with 23 three pairs let's stick with 2nal 4 for this example just like mitosis prophase 1 begins with DNA condensing from chromatin into chromosomes and the nuclear membrane disappearing unlike mitosis prophase 1 has homologous chromosomes pairing up to exchange segments of DNA by the process of crossing over homologous chromatids literally swap genes which means that some of the chromosomes distributed into gametes are now genetically different from the parent cell this event of crossing over is called de combination and it's one of the main contributors to genetic variation in gametes in metaphase 1 spindle fibers extend to arrange homologous pairs in a random order in the middle of the cell imagine that there are 20 students in your biology class and the teacher asks you to pair up with someone that is approximately your height and line up in the middle of the room some of you are lined up on the left While others are on the right similarly homologous chromosome pairs are arranged by spindle fibers during metaphase 1 at random there are no rules that say all genes from mom must be on the left to go into specific gametes while dad's genetic material needs to be on the right there are over 8 million different combinations possible for our 23 pairs of homologous chromosomes but only four combinations for our example cell this random arrangement of homologous pairs is called independent assortment and is yet another contributor to genetic variation when spindle fibers shorten and anaphase 1 homologous pairs are separated the AL of genes located on nonhomologous chromosomes sep operate without influencing each other and because centrom are still intact our chromosomes are in The Familiar X shape with sister chromatids connected til Phase 1 and cyto Kinesis usually overlap but we won't form the nuclear membranes or uncoil DNA into chromatin just yet with meiosis 1 complete we now have two haid daughter cells meiosis 1 and meiosis 2 are consecutive with no interface separating them meiosis 2 will also follow pmat with a lot of similarity to the steps of of mitosis because the purpose here is to make a copy of the haid cells we've already created prophase 2 has spindal fibers attached to centrom metaphase 2 has chromosomes pulled to the middle of the cell anaphase 2 has sister chromatid separated and kapase 2 has DNA uncoiled into chromatin and nuclear membranes reformed division of the cytoplasm is the final step with cyto Kinesis to form a total of four haid daughter cells each genetically unique from each other and from the original diploid parent cell often and haid cells continue to differentiate for specialized functions like how sperm have aella the process of meiosis is influenced by which sex organ is doing the gametogenesis the age of the organism varying hormone levels and even environmental factors for example human males can produce sperm from puberty until death whereas human female ovaries begin meiosis of their egg cells prior to their own birth Contin at puberty and only finish meiosis 2 if fertilization occurs in contrast cats reproduce seasonally and clownfish are protandrous able to activate dormant female reproductive parts if there's a need within a population don't worry you don't have to know all the details of any sexual reproduction cycles for plants or animals on the AP exam before we move on to genetics let's pause to contrast the process of meiosis and mitosis it can get confusing because they have a bunch of terminology and processes overlapping so the purpose of mitosis is to grow repair and reproduce a asexually while the purpose of meiosis is to form gametes for sexual reproduction mitosis creates two identical diploid cells through one division of Pat while meiosis forms four genetically unique haid cells through two divisions meiosis involves crossing over during prophase 1 and independent assortment in metaphase 1 while mitosis does not lastly mitosis involves a separation of sister chromatids only while meiosis first separates homologous pairs in anaphase 1 and then separates the chromatids in anaphase 2 Gregor mendle was an Austrian Monk and farmer who had the power of keen observation he wasn't exactly what we would classify today as a scientist while tending the monastery Garden in the 1850s mle noticed that certain traits appeared more often than others while some traits seem to disappear and reappear with time it's really convenient that mendle experimented with pea plants they're very small with observable phenotypes have quick generation times and make tons of Offspring also you can easily control mating through self and cross fertilization for his contributions to genetics Gregor mendal is regarded as a father of heredity okay clearly this isn't a history class but there are some big names in BIO that you should recognize like mendle with heredity Watson and Crick with DNA and Darwin with Evolution please don't get hung up on specific dates with any of their contributions but do acknowledge their big picture role and concept Association if the scientists show up on the exam as part of of a question there should be enough info in the prompt for you to recall their discoveries and any questions relevant to their experiments are more likely to be application based anyways two of mle's biggest observations are highly rooted in meiosis and the manner in which homologous chromosomes separate the first one I've already mentioned which is the Law of Independent Assortment a Le of genes located on nonhomologous chromosomes will separate during meiosis 1 without influencing each other so long as two genes are on different chromosomes there won't be a greater chance of inheriting them together they are not linked this is just like how flipping two coins next to each other won't influence how they land the second observation is a law of segregation which states that the two alals for each gene will separate during meiosis as diploid cells become haid so long as there hasn't been a myotic error you will end up with homologous chromosomes in the same gamt both of mle's laws can only be applied to genes that are on different chromosomes most of solving genetic problems is to look for patterns in order to explain and interpret results this is a lot easier if you can get into the habit of always making yourself a key to look back at for reference and when you think you've solved it reread the question again to make sure you've interpreted your results properly this summary video includes a brief overview of pent squares and pedigrees but there are a lot more genetic problems to solve with in-depth explanations on the practice sheet oh and Ki Square will be on there too to solve genetic problems we need to keep a few terms in mind alals are alternate forms of a gene which combine to create an organism's genotype a heterozygous genotype has two different Al while a homozygous has two of the same either dominant or recessive by convention dominant alal are written first if present so a heterozygous genotype would be capital P then lowercase p genotypes are interpreted to create an organism's phenotype the physical expression of the trait let's review the classic monohybrid one trait example for complete dominance in in flower expression a purple phenotype is dominant to White consider a cross between two heterozygous purple flowers and interpret the genotypes and phenotypes of The Offspring when we set up our punet Square the parental alals are independently aligned outside the squares this models the formation of gametes during meiosis just like the distributive property in math it doesn't matter if Mom's ales are written across the top of the ponet square or down the side you'll get the same answer each box within the punet square has a restored diploid number representing a potential Offspring when a Leal from each parent rejoins as homologous chromosomes during fertilization okay interpreting the results of our cross we have a 1:2:1 genotypic ratio with one homozygous dominant two heterozygous and one homozygous recessive phenotypically there is a 3:1 ratio of purple to White since purple is dominant the white phenotype reappears in the F1 generation since both parents were carriers of the recessive alil you can also complete genetic problems that follow two traits and a DI hybrid cross sticking with peas imagine we had a cross between two heterozygous parrot plants where purple is still dominant to White and tall is dominant to short we are going to foil our parent genotypes to get each of their gametes and then distribute them into The Offspring boxes a heterozygous cross needs a 16 box square and will produce a phenotypic ratio of 9 to 3 to 3: 1 the primary difference in non-m mil genetics is in how we interpret genotypic and phenotypic ratios in Offspring as for alals there are conventional ways for writing these types of problems so as to distinguish them from standard dominant scenarios but so long as you interpret the results correctly you can really write them however you want Even though these are different scenarios it is the same process of completing punet squares and applying the rules of probability first up incomplete dominance which is neither a fully dominant over the other and so both are partially expressed when present consider the Snapdragon flower with aals for the color red and white a homozygous flower can either be phenotypically red or white but a heao zous flower exhibits an entirely new intermediate phenotype pink another example of incomplete dominance is Cle cell anemia a heterozygous individual has CLE cell trait with some cells normally shaped and others CLE shaped CLE cell anemia is also a great example of evolution within humans a CLE cell trait provides malaria resist istence in certain environments next multiple Al and codominance which are both shown with blood typing there are three Al in the population that control the foundation of your blood type alal A B and O but even though there are three alals you can still only inherit two because you know two parents and those homologous chromosomes A and B are co-dominant over the recessive Al o considering all combinations there are four primary phenotypes a b AB or or o each blood type dictates different antigens expressed on the cell and antibodies produced in the plasma to distinguish self from non-self here is an example of a punet square that produces all four blood types from a single cross the recus factor is an additional antigen present which is how we have blood types such as AB positive or O Negative in humans females are genetically XX whereas males are genetically XY the Y chromosome although very small contains the sry y Gene which leads to development of male characteristics like testes the overwhelming majority of Sex Link traits are located on the X chromosome and are recessive since males only have one X chromosome they are hemizygous which will always express the trait if inherited for this reason Sex Link recessive disorders like red green color blindness and hemophilia are more common in men and often pass from unaffected mothers to affected sons and pedigrees it should be noted that some other species have sex determination with different chromosomes like ZW in birds and Hao Dio in bees the patterns that mendal observed were true for genes located on different chromosomes or at least those that were far apart on the same chromosome due to crossing over but when genes are located close enough to each other on the same chromosome they're more often inherited together and are said to be linked how close they are in a chromosome can be determined using data from genetic crosses to calculate recombination frequency or the number of offspring that show a recombination of traits not seen in the parental generation this segregation probability data can be further applied to calculate relative distance from one another on the chromosome this is often expressed as map units or sentim organs named after geneticist Sir Thomas Hunt Morgan the recombination frequency can never be greater than 50% since this would indicate that the alals are sorting independently several traits are the product of multiple genes like skin pigmentation and I color these are termed polygenetic traits and result in a phenotypic Range within a population be careful don't confuse this with pleotropic traits like morphan syndrome which result in one gene affecting multiple characteristics epistasis occurs when the phenotipic expression of one gene affects the expression of another Gene sometimes it depends on the other Gene for expression while other times it even masks are covers it up you won't find the term epistasis in the AP bioc CED but it provides another example of non-mendelian genetics at work and I give a full recap in episode 66 lastly there's non-nuclear inheritance remember that both chloroplast and mitochondria derive from independent procaryotic cells by endosymbiosis they both contain their own DNA which can be expressed as part of an individual's phenotype but here's the cool part in animals mitochondria are only found in egg cells not sperm and for plants mitochondria and chloroplast are only found in novul not pollen so both plants and animals have non-nuclear traits that are only maternally inherited phenotypic plasticity refers to the ability of an organism to exhibit different phenotypes in changing environmental conditions their genotype stays the same but the expression is different for example phenotypic plasticity in Arctic animals fur color allows for adaptation to changing seasons camouflage in snowy Winters and darker fuse in summer AIDS Survival by optimizing thermal regulation and Predator avoidance increased UV light causes more melanin production in animals which Alters phenotype temperature can even influence sex determination during embryonic development in reptiles cooler temperatures tend to produce males while warmer temperatures result in females highlighting the role of temperature sensitive genes regardless of the strategy the ability to respond to environmental changes provides organisms with evolutionary advantage certain human genetic disorders can be attributed to the inheritance of a single change Al or chromosomal error for example non-disjunction occurs when homologous chromosomes or sister chromatids don't properly separate during meiosis this can occur with autosomal or sex chromosomes and can result in nonviable gtes or gametes with an extra or missing chromosome one example is trcm 21 or down syndrome where there is a third copy of the 21st chromosome CLE cell disease is caused by a mutation in the hemoglobin gene on chromosome 11 tasac disease is an autosomal recessive disorder that damages brain cells with an error on chromosome 15 and Huntington's disease is a progressive brain disorder that presents later in an individual's life caused by an error in chromosome 4 non-disjunction of the sex chromosomes result in conditions like X Turner syndrome and xxy Klein filter syndrome the chromosomal basis of inheritance provides an understanding understanding of the pattern of transmission of genes from parent to offspring scientists have come up with a handy tool to analyze these patterns with the construction of pedigrees males or squares females or circles and connect with lines to show reproduction and Offspring through generations the circles and squares are shaded in to show an affected individual when analyzing pedigrees you are looking to see if the trait is autosomal or sex length dominant or recessive start with recessive first and look for Flaws in Logic for example if two affective parents have some offspring that do not have the treit then it can't be recessive because passing on alal from two homozygous recessive parents only has one outcome if you start to see a pattern of an affected mom and a disproportionate amount of affected Sons then it might be Sex Link recessive if even one parent to child interaction doesn't work then you have the wrong inheritance pattern to recap homologous chromosomes and their alals segregate during meiosis to form haid gametes unless L mutation or non-disjunction has occurred genetic variation is increased with crossing over independent assortment and random fertilization mendal might be the father of heredity but some inheritance patterns show different phenotypic ratios than he originally discovered fenyes can also be modified with changing environmental conditions When approaching genetic problems read The Prompt identify the parental gtes complete AET square and calculate your phenotypic and genotypic ratios and that's the end for unit 5 heredity now it's time to practice if you've already completed the unit 5 study guide for this video then go check your responses with the PDF answer key there's also the practice sheet practice video and practice multiple choice questions available in this unit thanks for watching and I'll see you next recap for unit 6 gene expression and regulation