AP Biology Unit 5 Study Guide PDF
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This document is a study guide for AP Biology Unit 5, focusing on meiosis and genetic diversity. It includes explanations, diagrams, and definitions related to topics like chromosomes, mitosis, meiosis, and the laws of inheritance.
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5.1 & 5.2 - Meiosis and Genetic diversity Chromosomes ○ Numbered based on their length, with 1 being the longest ○ Can be identified based on their length, banding pattern and centromere position ○ Have a short arm (p arm) a...
5.1 & 5.2 - Meiosis and Genetic diversity Chromosomes ○ Numbered based on their length, with 1 being the longest ○ Can be identified based on their length, banding pattern and centromere position ○ Have a short arm (p arm) and long arm (q arm) ○ The locus (location) of a particular gene is written like this 12p3 - chromosome 12 P arm Band 3 M itosisis used for almost all body cell divisions.It adds and removes cells throughout life. The goal is to produce daughter cells that are geneticallyIDENTICALto their mothers Meiosisis used for the production ofGAMETES/sexcells, its goal is to make daughter cells with exactly half as many chromosomes as the starting cell ○ Takes us from adiploidcell (two sets of chromosomes2n) to ahaploidcells (one with a single set of chromosomes) Human somatic cells: 2n = 46 ○ homologous chromosomesare diploid2n have the same length, position, and sequence of genes one is paternal and one is maternal Code for same genes but may carry different allele of those traits ○ Haploidmade in meiosis = sperm and eggs If gametes were not haploid, chromosome number would double every generation ○ When a sperm and an egg join in fertilization, the two haploid sets of chromosomes form a diploid: a new genome - Zygote: first cell formed from fusion of egg and sperm Phases of meiosis ○ Organizes and separates chromosomes → separate sister chromatids → separate homologous chromosomes ○ This is achieved thru two-step division ○ Homologous pairs separate during a first round of cell division (meiosis 1) sister chromatids separate during a second round called (meiosis 2) ○ One starting cell can produce 4 gametes/haploids ○ meiosis 1 remains double pairs (2) ○ meiosis 2 remains single pairs (4) >Because they are duplicates, the alleles for eachgene are exactly the same on sister chromatids. Meiosis 1 ○ Before entering meiosis 1, a cell must first go thru interphase (G1, S, G2) ○ Duringprophase 1,chromosomes begin to condense andpair up. Each chromosome carefully aligned with its homologue partner so that the two match up at corresponding position along their full length ○ Crossing overin which homologous pairs trade parts The spots where crossovers happen are more or less random, leafing to chromosomes with unique combinations of alleles R andom assortmentwhere crossing over has many possibilities on the chromosomes depending on how they’reordered(metaphase1) Independent assortmentrandom alignment of homologous chromosomes in metaphase fter crossing over, the spindle moves chromosomes to the center. During A metaphase 1homologous pairs - not individual chromosomes- line up in the middle ○ Inanaphase 1, the homologous chromosomes are pulled apart and move to opposite sides The sister chromatids remain attached to one another ○ Telophase 1, chromosomes arrive at opposite poles of the cell. Cytokinesis occurs at the same time as telophase 1, forming two haploid daughter cells Meiosis 2 ○ Go from meiosis 1 to 2 without copying DNA ○ Haploid (just have one chromosome from each homologous pair-but their chromosomes consist of two sister chromatids ○ In meiosis 2 the sister chromatids separate making haploid cells ○ Inprophase 2chromosomes condense and nuclear envelopebreaks down, chromosomes move apart and spindle forms ○ Metaphase 2, the chromosomes line up individuallyalong the metaphase plate. ○ Anaphase 2,sister chromatids separate and are pulledtowards opposite poles of the cell ○ Telophase 2nuclear membranes form around each setof chromosomes, cytokinesis splits the chromosome sets into new cells. 5.3 - Mendelian Genetics ➔ H eredity= the passing of traits from one generationto the next ➔ Before mendel people believed in theBlending modelof inheritance ◆ What about traits that skip generations ★ Mendel’s experiment ○ Started by creatingtrue breedinglines for a numberof traits (all tall x all tall pea plants) ○ Once he has true breed, he crossed on trait with another - p generation: tall x short The offspring all resemble just one parent - F1 generation: all tall ○ Then he crossed two of the offspring together: F1 generation: tall x tall The results were 3 tall to 1 short. F2 generation: He got a3:1 ratio ○ Explanation:Instead of traits being liquid, theywere carried on discrete particles (chromosomes) that can be separated back out later, allowing traits to reappear ★ Mendel’s laws ○ The Law of Dominance An organism with alternate forms of a gene (allele) will express the form that is dominant Some genes aredominant, and they’ll "hide" the othergenes, which are recessive. Even if you inherit a gene for blue eyes and one for brown eyes, the brown eye gene (dominant) will "win," so your eyes will look brown. ○ The Law of Segregation Each parent hastwo genesfor a trait, andeach parentpasses only oneof these genes to their offspring. If a parent has one gene for brown eyes and one for blue eyes, they’ll pass on only one of these genes randomly to their child. ○ The Law of Independent Assortment Different traits (like eye color and hair color) are passed down independently of each other. Having brown eyes doesn’t automatically mean you’ll have brown hair; the traits are like separate “lotteries.” Just because your mom gave you her brown eye gene doesn’t mean she’ll also give you her curly hair gene. Each trait is decided independently. Explained by the movement of chromosomes during meiosis ★ Monohybrid Crosses ○ 1:1 ratio = Hh x hh ○ 3:1 ratio = Hh x Hh ★ Dihybrid Crosses ○ Follows two traits ○ 9:3:3:1 ★ Calculating Probability ○ Addition rule If there are twoORmore different ways an event can happen, you add their probabilities. Multiplication rule ○ Use this rule when you’re figuring out the probability of both events happening at the same time.AND What is the chance of 2 coins landing tails? 5.4 & 5.5 - Non-Mendelian Genetics henotypic Plasticity(Environmental Effects) = theenvironment can produce different phenotypes in P organisms with the same genotype. - Example: Flowers in which the color depends on the pH level of the soil - One genotype can produce more than one phenotype Extra Nuclear Inheritance - DNA in mitochondria or chloroplasts instead of DNA from the nucleus - Maternally inherited Multiple alleles- there are than just two allelespossible for one gene - Example: Rabbit fur C(brown fur), c^ch(grey), c^h(himalayan fur), c(white) - Each individual still has 2 alleles, there are just more options - Example: Blood type Type A antigen → I^A ; Type B Antigen → I^B ; Type O (no antigen) → i Polygenic inheritance - Many human characters vary in population along a continuum (Ex; skin, color, height) - This often means that trait is influenced by more than one gene - Some traits are influenced by the environment + genes =multifactorial Linkage -genes that are on a chromosome together - Genes that are close together on a chromosome usually get inherited together - The likelihood of them getting separated during crossing over is low - Recombination frequency = recombinants total offspring x 100% Sex-linked Traits -genes on a sex chromosome together(X or Y) - Most problems will be X-linked - Morgan discovered a mutation that affected fly eye color. He observed that the mutation was inherited differently by male and female flies. - Based on the inheritance pattern, Morgan concluded that the eye color gene must be located on the X chromosome. - Sex determination in humans is controlled by X and Y chromosomes - Females and males aren’t always XX XY - SRY gene - Monosomies/trisomies - Androgen insensitivity - Different sex determination system exists in other species - Fruit fly is good choice because it breeds at a high rate, takes up little resource and time, have only 4 pairs of chromosomes, same sex system as humans 5.6 - Chromosomal Inheritance ❖ Pedigree - family tree used to show interrelationships of parents and offspring across generations ❖ ❖ W e can understand patterns of inheritance by tracing the movements of chromosomes from generation to generation ❖ Nondisjunction- chromosomes don't separate properlyduring meiosis; the resulting gametes have an atypical number of chromosomes ❖ Trisomy- 1 EXTRA chromosomes ❖ Monosomy- 1 LESS chromosome ❖ Aneuploidrefers to a condition in which a cell hasan abnormal number of chromosomes—more or fewer than the normal count. ❖ This is different from having an entire extra set of chromosomes (polyploidy) ❖ Karyogramshelp identifyweather or not there is a disorder
