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Ap Bio Mod 27-30
Ap Bio Module 27-30
| Question | Answer |
|---|---|
| P₁ | The original parents in a genetic cross; |
| F₁ | The offspring of the P1 cross; |
| monohybrid cross | A genetic cross that tracks one trait (one gene with two alleles), usually between heterozygous individuals -produces a 3:1 phenotype ratio in the F₂ generation. |
| Critical value | Threshold from chi-square table; if χ² (chi square) > critical value → reject null hypothesis. |
| Null hypothesis | Assumes no difference between observed and expected results. |
| Chi-square (χ²) | Tests if observed data fits expected ratios. |
| Incomplete dominance | when a Heterozygote genotype shows a phenotype that is the blend of the two alleles, - not full dominance. -Ex: Dominant flower color= Red , recessive= white flower color Heterozygous flower color= pink (mixture of the two) |
| Codominance | Both alleles are fully expressed in the heterozygote. Example: Blood type AB → both A and B antigens show. |
| Dihybrid cross | A genetic cross that tracks two traits (two genes), usually heterozygous for both. -Typical F₂ phenotype ratio: 9:3:3:1. - Ratios are out of 16 and represent phenotype possibilities |
| 9:3:3:1 ratio (from a dihybrid cross): | 9 → both dominant traits expressed (AABB) 3 → first dominant, second recessive (AAbb) 3 → first recessive, second dominant (aaBB) 1 → both recessive traits (aabb) -Occurs when Both parents are heterozygous for both traits Ex: (AaBb × AaBb). |
| Independent Assortment | Alleles for different genes separate independently during gamete formation. Explains why the 9:3:3:1 ratio appears—traits are inherited separately, not linked. |
| What does this mean in a pedigree? ⬛ | A male affected with a disease |
| What does this mean in a pedigree? ⬜ | A male that is not affected with a disease |
| What does this mean in a pedigree? ⚪ | A female not affected with the disease |
| What does this mean in a pedigree? ⚫ | A female affected with the disease |
| Pleiotropy | One gene affects multiple traits. Example: Sickle-cell allele affects blood shape, oxygen transport, and disease resistance. |
| Epistasis | One gene masks or modifies the expression of another gene. Ex:Mouse coat color: One gene determines fur color (black or brown). A second gene determines whether pigment is produced at all. |
| F₂ | The offspring produced by crossing F₁ individuals with each other. |
| Addition Rule (probability): | P(A or B)=P(A)+P(B)−P(A∩B) -use if problem says what is the probability that "either or happens" or "this or that happens" |
| Multiplication Rule (probability): | P(A and B)=P(A)×P(B) -use if asked "what is the probability that this and this happens" |
| When does 9:3:3:1 happen | -when genes are independently assorted (Mendelian Genetics only!) |
| Sex-linked genes: | Genes located on sex chromosomes (X or Y). Inheritance depends on the sex of the individual. |
| X-linked genes: | Located on the X chromosome. - Since males only 1 X while females have 2 Xs, males are more likely to get the disease as females can be carriers while males either have the disease or don't |
| Y-linked genes: | Located on the Y chromosome. Only males affected. |
| Describe the sex chromosomes provided by each parent during the production of haploid sex cells | Female offspring (XX):Receives one X chromosome from the mother and one X chromosome from the father Male offspring (XY): Receives one X chromosome from the mother and one Y chromosome from the father |
| Are there more X-linked or Y-Linked traits | -there are more X-linked traits so phenotypes usually come from the X chromosome. -Y chromosome has fewer genes than X chromosome so most traits come from the X and not the Y |
| Wild type (+) genotype | The “normal” or most common allele in a population Usually produces the standard phenotype (normal function) -noted as (+) |
| Mutant (c): | A variation of the gene that causes a different phenotype -less common than wild type - noted as "c" |
| SRY gene | Located on the Y chromosome Triggers male development by turning on genes that form testes Without the SRY gene female development occurs |
| How do you identify Y-linked genes on a pedigree? | Only males affected Passed father → son Appears in every generation in male line Females never show it |
| Linked genes | -Genes located on the same chromosome -Tend to be inherited together because they are physically close -The closer the genes, the less likely recombination separates them -Do not assort independently like Mendel’s genes |
| How do linked genes become unlinked form each other? | crossing over occurs during prophase I of meiosis, resulting in genes between homologous pairs switching places -thus one of the genes on one homolog ends up on another chromosome and is thus separated |
| Recombination | The exchange of genetic material between homologous chromosomes during meiosis Produces new combinations of alleles on the same chromosome |
| Recombination frequency (RF): | -Measures how often crossing-over occurs between two genes on the same chromosome -Genes that are closer to each other → lower RF -Genes that are farther apart→ higher RF (up to 50%) |
| Formula for recombination frequency | recombinants/total offspring x100 -used to map gene positons on a chromsome |
| How do you identify the recombinants in a genetics problems | - Look at the most common offspring phenotypes in a cross (they are usually the same as the parents) -Understand that any offspring showing allele combinations different from parents are recombinants -Parents: AB × ab - Recombinants= Ab or aB |
| The Law of Segregation | The two alleles for a gene separate (segregate) during gamete formation, so each gamete receives only one allele. |
| Dominant Inheritance Pattern on pedigrees | -Appears in every generation Affected individuals usually have at least one affected parent. If a parent is affected (heterozygous) and the other is not, about 50% of the children may be affected. |
| Recessive trait Inheritance Pattern on pedigrees | -Often skips generations. -Two unaffected parents can have an affected child (they are carriers). -The trait appears when a person inherits two recessive alleles. -If both parents are carriers, about 25% of offspring may be affected. |
| What is a chi-square (χ²) test? | A statistical test used to determine whether the difference between observed data and expected data is due to chance or if it is statistically significant. |
| When is a chi-square test commonly used in genetics? | To test whether observed offspring ratios match expected Mendelian ratios (such as 3:1 or 9:3:3:1). |
| : What are observed values in a chi-square test? | The actual number of individuals counted in each category during an experiment. |
| What is the null hypothesis in a chi-square test? | The hypothesis that any difference between observed and expected results is due to random chance. |
| What does it mean if our χ² value is below the critical value? | The difference is likely due to chance, so the null hypothesis is accepted (fail to reject). |
| What does it mean if our χ² value is above the critical value? | The difference is statistically significant, so the null hypothesis is rejected. |
| What is sex-linked inheritance? | When a gene is located on a sex chromosome (X or Y), its inheritance pattern depends on the sex of the parent and offspring. |
| What is X-linked inheritance? | -Inherited Genes located on the X chromosome. -Females: XX → can be carriers if heterozygous -Males: XY → only have one X, so one recessive allele can cause the trait |
| What is Y-linked inheritance? | Genes located on the Y chromosome. -Y-linked traits cannot be carried by females. |
| Which has a greater effect, X-linked or Y-linked inheritance, and why? | -Males are hemizygous for X → any recessive X-linked allele is always expressed. -X-linked traits appear in both sexes, but are more noticeable in males. -Y-linked inheritance affects fewer individuals (only males), so it has a more limited impact. |
| What is X-linked recessive? | -A trait caused by a recessive allele on the X chromosome. -Males (XY): Only one X → the trait always shows if they inherit the allele. -Females (XX): Need two copies to show the trait; one copy makes them a carrier. |
| What is X-linked dominant | -A trait caused by a dominant allele on the X chromosome. -Males (XY): One X → trait always shows if they inherit the allele. -Females (XX): One X with the dominant allele → trait also shows |
| Which sex chromosome does a mother pass to her children? | The mother always passes one of her X chromosomes to every child, male or female. |
| Which sex chromosome does a father pass to his children? | -Sons: Father passes his Y chromosome → XY male -Daughters: Father passes his X chromosome → XX female |
| How do sons inherit X-linked traits | -Sons inherit their X chromosome from their mother and Y from their father. - So, any X-linked traits in sons come from the mother. |
| : How do daughters inherit X-linked traits? | -Daughters inherit one X from the mother and one X from the father. - So, X-linked traits can come from either parent. |
| What is a wild type? | -The most common form of a gene, trait, or phenotype in a natural population. -Often considered the “normal” version. |
| What is a mutant | -A variant form of a gene or trait that differs from the wild type and is less likely to occur |
| What are linked genes | Genes that are located close together on the same chromosome and tend to be inherited together during meiosis. |
| How do linked genes affect inheritance? | -Linked genes do not assort independently, so the offspring do not always show the expected Mendelian ratios (like 9:3:3:1 for a dihybrid cross). |
| Can linked genes be separated? | -Yes, crossing over (recombination) during meiosis can separate linked genes, producing recombinant offspring with new combinations of traits. |
| How does the distance between linked genes affect recombination? | -Genes close together: Rarely separated → mostly inherited together. -Genes far apart: More likely to be separated → more recombinant offspring. |
| How can we map linked genes? | Recombination frequency (%)=Number of recombinant offspring/Total offspring ×100 -1% recombination = 1 map unit |
| Mitochondrial Inheritance | -Transmission of traits via mitochondrial DNA -Inherited from Mother only -Pedigree clue: Trait passed from mother → all children; affected -if fathers have a disorder → their kids aren't affected |
Created by:
KenechukwuIE