Heredity: 59 flashcards
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1. What is heredity?
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The transmission of traits from parents to offspring.
2. What are the units of heredity called?
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Genes.
3. What is the difference between genotype and phenotype?
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Genotype is the genetic makeup (alleles present), while phenotype is the observable physical or biochemical characteristics.
4. Define allele.
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Alternative forms of a gene that occupy the same locus on homologous chromosomes.
5. What is a dominant allele?
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An allele that expresses its phenotype even when only one copy is present (heterozygous).
6. What is a recessive allele?
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An allele that expresses its phenotype only when two copies are present (homozygous).
7. State Mendel's Law of Segregation.
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During gamete formation, the two alleles for a trait separate so that each gamete carries only one allele.
8. State Mendel's Law of Independent Assortment.
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Alleles of different genes assort independently of one another during gamete formation.
9. What is a monohybrid cross?
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A cross between two individuals that differ in one trait (e.g., tall vs. short).
10. What is a dihybrid cross?
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A cross between two individuals that differ in two traits (e.g., seed shape and color).
11. What phenotypic ratio is observed in the F2 generation of a monohybrid cross?
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3:1 (dominant:recessive).
12. What is the genotypic ratio in the F2 generation of a monohybrid cross?
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1:2:1 (homozygous dominant : heterozygous : homozygous recessive).
13. What is the phenotypic ratio in the F2 generation of a dihybrid cross?
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9:3:3:1.
14. What is a test cross?
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A cross between an individual with an unknown genotype and a homozygous recessive individual to determine the unknown genotype.
15. What is incomplete dominance?
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A condition where the phenotype of the heterozygote is intermediate between the two homozygotes.
16. What is codominance?
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A condition where both alleles express themselves fully in the heterozygote.
17. What are multiple alleles?
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More than two alleles for a gene exist in a population, though an individual can have only two.
18. What is pleiotropy?
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A single gene affects multiple phenotypic traits.
19. What is polygenic inheritance?
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A trait controlled by multiple genes, often showing continuous variation.
20. What is a karyotype?
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A visual arrangement of chromosomes from a cell, showing their number and structure.
21. What is the chromosomal basis of sex determination in humans?
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Males are XY and females are XX; the male gamete determines the sex of the offspring.
22. What is a sex-linked gene?
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A gene located on a sex chromosome, often the X chromosome.
23. What is a mutation?
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A sudden change in the DNA sequence that can alter gene function.
24. What is a pedigree chart?
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A diagram showing the inheritance of a trait across generations in a family.
25. What is the difference between homozygous and heterozygous?
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Homozygous has two identical alleles for a gene; heterozygous has two different alleles.
26. What is a carrier in genetics?
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An individual who is heterozygous for a recessive trait and does not show the phenotype but can pass the allele to offspring.
27. What is the F1 generation?
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The first filial generation, offspring of the parental (P) generation.
28. What is the F2 generation?
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The second filial generation, offspring of the F1 generation.
29. What is a Punnett square?
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A diagram used to predict the genotypes and phenotypes of offspring from a cross.
30. What is the law of dominance?
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In a heterozygote, one allele (dominant) masks the expression of the other (recessive).
31. What are the two types of chromosomes based on function?
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Autosomes (non-sex chromosomes) and sex chromosomes (X and Y).
32. What is nondisjunction?
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Failure of chromosomes to separate properly during meiosis, leading to gametes with abnormal chromosome numbers.
33. What is a genetic disorder?
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A disease caused by abnormalities in genes or chromosomes.
34. What is the genotype of a person with blood group AB?
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$I^A I^B$
35. What is the genotype of a person with blood group O?
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$ii$
36. What is the phenotypic ratio of a test cross between a heterozygous tall plant and a homozygous short plant?
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1:1 (tall:short).
37. What is the probability of a child being male in humans?
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50% (1/2).
38. What is the chromosomal abnormality in Down syndrome?
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Trisomy of chromosome 21 (three copies).
39. What is the chromosomal abnormality in Turner syndrome?
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Monosomy of X chromosome (45, X0).
40. What is the chromosomal abnormality in Klinefelter syndrome?
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Extra X chromosome in males (47, XXY).
41. What is the difference between autosomes and sex chromosomes?
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Autosomes are non-sex chromosomes (22 pairs in humans); sex chromosomes determine sex (1 pair).
42. What is the significance of Mendel's work?
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He established the fundamental laws of inheritance through experiments on pea plants.
43. Why did Mendel choose pea plants for his experiments?
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They are easy to grow, have clear contrasting traits, and can be self-pollinated or cross-pollinated.
44. What is the difference between a trait and a character?
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A character is a feature (e.g., height), while a trait is a specific form of that character (e.g., tall or short).
45. What is a hybrid?
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An offspring resulting from a cross between two genetically different individuals.
46. What is the law of independent assortment based on?
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The random alignment of homologous chromosome pairs during metaphase I of meiosis.
47. What is the probability of a homozygous recessive offspring from a cross between two heterozygous parents?
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25% (1/4).
48. What is the probability of a heterozygous offspring from a cross between a homozygous dominant and a homozygous recessive parent?
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100%.
49. What is the genotype of a carrier for a recessive disorder?
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Heterozygous (one dominant normal allele, one recessive mutant allele).
50. What is the difference between a monohybrid and a dihybrid cross?
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Monohybrid involves one trait; dihybrid involves two traits.
51. What is the expected phenotypic ratio in the F2 of a dihybrid cross if genes are linked?
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Not 9:3:3:1; it deviates due to linkage.
52. What is linkage?
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The tendency of genes on the same chromosome to be inherited together.
53. What is recombination?
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The process by which genetic material is rearranged, producing new allele combinations.
54. What is the role of crossing over in heredity?
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It increases genetic variation by exchanging segments between homologous chromosomes.
55. What is a sex-linked disorder?
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A disorder caused by a gene on a sex chromosome, often X-linked.
56. Why are X-linked recessive disorders more common in males?
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Males have only one X chromosome, so a single recessive allele on X expresses the disorder.
57. What is the genotype of a colorblind male?
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$X^c Y$
58. What is the genotype of a carrier female for colorblindness?
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$X^C X^c$
59. What is the probability of a colorblind son from a carrier mother and normal father?
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50% of sons will be colorblind.
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