Genetics Review (incomplete)

1. The chromosomal theory of inheritance states that genes are located on chromosomes; chromosomes and their associated genes undergo segregation during meiosis, and chromosomes and their associated genes undergo independent assortment in gamete formation.

2.The genotypic ratio resulting from a cross can be predicted with a Punnett square.

3. A wild type is the phenotype found most commonly in nature.

4.The phenotypic ratio of a dihybrid cross will include all the different phenotypic combinations of gametes.

5. Sex linked traits are coded for by genes located on a sex chromosome (generally the X chromosome in humans).

6. A multifactorial disease has both genetic and environmental causes.

7. Genetic and cytological maps for the same chromosome have the same sequence of genes but different intergenic distances.

8. Genetic recombination results in recombinant offspring; occurs in the fertilization process; and occurs by independent assortment and crossing over in the formation of gametes.

9. The F2 generation is the result of the self-fertilization or crossing of F1 individuals.

10. A 1:1:1:1 ratio of offspring from a dihybrid testcross indicates that the genes are not linked. For instance what is the ratio in the following test cross AaBa x aabb. Do the Punnett square to SEE the 1:1:1:1 ratio.

11. According to Mendel's law of independent assortment gene pairs segregate independelntly of other genes in gamete formation.

12. According to Mendel's law of segregation , allele pairs separate in gamete formation.

13. A 1:1 phenotypic ratio in a testcross indicates that the dominant phenotype parent was a heterozygote .

14. Two genes will probably assort independently if they are on nonhomologous chromosomes or are far apart on homologous chromosomes.

15. According to Mendel's law of independent assortment, the F2 phenotypic ratio of a dihybrid cross of two true breeding varieties should be 9:3:3:1 and 3:1 for a monohybrid cross.

16. The genetic event that results in metafemales (XXX) is probably nondisjunction .

17. A son inherits color blindness from his mother .

18. Quantitative traits may exist in a normal distribution within a population (bell shaped curve.

19. Genomic imprinting explains cases where the gender of the parent from whom an allele is inherited affects the expression of that allele.

20. The probability that a particular genotype may result from a cross can be determined as the product of the probabilities of the formation of the gametes needed to produce the genotype; can be determined from the genotypic ratio for the cross; and will depend upon the genotypes of the parents.

21. Carriers of a disease are heterozygotes for the gene that can cause the disease.

22. Nondisjunction occurs when homologous chromosomes do not separate properly in meiosis I or may occur when sister chromatids do not separate in meiosis II . It can result in both trisomic and monosomic offspring.

23. A lethal recessive allele is more likely to be maintained in a population if it is somehow beneficial in the heterozygous condition or if it is not expressed until late in life.

24. In translocation a fragment of a chromosome joins to a nonhomologous chromosome.

25. Extra dosages of genes usually have deleterious effects, can be caused by __________________ and are found in Down , Patau, and Edwards syndromes.

26. With amniocentesis fetal cells from the protective fluid can be cultured and then karyotyped .

27. If both parents are carriers of a lethal recessive gene, the probability that their child will inherit and express the disorder is 1 / 4 (one in four) .

28. Sex-chromosome aneuploidies upset genetic balance less than do autosomal aneuploidies because extra X chromosomes are inactivated as Barr bodies.

29. Feather color in budgies (fig 13.9) is determined by two different genes that affect the pigmentation of the outer feather and its core. Y_B_ is green; yyB_ is blue; Y_bb is yellow; and yybb is white. A green budgie is crossed to another green budgie (Y_B_ x Y_B_). You do not know the complete genotype of either bird all of the phenotypes listed are possible, but with different probabilities .

30. The following is true of maternal inheritance? It is the result of the larger contribution of egg cytoplasm It gave evidence for the existence of cytoplasmic genes for instance mitochondrial, and plant plastid genes come from the mother. It does not follow Mendelian principles of inheritance.

31. After obtaining three heads from three tosses of a coin, the probability of anyone tossing the coin and obtaining a head is: 1 / 2 (one in two) .

32. The probability of tossing four coins simultaneously and obtaining four heads is: 1 / 16 (one in sixteen) .

33. The work of Mary Lyon showed that the selection of which X chromosomes form Barr bodies during early embryonic development is random.

34. In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A sex-linked lethal recessive gene occurs in pigeons. What would be the sex ratio in the offspring of a cross between a male heterozygous for the lethal gene and a normal female? 2 : 1 male to female