Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. Given the fact that embryos with 48 chromosomes (four #21 chromosomes) are not likely to survive early development, what percentage of surviving offspring would be expected to have Down syndrome if both parents have Down syndrome?     all     2/3     1/2     1/3     none

In fruit flies, chromosomal crossing over does not occur in meiosis in males, whereas crossing over does occur in meiosis in females. In fruit flies that are heterozygous at many genes (i.e. many maternal and paternal versions of the genes differ), at what stage would cells no longer be heterozygous for any gene during the process of meiosis? a)After the second meiotic division in males, and after the first meiotic division in females. b)After the second meiotic division in both males and females. c)After the first meiotic division in both males and females. d)After the first meiotic division in males, and after the second meiotic division in females.

Identify each of the following statements as true or false. The chromosomes in B are the result of mitosis from the chromosomes in A.  Alleles B and C are more likely to segregate together during anaphase I than alleles B and A.  The two white chromosomes in B are homologous chromosomes.  Genes A, B, and C are linked genes.  A trihybrid Punnett square can be used to determine the possible combinations of the F1 generation.

Knowing that wrong number of chromosomes has serious, usually lethal consequences, briefly describe the most common inherited abnormalities in case of trisomy 21 and trisomy 13.

In Pop-Bead Meiosis, you start with 4 chromosomes: 1 big red, 1 little red, 1 big yellow, and 1 little yellow. After meiosis I, how many chromosomes will be present in each daughter cell? How many “big” chromosomes per cell? How many “little” chromosomes per cell?